Characteristics of meiofaunal community in the subtidal zone near Hupo, anticipating ocean acidification in the East Sea of Korea

Characteristics of meiofaunal community in the subtidal zone near Hupo, anticipating ocean acidification in the East Sea of Korea | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Characteristics of meiofaunal community in the subtidal zone near Hupo, anticipating ocean acidification in the East Sea of Korea Je Hyeok Oh, Teawook Kang, Dongsung Kim, Ayoung Shin, Min Gyu Jung, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3034005/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 18 Mar, 2026 Read the published version in Thalassas: An International Journal of Marine Sciences → Version 1 posted 7 You are reading this latest preprint version Abstract This study aimed to investigate the meiofauna community characteristics in coastal waters highly affected by ocean acidification. Therefore, the meiofauna communities in the coastal waters of Hupo in Uljin-gun, a county bordering the East Sea of Korea, were monitored over five years. During the study period, the mean abundance of total meiofauna communities expressed in population density was 614.4 individuals (Inds.)/10 cm 2 , similar to the reported meiofauna abundance in the subtidal zone in the Yellow Sea of Korea, an area with sandy sedimentary facies. The most dominant taxa were nematodes (65–70%) and harpacticoids (7–20%); these two taxa accounted for approximately 80% of the total meiofauna abundance. Among the stations studied, station (St.) 10 showed the lowest seawater pH value, and in 2011, when the measured pH was the lowest at 7.82, St. 10 showed the lowest abundance values for total meiofauna and harpacticoids in the 5-year period. To examine the effect of ocean acidification on meiofauna communities at the species level, species of nematodes, the most dominant taxon, were analyzed. The results indicated that the number of nematode species at St. 10 in 2009, when the pH value was low, was 8, which was very low compared to that in the other years of the study period. According to the feeding type, epistrate feeders (2A) accounted for a remarkably high proportion at St. 10, which showed a low pH. This study provides various data on meiobenthic community characteristics to understand the effects of ocean acidification on coastal ecosystems. Meiofauna community Ocean acidification Carbon dioxide Nematodes Feeding type Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Carbon dioxide (CO 2 ) is one of the most important greenhouse gases in the atmosphere, and its concentration in the atmosphere has been continuously increasing because of the growing consumption of fossil fuels following industrial development and economic growth; it has thus been drawing attention as a major source of global warming and a cause of climate change (Solomon et al. 2007 ). An increase in atmospheric CO 2 concentration results in seawater acidification, posing a threat to the safety of marine life and ecosystems. Oceans have played a major role in alleviating the accelerating pace of global warming via uptake of atmospheric CO 2 ; however, this has resulted in ocean acidification, wherein the pH of seawater decreases owing to an increase in the CO 2 flowing into the ocean from an increase in atmospheric CO 2 concentration (Zeebe et al. 2008 ). The pH of the ocean has decreased by about 0.1 compared to the preindustrial level and is expected to decrease by approximately 0.2–0.4 within the next 100 years. Seawater temperature has also increased by 0.76°C compared to that in the previous century, and is predicted to increase by more than 2°C within the next 100 years (Brewer 1997 ; IPCC 2007 ). In response to these environmental changes, studies on the effects of ocean acidification on marine organisms have been undertaken using various approaches. The results of recent studies indicate that ocean acidification has a negative impact on the growth, reproduction, and survival of organisms in many cases; however, it has also shown a positive impact on some species (Kroeker et al. 2010 ). Some studies have reported that ocean acidification impacts the calcification of shellfish and is associated with a decline in calcification rates and a decrease in shell growth (Gazeau et al. 2007 ). Most studies on the effects of ocean acidification on benthic ecosystems have focused on benthic macrofauna (Kroeker et al. 2010 ; Manno et al. 2017 ; Barry et al. 2014 ; Fosså et al. 2012 ; Thomsen et al. 2010). The responses of marine organisms to ocean acidification vary depending on the species, regions, and communities (Dupont and Thorndyke 2008 , 2009 ; Melzner et al. 2009 ; Przeslawski et al. 2009 ). Therefore, to understand the changes caused by ocean acidification in ecosystems, studies considering ecological niches are required. Further, because benthic fauna lack the ability to quickly respond to environmental changes owing to their sluggish locomotion, they are more vulnerable to environmental changes such as ocean acidification (Fabry et al. 2008 ). Among benthic fauna, meiofauna have been reported as highly useful for studying the effects of environmental disturbances such as pollution (Coull and Chandler 1992 ). Despite the pressing need for research on the effects of ocean acidification on meiofauna, which play an important role as food source for fish or secondary producers in the benthic ecosystem, few studies on these have been undertaken in Korea. Some recent studies on meiofauna included experimental studies to examine the impact of ocean acidification on harpacticoid copepods (Oh et al. 2017 ; Oh et al. 2022 ). Meiofauna are organisms dwelling in almost any type of aquatic environment; they live in marine as well as fresh water and are widely distributed from shallow coastal waters to deep seas, and from tropical to polar regions. Further, meiofauna inhabit a wide range of sedimentary environments from muddy benthic sediments with small particle sizes to coarse shell sand with large particles; notably, some species have adhesive organs to hold onto the surface of large birds and various animals. Typically, meiofauna inhabit within the top 2 cm of sediments, and in terms of vertical distribution, the range of meiofauna distribution is controlled by the depth of the Redox Potential Discontinuity (RPD, a layer of the transition from oxygenated to anoxic conditions) layer within the sediments; however, some species may prefer anoxic or hypoxic conditions, i.e., anaerobic conditions (Higgins and Thiel 1988 ). Compared to benthic macrofauna, meiofauna have smaller sizes, shorter life spans, and shorter generation times; their larval settlement is found in marine sediments. Meiofauna are a biological group serving as an effective tool for ecological research or assessment of environmental impact. Owing to their high abundance, detection of changes in their population density is easier than that in other types of organisms, and they have many taxa that show sensitive responses to environmental changes. In terms of survey methods, meiofauna can be analyzed by collecting only a small amount of samples from sediments, thereby minimizing the damage to the natural environment caused by sampling (Moore and Bett 1989 ). Although meiofauna are tiny organisms, their population density is typically 10 4 − 10 5 individuals per square meter even in oligotrophic environments, and under more favorable environmental conditions for meiofauna habitats, a high abundance of 10 5 – 10 8 individuals/m 2 has been reported (Giere 1993 ). In general, the number of meiofauna individuals per unit area is relatively high in the intertidal zone, and their number decreases with increasing water depth and further from the coast; in general, the population density of meiofauna is determined by factors such as interstitial space in the sediments, organic matter content, and oxygen content in the interstitial water. Thus, this study aimed to investigate how meiofauna communities, an integral part of the benthic ecosystem, are affected in the coastal waters of Hupo in Uljin, an area that is highly subject to the trend of ocean acidification among the coastal waters of Korea. Materials and methods Sampling Sites The coastal waters of Hupo in Uljin on the east coast of Korea were selected as the study area. For determining of the study area among the coastal waters of East Sea, the patterns of time-series changes in the factors representing the marine environment alterations related to climate change, such as seawater temperature and pH, were analyzed; based on these results, the sea area of Hupo was selected as appropriate for conducting monitoring surveys. In total, 10 stations were selected in the coastal waters of Hupo, and meiofauna samples were collected in summer (July-August), the period with the largest biomass, for a total of five years (2009, 2010, 2011, 2013, and 2014) (Fig. 1 , Table 1 ). Sampling and analysis methods For collecting sediment samples, an acrylic core (10 cm 2 ) was used to sample the top 3 cm of the sediment layer; the samples were immediately fixed with 5% formalin and moved to the laboratory. For the sediment samples moved to the laboratory, Ludox HS40 (DuPont, specific gravity 1.18) was used to extract meiofaunal organisms from the sediments. (Burgess 2001 ). Meiofauna isolated from the sediments were examined and counted at the taxon level under a stereomicroscope (Leica MZ16). The nematodes that appeared at some of the stations (St. 5, St. 7, and St. 10) expected to show a strong trend of ocean acidification were transferred to a 3% glycerin solution for species identification. The nematodes appearing at each station were prepared as slide samples and analyzed up to the genus level using an optical microscope (Olympus BX51, Platt and Warwick 1983 ). Further, the nematodes were classified into four feeding types (1A, selective deposit feeders; 1B, non-selective deposit feeders; 2A, epistrate feeders; 2B, predators/omnivores) as proposed by Wieser (1953). To examine the differences between meiofauna communities from respective sampling sites, CLUSTER and SIMPROF (similarity profiles) analyses were performed based on Bray-Curtis similarity. In the analyses used in this study, fourth root transformed values were used to determine the total meiofauna abundance. For CLUSTER and SIMPROF analyses, the software PRIMER (v. 6.1.12) was used (Clarke and Gorley 2001 ). Results Environmental characteristics Table 2 and Fig. 2 present the bottom layer water temperatures during the monitoring period in Hupo, Uljin. The bottom layer temperature measurement in the summer of 2009 revealed that the highest water temperature was measured as 18.6°C at St. 9, a station at shallow depth, and the lowest water temperature was 10.9℃ at St. 5, which was at a depth of 35 m. The bottom layer temperature measurement in the summer of 2010 revealed that the highest temperature was 22.3°C at St. 9, the same station as in 2009, and the lowest temperature was 11.3°C at St. 5, also the same station as in 2009. In the summer of 2011, the highest temperature was 20.5°C at St. 9, the same station as the previous two years, and likewise, the lowest temperature was 9.7°C at St. 5. In the summer of 2013, the highest bottom layer water temperature was 24.5°C at St. 9, the same station as before, and the lowest water temperature was 10.1°C, this year at St. 10, the station with the greatest water depth. In the summer of 2014, the highest temperature was 12.7°C at St. 6 but not St. 9, which had showed the highest water temperature during the previous years, and the lowest water temperature was 6.9°C at St. 10, the station with the greatest water depth as in the previous year. The mean bottom layer temperature for each year was as follows: 14.3°C in 2009, 16.5°C in 2010, 9.6°C in 2011, 17.3°C in 2013, and 10.7°C in 2014, showing the highest temperature in 2013 and the lowest in 2014. Table 2 and Fig. 2 present the bottom layer salinity during the monitoring period in Hupo, Uljin. Analysis of salinity in 2009 revealed that the highest salinity was 34.12 psu obtained at St. 10, the station with the greatest water depth, and the lowest salinity was 33.07 psu at St. 9, the station with the lowest water depth. In 2010, the highest salinity was 35.64 psu at St. 4, the station with a relatively great water depth, and the lowest salinity was 33.62 psu at St. 7. In 2011, the highest salinity was 34.96 psu at St. 7, and the lowest salinity was 33.14 psu at St. 9, the same station as in 2009. In 2013, the highest salinity was 35.14 psu at St. 2, and the lowest salinity was 32.83 psu at St. 9, the same as in the previous years. In 2014, the highest salinity was 34.38 psu at St. 1, and the lowest salinity was 34.11 psu at St. 10, the station at the greatest water depth. The mean bottom layer salinity for each year was 33.8 psu in 2009, 34.5 psu in 2010, 33.8 psu in 2011, 33.7 psu in 2013, and 34.3 psu in 2014, showing the highest salinity in 2010 and the lowest in 2013. Table 2 and Fig. 2 present the bottom layer pH during the monitoring period in Hupo, Uljin. Analysis of the pH in 2009 revealed that the highest pH was 8.192 at St. 7, a station with the relatively low water depth, and the lowest pH was 7.887 at St. 10, the deepest station. In 2010, the highest pH was 8.653 at St. 1 with low depth and the lowest pH was 8.361 at St. 9, also a station at low depth. In 2011, the highest pH was 7.973 at St. 8 and the lowest pH was 7.812 at St. 5. In 2013, the highest pH was 8.916 at St. 1, the same station as in 2010, and the lowest pH was 7.959 at St. 5, the same station as in the previous year. In 2014, the highest pH was 8.832 at St. 2 and the lowest pH was 8.633 at St. 4. The mean bottom layer pH for each year was 8.032 in 2009, 8.504 in 2010, 7.886 in 2011, 8.414 in 2013, and 8.696 in 2014, with the highest pH in 2014 and the lowest pH in 2011. Examining the pH analysis results by station, the pH values ranged from 8.195–8.465, and the lowest pH value was obtained at St. 10, the station at the greatest water depth and the southernmost point, and the highest pH value was obtained at St. 1, the station at the northernmost point. Characteristics of meiofauna communities in the study area In total, 23 meiofauna taxa were identified in samples collected over the five-year period in the entire study area as follows (Tables 3 , 4 , 5 , 6 , and 7 ): nematodes (Nematoda), harpacticoids (Harpacticoida), copepod nauplii (Nauplii), benthic foraminifera/sarcomastigophorans (Sarcomastigophora), polychaetes (Polychaeta), ostracods (Ostracoda), bivalves (Bivalvia), amphipods (Amphipoda), tanaidaceans (Tanaidacea), isopods, cumaceans (Cumacea), kinorhynchs (Kinorhyncha), tardigrades (Tardigrada), nemertines (Nemertea), turbellarians (Turbellaria), halacaroideans (Halacaroidea), gnathostomulids (Gnathostomulida), gastrotrichs (Gastrotricha), priapulids (Priapulida), syncarids (Syncarida), gastropods (Gastropoda), and echinoderms (Echinoderm). The mean abundance of meiofauna by year during the monitoring period was 473.6 ± 65.1 Inds./10 cm 2 in 2009, 541.0 ± 97.0 Inds./10 cm 2 in 2010, 443.2 ± 66.2 Inds./10 cm 2 in 2011, 700.4 ± 122.4 Inds./10 cm 2 in 2013, and 916.5 ± 79.8 Inds./10 cm 2 in 2014. The meiofauna abundance by year at each station during the study period was as follows. In 2009, the highest value of meiofauna abundance was 1521.0 ± 138.7 Inds./10 cm 2 at St. 9 and the lowest was 184.0 ± 51.4 Inds./10 cm 2 at St. 1. In 2010, the highest value of meiofauna abundance was 1235.0 ± 172.1 Inds./10 cm 2 at St. 4, and the lowest value was 192.3 ± 41.3 Inds./10 cm 2 at St. 7. In 2011, the highest value of meiofauna abundance was 751.3 ± 115.7 Inds./10 cm 2 at St. 4, the same station as in the previous year, and the lowest value was 221.7 ± 34.7 Inds./10 cm 2 at St. 3. In 2013, the highest value of meiofauna abundance was 1163.0 ± 73.2 Inds./10 cm 2 at St. 6, and the lowest value was 442.0 ± 116.0 Inds./10 cm 2 at St. 3, the same station as in the year 2011. In 2014, the highest value of meiofauna abundance was 1373.0 ± 67.6 Inds./10 cm 2 at St. 7, and the lowest value was 337.7 ± 16.1 Inds./10 cm 2 at St. 6. Upon examining the mean meiofauna abundance by station, the values ranged from 507.6 ± 68.9–928.3 ± 97.1 Inds./10 cm 2 , with the highest value at St. 9 and the lowest at St. 1. The mean meiofauna abundance at St. 10, the station with the lowest pH value in the environmental data, was 614.4 ± 115.1 Inds./10 cm 2 , with the highest value at 1010.7 ± 23.0 Inds./10 cm 2 in 2014, and the lowest value at 381.3 ± 133.4 Inds. /10 cm 2 in 2010. The results of analyzing the abundance of nematodes, the most dominant taxon among the meiofauna, which appeared during the monitoring period, are as follows. The mean abundance of nematodes for each year in the study period was as follows: 307.4 ± 43.7 Inds./10 cm 2 in 2009, 351.1 ± 101.7 Inds./10 cm 2 in 2010, 307.4 ± 48.5 Inds./10 cm 2 in 2011, 499.5 ± 179.1 Inds./10 cm 2 in 2013, and 557.3 ± 24.6 Inds./10 cm 2 in 2014. The abundance of nematodes was analyzed by year and station (Fig. 3 ). In 2009, the highest value of abundance was 604.0 ± 105.2 Inds./10 cm 2 at St. 5, and the lowest value was 110.3 ± 12.3 Inds./10 cm 2 at St. 8. In 2010, the highest value of abundance was 802.7 ± 94.9 Inds./10 cm 2 at St. 6, and the lowest value was 83.0 ± 12.3 Inds./10 cm 2 at St. 3. The highest value of nematode abundance in 2011 was 641.7 ± 129.1 Inds./10 cm 2 at St. 4, the station where the meiofauna abundance was high, and the lowest value was 125.0 ± 20.8 Inds./10 cm 2 at St. 3, the same station as the previous year. The highest value of nematode abundance in 2013 was 775.0 ± 36.9 Inds./10 cm 2 at St. 6, the same station as in 2010, and the lowest value was 201.3 ± 58.1 Inds./10 cm 2 at St. 3, the same station as in the previous years. The highest value of nematode abundance in 2014 was 948.3 ± 32.2 Inds./10 cm 2 at St. 7, the station where the total meiofauna abundance was high, and the lowest value was 157.0 ± 13.3 Inds./10 cm 2 at St. 4, where the abundance was the highest in 2011. Examining the mean abundance of nematodes by station, the values ranged from 228.9 ± 34.8 to 557.0 ± 69.3 Inds./10 cm 2 , with the highest value at St. 4 and the lowest value at St. 8. The mean abundance of nematodes at St. 10, the station with the lowest pH value in the environmental data, was 429.1 ± 91.7 Inds./10 cm 2 , and showed the highest value of 685.0 ± 179.1 Inds./10 cm 2 in 2013 and the lowest value of 265.0 ± 104.5 Inds. /10 cm 2 in 2009. Among the wide range of meiofauna taxa that appeared during the study period, the second most dominant taxon after nematodes was harpacticoids, and their abundance based on population density was as follows: The mean abundance of harpacticoids for each year during the study period was 94.6 ± 9.3 Inds./10 cm 2 in 2009, 116.2 ± 29.2 Inds./10 cm 2 in 2010, 34.3 ± 8.2 Inds./10 cm 2 in 2011, and 136.3 ± 46.0 Inds./10 cm 2 in 2013, and 86.7 ± 12.7 Inds./10 cm 2 in 2014. The abundance of harpacticoids is analyzed annually and per station. In 2009, harpacticoid abundance peaked at 602.3 ± 35.7 Inds./10 cm2 at St. 9, and the minimum was 10.7 ± 1.5 Inds./10 cm 2 at St. 2. In 2010, the peak was 378.7 ± 75.6 Inds./10 cm 2 at St. 3, and the lowest was 23.3 ± 9.4 Inds./10 cm 2 at St. 5. In 2011, the highest harpacticoid abundance was 87.3 ± 12.3 Inds./10 cm 2 at St. 9, and the lowest was 13.0 ± 1.0 Inds./10 cm 2 at St. 3, the station with the highest harpacticoid abundance in 2010. In 2013, the highest harpacticoid abundance was 318.0 ± 153.5 Inds./10 cm 2 at St. 8, and the lowest was 34.7 ± 19.3 Inds./10 cm 2 at St. 5. The highest abundance in 2014 was 169.7 ± 24.4 Inds./10 cm 2 at St. 1, and the lowest was 13.7 ± 5.9 Inds./10 cm 2 at St. 2, the same station as 2009. The mean abundance of harpacticoids per station ranged from 32.9 ± 11.5 to 231.1 ± 25.7 Inds./10 cm 2 , with the highest abundance at St. 9 and the lowest at St. 2. St. 10, which had the lowest pH value, exhibited a mean harpacticoid abundance of 58.5 ± 20.1 Inds./10 cm 2 . Here, the highest harpacticoid abundance (110.0 ± 62.2 Inds./10 cm 2 ) was recorded in 2013, the year with the highest nematode abundance, while the lowest abundance (56.7 ± 1.2 Inds. /10 cm 2 ) was recorded in 2014. Nematodes, the most dominant taxon, accounted for 65.8% of the total meiofauna abundance, while harpacticoids, the second most dominant taxon, accounted for 15.2% (Fig. 4 ). Together, these two taxa constituted 81.0% of the total meiofauna abundance. Other taxa comprising more than 1% of the composition included sarcomastigophorans (8.6%), copepod nauplii (4.5%), and polychaetes (3.3%). The annual composition of dominant (more than 1%) meiofauna taxa varied. In 2009, the composition of major taxa was nematodes (64.9%), followed by harpacticoids (20.0%), copepod nauplii (5.7%), sarcomastigophorans (4.0%), and polychaetes (2.4%). A similar composition was observed in 2010: nematodes (64.9%) are dominant, followed by harpacticoids (21.5%), sarcomastigophorans (7.2%), polychaetes (2.2%), and copepod nauplii (2.1%). In 2011, however, sarcomastigophorans (8.4%) overtook harpacticoids (7.7%) in the second position. By 2014, the composition of major taxa had shifted, with nematodes (60.8%) followed by sarcomastigophorans (18.5%). Using the number of respective meiofauna taxa and their abundance over the survey period, the taxa diversity index, richness, and evenness were calculated (Fig. 5 ). The values of the taxa diversity index (H’) by year are as follows: 0.86 in 2009, 0.94 in 2010, 1.12 in 2011, 0.79 in 2013, and 1.15 in 2014, with 2014 showing the highest value and 2013 showing the lowest value of the diversity index. The taxa diversity index ranged from 0.54 to 1.34 across the stations, with St. 5 having the lowest index and St. 8 having the highest. For St. 10, the station with the lowest pH, the mean taxa diversity index was 0.93, reaching its peak in 2009 (1.24) and minimum (0.75) in 2010. There were substantial differences by station and year in the values of meiofauna richness and evenness, but no clear relationship between the variations could be observed. One pattern that was observed was that richness and the diversity index both exhibited a similar trend. CLUSTER and SIMPROF analyses were applied to generate similarity profiles and classify meiofauna communities by station and year (Fig. 6 ). The analysis yielded four distinct groups. The first group was dominated by 2009 and 2011 meiofauna communities, whereas the second group was characterized by 2014 communities and those from St. 8 and St. 9 in 2009, 2010, and 2011. The final two groups were primarily comprised of 2013 meiofauna communities (SIMPROF test, p < 0.05). Characteristics of nematodes communities The study area yielded a diverse assemblage of nematodes, with a total of 39 genera recorded across the years of observation (Table 8 ). In 2009, the most dominant nematode genus was Chromadorita, represented by 10 individuals. Closely following were the genera Dorylaimopsis and Retrotheristus, with 9 individuals each identified in the study area. Richtersia and Sabatieria each had six individuals, while Halalaimus and Metachromadora each had 5 individuals. In the subsequent year, 2010, Dorylaimopsis emerged as the dominant genus, with 14 individuals. Chromadorita and Sabatieria were also notable, each with 9 individuals. Enoplolaimus and Oxystomina were present with 5 individuals each. In 2011, Chromadorita and Oxystomina demonstrated comparable prevalence, both accounting for 12 individuals. Richtersia and Sabatieria followed with 6 individuals each, while Dorylaimopsis and Enopplolaimus had 5 individuals each. In 2013, Dorylaimopsis exhibited the highest prevalence among the nematode genera, with a total of 13 individuals. Richtersia followed with 10 individuals, while Halalaimus , Enoplolaimus , and Microlaimus accounted for 8, 6, and 5 individuals, respectively. Lastly, in 2014, Chromadorita was again the most dominant genus, with 13 individuals. It was followed by Dorylaimopsis , which had 11 individuals, and then Enoplolaimus and Oxystomina , which each had 8. Furthermore, Richtersia contributed to the composition with 7 individuals. The number of nematode species observed in each year and station is as follows: In 2009, 15 species appeared in St. 5, 13 species in St. 7, and 8 species in St. 10. In 2010, there were 12 species in St. 5, 15 species in St. 7, and 12 species in St. 10. In 2011, 16 species were identified in St. 5, 11 species in St. 7, and 16 species in St. 10. For 2013, there were 11 species in St. 5, 15 species in St. 7, and 10 species in St. 10. Lastly, in 2014, 13 species were observed in St. 5, 15 species in St. 7, and 15 species in St. 10. On average, the number of nematode species per station was 13.4 in St. 5, 13.8 in St. 7, and 12.2 in St. 10. Table 9 presents the changes in the composition of nematodes based on feeding types at the main stations (St. 5, St. 7, St. 10) in the study area. The feeding types observed for each year are as follows: In 2009, epistrate feeders (2A) were the most abundant feeding type across all stations, constituting over 50% of the nematode composition in St. 5 and St. 10. Non-selective deposit feeders (1B) were absent in St. 10, the station characterized by deeper water depths and a lower pH. In 2010, epistrate feeders (2A) were the predominant feeding type in St. 5 and St. 10, while non-selective deposit feeders (1B) were the most frequently observed type in St. 7. In 2011, epistrate feeders (2A) continued to dominate in St. 5 and St. 10, while selective deposit feeders (1A) were the most abundant type in St. 7. In 2013, non-selective deposit feeders (1B) were the most common feeding type in St. 5 and St. 7, while epistrate feeders (2A) were most abundant in St. 10. Finally, in 2014, epistrate feeders (2A) exhibited the highest abundance across all stations. Upon analyzing the feeding types of nematodes by station, notable patterns emerged. In St. 5, epistrate feeders (2A) consistently exhibited the highest proportion in the composition throughout the entire study period. Conversely, predators/omnivores (2B) consistently displayed the lowest ratio, with the exception of 2011. In St. 7, the predominant feeding types varied by year. Epistrate feeders (2A) held the highest ratio in 2009 and 2014, while non-selective deposit feeders (1B) dominated in 2010 and 2013. In 2011, selective deposit feeders (1A) were the most prevalent feeding type in St. 7. Similarly, in St. 10, epistrate feeders (2A) consistently maintained the highest ratio in the composition across all years during the study period. Discussion To examine the occurrence and trends of ocean acidification along the East Sea coast of Korea, the study focused on the coastal region, which was divided into 18 distinct water areas. The analysis primarily utilized seawater temperature and pH data collected from 1993 to 2007. From this comprehensive dataset, the coastal waters of Hupo, located in Gyeongsangbuk-do, were specifically chosen as the study area for this study (KIOST, 2016 ). The average temperature of the bottom layer in the study area was found to be 14.9 ℃. Notably, in 2014, specific stations (St. 4, St. 5, and St. 10) experienced temperatures below 10 ℃. It is important to note that while the coastal waters of the East Sea witness surface layer temperatures rising to 27–29 ℃ during the summer season in Korea, the bottom layer exhibits the presence of a cold water mass with temperatures ranging from 3–10 ℃. This cold water mass forms an undercurrent flowing southwest along the bottom (Lim, D. B. and Jang, S., 1969). Consequently, a significant stratification occurs between the surface and bottom layers during the summer, leading to the development of a cold water zone in the southern waters of the East Coast of Korea from June to September (Lie, H.J. et al., 1992). The average salinity in the study area was 34.0 psu. Notably, in 2009, 2011, and 2013, the mean salinity fell below 34 psu, while in 2010 and 2014, it exceeded 34 psu. Examining the interannual variations of salinity in the Jukbyeon area, located slightly north of the study area, during 2012, measurements revealed a salinity of 34.2 psu in winter, 34 psu in summer, and 33 psu in autumn at 20 m depth. These findings indicate significant variability in coastal water salinity depending on the season of measurement (Jung, H.D. et al., 2013). The mean bottom water pH in the study area was determined to be 8.306. The pH exhibited variation across different time periods, with a minimum of 7.886 in 2011 and a maximum of 8.696 in 2014. Along the coasts of Goseong and Yeongdeok in the East Sea, the pH in surface water ranged from 7.95 to 8.30, while in the bottom water, it ranged from 7.75 to 8.29 throughout the year. Generally, the pH of bottom water tends to be lower than that of surface water, with the pH difference between the two layers increasing during summer due to heightened vertical mixing occurring predominantly in winter (Lee, Y.W. et al., 2016). The coastal region of East Sea is affected by the high-temperature and high-salinity Tsushima Warm Current flowing in from the Korea Strait and the low-temperature and low-salinity North Korean Cold