Comparison of seaweed species composition and coverage of Sargassum and Myagropsis communities between artificial and natural reefs in Wakasa Bay, Japan

Comparison of seaweed species composition and coverage of Sargassum and Myagropsis communities between artificial and natural reefs in Wakasa Bay, Japan | 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 Comparison of seaweed species composition and coverage of Sargassum and Myagropsis communities between artificial and natural reefs in Wakasa Bay, Japan Akira Matsui, Masakatsu Kawamura, Shigehiro Nozawa, Masatomo Takeyama, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4459311/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The threat of declining seaweed beds has been a concern around the world. Seagrass and seaweed (brown algae) beds are essential habitats supporting fisheries. However, approximately 22% of these habitats have been lost in Japan due to increased coastal landfill sites and ports. This study aims to rehabilitate the depletion of these habitats by constructing an artificial reef in Wakasa Bay, Japan, and monitoring brown algae ( Sargassum and Myagropsis ) succession in 2 years and 4 years after the construction was completed. In this study, we set up five sites on the artificial reef as a treatment area and one site on the natural reef as a control area and then identified the seaweed species composition of the Sargassum and Myagropsis communities and their coverage on each reef using underwater visual observation by scuba divers. The seaweed coverage on the artificial reef was already close to that on the natural reef in 2 years after construction. However, the dominant species on the artificial reef was not conformable to that on the natural reef in 2 years after construction. The dominant species on the artificial reef changed to S . horneri / S . confusum in 2 years after construction and M . myagroides in 4 years after construction. On the other hand, the dominant species on the natural reef changed to S . patens in 2 years after construction and M . myagroides in 4 years after construction. That is, the species composition on the artificial reef was close to that on the natural reef in 4 years after construction. Thus, the recovery of species composition takes longer than that of seaweed coverage on the artificial reef. Artificial and natural reefs Monitoring Seaweed community succession Seaweed coverage Seaweed species composition Wakasa Bay – Japan Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Seaweed beds of brown algal communities of Sargassum are formed in the coastal Japan Sea. The brown algal communities of Sargassum play an important role in useful marine functions, i.e., habitats, feeding grounds, and spawning grounds (Steneck et al. 2002; Harley et al. 2012). The construction, maintenance, and management of seaweed beds are thus important issues in the field of fisheries (Yoshikawa 1987). Unfortunately, 6,400 ha of seagrass and seaweed beds have been lost along Japan's coast, of which Sargassum beds accounted for 22% from 1978 to 1991 due to the increase in coastal landfill sites at ports (Terawaki et al. 2003). The 4th Basic Survey of Nature Conservation conducted by Japan's Ministry of the Environment from 1989 to 1991 identified 201,212 ha of seaweed beds. Seaweed-bed surveys were also conducted by Japan's Fisheries Agency from 2006 to 2008, and information was obtained on 41.6% of the seaweed beds described in the 4th Basic Survey of Nature Conservation. These surveys demonstrated that the area of seaweed beds on Japan's coasts decreased from 83,798 ha to 65,260 ha over 17 years (Baba 2021). More recently, according to the results of a seaweed bed survey conducted in 2018-2020, the total area of seaweed beds nationwide, excluding some closed sea areas, was 164,340 ha (Ministry of the Environment 2021). As mentioned above, the threat of declining seaweed beds has been a concern not only in Japan but also around the world (e.g., Frederick and Wyllie-Echeverria 1996; Krumhansl et al. 2016; Wernberg et al. 2019; Smale 2020). To rehabilitate or mitigate against these losses, attempts have mainly been made to construct seaweed beds worldwide, such as in Japan since the 1980s (e.g., Tomiyama 1981; Yamauchi 1984; Ohno et al. 1990; Watanuki and Yamamoto 1990; Ohno 1993; Choi et al. 2000; Choi et al. 2002; Terawaki et al. 2003; Choi et al. 2006); in USA (e.g., Reed and Foster 1984; Arkema et al. 2009; Benes and Carpenter 2015; Schroeter et al. 2015); and in Korea (e.g., Jung et al. 2020). It is important to know which types of seaweed will colonize at an installed artificial substrate, undergo growth transition, and eventually