Current flowing southward along the coast from the north. When the two currents meet, a frontal zone is formed around 37–38°N (Chang, K.I. et al., 2002, 2004; Kim, Y.H. and Min, H.S. 2008). Ocean acidification has been found to impact the community structure of benthic organisms, as indicated by previous studies through experiments and field surveys. Specifically, the dominance of algae, such as fast-growing seaweeds, tends to increase under ocean acidification conditions. This shift in dominance can lead to a reduction in the abundance of benthic fauna species, as they face increased competition with algae. Consequently, there is a decline in species diversity (Kroeker et al., 2013 ). These findings highlight the potential consequences of ocean acidification on benthic communities and emphasize the importance of further understanding its ecological impacts. This study aimed to investigate the relationship between benthic meiofauna communities and ocean acidification by conducting a 5-year survey at 10 stations in the coastal waters of Hupo. The mean abundance of meiofauna, or meiofaunal density, averaged over the survey period was 614.4 Inds./10 cm 2 . This value falls within a smaller range compared to the meiofauna abundance reported in the intertidal zone of the West Sea, which ranged from 1,521 to 7,849 Inds./10 cm 2 , with a mean abundance of 4,161 Inds./10 cm 2 (Kim et al. 1998 ). Similarly, in the intertidal zone of Daebudo, Korea, the range of meiofauna abundance was 30 to 1,382 Inds./10 cm 2 , with a mean abundance of 751 Inds./10 cm 2 (Min et al. 2006 ). The meiofaunal densities observed in this study are more comparable to the meiofauna abundance reported in the subtidal zone of the West Sea, which ranged from 17 to 853 Inds./10 cm 2 (Kang, T.W. et al., 2011). This discrepancy can be attributed to the sedimentary facies in the coastal waters. The West Sea intertidal zone consists of smaller-grained sediments compared to the sandy sedimentary facies of the East Sea subtidal zone, resulting in higher meiofauna abundance in the former. Moreover, the abundance values in this study are similar to that with the West Sea subtidal zone, which also had sandy sedimentary facies. The mean meiofauna abundance in this study is higher compared to the reported abundance, which ranges from 49.8 to 1,959.1 Inds./10 cm2, averaging at 591 Inds./10 cm2, in the northeastern subtidal zone of Jeju Island (Kang, T.W. and Kim, D., 2020). Nematodes and harpacticoids were the dominant taxa among meiofauna in the study area, with copepod nauplii, sarcomastigophorans, and polychaetes also present in significant proportions. This composition is similar to the meiofauna community structure observed in the West Sea (Kim et al., 2004 ; Kim and Lee, 2000 ). Previous studies have consistently reported the presence of nematodes, harpacticoids, tardigrades, platyhelminths, kinorhynchs, and gastrotrichs as representative meiofauna in various marine ecosystems (Dorris et al., 1999 ). This study revealed that nematodes constituted approximately 65 to 70% of the meiofauna composition, while harpacticoids accounted for approximately 7 to 20%, together representing about 80% of the total meiofauna abundance. Nematodes and harpacticoids are commonly observed in high abundance across marine benthic ecosystems (James and Mark, 2004). Nematodes, in particular, are recognized for their dominance within meiofauna communities in terms of abundance and biomass. Previous studies have reported nematodes to comprise around 90 to 95% of the total meiofauna abundance and contribute to 50 to 90% of the biomass (Giere, 1993 ). Given that the study area consists of sandy facies in the East Sea, the proportion of harpacticoids is relatively higher compared to coastal regions characterized by muddy facies. For instance, investigations in Gwangyang Bay and Gamak Bay, which primarily feature muddy facies, revealed nematodes accounting for over 70% of the composition in most stations, with some stations exclusively inhabited by nematodes (Kim, D. et al., 2000 ; Lee H.G. et al., 2019). Among the monitored environmental factors in this study, St. 10 exhibited the lowest pH value, particularly reaching a very low pH of 7.821 in 2011. Correspondingly, the meiofauna and harpacticoid abundances at St. 10 were the lowest during the 5-year study period. It is widely recognized that ocean acidification exerts significant impacts on marine communities, particularly leading to a reduced abundance of benthic fauna, especially those species involved in shell formation or calcification (Fabry et al., 2008 ). Consistent with this understanding, the findings of this study indicate a decrease in the abundance of harpacticoids, which are known for their sensitivity to environmental changes and possession of external shells, in response to the decline in seawater pH. However, the impact on the abundance of nematodes in St. 10, despite being the station with the lowest pH, was not significant. Nematodes are generally considered less susceptible to environmental stress compared to harpacticoids (Croll and Mathews, 1977 ; Platt et al., 1984 ). Notably, the abundance of nematodes in St. 10 was 429.1 Inds./10 cm 2 , surpassing the overall mean abundance. The impact of ocean acidification on benthic faunal communities, particularly at the meiofauna level, has received limited research attention. Only a few empirical studies conducted under field conditions have addressed this topic. One such study focused on a coral reef meiofauna community and found that changes in community structure were observed after 30 days of exposure to low pH conditions associated with ocean acidification. Among the taxa examined, Nematoda , Ostracoda , Turbellaria , and Tardigrada exhibited the highest density in the low pH environment. Harpacticoid nauplii were found to be particularly affected by the low seawater pH levels. However, no significant differences were observed in the abundance of Harpacticoida and Polychaeta in response to pH changes (Sarmento et al., 2015 ). The analysis of nematode species composition at the three stations revealed a smaller number of taxa at St. 10, which had low pH conditions. This aligns with the known effects of ocean acidification, which can lead to reduced abundance and species diversity. In 2009, when St. 10 exhibited low seawater pH levels, the number of nematode taxa was only 8, significantly lower than in other years of the study. Interestingly, a previous mesocosm experiment investigating the impact of ocean acidification on nematodes did not observe significant effects, suggesting that nematodes in shallow-water areas may have developed greater resistance to environmental variations and stress (Esteves et al., 2022 ). The c-p value (colonizer-persister) value for nematode species is the value proposed by Bongers et al ( 1991 ), which ecologically divides nematodes into 5 groups and assigns a value between 1 and 5 to each group. A low value is assigned to a group belonging to an opportunistic species with a short life cycle, and a high value is assigned to a group that is sensitive to environmental changes and prefers a stable environment with a long life cycle. The species composition analysis of nematodes at stations St. 5, St. 7, and St. 10, which experience more severe ocean acidification compared to other stations, revealed that the dominant species in all three stations were Chromadorita spp. and Dorylaimopsis spp. Chromadorita spp. has a c-p value of 3, indicating it has a relatively long generation time and is sensitive to environmental disturbances (Table 8 ). On the other hand, Dorylaimopsis spp. has a c-p value of 2, suggesting it is highly resistant to environmental pollution or disturbances. It is expected that the proportion of these resistant species will increase in the species composition as environmental changes continue to unfold. Although the impact of ocean acidification on nematode communities could not be conclusively determined in this study due to the presence of both sensitive and resistant species, the abundance of these species can serve as a valuable indicator of the impact of sedimentary environmental changes. Therefore, the study area where these species are abundant is considered suitable for investigating the effects of ocean acidification on nematodes in the future (Semprucci et al., 2015 ). Upon examination of the dominant feeding types among nematodes, epistrate feeders (2A) were found to have the highest proportion throughout the study period, accounting for 43.4% of the total nematode composition. Non-selective deposit feeders (1B) were the second most dominant feeding type, comprising approximately 26.2%, followed by selective deposit feeders (1A) at 18.6% and predators/omnivores (2B) at 11.8%. In St. 10, which had the lowest pH level, epistrate feeders (2A) consistently had the highest ratio among the feeding types. It is known that variations in nematode feeding types occur in response to environmental changes, and analyzing the distribution of feeding types provides insights into the food web dynamics of benthic ecosystems (Beier and Traunspurger, 2001 ). While epistrate feeders (2A) dominated in all stations, their proportion was particularly high at 52.8% in St. 10, the station with the lowest pH. The proportions of other feeding types ranged from 11.1–19.4%. In contrast, St. 7 exhibited a more balanced distribution of feeding types, with selective deposit feeders (1A) accounting for 21.4%, non-selective deposit feeders (1B) accounting for 31.0%, epistrate feeders (2A) accounting for 32.4%, and predators/omnivores (2B) accounting for 15.2%. This suggests that St. 7 experiences higher environmental stability compared to other stations. To comprehensively investigate the impact of ocean acidification on meiofauna communities, it is crucial to analyze the species composition of dominant taxa and consider various environmental conditions. Previous studies have highlighted the influence of sediment type on meiofauna diversity and community structure while indicating limited impacts of CO2 concentration and temperature (Ingels et al. 2018 ). In the present study, no visible impact of ocean acidification on meiofauna communities was observed within the 5-year study period, likely due to the short duration and focus on limited meiofauna communities in the coastal waters of Hupo. Since environmental changes occur gradually over an extended timeframe, long-term monitoring is necessary to better understand the effects. It is also important to conduct comparative analyses across different regions and research datasets, considering that ocean acidification is a global phenomenon. Moreover, meiofauna serves as a valuable research subject for investigating the impacts of environmental changes, given its restricted distribution range and short life cycle compared to other benthic organisms. Declarations Acknowledgements This research was supported by Korean Institute of Marine Science & Technology Promotion (KIMST) funded by the Ministry of Oceans and Fisheries (20170411), Korea. Ethical Approval The authors declared no potential conflicts of interest for the research, authorship, and/or publication of this article. Competing interests The authors have no competing interests to declare that are relevant to the content of this article. Authors' contributions Je Hyeok Oh and Teawook Kang wrote the main manuscript text and prepared all figures. Ayoung Shin and Min Gyu Jung prepared all figures and tables. Dongsung Kim and Wonchoel Lee reviewed the total manuscript. Funding not applicable Availability of data and materials not applicable References Barry JP, Lovera C, Buck KR, Peltzer ET, Taylor JR (2014) Ocean acidification responses in deep sea snail communities. Proceedings of the Royal Society B: Biological Sciences 281(1779):20133281 Beier S, Traunspurger W (2001) The meiofauna community of two small German streams as indicator of pollution. J Aquat Ecosyst Stress Recover 8:387–405 Bongers T, Alkemade R, Yeates GW (1991) Interpretation of disturbance-induced maturity decrease in marine nematode assemblages by means of the Maturity Index. Mar Ecol Prog Ser 76:135-142 Brewer PG (1997) Ocean chemistry of the fossil fuel CO2 signal: The haline signal of "business as usual". Geophys Res Lett 24:1367-1369 Burgess R (2001) An improved protocol for separating meiofauna from sediments using colloidal silica sols. Mar Ecol Prog Ser 214:161-165 Chang KI, Hogg N, Suk MS, Byun SK, Kim YG, Kim K (2002) Mean Flow and Variability in the Southwestern East Sea. Deep Sea Res I 49:2261-2279 Chang KI, Teague WJ, Lyn SJ, Perkins HT, Lee DK,Watts DR, Kim YB, Mitchell DA, Lee CM, Kim K (2004) Circulation and Currents in the Southwestern East/Japan Sea: Overview and Review. Prog Oceangr 61:105-156 Clarke KR, Gorley RN (2001) PRIMER v5 User manual Plymouth: PRIMER-E Coull BC, Chandler GT (1992) Pollution and meiofauna: field, laboratory and mesocosm studies. Oceanogr Mar Biol Annu Rev 30:191-271 Croll NA, Mathews GB (1977) Biology of Nematodes. Glassgow: Blackie & Sons Ltd Dorris M, Ley PD, Blaxter ML (1999) Molecular analysis of nematode diversity and the evolution of parasitism. Parasitol Today 15(5):188-193 Dupont S, Thorndyke MC (2008) Ocean acidification and its impact on the early life-history stages of marine animals. In: Impacts of acidification on biological, chemical and physical systems in the Mediterranean and Black Seas. CIESM Monogr 36: 89-97 Dupont S, Thorndyke MC (2009) Impact of CO2-driven ocean acidification on invertebrates early life-history - Want we know, what we need to know and what we can do. Journal of Biogeosciences Discuss 6:3109-3131 Esteves AM, Souza TP, Sarmento VDC, Maria TF, Santos PJPD (2022) Effects of the ocean acidification on the functional structure of coral reef nematodes. Coral Reefs 41(5):1481-1494 Fabry VJ, Seibel BA, Feely RA, Orr JC (2008) Impacts of ocean acidification on marine fauna and ecosystem processes. ICES Journal of Marine Science 65(3):414-432 Ferris H, Bongers T (2009) Indices developed specifically for analysis of nematode assemblages. In M. J. Wilson and T. Kakouli-Duarte (eds.). Nematodes as environmental indicators. Wallingford: CAB International 124-145 Fosså JH, Mortensen PB, Furevik DM, Ellingsen KE (2012) The deep-water coral Lophelia pertusa in Norwegian waters: distribution and fishery impacts. Hydrobiologia 687(1):53-65 Gazeau F, Quiblier C, Jansen JM, Gattuso JP, Middelburg JJ, Heip CH (2007) Impact of elevated CO2 on shellfish calcification. Geophysical Research Letters 34(7) Giere O (1993) Meiobenthology: The microscopic fauna in aquatic sediments. Springer-Verlag Berlin, Heidelberg, New York Higgins RP, Thiel H (1988) Introduction to the study of meiofauna. Washington, DC: Smithsonian Institution Press Ingels J, dos Santos G, Hicks N, Vazquez YV, Neres PF, Pontes LP ... Widdicombe S (2018) Short-term CO2 exposure and temperature rise effects on metazoan meiofauna and free-living nematodes in sandy and muddy sediments: results from a flume experiment. Journal of Experimental Marine Biology and Ecology 502:211-226 IPCC (2007) Summary for policymakers in climate change 2007: the physical science basis. Contribution of working group I to the fourth assessment report of the Intergovernmental Panel on Climate Change. Cambridge (UK): University Press Nybakken JW, Bertness MD (2004) Marine Biology:An ecological approach. Person Education, Inc Jung HD, Kim SW, Kwon K, Lim JW, Kwoun CH (2013) Oceanographic Features Around Aquaculture Areas of the Eastern Coast of Korea. Korean Soc Mar Environ Saf 19(4):34-344 Kang TW, Kim D, Min WG, Rho HS, Hong JS (2011) Characteristics of Meiobenthic Community Inhabiting Sandy Sediment in the Yellow Sea, Korea. Ocean Polar Res 33(3):193–209 Kang TW, Kim D (2020) Meiobenthic Community Structure on the Northeast Coastal Area of Jeju Island, Korea. Ocean Polar Res 42(1):1-13 Kim D, Choi JW, Je JG, Lee JH (1998) Community Structure of Meiobenthos in Tidal Flats at Taebudo, West Coast of Korea. Ocean Polar Res 20(2):81–87 Kim D, Je JG, Shin SH (2000) Utilization of meiobenthos for pollution monitoring in the Gamak Bay, Korea. Journal of the Korean Fisheries Society 33(4):307-319 Kim D, Lee JH (2000) Impacts of Contaminated Water Outflow from the Lake Sihwa on the Meiobenthic Animals Living in the Coastal Zones of the Kyonggi Bay. Korean J Environ Biol 18(2):205-216 Kim D, Min WG, Lee JH (2004) Variation of Meiobenthic Community in the Sediment of Coastal Area in Bangameori Daebudo, Korea. Korean J Environ Biol 22(2): 308-320 Kim YH, Min HS (2008) Seasonal and Interannual Variability of the North Korean Cold Current in the East Sea Reanalysis Data. Ocean and Polar Res 31(1):21-31 KIOST (2016) Ecological Impacts of Ocean Acidicfication (EcoAcid). KIOST (Korea Institute of Ocean Science & Technology), Final Report BSPE99317-10976-3 Kroeker KJ, Kordas RL, Crim RN, Singh GG (2010) Meta-analysis reveals negative yet variable effects of ocean acidification on marine organisms. Ecology Letters 13(11):1419-1434 Kroeker KJ, Micheli F, Gambi MC (2013) Ocean acidification causes ecosystem shifts via altered competitive interactions. Nature Climate Change 3(2):156-159 Lee HG, Kang TW, Rho HS, Kim D (2019) Seasonal Distribution Characteristics of Meiobenthos at Gwangyang Bay, Korea. J Korean Soc Oceanogr 24(3):400-421 Lee YW, Park MO, Kim SS (2016) Spatiotemporal Variations of Marine Environmental Characteristics in the Middle East Coast of Korea in 2013-2014. J Korean Soc Mar Environ Energy 19(4):274-285 Lie HJ, Shin CW, Seung YH (1992) Internal Tidal Oscillations of Temperature off Jukbyun on the East Coast of Korea. J. Korean Soc Oceanogr 27(3):228-236 Lim DB, Jang S (1969) On the cold water in the Korea Strait. J Korean Soc Oceanogr 4(2):71-82 Manno C, Stumpp M, Saderne V, Pörtner HO, Tubau X (2017) Resilience of the blue mussel Mytilus edulis to seawater acidification depends on the nutritional value of its diet. Estuarine, Coastal and Shelf Science 189:158-168 Melzner F, Gobel S, Langenbuch M (2009) Swimming performance in Atlantic Cod (Gadus morhua) following long-term (4-12 months) acclimation to elevated seawater pCO2. Aquatic toxicology 92(1):30-37 Min WG, Kim D, and Lee JH (2006) Community Structure and Spatial Variation of Meiobenthos Associated with an Artificial Structure. Korean J Fish Aquat Sci 39(1):223–230 Moore CG, Bett BJ (1989) The use of meiofauna in marine pollution impact assessment. Zool J Linn Soc 96:263-280 Oh JH, Kang T, Shin A, Kim T, Yu OH, Lee W, Kim D (2022) Effect of Different p CO2 Concentrations in Seawater on Meiofauna: Abundance of Communities in Sediment and Survival Rate of Harpacticoid Copepods. Ocean Science Journal 57(2):279-286 Oh JH, Kim D, Kim TW, Kang T, Yu OH, Lee W (2017) Effect of increased p CO2 in seawater on survival rate of different developmental stages of the harpacticoid copepod Tigriopus japonicus. Animal Cells and Systems 21(3):217-222 Platt HM, Warwick RM (1983) A Synopsis of the Free-living Marine Nematodes. Part I. British Enoplids. Cambridge University Press, Cambridge, pp 35-85 Platt HM, Shaw KM, Lambshead PJD (1984) Nematode species abundance patterns and their use in the detection of environmental perturbations. Hydrobiologia 118:59-66 Przeslawski R, Zhu Q, Aller R (2009) Effects of abiotic stressors on infaunal burrowing and associated sediment characteristics. Mar Ecol Prog Ser 392:33-42 Sarmento VC, Souza TP, Esteves AM, Santos PJP (2015) Effects of seawater acidification on a coral reef meiofauna community. Coral Reefs 34:955-966 Semprucci F, Losi V, Moreno M (2015) A review of Italian research on free-living marine nematodes and the future perspectives in their use as ecological indicators (EcoInd). Mediterr Mar Sci 16:352-365 Solomon S, Qin D, Manning M, Chen Z, Marquis M, Averyt KB, Tignor M, Miller HL (2007) Climate Change 2007: The Physical Science Basis - Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cam-bridge Thomsen J, Melzner F (2010) Moderate seawater acidification does not elicit long-term metabolic depression in the blue mussel Mytilus edulis. Marine Biology 157(12):2667-2676 Zeebe RE, Zachos JC, Caldeira K, Tyrrell T (2008) Carbon emissions and acidification. Science 32:51–52 Tables Tables are available in Supplementary Files section. Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3034005","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":208224580,"identity":"da5422f1-5168-4d11-9380-9be1fcb58ec4","order_by":0,"name":"Je Hyeok Oh","email":"","orcid":"","institution":"Korea Institute of Ocean Science and Technology","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Je","middleName":"Hyeok","lastName":"Oh","suffix":""},{"id":208224581,"identity":"8b3816f4-b52f-4905-bfc0-2c64f44bae0e","order_by":1,"name":"Teawook Kang","email":"","orcid":"","institution":"National Park Research 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2","display":"","copyAsset":false,"role":"figure","size":45318,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of yearly trends in the environmental characteristics at each station in the study area\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3034005/v1/c64246cd9c0b379657277b10.png"},{"id":38410620,"identity":"c0f41ec8-d61e-4847-bc03-c928667693dc","added_by":"auto","created_at":"2023-06-12 15:15:48","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":69292,"visible":true,"origin":"","legend":"\u003cp\u003eYearly trends in the abundance of major meiofauna taxa in the study area\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3034005/v1/038f7e890ef1ba990da2fe10.png"},{"id":38408267,"identity":"50d4a389-379a-49d3-bb0c-81183c07a890","added_by":"auto","created_at":"2023-06-12 14:59:48","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":55802,"visible":true,"origin":"","legend":"\u003cp\u003eComposition of meiofaunal dominant taxa across various stations in the study area\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3034005/v1/42afaa3086aa75664b8895aa.png"},{"id":38408269,"identity":"f52efb34-93c3-4cf8-a0b2-26eecafb05dc","added_by":"auto","created_at":"2023-06-12 14:59:48","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":53477,"visible":true,"origin":"","legend":"\u003cp\u003eNumber of taxa, richness, evenness and diversity index for meiofauna in the study area\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3034005/v1/c33184c5240fc49cd69ef3dc.png"},{"id":38409604,"identity":"705e2bfb-70e1-45cf-a634-886c84463903","added_by":"auto","created_at":"2023-06-12 15:07:48","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":27808,"visible":true,"origin":"","legend":"\u003cp\u003eCLUSTER analysis based on Bray-Curtis similarities among the meiofaunal communities at each station in study area\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-3034005/v1/9f7352cc59761cc9777f3be5.png"},{"id":105223423,"identity":"d12bc974-2a88-4f06-876c-fa381290c772","added_by":"auto","created_at":"2026-03-23 16:06:18","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1078154,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3034005/v1/7fbd9746-48c6-4f28-b2bc-971d50f9f8b9.pdf"},{"id":38408265,"identity":"db563a61-a8ce-4008-bea2-64e7155ef626","added_by":"auto","created_at":"2023-06-12 14:59:48","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":71024,"visible":true,"origin":"","legend":"","description":"","filename":"Tables.docx","url":"https://assets-eu.researchsquare.com/files/rs-3034005/v1/9d7e228d7143de1eadc0d2a6.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Characteristics of meiofaunal community in the subtidal zone near Hupo, anticipating ocean acidification in the East Sea of Korea","fulltext":[{"header":"Introduction","content":"\u003cp\u003eCarbon dioxide (CO\u003csub\u003e2\u003c/sub\u003e) is one of the most important greenhouse gases in the atmosphere, and its concentration in the atmosphere has been continuously increasing because of the growing consumption of fossil fuels following industrial development and economic growth; it has thus been drawing attention as a major source of global warming and a cause of climate change (Solomon et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). An increase in atmospheric CO\u003csub\u003e2\u003c/sub\u003e concentration results in seawater acidification, posing a threat to the safety of marine life and ecosystems. Oceans have played a major role in alleviating the accelerating pace of global warming via uptake of atmospheric CO\u003csub\u003e2\u003c/sub\u003e; however, this has resulted in ocean acidification, wherein the pH of seawater decreases owing to an increase in the CO\u003csub\u003e2\u003c/sub\u003e flowing into the ocean from an increase in atmospheric CO\u003csub\u003e2\u003c/sub\u003e concentration (Zeebe et al. \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). The pH of the ocean has decreased by about 0.1 compared to the preindustrial level and is expected to decrease by approximately 0.2\u0026ndash;0.4 within the next 100 years. Seawater temperature has also increased by 0.76\u0026deg;C compared to that in the previous century, and is predicted to increase by more than 2\u0026deg;C within the next 100 years (Brewer \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; IPCC \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2007\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn response to these environmental changes, studies on the effects of ocean acidification on marine organisms have been undertaken using various approaches. The results of recent studies indicate that ocean acidification has a negative impact on the growth, reproduction, and survival of organisms in many cases; however, it has also shown a positive impact on some species (Kroeker et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Some studies have reported that ocean acidification impacts the calcification of shellfish and is associated with a decline in calcification rates and a decrease in shell growth (Gazeau et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). Most studies on the effects of ocean acidification on benthic ecosystems have focused on benthic macrofauna (Kroeker et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Manno et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Barry et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Foss\u0026aring; et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Thomsen et al. 2010).\u003c/p\u003e \u003cp\u003eThe responses of marine organisms to ocean acidification vary depending on the species, regions, and communities (Dupont and Thorndyke \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2008\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Melzner et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Przeslawski et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Therefore, to understand the changes caused by ocean acidification in ecosystems, studies considering ecological niches are required. Further, because benthic fauna lack the ability to quickly respond to environmental changes owing to their sluggish locomotion, they are more vulnerable to environmental changes such as ocean acidification (Fabry et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Among benthic fauna, meiofauna have been reported as highly useful for studying the effects of environmental disturbances such as pollution (Coull and Chandler \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1992\u003c/span\u003e). Despite the pressing need for research on the effects of ocean acidification on meiofauna, which play an important role as food source for fish or secondary producers in the benthic ecosystem, few studies on these have been undertaken in Korea. Some recent studies on meiofauna included experimental studies to examine the impact of ocean acidification on harpacticoid copepods (Oh et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Oh et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eMeiofauna are organisms dwelling in almost any type of aquatic environment; they live in marine as well as fresh water and are widely distributed from shallow coastal waters to deep seas, and from tropical to polar regions. Further, meiofauna inhabit a wide range of sedimentary environments from muddy benthic sediments with small particle sizes to coarse shell sand with large particles; notably, some species have adhesive organs to hold onto the surface of large birds and various animals. Typically, meiofauna inhabit within the top 2 cm of sediments, and in terms of vertical distribution, the range of meiofauna distribution is controlled by the depth of the Redox Potential Discontinuity (RPD, a layer of the transition from oxygenated to anoxic conditions) layer within the sediments; however, some species may prefer anoxic or hypoxic conditions, i.e., anaerobic conditions (Higgins and Thiel \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e1988\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eCompared to benthic macrofauna, meiofauna have smaller sizes, shorter life spans, and shorter generation times; their larval settlement is found in marine sediments. Meiofauna are a biological group serving as an effective tool for ecological research or assessment of environmental impact. Owing to their high abundance, detection of changes in their population density is easier than that in other types of organisms, and they have many taxa that show sensitive responses to environmental changes. In terms of survey methods, meiofauna can be analyzed by collecting only a small amount of samples from sediments, thereby minimizing the damage to the natural environment caused by sampling (Moore and Bett \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e1989\u003c/span\u003e). Although meiofauna are tiny organisms, their population density is typically 10\u003csup\u003e4\u003c/sup\u003e \u0026minus;\u0026thinsp;10\u003csup\u003e5\u003c/sup\u003e individuals per square meter even in oligotrophic environments, and under more favorable environmental conditions for meiofauna habitats, a high abundance of 10\u003csup\u003e5\u003c/sup\u003e \u0026ndash; 10\u003csup\u003e8\u003c/sup\u003e individuals/m\u003csup\u003e2\u003c/sup\u003e has been reported (Giere \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1993\u003c/span\u003e). In general, the number of meiofauna individuals per unit area is relatively high in the intertidal zone, and their number decreases with increasing water depth and further from the coast; in general, the population density of meiofauna is determined by factors such as interstitial space in the sediments, organic matter content, and oxygen content in the interstitial water.