dominate to create effective seaweed beds. Regarding such vegetation succession, pioneer species cannot grow in the presence of successor species (conversely, pioneer species can grow without successor species). The influences of pioneer species on successor species can be divided into three pattern models: (i). The facilitation model indicates the presence of earlier species facilitates the colonization and growth of later species; (ii). The inhibition model indicates later species can colonize and grow only when earlier species disappear; (iii). In the tolerance model, later species can colonize and grow in the presence of earlier species (Connell and Slatyer 1977; Connell et al. 1987). A limited number of studies have compared the artificial and natural reefs (e.g., Badalamenti et al. 2002; Douke et al. 2004; Oyamada et al. 2008). Regarding the artificial reef that we have been interested in, there are two research questions: (i) will the vegetation on an artificial reef approach that on a neighboring natural reef everywhere? and (ii) can it be said that the vegetation on a natural reef has reached the climax without any change? Matsui (unpublished) reported that seaweed species composition and coverage on an artificial reef had not caught up with those on a natural reef in 3 years after the reef construction. The seaweed on the artificial reef is thus considered to be in the vegetation succession process, which has not reached the climax condition, while the natural reef almost reached the climax phase. On the other hand, Douke et al. (2004) reported that the vegetation on the artificial reef became close to that of the neighboring natural reef in 3 years after artificial reef construction. However, Douke et al. (2004) did not statistically verify the difference between artificial and natural reefs. Therefore, the vegetation on the artificial reef reported by Douke et al. (2004) may not statistically match that on the natural reef. Then, we have been interested in a research question: how many years will it take for the seaweed species composition and coverage on the artificial reef to catch up with those on the natural reef? Thus, to address the above research questions, the objective of this study is to monitor and compare the brown seaweed, especially the Sargassum and Myagropsis species distribution and coverage multi-temporally at four points, as well as to investigate their succession over the observation times (years 2 and 4) on the artificial reef constructed in Wakasa Bay, Japan, and to compare them to the natural reef. Materials and Methods Survey sites The artificial reefs were constructed in Wakasa Bay (Fig. 1). This bay is located in the Japan Sea at Honshu Island between the Cape Echizen at the east and the Cape Kyoga at the west. The artificial reef was installed to northwest of fishing port in the east part of the bay near the natural reef. Table 1 provides the coordinates (latitude/longitude) at each survey site. The distance between the artificial and the natural reefs is approximately 50 m. The total area of the artificial reef was 1.8 ha; 1.5 ha on the east side and 0.3 ha on the west side. The construction was started in April 2017 and was completed in November 2017. The water depth on the east side (Stns. E-1 to E-4) is approximately 8–10 m and that on the west side (Stn. W-1) is approximately 6–8 m, and the bottom sediment is sand. There is a natural reef extending from the artificial reef toward the land side. The water depth on the natural reef is approximately 5–6 m, and the bottom sediment is greenstone (Nakae et al. 2002). The structure on the artificial reef consists of paving stones on the seabed and X-blocks on the top (Fig. 2). The type of paving stone is granite from Tsuruga City, Fukui Prefecture. The paving stone weight is approximately 50–200 kg, while X-Block weight is approximately 2,000 kg. The paving stones were placed at 5.3-m intervals. Survey period and method The first and second monitoring studies were conducted in May and October 2019 in 2 years after artificial reef construction. The third and fourth monitoring studies were performed in June and October 2021 in 4 years after artificial reef construction. As part of each monitoring study, we investigated the seaweed species composition and coverage to determine whether those on the artificial reef approached those on the natural reef. The seaweed species composition and coverage were observed visually and recorded by scuba divers. The scuba divers who use underwater lights are expert persons and can identify seaweed at the species level by direct visualization. If the species name was unknown, the scuba divers brought back