\u003c/p\u003e \u003cp\u003eThus, this study aimed to investigate how meiofauna communities, an integral part of the benthic ecosystem, are affected in the coastal waters of Hupo in Uljin, an area that is highly subject to the trend of ocean acidification among the coastal waters of Korea.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003eSampling Sites\u003c/h2\u003e\n \u003cp\u003eThe coastal waters of Hupo in Uljin on the east coast of Korea were selected as the study area. For determining of the study area among the coastal waters of East Sea, the patterns of time-series changes in the factors representing the marine environment alterations related to climate change, such as seawater temperature and pH, were analyzed; based on these results, the sea area of Hupo was selected as appropriate for conducting monitoring surveys. In total, 10 stations were selected in the coastal waters of Hupo, and meiofauna samples were collected in summer (July-August), the period with the largest biomass, for a total of five years (2009, 2010, 2011, 2013, and 2014) (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003eSampling and analysis methods\u003c/h2\u003e\n \u003cp\u003eFor collecting sediment samples, an acrylic core (10 cm\u003csup\u003e2\u003c/sup\u003e) was used to sample the top 3 cm of the sediment layer; the samples were immediately fixed with 5% formalin and moved to the laboratory. For the sediment samples moved to the laboratory, Ludox HS40 (DuPont, specific gravity 1.18) was used to extract meiofaunal organisms from the sediments. (Burgess \u003cspan class=\"CitationRef\"\u003e2001\u003c/span\u003e). Meiofauna isolated from the sediments were examined and counted at the taxon level under a stereomicroscope (Leica MZ16).\u003c/p\u003e\n \u003cp\u003eThe nematodes that appeared at some of the stations (St. 5, St. 7, and St. 10) expected to show a strong trend of ocean acidification were transferred to a 3% glycerin solution for species identification. The nematodes appearing at each station were prepared as slide samples and analyzed up to the genus level using an optical microscope (Olympus BX51, Platt and Warwick \u003cspan class=\"CitationRef\"\u003e1983\u003c/span\u003e). Further, the nematodes were classified into four feeding types (1A, selective deposit feeders; 1B, non-selective deposit feeders; 2A, epistrate feeders; 2B, predators/omnivores) as proposed by Wieser (1953).\u003c/p\u003e\n \u003cp\u003eTo examine the differences between meiofauna communities from respective sampling sites, CLUSTER and SIMPROF (similarity profiles) analyses were performed based on Bray-Curtis similarity. In the analyses used in this study, fourth root transformed values were used to determine the total meiofauna abundance. For CLUSTER and SIMPROF analyses, the software PRIMER (v. 6.1.12) was used (Clarke and Gorley \u003cspan class=\"CitationRef\"\u003e2001\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n \u003ch2\u003eEnvironmental characteristics\u003c/h2\u003e\n \u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e present the bottom layer water temperatures during the monitoring period in Hupo, Uljin. The bottom layer temperature measurement in the summer of 2009 revealed that the highest water temperature was measured as 18.6\u0026deg;C at St. 9, a station at shallow depth, and the lowest water temperature was 10.9℃ at St. 5, which was at a depth of 35 m. The bottom layer temperature measurement in the summer of 2010 revealed that the highest temperature was 22.3\u0026deg;C at St. 9, the same station as in 2009, and the lowest temperature was 11.3\u0026deg;C at St. 5, also the same station as in 2009. In the summer of 2011, the highest temperature was 20.5\u0026deg;C at St. 9, the same station as the previous two years, and likewise, the lowest temperature was 9.7\u0026deg;C at St. 5. In the summer of 2013, the highest bottom layer water temperature was 24.5\u0026deg;C at St. 9, the same station as before, and the lowest water temperature was 10.1\u0026deg;C, this year at St. 10, the station with the greatest water depth. In the summer of 2014, the highest temperature was 12.7\u0026deg;C at St. 6 but not St. 9, which had showed the highest water temperature during the previous years, and the lowest water temperature was 6.9\u0026deg;C at St. 10, the station with the greatest water depth as in the previous year. The mean bottom layer temperature for each year was as follows: 14.3\u0026deg;C in 2009, 16.5\u0026deg;C in 2010, 9.6\u0026deg;C in 2011, 17.3\u0026deg;C in 2013, and 10.7\u0026deg;C in 2014, showing the highest temperature in 2013 and the lowest in 2014.\u003c/p\u003e\n \u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e present the bottom layer salinity during the monitoring period in Hupo, Uljin. Analysis of salinity in 2009 revealed that the highest salinity was 34.12 psu obtained at St. 10, the station with the greatest water depth, and the lowest salinity was 33.07 psu at St. 9, the station with the lowest water depth. In 2010, the highest salinity was 35.64 psu at St. 4, the station with a relatively great water depth, and the lowest salinity was 33.62 psu at St. 7. In 2011, the highest salinity was 34.96 psu at St. 7, and the lowest salinity was 33.14 psu at St. 9, the same station as in 2009. In 2013, the highest salinity was 35.14 psu at St. 2, and the lowest salinity was 32.83 psu at St. 9, the same as in the previous years. In 2014, the highest salinity was 34.38 psu at St. 1, and the lowest salinity was 34.11 psu at St. 10, the station at the greatest water depth. The mean bottom layer salinity for each year was 33.8 psu in 2009, 34.5 psu in 2010, 33.8 psu in 2011, 33.7 psu in 2013, and 34.3 psu in 2014, showing the highest salinity in 2010 and the lowest in 2013.\u003c/p\u003e\n \u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e present the bottom layer pH during the monitoring period in Hupo, Uljin. Analysis of the pH in 2009 revealed that the highest pH was 8.192 at St. 7, a station with the relatively low water depth, and the lowest pH was 7.887 at St. 10, the deepest station. In 2010, the highest pH was 8.653 at St. 1 with low depth and the lowest pH was 8.361 at St. 9, also a station at low depth. In 2011, the highest pH was 7.973 at St. 8 and the lowest pH was 7.812 at St. 5. In 2013, the highest pH was 8.916 at St. 1, the same station as in 2010, and the lowest pH was 7.959 at St. 5, the same station as in the previous year. In 2014, the highest pH was 8.832 at St. 2 and the lowest pH was 8.633 at St. 4. The mean bottom layer pH for each year was 8.032 in 2009, 8.504 in 2010, 7.886 in 2011, 8.414 in 2013, and 8.696 in 2014, with the highest pH in 2014 and the lowest pH in 2011. Examining the pH analysis results by station, the pH values ranged from 8.195\u0026ndash;8.465, and the lowest pH value was obtained at St. 10, the station at the greatest water depth and the southernmost point, and the highest pH value was obtained at St. 1, the station at the northernmost point.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n \u003ch2\u003eCharacteristics of meiofauna communities in the study area\u003c/h2\u003e\n \u003cp\u003eIn total, 23 meiofauna taxa were identified in samples collected over the five-year period in the entire study area as follows (Tables \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e, \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e, and \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e): nematodes (Nematoda), harpacticoids (Harpacticoida), copepod nauplii (Nauplii), benthic foraminifera/sarcomastigophorans (Sarcomastigophora), polychaetes (Polychaeta), ostracods (Ostracoda), bivalves (Bivalvia), amphipods (Amphipoda), tanaidaceans (Tanaidacea), isopods, cumaceans (Cumacea), kinorhynchs (Kinorhyncha), tardigrades (Tardigrada), nemertines (Nemertea), turbellarians (Turbellaria), halacaroideans (Halacaroidea), gnathostomulids (Gnathostomulida), gastrotrichs (Gastrotricha), priapulids (Priapulida), syncarids (Syncarida), gastropods (Gastropoda), and echinoderms (Echinoderm).\u003c/p\u003e\n \u003cp\u003eThe mean abundance of meiofauna by year during the monitoring period was 473.6\u0026thinsp;\u0026plusmn;\u0026thinsp;65.1 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e in 2009, 541.0\u0026thinsp;\u0026plusmn;\u0026thinsp;97.0 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e in 2010, 443.2\u0026thinsp;\u0026plusmn;\u0026thinsp;66.2 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e in 2011, 700.4\u0026thinsp;\u0026plusmn;\u0026thinsp;122.4 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e in 2013, and 916.5\u0026thinsp;\u0026plusmn;\u0026thinsp;79.8 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e in 2014.\u003c/p\u003e\n \u003ctable id=\"Tab3\" border=\"1\"\u003e\u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003eThe meiofauna abundance by year at each station during the study period was as follows. In 2009, the highest value of meiofauna abundance was 1521.0\u0026thinsp;\u0026plusmn;\u0026thinsp;138.7 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 9 and the lowest was 184.0\u0026thinsp;\u0026plusmn;\u0026thinsp;51.4 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 1. In 2010, the highest value of meiofauna abundance was 1235.0\u0026thinsp;\u0026plusmn;\u0026thinsp;172.1 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 4, and the lowest value was 192.3\u0026thinsp;\u0026plusmn;\u0026thinsp;41.3 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 7. In 2011, the highest value of meiofauna abundance was 751.3\u0026thinsp;\u0026plusmn;\u0026thinsp;115.7 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 4, the same station as in the previous year, and the lowest value was 221.7\u0026thinsp;\u0026plusmn;\u0026thinsp;34.7 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 3. In 2013, the highest value of meiofauna abundance was 1163.0\u0026thinsp;\u0026plusmn;\u0026thinsp;73.2 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 6, and the lowest value was 442.0\u0026thinsp;\u0026plusmn;\u0026thinsp;116.0 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 3, the same station as in the year 2011. In 2014, the highest value of meiofauna abundance was 1373.0\u0026thinsp;\u0026plusmn;\u0026thinsp;67.6 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 7, and the lowest value was 337.7\u0026thinsp;\u0026plusmn;\u0026thinsp;16.1 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 6.\u003c/p\u003e\n \u003cp\u003eUpon examining the mean meiofauna abundance by station, the values ranged from 507.6\u0026thinsp;\u0026plusmn;\u0026thinsp;68.9\u0026ndash;928.3\u0026thinsp;\u0026plusmn;\u0026thinsp;97.1 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e, with the highest value at St. 9 and the lowest at St. 1. The mean meiofauna abundance at St. 10, the station with the lowest pH value in the environmental data, was 614.4\u0026thinsp;\u0026plusmn;\u0026thinsp;115.1 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e, with the highest value at 1010.7\u0026thinsp;\u0026plusmn;\u0026thinsp;23.0 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e in 2014, and the lowest value at 381.3\u0026thinsp;\u0026plusmn;\u0026thinsp;133.4 Inds. /10 cm\u003csup\u003e2\u003c/sup\u003e in 2010.\u003c/p\u003e\n \u003cp\u003eThe results of analyzing the abundance of nematodes, the most dominant taxon among the meiofauna, which appeared during the monitoring period, are as follows. The mean abundance of nematodes for each year in the study period was as follows: 307.4\u0026thinsp;\u0026plusmn;\u0026thinsp;43.7 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e in 2009, 351.1\u0026thinsp;\u0026plusmn;\u0026thinsp;101.7 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e in 2010, 307.4\u0026thinsp;\u0026plusmn;\u0026thinsp;48.5 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e in 2011, 499.5\u0026thinsp;\u0026plusmn;\u0026thinsp;179.1 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e in 2013, and 557.3\u0026thinsp;\u0026plusmn;\u0026thinsp;24.6 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e in 2014.