the seaweed to the laboratory and identified based on the reference books of Tanaka and Nakamura (2004) and Yoshida et al. (2015). The species identification and coverage counting of seaweeds on the artificial and natural areas were recorded by the divers using two-3.2 m scale bares, which cover observation areas of 3.2 m by 3.2 m (10.24 m 2 ). The seaweed coverage was then estimated using the percentage coverage; the seaweed coverage is 100% when seaweeds cover the entire square (Braun-Blanquet, 1964). When seaweeds are scarce, they are indicated as +, and the coverage is assumed to be 1% (see Table S1 in the online Supplementary Material). We measured the seaweed growing environment at each monitoring site in the four monitoring studies (May 2019, October 2019, June 2021, and October 2021). We measured environmental parameters (water depth, water temperature, pH, dissolved oxygen (DO) concentration, salinity, and turbidity) using a portable multi-item water quality meter (WQC-24, DKK-TOA Corp., Tokyo) once at each survey site and during the monitoring campaign. A self-recording water temperature logger (Thermochron SL-type, KN Laboratories, Inc., Osaka) that was set to record at 3-hour intervals was placed on the seabed near the artificial reef and left there for 9 months from June 2021 to February 2022 (Fig. 1). We investigated the water temperatures at Hiruga and Shitsumi offings in Wakasa Bay over the past 15 years (2006-2020). Hiruga offing is in the present study area and Shitsumi offing is in the previous study area where the seaweed species that have dominated on the natural reef was S . patens / S . macrocarpum . To understand the water pollution situation in public water areas, we used online data based on the Water Pollution Control Law in Fukui Prefecture (Fukui Prefecture). The water temperature was recorded in May, August, November, and March. Analysis method We investigated the difference in the average brown seaweed coverage between the first (May 2019), second (October 2019), third (June 2021), and fourth (October 2021) monitoring studies and between the artificial and natural reefs. We compared eight groups corresponding to the two reef types (Artificial VS Natural reefs) and four observation times (First, Second, Third, and fourth monitoring times) and then examined the normality of the survey data by the Kolmogorov‒Smirnov test. When normality was confirmed, paired two-way analysis of variance (ANOVA) was performed. Additionally, we performed a Wilcoxon's rank sum test for the seaweed growing environment. These analyses were performed by the statistical software EZR (version 2.7-1) (Kanda 2013). Results Seaweed species composition Forty-three species were successfully identified in the four monitoring studies conducted in May 2019 (the first monitoring study), October 2019 (the second monitoring study), June 2021 (the third monitoring study), and October 2021 (the fourth monitoring study) (Table S1 in the online Supplementary Material). Regarding species diversity, ten species of large brown seaweed of Sargassum and Myagropsis were confirmed as S . confusum , S . hemiphyllum , S . horneri , S . macrocarpum , S . micracanthum , S . patens , S . piluliferum , S . ringgoldianum ssp. Coreanum , S . siliquastrum , and Myagropsis myagroides (Table S1). Based on Table S1, the ranges of large brown seaweed observed at the five artificial reef sites (Stns. E-1 to E-4, W-1) were 5 to 7 species ( S . confusum , S . hemiphyllum , S . horneri , S . macrocarpum , S . patens , S . piluliferum , S . ringgoldianum ssp. Coreanum , S . siliquastrum , and M . myagroides ), 4 to 9 species ( S . confusum , S . hemiphyllum , S . horneri , S . macrocarpum , S . patens , S . piluliferum , S . ringgoldianum ssp. Coreanum , S . siliquastrum , and M . myagroides ), 4 to 6 species ( S . confusum , S . hemiphyllum , S . horneri , S . macrocarpum , S . patens , S . piluliferum , S . siliquastrum , and M . myagroides ), and 5 to 7 species ( S . confusum , S . hemiphyllum , S . horneri , S . macrocarpum , S . micracanthum , S . patens , S . piluliferum , S . siliquastrum , and M . myagroides ) with an average of 6.2, 6.0, 5.4, and 6.0 species for the first, second, third, and fourth monitoring studies, respectively. At the one natural reef sites (Stn. N-1), the ranges were 3 to 6 species ( S . confusum , S . hemiphyllum , S . horneri , S . patens , S . piluliferum , S . siliquastrum , and M . myagroides ). Regarding seaweed coverage of all seaweed species, on the artificial reef, S . horneri was confirmed in the first monitoring study, however S . horneri decreased and S . confusum increased in the second monitoring study. After that, S . confusum decreased and M . myagroides increased in the third and fourth monitoring studies. On the natural reef, S. patens dominated in the first and second monitoring studies. And then, S. patens decreased and M . myagroides increased in the third and fourth monitoring studies (Fig. 3). Seaweed coverage The average seaweed coverage of all seaweed species on the artificial reef was 83%, 84%, 94%, and 86% in the first, second, third, and fourth monitoring studies, respectively. Similarly, that on the natural reef was 85%, 90%, 90%, and 90% in the first, second, third, and fourth monitoring studies, respectively (Fig. 4). Statistical analysis (ANOVA) showed that there were not significant differences in the average seaweed coverage for all seaweed species, including green algae, brown algae, and red algae. A significant difference was not confirmed for reef types (Artificial VS Natural reefs), observation times (First, Second, Third, and fourth monitoring times), and the interaction of these two factors. Growing environment for all seaweeds As a result of Wilcoxon's rank sum test for water depth, water temperature, pH, DO concentration, salinity, and turbidity, a significant difference was confirmed between the artificial and natural reefs only in water depth (p=0.002) (Table 2). Regarding the water temperature for 9 months, the maximum value was 30.0°C (July 31, 2021), and the minimum value was 7.2°C (February 23, 2022) in the present study area. Seasonal changes in water temperature in the Hiruga and Shitsumi offings are shown in Fig. 5. The water temperature in the Hiruga offing is higher than that in the Shitsumi offing throughout the season. Particularly, the results of Wilcoxon’s rank sum test on the seasonal changes in water temperature in the two offings showed a significant difference in March (p = 0.051). Discussion Brown seaweeds in 4 years after artificial reef construction The seaweed coverage of Sargassum and Myagropsis species on the artificial reef approached that on the natural reef in 2 years after construction. However, the seaweed species composition of brown seaweeds differs between the artificial and natural reefs in 2 years after construction. The results of the first monitoring study on the artificial reef showed that nine species of Sargassum and one species of Myagropsis existed, but only two species of S . horneri / S . confusum dominated the Sargassum community, with a percent cover of 55% and 22%, respectively; nine species in the second monitoring study, but only one species of S . confusum dominated the Sargassum community, with a percent cover of 64%. In the third monitoring study, eight species were found but dominated by only two species of M . myagroides / S . confusum with a percent cover of 56% and 32%, respectively; nine species in the fourth monitoring study, but only three species of M . myagroides / S . patens / S . confusum dominated with a percent cover of 35%, 15%, and 13%, respectively (Fig. 6a). Meanwhile, on the natural reef, six species existed in the first monitoring study, with a high percent cover of S . patens of 70%, while six species in the second monitoring study, but only S . patens / M . myagroides dominated with a percent cover of 55% and 20%, respectively. However, in the third and fourth monitoring studies, only one species of M . myagroides dominated with a percent cover of 80% and 50%, respectively (Fig. 6b). Since both the artificial and natural reefs were dominated by only one species of M . myagroides , it could be assumed that M . myagroides may be the climax-forming species in this region (Fig. 6). That is, S . horneri / S . confusum were dominant on the artificial reef and S . patens / M . myagroides were dominant on the natural reef in 2 years after construction. After that, M . myagroides dominated on both the artificial and natural reefs in 4 years after construction. It is thus estimated that the seaweed coverage on the artificial reef approaches that on the natural reef immediately, while the seaweed species composition takes time to approach that on the natural reef. Sargassum confusum is often the first species of brown algae of Sargassum to be colonized when an artificial reef is constructed, and S . confusum may have characteristics that other Sargassum seaweeds do not have, i.e., ( i ) it attaches easily to new substrates, and ( ii ) it is difficult for phytophagous animals to eat the juvenile form of this seaweed (Kyoto Prefectural Agriculture, Forestry and Fisheries Technology Center, Fisheries Technology Department). A common feature of S . confusum is that it can adapt to unstable environments where other Sargassum seaweeds cannot grow. As time passes, species other than S . confusum will dominate (Douke et al. 2004). In the present study, as it changed from S . horneri to S . confusum in 2 years after construction and from S . confusum to M . myagroides in 4 years after construction, the seaweed species composition on the artificial reef was consistent with previous studies. Regarding the reason for the decrease in S . confusum and the increase in M . myagroides on the artificial reef, it is considered that the fact that M . myagroides covers the upper part of S . confusum is advantageous in terms of competition for light (Yatsuya et al. 2005). Therefore, these changes are considered to be a process of vegetation succession. Vegetation succession: Further research challenges Sargassum horneri has been reported to appear only in 1 year after artificial reef construction. That is, annual seaweeds settle in the first year, and perennial seaweeds follow (Douke et al. 2004; Yatsuya et al. 2008; Endo et al. 2019). In the present study, S . horneri was dominant in the first monitoring study on the artificial reef, but it was hardly confirmed in the other three monitoring studies on both the artificial and natural reefs. Thus, these results coincided with those of previous studies. Additionally, it is estimated that the reason why S . horneri appeared even 2 years after construction instead of 1 year after construction was that the seaweed did not grow in time for the following spring because the construction was completed in November 2017. Previous studies have determined that natural reefs are in a state of climax (Douke et al. 2004). On the other hand, the present findings did not advocate the previous studies because S . patens was dominant in 2 years after construction, while M . myagroides dominated in 4 years after construction on the natural reef. Further vegetation succession research can be expected to establish whether this change is simply an annual variation or constitutes vegetation succession. The seaweed species that have dominated on the natural reef has differed among the perennials of Sargassum : S . fulvellum (Douke et al. 2004), S . patens / S . piluliferum (Yatsuya et al. 2008; Endo et al. 2019), S . patens / S . macrocarpum at Shitsumi offing in the previous study, and M . myagroides at Hiruga offing in the present investigation. The survey sites used by Douke et al. (2004) are located outside Wakasa Bay, whereas Wakasa Bay sites were examined by Yatsuya et al. (2008), Endo et al. (2019), the previous study, and the present investigation. The survey sites evaluated in the Yatsuya and Endo studies are located in western Wakasa Bay, and Shitsumi offing and Hiruga offing are located in the center of Wakasa Bay. It seems likely that the water temperature varies slightly depending on the survey sites (Matsui et al. 2023). Therefore, the water temperature varies at each location within Wakasa Bay, and it is estimated that seaweed growth depends on the water temperature. The upper limit temperature for the growth of M . myagroides is 30°C (Haraguchi et al. 2005), it is possible that this study area, where the water temperature does not exceed 30°C, is suitable for the growth of M . myagroides . In addition, the maturity period of M . myagroides and S . macrocarpum / S . patens is February-March and May-June, respectively (Kyoto Prefectural Agriculture, Forestry and Fisheries Technology Center, Fisheries Technology Department 2009). It encourages M . myagroides to grow such that the water temperature at Hiruga offing is higher than that at Shitsumi offing in March. Conclusion An artificial reef was constructed in Wakasa Bay, Japan, and we monitored the reef in 2 years and 4 years after the construction was completed. We set up five sites on the artificial reef as a treatment area and one site on the natural reef as a control area and then identified the seaweed species composition of the Sargassum and Myagropsis communities and their coverage on each reef. The seaweed coverage on the artificial reef was already close to that on the natural reef in 2 years after construction. However, the dominant species on the artificial reef was not conformable to that on the natural reef in 2 years after construction. Especially, on the artificial reef, the presence of S . horneri / S . confusum was dominant in 2 years after construction and that of M . myagroides was dominant in 4 years after construction. Whereas on the natural reef, the presence of S . patens dominated in 2 years after construction and that of M . myagroides dominated in 4 years after construction. That is, the species composition on the artificial reef was close to that on the natural reef in 4 