\u003c/p\u003e\n \u003cp\u003eThe abundance of nematodes was analyzed by year and station (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). In 2009, the highest value of abundance was 604.0\u0026thinsp;\u0026plusmn;\u0026thinsp;105.2 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 5, and the lowest value was 110.3\u0026thinsp;\u0026plusmn;\u0026thinsp;12.3 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 8. In 2010, the highest value of abundance was 802.7\u0026thinsp;\u0026plusmn;\u0026thinsp;94.9 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 6, and the lowest value was 83.0\u0026thinsp;\u0026plusmn;\u0026thinsp;12.3 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 3. The highest value of nematode abundance in 2011 was 641.7\u0026thinsp;\u0026plusmn;\u0026thinsp;129.1 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 4, the station where the meiofauna abundance was high, and the lowest value was 125.0\u0026thinsp;\u0026plusmn;\u0026thinsp;20.8 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 3, the same station as the previous year. The highest value of nematode abundance in 2013 was 775.0\u0026thinsp;\u0026plusmn;\u0026thinsp;36.9 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 6, the same station as in 2010, and the lowest value was 201.3\u0026thinsp;\u0026plusmn;\u0026thinsp;58.1 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 3, the same station as in the previous years. The highest value of nematode abundance in 2014 was 948.3\u0026thinsp;\u0026plusmn;\u0026thinsp;32.2 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 7, the station where the total meiofauna abundance was high, and the lowest value was 157.0\u0026thinsp;\u0026plusmn;\u0026thinsp;13.3 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 4, where the abundance was the highest in 2011. Examining the mean abundance of nematodes by station, the values ranged from 228.9\u0026thinsp;\u0026plusmn;\u0026thinsp;34.8 to 557.0\u0026thinsp;\u0026plusmn;\u0026thinsp;69.3 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e, with the highest value at St. 4 and the lowest value at St. 8. The mean abundance of nematodes at St. 10, the station with the lowest pH value in the environmental data, was 429.1\u0026thinsp;\u0026plusmn;\u0026thinsp;91.7 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e, and showed the highest value of 685.0\u0026thinsp;\u0026plusmn;\u0026thinsp;179.1 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e in 2013 and the lowest value of 265.0\u0026thinsp;\u0026plusmn;\u0026thinsp;104.5 Inds. /10 cm\u003csup\u003e2\u003c/sup\u003e in 2009.\u003c/p\u003e\n \u003cp\u003eAmong the wide range of meiofauna taxa that appeared during the study period, the second most dominant taxon after nematodes was harpacticoids, and their abundance based on population density was as follows: The mean abundance of harpacticoids for each year during the study period was 94.6\u0026thinsp;\u0026plusmn;\u0026thinsp;9.3 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e in 2009, 116.2\u0026thinsp;\u0026plusmn;\u0026thinsp;29.2 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e in 2010, 34.3\u0026thinsp;\u0026plusmn;\u0026thinsp;8.2 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e in 2011, and 136.3\u0026thinsp;\u0026plusmn;\u0026thinsp;46.0 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e in 2013, and 86.7\u0026thinsp;\u0026plusmn;\u0026thinsp;12.7 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e in 2014.\u003c/p\u003e\n \u003cp\u003eThe abundance of harpacticoids is analyzed annually and per station. In 2009, harpacticoid abundance peaked at 602.3\u0026thinsp;\u0026plusmn;\u0026thinsp;35.7 Inds./10 \u003csup\u003ecm2\u003c/sup\u003e at St. 9, and the minimum was 10.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 2. In 2010, the peak was 378.7\u0026thinsp;\u0026plusmn;\u0026thinsp;75.6 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 3, and the lowest was 23.3\u0026thinsp;\u0026plusmn;\u0026thinsp;9.4 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 5. In 2011, the highest harpacticoid abundance was 87.3\u0026thinsp;\u0026plusmn;\u0026thinsp;12.3 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 9, and the lowest was 13.0\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 3, the station with the highest harpacticoid abundance in 2010. In 2013, the highest harpacticoid abundance was 318.0\u0026thinsp;\u0026plusmn;\u0026thinsp;153.5 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 8, and the lowest was 34.7\u0026thinsp;\u0026plusmn;\u0026thinsp;19.3 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 5. The highest abundance in 2014 was 169.7\u0026thinsp;\u0026plusmn;\u0026thinsp;24.4 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 1, and the lowest was 13.7\u0026thinsp;\u0026plusmn;\u0026thinsp;5.9 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e at St. 2, the same station as 2009. The mean abundance of harpacticoids per station ranged from 32.9\u0026thinsp;\u0026plusmn;\u0026thinsp;11.5 to 231.1\u0026thinsp;\u0026plusmn;\u0026thinsp;25.7 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e, with the highest abundance at St. 9 and the lowest at St. 2. St. 10, which had the lowest pH value, exhibited a mean harpacticoid abundance of 58.5\u0026thinsp;\u0026plusmn;\u0026thinsp;20.1 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e. Here, the highest harpacticoid abundance (110.0\u0026thinsp;\u0026plusmn;\u0026thinsp;62.2 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e) was recorded in 2013, the year with the highest nematode abundance, while the lowest abundance (56.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2 Inds. /10 cm\u003csup\u003e2\u003c/sup\u003e) was recorded in 2014.\u003c/p\u003e\n \u003cp\u003eNematodes, the most dominant taxon, accounted for 65.8% of the total meiofauna abundance, while harpacticoids, the second most dominant taxon, accounted for 15.2% (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). Together, these two taxa constituted 81.0% of the total meiofauna abundance. Other taxa comprising more than 1% of the composition included sarcomastigophorans (8.6%), copepod nauplii (4.5%), and polychaetes (3.3%).\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003eThe annual composition of dominant (more than 1%) meiofauna taxa varied. In 2009, the composition of major taxa was nematodes (64.9%), followed by harpacticoids (20.0%), copepod nauplii (5.7%), sarcomastigophorans (4.0%), and polychaetes (2.4%). A similar composition was observed in 2010: nematodes (64.9%) are dominant, followed by harpacticoids (21.5%), sarcomastigophorans (7.2%), polychaetes (2.2%), and copepod nauplii (2.1%). In 2011, however, sarcomastigophorans (8.4%) overtook harpacticoids (7.7%) in the second position. By 2014, the composition of major taxa had shifted, with nematodes (60.8%) followed by sarcomastigophorans (18.5%).\u003c/p\u003e\n \u003cp\u003eUsing the number of respective meiofauna taxa and their abundance over the survey period, the taxa diversity index, richness, and evenness were calculated (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e). The values of the taxa diversity index (H\u0026rsquo;) by year are as follows: 0.86 in 2009, 0.94 in 2010, 1.12 in 2011, 0.79 in 2013, and 1.15 in 2014, with 2014 showing the highest value and 2013 showing the lowest value of the diversity index.\u003c/p\u003e\n \u003cp\u003eThe taxa diversity index ranged from 0.54 to 1.34 across the stations, with St. 5 having the lowest index and St. 8 having the highest. For St. 10, the station with the lowest pH, the mean taxa diversity index was 0.93, reaching its peak in 2009 (1.24) and minimum (0.75) in 2010. There were substantial differences by station and year in the values of meiofauna richness and evenness, but no clear relationship between the variations could be observed. One pattern that was observed was that richness and the diversity index both exhibited a similar trend.\u003c/p\u003e\n \u003cp\u003eCLUSTER and SIMPROF analyses were applied to generate similarity profiles and classify meiofauna communities by station and year (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e). The analysis yielded four distinct groups. The first group was dominated by 2009 and 2011 meiofauna communities, whereas the second group was characterized by 2014 communities and those from St. 8 and St. 9 in 2009, 2010, and 2011. The final two groups were primarily comprised of 2013 meiofauna communities (SIMPROF test, p\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003eCharacteristics of nematodes communities\u003c/h2\u003e\n \u003cp\u003eThe study area yielded a diverse assemblage of nematodes, with a total of 39 genera recorded across the years of observation (Table \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e). In 2009, the most dominant nematode genus was Chromadorita, represented by 10 individuals. Closely following were the genera Dorylaimopsis and Retrotheristus, with 9 individuals each identified in the study area. Richtersia and Sabatieria each had six individuals, while Halalaimus and Metachromadora each had 5 individuals. In the subsequent year, 2010, \u003cem\u003eDorylaimopsis\u003c/em\u003e emerged as the dominant genus, with 14 individuals. \u003cem\u003eChromadorita\u003c/em\u003e and \u003cem\u003eSabatieria\u003c/em\u003e were also notable, each with 9 individuals. \u003cem\u003eEnoplolaimus\u003c/em\u003e and \u003cem\u003eOxystomina\u003c/em\u003e were present with 5 individuals each. In 2011, \u003cem\u003eChromadorita\u003c/em\u003e and \u003cem\u003eOxystomina\u003c/em\u003e demonstrated comparable prevalence, both accounting for 12 individuals. \u003cem\u003eRichtersia\u003c/em\u003e and \u003cem\u003eSabatieria\u003c/em\u003e followed with 6 individuals each, while \u003cem\u003eDorylaimopsis\u003c/em\u003e and \u003cem\u003eEnopplolaimus\u003c/em\u003e had 5 individuals each. In 2013, \u003cem\u003eDorylaimopsis\u003c/em\u003e exhibited the highest prevalence among the nematode genera, with a total of 13 individuals. \u003cem\u003eRichtersia\u003c/em\u003e followed with 10 individuals, while \u003cem\u003eHalalaimus\u003c/em\u003e, \u003cem\u003eEnoplolaimus\u003c/em\u003e, and \u003cem\u003eMicrolaimus\u003c/em\u003e accounted for 8, 6, and 5 individuals, respectively. Lastly, in 2014, \u003cem\u003eChromadorita\u003c/em\u003e was again the most dominant genus, with 13 individuals. It was followed by \u003cem\u003eDorylaimopsis\u003c/em\u003e, which had 11 individuals, and then \u003cem\u003eEnoplolaimus\u003c/em\u003e and \u003cem\u003eOxystomina\u003c/em\u003e, which each had 8. Furthermore, \u003cem\u003eRichtersia\u003c/em\u003e contributed to the composition with 7 individuals.\u003c/p\u003e\n \u003ctable id=\"Tab8\" border=\"1\"\u003e\u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003eThe number of nematode species observed in each year and station is as follows: In 2009, 15 species appeared in St. 5, 13 species in St. 7, and 8 species in St. 10. In 2010, there were 12 species in St. 5, 15 species in St. 7, and 12 species in St. 10. In 2011, 16 species were identified in St. 5, 11 species in St. 7, and 16 species in St. 10. For 2013, there were 11 species in St. 5, 15 species in St. 7, and 10 species in St. 10. Lastly, in 2014, 13 species were observed in St. 5, 15 species in St. 7, and 15 species in St. 10. On average, the number of nematode species per station was 13.4 in St. 5, 13.8 in St. 7, and 12.2 in St. 10.\u003c/p\u003e\n \u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e presents the changes in the composition of nematodes based on feeding types at the main stations (St. 5, St. 7, St. 10) in the study area. The feeding types observed for each year are as follows:\u003c/p\u003e\n \u003cp\u003eIn 2009, epistrate feeders (2A) were the most abundant feeding type across all stations, constituting over 50% of the nematode composition in St. 5 and St. 10. Non-selective deposit feeders (1B) were absent in St. 10, the station characterized by deeper water depths and a lower pH. In 2010, epistrate feeders (2A) were the predominant feeding type in St. 5 and St. 10, while non-selective deposit feeders (1B) were the most frequently observed type in St. 7. In 2011, epistrate feeders (2A) continued to dominate in St. 5 and St. 10, while selective deposit feeders (1A) were the most abundant type in St. 7. In 2013, non-selective deposit feeders (1B) were the most common feeding type in St. 5 and St. 7, while epistrate feeders (2A) were most abundant in St. 10. Finally, in 2014, epistrate feeders (2A) exhibited the highest abundance across all stations.\u003c/p\u003e\n \u003cp\u003eUpon analyzing the feeding types of nematodes by station, notable patterns emerged. In St. 5, epistrate feeders (2A) consistently exhibited the highest proportion in the composition throughout the entire study period. Conversely, predators/omnivores (2B) consistently displayed the lowest ratio, with the exception of 2011. In St. 7, the predominant feeding types varied by year. Epistrate feeders (2A) held the highest ratio in 2009 and 2014, while non-selective deposit feeders (1B) dominated in 2010 and 2013. In 2011, selective deposit feeders (1A) were the most prevalent feeding type in St. 7. Similarly, in St. 10, epistrate feeders (2A) consistently maintained the highest ratio in the composition across all years during the study period.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eTo examine the occurrence and trends of ocean acidification along the East Sea coast of Korea, the study focused on the coastal region, which was divided into 18 distinct water areas. The analysis primarily utilized seawater temperature and pH data collected from 1993 to 2007. From this comprehensive dataset, the coastal waters of Hupo, located in Gyeongsangbuk-do, were specifically chosen as the study area for this study (KIOST, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe average temperature of the bottom layer in the study area was found to be 14.9 ℃. Notably, in 2014, specific stations (St. 4, St. 5, and St. 10) experienced temperatures below 10 ℃. It is important to note that while the coastal waters of the East Sea witness surface layer temperatures rising to 27\u0026ndash;29 ℃ during the summer season in Korea, the bottom layer exhibits the presence of a cold water mass with temperatures ranging from 3\u0026ndash;10 ℃. This cold water mass forms an undercurrent flowing southwest along the bottom (Lim, D. B. and Jang, S., 1969). Consequently, a significant stratification occurs between the surface and bottom layers during the summer, leading to the development of a cold water zone in the southern waters of the East Coast of Korea from June to September (Lie, H.J. et al., 1992).\u003c/p\u003e \u003cp\u003eThe average salinity in the study area was 34.0 psu. Notably, in 2009, 2011, and 2013, the mean salinity fell below 34 psu, while in 2010 and 2014, it exceeded 34 psu. Examining the interannual variations of salinity in the Jukbyeon area, located slightly north of the study area, during 2012, measurements revealed a salinity of 34.2 psu in winter, 34 psu in summer, and 33 psu in autumn at\u003c/p\u003e \u003cp\u003e20 m depth. These findings indicate significant variability in coastal water salinity depending on the season of measurement (Jung, H.D. et al., 2013).