years after construction. Thus, the recovery of species composition takes longer than that of seaweed coverage on the artificial reef. Declarations Authors contributions AM wrote the main manuscript text, figures 1-6, and Tables 1-2. MK, SN, and MT are scuba divers. They observed visually and recorded the seaweed species composition and coverage. NI is a research assistant. All authors reviewed the manuscript. Funding The authors did not receive support from any organization for the submitted work. Data Availability The data that support the findings of this study are available in the supplementary material of this article (Table S1). Conflict of interest The authors have no relevant financial or nonfinancial interests to disclose. Acknowledgments We would like to express our deepest gratitude to all of the following individuals. Shuhei Kajimura and Kazuyuki Miyanaga (Forestry and Fisheries Department, Reinan Promotion Bureau, Fukui Prefecture) agreed to publish the survey results and provided earlier reports. Dr. Hikaru Endo (Faculty of Fisheries, Department of Fisheries Science and Technology, Kagoshima University) provided research papers and useful advice on vegetation succession. Dr. Yoshitake Takada (Fisheries Technology Institute, Japan Fisheries Research and Education Agency) advised on how to analyze community compositions using the statistical software R. References Arkema KK, Reed DC, Schroeter SC (2009) Direct and indirect effects of giant kelp determine benthic community structure and dynamics. 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In: Borowitzka MA, Critchley AT, Kraan S, Peters A, Sjøtun K, Notoya M (eds) Nineteenth International Seaweed Symposium. Developments in Applied Phycology, vol 2. Springer, Dordrecht, pp 413–418. https://doi.org/10.1007/978-1-4020-9619-8_50 Reed DC, Foster MS (1984) The effects of canopy shadings on algal recruitment and growth in a giant kelp forest. Ecology 65(3): 937–948. https://doi.org/10.2307/1938066 Schroeter SC, Reed DC, Raimondi PT (2015) Effects of reef physical structure on development of benthic reef community: a large-scale artificial reef experiment. Marine Ecology Progress Series 540: 43–55. https://doi.org/10.3354/meps11483 Smale DA (2020) Impacts of ocean warming on kelp forest ecosystems. New Phytologist 225(4): 1447–1454. https://doi.org/10.1111/nph.16107 Steneck RS, Graham MH, Bourque BJ, Corbett D, Erlandson JM, Estes JA, Tegner MJ (2002) Kelp forest ecosystems: biodiversity, stability, resilience and future. Environmental Conservation 29(4): 436–459. https://doi.org/10.1017/S0376892902000322 Tanaka J, Nakamura T (2004) A photographic Guide; Japanese Seaweeds (in Japanese). Heibonsha Limited, Publishers, Tokyo Terawaki T, Yoshikawa K, Yoshida G, Uchimura M, Iseki K (2003) Ecology and restoration techniques for Sargassum beds in the Seto Inland Sea, Japan. Marine Pollution Bulletin 47(1-6): 198–201. https://doi.org/10.1016/S0025-326X(03)00054-7 Tomiyama A (1981) Aquatic afforestation with Sargassum (in Japanese). In: The Japanese Society of Fisheries Science (ed) Seaweed beds. KOUSEISHA KOUSEIKAKU Co., Ltd., Tokyo, pp 142–157 Watanuki A, Yamamoto A (1990) Settlement of seaweeds on coastal structures. Hydrobiologia 204(1): 275–280. https://doi.org/10.1007/BF00040245 Wernberg T, Krumhansl K, Filbee-Dexter K, Pedersen MF (2019) Status and trends for the world’s kelp forests. In: Sheppard C (ed) World Seas: An Environmental Evaluation: Ecological Issues and Environmental Impacts, 2nd edn. Academic Press, Massachusetts, pp 57–78 Yamauchi K (1984) The formation of Sargassum beds on artificial substrata by transplanting seedlings of S . horneri (T URNER ) C. A GARDH and S . muticum (Y ENDO ) F ENSHOLT . Bulletin of the Japanese Society of Scientific Fisheries 50(7): 1115–1123. https://doi.org/10.2331/suisan.50.1115 Yatsuya K, Nishigaki T, Douke A, Itani M, Wada Y (2005) Succession of a Sargassaceae community on an artificially installed stone bed off Amino, Japan Sea Ⅱ Productive structure of Sargassaceae community and age composition of Sargassum confusum . (in Japanese with English abstract). Bulletin of the Kyoto Institute of Oceanic and Fisheries Science 27: 19–24. Yatsuya K, Nishigaki T, Shirafuji N, Takeno K (2008) Effect of drifting seaweeds captured by a floating rope on the supply of embryos to new substrata of an artificial reef area off Yoro-Oshima, and algal succession in this area (in Japanese with English abstract). Bulletin of the Kyoto Institute of Oceanic and Fisheries Science 30: 31–37. Yoshida T, Suzuki M, Yoshinaga K (2015) Checklist of marine algae of Japan (Revised in 2015) (in Japanese). The Japanese Journal of Phycology 63(3): 