\u003c/p\u003e \u003cp\u003eThe mean bottom water pH in the study area was determined to be 8.306. The pH exhibited variation across different time periods, with a minimum of 7.886 in 2011 and a maximum of 8.696 in 2014. Along the coasts of Goseong and Yeongdeok in the East Sea, the pH in surface water ranged from 7.95 to 8.30, while in the bottom water, it ranged from 7.75 to 8.29 throughout the year. Generally, the pH of bottom water tends to be lower than that of surface water, with the pH difference between the two layers increasing during summer due to heightened vertical mixing occurring predominantly in winter (Lee, Y.W. et al., 2016). The coastal region of East Sea is affected by the high-temperature and high-salinity Tsushima Warm Current flowing in from the Korea Strait and the low-temperature and low-salinity North Korean Cold Current flowing southward along the coast from the north. When the two currents meet, a frontal zone is formed around 37\u0026ndash;38\u0026deg;N (Chang, K.I. et al., 2002, 2004; Kim, Y.H. and Min, H.S. 2008).\u003c/p\u003e \u003cp\u003eOcean acidification has been found to impact the community structure of benthic organisms, as indicated by previous studies through experiments and field surveys. Specifically, the dominance of algae, such as fast-growing seaweeds, tends to increase under ocean acidification conditions. This shift in dominance can lead to a reduction in the abundance of benthic fauna species, as they face increased competition with algae. Consequently, there is a decline in species diversity (Kroeker et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). These findings highlight the potential consequences of ocean acidification on benthic communities and emphasize the importance of further understanding its ecological impacts.\u003c/p\u003e \u003cp\u003eThis study aimed to investigate the relationship between benthic meiofauna communities and ocean acidification by conducting a 5-year survey at 10 stations in the coastal waters of Hupo. The mean abundance of meiofauna, or meiofaunal density, averaged over the survey period was 614.4 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e. This value falls within a smaller range compared to the meiofauna abundance reported in the intertidal zone of the West Sea, which ranged from 1,521 to 7,849 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e, with a mean abundance of 4,161 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e (Kim et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). Similarly, in the intertidal zone of Daebudo, Korea, the range of meiofauna abundance was 30 to 1,382 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e, with a mean abundance of 751 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e (Min et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe meiofaunal densities observed in this study are more comparable to the meiofauna abundance reported in the subtidal zone of the West Sea, which ranged from 17 to 853 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e (Kang, T.W. et al., 2011). This discrepancy can be attributed to the sedimentary facies in the coastal waters. The West Sea intertidal zone consists of smaller-grained sediments compared to the sandy sedimentary facies of the East Sea subtidal zone, resulting in higher meiofauna abundance in the former. Moreover, the abundance values in this study are similar to that with the West Sea subtidal zone, which also had sandy sedimentary facies. The mean meiofauna abundance in this study is higher compared to the reported abundance, which ranges from 49.8 to 1,959.1 Inds./10 cm2, averaging at 591 Inds./10 cm2, in the northeastern subtidal zone of Jeju Island (Kang, T.W. and Kim, D., 2020).\u003c/p\u003e \u003cp\u003eNematodes and harpacticoids were the dominant taxa among meiofauna in the study area, with copepod nauplii, sarcomastigophorans, and polychaetes also present in significant proportions. This composition is similar to the meiofauna community structure observed in the West Sea (Kim et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Kim and Lee, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). Previous studies have consistently reported the presence of nematodes, harpacticoids, tardigrades, platyhelminths, kinorhynchs, and gastrotrichs as representative meiofauna in various marine ecosystems (Dorris et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1999\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThis study revealed that nematodes constituted approximately 65 to 70% of the meiofauna composition, while harpacticoids accounted for approximately 7 to 20%, together representing about 80% of the total meiofauna abundance. Nematodes and harpacticoids are commonly observed in high abundance across marine benthic ecosystems (James and Mark, 2004). Nematodes, in particular, are recognized for their dominance within meiofauna communities in terms of abundance and biomass. Previous studies have reported nematodes to comprise around 90 to 95% of the total meiofauna abundance and contribute to 50 to 90% of the biomass (Giere, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1993\u003c/span\u003e). Given that the study area consists of sandy facies in the East Sea, the proportion of harpacticoids is relatively higher compared to coastal regions characterized by muddy facies. For instance, investigations in Gwangyang Bay and Gamak Bay, which primarily feature muddy facies, revealed nematodes accounting for over 70% of the composition in most stations, with some stations exclusively inhabited by nematodes (Kim, D. et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Lee H.G. et al., 2019).\u003c/p\u003e \u003cp\u003eAmong the monitored environmental factors in this study, St. 10 exhibited the lowest pH value, particularly reaching a very low pH of 7.821 in 2011. Correspondingly, the meiofauna and harpacticoid abundances at St. 10 were the lowest during the 5-year study period. It is widely recognized that ocean acidification exerts significant impacts on marine communities, particularly leading to a reduced abundance of benthic fauna, especially those species involved in shell formation or calcification (Fabry et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Consistent with this understanding, the findings of this study indicate a decrease in the abundance of harpacticoids, which are known for their sensitivity to environmental changes and possession of external shells, in response to the decline in seawater pH. However, the impact on the abundance of nematodes in St. 10, despite being the station with the lowest pH, was not significant. Nematodes are generally considered less susceptible to environmental stress compared to harpacticoids (Croll and Mathews, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e1977\u003c/span\u003e; Platt et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e1984\u003c/span\u003e). Notably, the abundance of nematodes in St. 10 was 429.1 Inds./10 cm\u003csup\u003e2\u003c/sup\u003e, surpassing the overall mean abundance.\u003c/p\u003e \u003cp\u003eThe impact of ocean acidification on benthic faunal communities, particularly at the meiofauna level, has received limited research attention. Only a few empirical studies conducted under field conditions have addressed this topic. One such study focused on a coral reef meiofauna community and found that changes in community structure were observed after 30 days of exposure to low pH conditions associated with ocean acidification. Among the taxa examined, \u003cem\u003eNematoda\u003c/em\u003e, \u003cem\u003eOstracoda\u003c/em\u003e, \u003cem\u003eTurbellaria\u003c/em\u003e, and \u003cem\u003eTardigrada\u003c/em\u003e exhibited the highest density in the low pH environment. \u003cem\u003eHarpacticoid\u003c/em\u003e nauplii were found to be particularly affected by the low seawater pH levels. However, no significant differences were observed in the abundance of \u003cem\u003eHarpacticoida\u003c/em\u003e and \u003cem\u003ePolychaeta\u003c/em\u003e in response to pH changes (Sarmento et al., \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe analysis of nematode species composition at the three stations revealed a smaller number of taxa at St. 10, which had low pH conditions. This aligns with the known effects of ocean acidification, which can lead to reduced abundance and species diversity. In 2009, when St. 10 exhibited low seawater pH levels, the number of nematode taxa was only 8, significantly lower than in other years of the study. Interestingly, a previous mesocosm experiment investigating the impact of ocean acidification on nematodes did not observe significant effects, suggesting that nematodes in shallow-water areas may have developed greater resistance to environmental variations and stress (Esteves et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe c-p value (colonizer-persister) value for nematode species is the value proposed by Bongers et al (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e1991\u003c/span\u003e), which ecologically divides nematodes into 5 groups and assigns a value between 1 and 5 to each group. A low value is assigned to a group belonging to an opportunistic species with a short life cycle, and a high value is assigned to a group that is sensitive to environmental changes and prefers a stable environment with a long life cycle. The species composition analysis of nematodes at stations St. 5, St. 7, and St. 10, which experience more severe ocean acidification compared to other stations, revealed that the dominant species in all three stations were \u003cem\u003eChromadorita\u003c/em\u003e spp. and \u003cem\u003eDorylaimopsis\u003c/em\u003e spp. \u003cem\u003eChromadorita\u003c/em\u003e spp. has a c-p value of 3, indicating it has a relatively long generation time and is sensitive to environmental disturbances (Table\u0026nbsp;\u003cspan refid=\"Tab8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). On the other hand, \u003cem\u003eDorylaimopsis\u003c/em\u003e spp. has a c-p value of 2, suggesting it is highly resistant to environmental pollution or disturbances. It is expected that the proportion of these resistant species will increase in the species composition as environmental changes continue to unfold. Although the impact of ocean acidification on nematode communities could not be conclusively determined in this study due to the presence of both sensitive and resistant species, the abundance of these species can serve as a valuable indicator of the impact of sedimentary environmental changes. Therefore, the study area where these species are abundant is considered suitable for investigating the effects of ocean acidification on nematodes in the future (Semprucci et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eUpon examination of the dominant feeding types among nematodes, epistrate feeders (2A) were found to have the highest proportion throughout the study period, accounting for 43.4% of the total nematode composition. Non-selective deposit feeders (1B) were the second most dominant feeding type, comprising approximately 26.2%, followed by selective deposit feeders (1A) at 18.6% and predators/omnivores (2B) at 11.8%. In St. 10, which had the lowest pH level, epistrate feeders (2A) consistently had the highest ratio among the feeding types. It is known that variations in nematode feeding types occur in response to environmental changes, and analyzing the distribution of feeding types provides insights into the food web dynamics of benthic ecosystems (Beier and Traunspurger, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). While epistrate feeders (2A) dominated in all stations, their proportion was particularly high at 52.8% in St. 10, the station with the lowest pH. The proportions of other feeding types ranged from 11.1\u0026ndash;19.4%. In contrast, St. 7 exhibited a more balanced distribution of feeding types, with selective deposit feeders (1A) accounting for 21.4%, non-selective deposit feeders (1B) accounting for 31.0%, epistrate feeders (2A) accounting for 32.4%, and predators/omnivores (2B) accounting for 15.2%. This suggests that St. 7 experiences higher environmental stability compared to other stations.\u003c/p\u003e \u003cp\u003eTo comprehensively investigate the impact of ocean acidification on meiofauna communities, it is crucial to analyze the species composition of dominant taxa and consider various environmental conditions. Previous studies have highlighted the influence of sediment type on meiofauna diversity and community structure while indicating limited impacts of CO2 concentration and temperature (Ingels et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). In the present study, no visible impact of ocean acidification on meiofauna communities was observed within the 5-year study period, likely due to the short duration and focus on limited meiofauna communities in the coastal waters of Hupo. Since environmental changes occur gradually over an extended timeframe, long-term monitoring is necessary to better understand the effects. It is also important to conduct comparative analyses across different regions and research datasets, considering that ocean acidification is a global phenomenon. Moreover, meiofauna serves as a valuable research subject for investigating the impacts of environmental changes, given its restricted distribution range and short life cycle compared to other benthic organisms.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by Korean Institute of Marine Science \u0026amp; Technology Promotion (KIMST) funded by the Ministry of Oceans and Fisheries (20170411), Korea.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eEthical Approval\u0026nbsp;\u003c/strong\u003e\u003cbr\u003e\u0026nbsp;The authors declared no potential conflicts of interest for the research, authorship, and/or publication of this article.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eCompeting interests\u0026nbsp;\u003c/strong\u003e\u003cbr\u003e\u0026nbsp;The authors have no competing interests to declare that are relevant to the content of this article.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eAuthors\u0026apos; contributions\u0026nbsp;\u003c/strong\u003e\u003cbr\u003e\u0026nbsp;Je Hyeok Oh and Teawook Kang wrote the main manuscript text and prepared all figures. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAyoung Shin and Min Gyu Jung prepared all figures and tables.\u003c/p\u003e\n\u003cp\u003eDongsung Kim and Wonchoel Lee reviewed the total manuscript.