129–189. Yoshikawa K (1987) Studies on the formation of Sargassum beds-Ⅲ The formation of Sargassum beds by setting campus sheets for embryo to settle down effectively (in Japanese with English abstract). Bulletin of the Nansei Regional Fisheries Research Laboratory 21: 25–35. Tables Tables 1 and 2 are available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files TableS1.xlsx Tables.pdf Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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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-4459311","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":309620896,"identity":"8a141416-b103-429c-9636-e3536e3008dd","order_by":0,"name":"Akira Matsui","email":"data:image/png;base64,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","orcid":"","institution":"Keifuku Consultant Co., Ltd.","correspondingAuthor":true,"prefix":"","firstName":"Akira","middleName":"","lastName":"Matsui","suffix":""},{"id":309620897,"identity":"23731c36-6b70-4aeb-987d-e4c7a6ebb2b6","order_by":1,"name":"Masakatsu Kawamura","email":"","orcid":"","institution":"SHINSEN Co., Ltd.","correspondingAuthor":false,"prefix":"","firstName":"Masakatsu","middleName":"","lastName":"Kawamura","suffix":""},{"id":309620898,"identity":"c834ccfc-e96b-48e0-924c-3f0107635e1a","order_by":2,"name":"Shigehiro Nozawa","email":"","orcid":"","institution":"SHINSEN Co., Ltd.","correspondingAuthor":false,"prefix":"","firstName":"Shigehiro","middleName":"","lastName":"Nozawa","suffix":""},{"id":309620899,"identity":"f865c36e-3eeb-4a86-beb2-10daed5d1e57","order_by":3,"name":"Masatomo Takeyama","email":"","orcid":"","institution":"MOVE. Ltd.","correspondingAuthor":false,"prefix":"","firstName":"Masatomo","middleName":"","lastName":"Takeyama","suffix":""},{"id":309620900,"identity":"efd7d5d7-d0e6-4e23-b480-ca5098fa900d","order_by":4,"name":"Naoya Inoue","email":"","orcid":"","institution":"Keifuku Consultant Co., Ltd.","correspondingAuthor":false,"prefix":"","firstName":"Naoya","middleName":"","lastName":"Inoue","suffix":""}],"badges":[],"createdAt":"2024-05-22 08:22:12","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4459311/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4459311/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":57701606,"identity":"66130c11-5e33-44e4-964e-e74cd05a8cec","added_by":"auto","created_at":"2024-06-04 14:02:52","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":100706,"visible":true,"origin":"","legend":"\u003cp\u003eThe locations of the survey sites. Black circles: The survey sites on the artificial reef in Wakasa Bay, Japan. White circle: The survey site on the natural reef. Green line: The extent of the natural reef. Survey areas investigated by Yatsuya et al. 2008: white\u003c/p\u003e\n\u003cp\u003etriangle; Endo et al. 2019: white square; Douke et al. 2004: white star; and our previous study area: black star.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4459311/v1/1d486e40acd3282bc427e18d.jpg"},{"id":57702216,"identity":"87cb8c71-97aa-489d-838a-73a71785b9c9","added_by":"auto","created_at":"2024-06-04 14:10:52","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":52488,"visible":true,"origin":"","legend":"\u003cp\u003eThe artificial reef's a ground plan and b structure. The paving stones weight is 50–200 kg. The amount of X-Blocks used for the artificial reef is 2,000 kg. The XBlocks were placed at 5.3-m intervals.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4459311/v1/648bb943d04eb36ffd08cc4b.jpg"},{"id":57701608,"identity":"9e139aa0-21a2-4464-ad0f-5e73caa76586","added_by":"auto","created_at":"2024-06-04 14:02:52","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":96183,"visible":true,"origin":"","legend":"\u003cp\u003eSeaweed vegetation coverage on the artificial and natural reefs in this study’s (a) first monitoring study (May 14, 2019), (b) second monitoring study (October 28, 2019), (c) third monitoring study (June 18, 2021), and (d) fourth monitoring study (October 19, 2021).\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4459311/v1/2e4ac16f638a097e0852d574.jpg"},{"id":57701607,"identity":"175281ad-59ed-435c-a44e-69a3d6961a5f","added_by":"auto","created_at":"2024-06-04 14:02:52","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":39748,"visible":true,"origin":"","legend":"\u003cp\u003eAverage seaweed coverage of all seaweed species on the artificial and natural reefs.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4459311/v1/1853d98170958c0ea713b8a5.jpg"},{"id":57701610,"identity":"63323479-3aa7-4f16-8c53-0f271a8acb29","added_by":"auto","created_at":"2024-06-04 14:02:53","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":31159,"visible":true,"origin":"","legend":"\u003cp\u003eSeasonal changes in water temperature between Hiruga offing and Shitsumi offing.