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003enot applicable\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eAvailability of data and materials\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003enot applicable\u003c/strong\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBarry JP, Lovera C, Buck KR, Peltzer ET, Taylor JR (2014) Ocean acidification responses in deep sea snail communities. Proceedings of the Royal Society B: Biological Sciences 281(1779):20133281\u003c/li\u003e\n\u003cli\u003eBeier S, Traunspurger W (2001) The meiofauna community of two small German streams as indicator of pollution. J Aquat Ecosyst Stress Recover 8:387\u0026ndash;405 \u003c/li\u003e\n\u003cli\u003eBongers T, Alkemade R, Yeates GW (1991) Interpretation of disturbance-induced maturity decrease in marine nematode assemblages by means of the Maturity Index. Mar Ecol Prog Ser 76:135-142 \u003c/li\u003e\n\u003cli\u003eBrewer PG (1997) Ocean chemistry of the fossil fuel CO2 signal: The haline signal of \u0026quot;business as usual\u0026quot;. Geophys Res Lett 24:1367-1369 \u003c/li\u003e\n\u003cli\u003eBurgess R (2001) An improved protocol for separating meiofauna from sediments using colloidal silica sols. Mar Ecol Prog Ser 214:161-165\u003c/li\u003e\n\u003cli\u003eChang KI, Hogg N, Suk MS, Byun SK, Kim YG, Kim K (2002) Mean Flow and Variability in the Southwestern East Sea. Deep Sea Res I 49:2261-2279\u003c/li\u003e\n\u003cli\u003eChang KI, Teague WJ, Lyn SJ, Perkins HT, Lee DK,Watts DR, Kim YB, Mitchell DA, Lee CM, Kim K (2004) Circulation and Currents in the Southwestern East/Japan Sea: Overview and Review. Prog Oceangr 61:105-156\u003c/li\u003e\n\u003cli\u003eClarke KR, Gorley RN (2001) PRIMER v5 User manual Plymouth: PRIMER-E \u003c/li\u003e\n\u003cli\u003eCoull BC, Chandler GT (1992) Pollution and meiofauna: field, laboratory and mesocosm studies. Oceanogr Mar Biol Annu Rev 30:191-271\u003c/li\u003e\n\u003cli\u003eCroll NA, Mathews GB (1977) Biology of Nematodes. Glassgow: Blackie \u0026amp; Sons Ltd\u003c/li\u003e\n\u003cli\u003eDorris M, Ley PD, Blaxter ML (1999) Molecular analysis of nematode diversity and the evolution of parasitism. Parasitol Today 15(5):188-193 \u003c/li\u003e\n\u003cli\u003eDupont S, Thorndyke MC (2008) Ocean acidification and its impact on the early life-history stages of marine animals. In: Impacts of acidification on biological, chemical and physical systems in the Mediterranean and Black Seas. CIESM Monogr 36: 89-97 \u003c/li\u003e\n\u003cli\u003eDupont S, Thorndyke MC (2009) Impact of CO2-driven ocean acidification on invertebrates early life-history - Want we know, what we need to know and what we can do. Journal of Biogeosciences Discuss 6:3109-3131 \u003c/li\u003e\n\u003cli\u003eEsteves AM, Souza TP, Sarmento VDC, Maria TF, Santos PJPD (2022) Effects of the ocean acidification on the functional structure of coral reef nematodes. Coral Reefs 41(5):1481-1494\u003c/li\u003e\n\u003cli\u003eFabry VJ, Seibel BA, Feely RA, Orr JC (2008) Impacts of ocean acidification on marine fauna and ecosystem processes. ICES Journal of Marine Science 65(3):414-432 \u003c/li\u003e\n\u003cli\u003eFerris H, Bongers T (2009) Indices developed specifically for analysis of nematode assemblages. In M. J. Wilson and T. Kakouli-Duarte (eds.). Nematodes as environmental indicators. Wallingford: CAB International 124-145 \u003c/li\u003e\n\u003cli\u003eFoss\u0026aring; JH, Mortensen PB, Furevik DM, Ellingsen KE (2012) The deep-water coral Lophelia pertusa in Norwegian waters: distribution and fishery impacts. Hydrobiologia 687(1):53-65 \u003c/li\u003e\n\u003cli\u003eGazeau F, Quiblier C, Jansen JM, Gattuso JP, Middelburg JJ, Heip CH (2007) Impact of elevated CO2 on shellfish calcification. Geophysical Research Letters 34(7) \u003c/li\u003e\n\u003cli\u003eGiere O (1993) Meiobenthology: The microscopic fauna in aquatic sediments. Springer-Verlag Berlin, Heidelberg, New York\u003c/li\u003e\n\u003cli\u003eHiggins RP, Thiel H (1988) Introduction to the study of meiofauna. Washington, DC: Smithsonian Institution Press\u003c/li\u003e\n\u003cli\u003eIngels J, dos Santos G, Hicks N, Vazquez YV, Neres PF, Pontes LP ... Widdicombe S (2018) Short-term CO2 exposure and temperature rise effects on metazoan meiofauna and free-living nematodes in sandy and muddy sediments: results from a flume experiment. Journal of Experimental Marine Biology and Ecology 502:211-226\u003c/li\u003e\n\u003cli\u003eIPCC (2007) Summary for policymakers in climate change 2007: the physical science basis. Contribution of working group I to the fourth assessment report of the Intergovernmental Panel on Climate Change. Cambridge (UK): University Press \u003c/li\u003e\n\u003cli\u003eNybakken JW, Bertness MD (2004) Marine Biology:An ecological approach. Person Education, Inc\u003c/li\u003e\n\u003cli\u003eJung HD, Kim SW, Kwon K, Lim JW, Kwoun CH (2013) Oceanographic Features Around Aquaculture Areas of the Eastern Coast of Korea. Korean Soc Mar Environ Saf 19(4):34-344 \u003c/li\u003e\n\u003cli\u003eKang TW, Kim D, Min WG, Rho HS, Hong JS (2011) Characteristics of Meiobenthic Community Inhabiting Sandy Sediment in the Yellow Sea, Korea. Ocean Polar Res 33(3):193\u0026ndash;209 \u003c/li\u003e\n\u003cli\u003eKang TW, Kim D (2020) Meiobenthic Community Structure on the Northeast Coastal Area of Jeju Island, Korea. Ocean Polar Res 42(1):1-13 \u003c/li\u003e\n\u003cli\u003eKim D, Choi JW, Je JG, Lee JH (1998) Community Structure of Meiobenthos in Tidal Flats at Taebudo, West Coast of Korea. Ocean Polar Res 20(2):81\u0026ndash;87 \u003c/li\u003e\n\u003cli\u003eKim D, Je JG, Shin SH (2000) Utilization of meiobenthos for pollution monitoring in the Gamak Bay, Korea. Journal of the Korean Fisheries Society 33(4):307-319 \u003c/li\u003e\n\u003cli\u003eKim D, Lee JH (2000) Impacts of Contaminated Water Outflow from the Lake Sihwa on the Meiobenthic Animals Living in the Coastal Zones of the Kyonggi Bay. Korean J Environ Biol 18(2):205-216 \u003c/li\u003e\n\u003cli\u003eKim D, Min WG, Lee JH (2004) Variation of Meiobenthic Community in the Sediment of Coastal Area in Bangameori Daebudo, Korea. Korean J Environ Biol 22(2): 308-320 \u003c/li\u003e\n\u003cli\u003eKim YH, Min HS (2008) Seasonal and Interannual Variability of the North Korean Cold Current in the East Sea Reanalysis Data. Ocean and Polar Res 31(1):21-31 \u003c/li\u003e\n\u003cli\u003eKIOST (2016) Ecological Impacts of Ocean Acidicfication (EcoAcid). KIOST (Korea Institute of Ocean Science \u0026amp; Technology), Final Report BSPE99317-10976-3 \u003c/li\u003e\n\u003cli\u003eKroeker KJ, Kordas RL, Crim RN, Singh GG (2010) Meta-analysis reveals negative yet variable effects of ocean acidification on marine organisms. Ecology Letters 13(11):1419-1434\u003c/li\u003e\n\u003cli\u003eKroeker KJ, Micheli F, Gambi MC (2013) Ocean acidification causes ecosystem shifts via altered competitive interactions. Nature Climate Change 3(2):156-159 \u003c/li\u003e\n\u003cli\u003eLee HG, Kang TW, Rho HS, Kim D (2019) Seasonal Distribution Characteristics of Meiobenthos at Gwangyang Bay, Korea. J Korean Soc Oceanogr 24(3):400-421 \u003c/li\u003e\n\u003cli\u003eLee YW, Park MO, Kim SS (2016) Spatiotemporal Variations of Marine Environmental Characteristics in the Middle East Coast of Korea in 2013-2014. J Korean Soc Mar Environ Energy 19(4):274-285\u003c/li\u003e\n\u003cli\u003eLie HJ, Shin CW, Seung YH (1992) Internal Tidal Oscillations of Temperature off Jukbyun on the East Coast of Korea. J. Korean Soc Oceanogr 27(3):228-236 \u003c/li\u003e\n\u003cli\u003eLim DB, Jang S (1969) On the cold water in the Korea Strait. J Korean Soc Oceanogr 4(2):71-82 \u003c/li\u003e\n\u003cli\u003eManno C, Stumpp M, Saderne V, P\u0026ouml;rtner HO, Tubau X (2017) Resilience of the blue mussel Mytilus edulis to seawater acidification depends on the nutritional value of its diet. Estuarine, Coastal and Shelf Science 189:158-168 \u003c/li\u003e\n\u003cli\u003eMelzner F, Gobel S, Langenbuch M (2009) Swimming performance in Atlantic Cod (Gadus morhua) following long-term (4-12 months) acclimation to elevated seawater pCO2. Aquatic toxicology 92(1):30-37 \u003c/li\u003e\n\u003cli\u003eMin WG, Kim D, and Lee JH (2006) Community Structure and Spatial Variation of Meiobenthos Associated with an Artificial Structure. Korean J Fish Aquat Sci 39(1):223\u0026ndash;230 \u003c/li\u003e\n\u003cli\u003eMoore CG, Bett BJ (1989) The use of meiofauna in marine pollution impact assessment. Zool J Linn Soc 96:263-280 \u003c/li\u003e\n\u003cli\u003eOh JH, Kang T, Shin A, Kim T, Yu OH, Lee W, Kim D (2022) Effect of Different p CO2 Concentrations in Seawater on Meiofauna: Abundance of Communities in Sediment and Survival Rate of Harpacticoid Copepods. Ocean Science Journal 57(2):279-286 \u003c/li\u003e\n\u003cli\u003eOh JH, Kim D, Kim TW, Kang T, Yu OH, Lee W (2017) Effect of increased p CO2 in seawater on survival rate of different developmental stages of the harpacticoid copepod Tigriopus japonicus. Animal Cells and Systems 21(3):217-222 \u003c/li\u003e\n\u003cli\u003ePlatt HM, Warwick RM (1983) A Synopsis of the Free-living Marine Nematodes. Part I. British Enoplids. Cambridge University Press, Cambridge, pp 35-85\u003c/li\u003e\n\u003cli\u003ePlatt HM, Shaw KM, Lambshead PJD (1984) Nematode species abundance patterns and their use in the detection of environmental perturbations. Hydrobiologia 118:59-66 \u003c/li\u003e\n\u003cli\u003ePrzeslawski R, Zhu Q, Aller R (2009) Effects of abiotic stressors on infaunal burrowing and associated sediment characteristics. Mar Ecol Prog Ser 392:33-42 \u003c/li\u003e\n\u003cli\u003eSarmento VC, Souza TP, Esteves AM, Santos PJP (2015) Effects of seawater acidification on a coral reef meiofauna community. Coral Reefs 34:955-966 \u003c/li\u003e\n\u003cli\u003eSemprucci F, Losi V, Moreno M (2015) A review of Italian research on free-living marine nematodes and the future perspectives in their use as ecological indicators (EcoInd). Mediterr Mar Sci 16:352-365 \u003c/li\u003e\n\u003cli\u003eSolomon S, Qin D, Manning M, Chen Z, Marquis M, Averyt KB, Tignor M, Miller HL (2007) Climate Change 2007: The Physical Science Basis - Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cam-bridge\u003c/li\u003e\n\u003cli\u003eThomsen J, Melzner F (2010) Moderate seawater acidification does not elicit long-term metabolic depression in the blue mussel Mytilus edulis. Marine Biology 157(12):2667-2676 \u003c/li\u003e\n\u003cli\u003eZeebe RE, Zachos JC, Caldeira K, Tyrrell T (2008) Carbon emissions and acidification. Science 32:51\u0026ndash;52 \u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTables are available in Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"thalassas-an-international-journal-of-marine-sciences","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"thal","sideBox":"Learn more about [Thalassas: An International Journal of Marine Sciences](http://link.springer.com/journal/41208)","snPcode":"41208","submissionUrl":"https://submission.nature.com/new-submission/41208/3","title":"Thalassas: An International Journal of Marine Sciences","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Meiofauna community, Ocean acidification, Carbon dioxide, Nematodes, Feeding type","lastPublishedDoi":"10.21203/rs.3.rs-3034005/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3034005/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study aimed to investigate the meiofauna community characteristics in coastal waters highly affected by ocean acidification. Therefore, the meiofauna communities in the coastal waters of Hupo in Uljin-gun, a county bordering the East Sea of Korea, were monitored over five years. During the study period, the mean abundance of total meiofauna communities expressed in population density was 614.4 individuals (Inds.)/10 cm\u003csup\u003e2\u003c/sup\u003e, similar to the reported meiofauna abundance in the subtidal zone in the Yellow Sea of Korea, an area with sandy sedimentary facies. The most dominant taxa were nematodes (65\u0026ndash;70%) and harpacticoids (7\u0026ndash;20%); these two taxa accounted for approximately 80% of the total meiofauna abundance. Among the stations studied, station (St.) 10 showed the lowest seawater pH value, and in 2011, when the measured pH was the lowest at 7.82, St. 10 showed the lowest abundance values for total meiofauna and harpacticoids in the 5-year period. To examine the effect of ocean acidification on meiofauna communities at the species level, species of nematodes, the most dominant taxon, were analyzed. The results indicated that the number of nematode species at St. 10 in 2009, when the pH value was low, was 8, which was very low compared to that in the other years of the study period. According to the feeding type, epistrate feeders (2A) accounted for a remarkably high proportion at St. 10, which showed a low pH. This study provides various data on meiobenthic community characteristics to understand the effects of ocean acidification on coastal ecosystems.\u003c/p\u003e","manuscriptTitle":"Characteristics of meiofaunal community in the subtidal zone near Hupo, anticipating ocean acidification in the East Sea of Korea","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-06-12 14:59:43","doi":"10.21203/rs.3.rs-3034005/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revision","date":"2023-10-23T15:41:38+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2023-07-11T04:23:39+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"504d7b12-a437-4e77-83fd-fce4c0d097fa","date":"2023-06-28T02:12:51+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2023-06-09T15:43:52+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2023-06-09T15:35:04+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2023-06-09T04:33:04+00:00","index":"","fulltext":""},{"type":"submitted","content":"Thalassas: An International Journal of Marine Sciences","date":"2023-06-07T11:13:56+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"thalassas-an-international-journal-of-marine-sciences","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"thal","sideBox":"Learn more about [Thalassas: An International Journal of Marine Sciences](http://link.springer.com/journal/41208)","snPcode":"41208","submissionUrl":"https://submission.nature.com/new-submission/41208/3","title":"Thalassas: An International Journal of Marine Sciences","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"3b92fd41-d954-4888-8c61-02f9047f2e28","owner":[],"postedDate":"June 12th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-03-23T16:02:36+00:00","versionOfRecord":{"articleIdentity":"rs-3034005","link":"https://doi.org/10.1007/s41208-026-01077-5","journal":{"identity":"thalassas-an-international-journal-of-marine-sciences","isVorOnly":false,"title":"Thalassas: An International Journal of Marine Sciences"},"publishedOn":"2026-03-18 15:58:13","publishedOnDateReadable":"March 18th, 2026"},"versionCreatedAt":"2023-06-12 14:59:43","video":"","vorDoi":"10.1007/s41208-026-01077-5","vorDoiUrl":"https://doi.org/10.1007/s41208-026-01077-5","workflowStages":[]},"version":"v1","identity":"rs-3034005","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3034005","identity":"rs-3034005","version":["v1"]},"buildId":"WrCJVZZCHTDjtuVLN7oU0","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}