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4459311/v1/8204738d078c8c2e8c85a680.jpg"},{"id":57701609,"identity":"27ae8c2d-2109-43aa-b9e9-af63bb352c0e","added_by":"auto","created_at":"2024-06-04 14:02:53","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":38685,"visible":true,"origin":"","legend":"\u003cp\u003eSecular changes in seaweed coverage of Sargassum horneri, Sargassum confusum, Sargassum patens, Myagropsis myagroides on the a artificial and b natural\u003c/p\u003e\n\u003cp\u003ereefs.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4459311/v1/0231e34637b0887444b0039a.jpg"},{"id":58882087,"identity":"d580e517-afdc-4988-86f1-5ea78411d988","added_by":"auto","created_at":"2024-06-23 07:37:26","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":818937,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4459311/v1/4b5ab0e8-507f-4add-a57b-15e28a5b2aa8.pdf"},{"id":57701604,"identity":"f849a2ee-fff5-49e2-afbc-e379375f90ca","added_by":"auto","created_at":"2024-06-04 14:02:52","extension":"xlsx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":20574,"visible":true,"origin":"","legend":"","description":"","filename":"TableS1.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-4459311/v1/68ea7e4f9d9c5583118da719.xlsx"},{"id":57703025,"identity":"843e4cde-e155-435e-8a45-86244af1bae9","added_by":"auto","created_at":"2024-06-04 14:18:52","extension":"pdf","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":91372,"visible":true,"origin":"","legend":"","description":"","filename":"Tables.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4459311/v1/105b97fd47d3cfd5c5a16efb.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Comparison of seaweed species composition and coverage of Sargassum and Myagropsis communities between artificial and natural reefs in Wakasa Bay, Japan","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSeaweed beds of brown algal communities of \u003cem\u003eSargassum\u003c/em\u003e are formed in the coastal Japan Sea. The brown algal communities of \u003cem\u003eSargassum\u003c/em\u003e play an important role in useful marine functions, i.e., habitats, feeding grounds, and spawning grounds (Steneck et al. 2002; Harley et al. 2012). The construction, maintenance, and management of seaweed beds are thus important issues in the field of fisheries (Yoshikawa 1987).\u003c/p\u003e\n\u003cp\u003eUnfortunately, 6,400 ha of seagrass and seaweed beds have been lost along Japan\u0026apos;s coast, of which \u003cem\u003eSargassum\u003c/em\u003e beds accounted for 22% from 1978 to 1991 due to the increase in coastal landfill sites at ports (Terawaki et al. 2003). The 4th Basic Survey of Nature Conservation conducted by Japan\u0026apos;s Ministry of the Environment from 1989 to 1991 identified 201,212 ha of seaweed beds.\u0026nbsp;Seaweed-bed surveys were also conducted by Japan\u0026apos;s Fisheries Agency from 2006 to 2008, and information was obtained on 41.6% of the seaweed beds described in the 4th Basic Survey of Nature Conservation. These surveys demonstrated that the area of seaweed beds on Japan\u0026apos;s coasts decreased from 83,798 ha to 65,260 ha over 17 years\u0026nbsp;(Baba 2021). More recently, according to the results of a seaweed bed survey conducted in 2018-2020, the total area of seaweed beds nationwide, excluding some closed sea areas, was 164,340 ha (Ministry of the Environment 2021).\u0026nbsp;As mentioned above, the threat of declining seaweed beds has been a concern not only in Japan but also around the world (e.g., Frederick and Wyllie-Echeverria 1996; Krumhansl et al. 2016; Wernberg et al. 2019; Smale 2020).\u003c/p\u003e\n\u003cp\u003eTo rehabilitate or mitigate against these losses, attempts have mainly been made to construct seaweed beds worldwide, such as in Japan since the 1980s (e.g., Tomiyama 1981; Yamauchi 1984; Ohno et al. 1990; Watanuki and Yamamoto 1990; Ohno 1993; Choi et al. 2000; Choi et al. 2002; Terawaki et al. 2003; Choi et al. 2006); in USA (e.g., Reed and Foster 1984; Arkema et al. 2009; Benes and Carpenter 2015; Schroeter et al. 2015); and in Korea (e.g., Jung et al. 2020). It is important to know which types of seaweed will colonize at an installed artificial substrate, undergo growth transition, and eventually dominate to create effective seaweed beds.\u0026nbsp;Regarding such vegetation succession, pioneer species cannot grow in the presence of successor species (conversely, pioneer species can grow without successor species). The influences of pioneer species on successor species can be divided into three pattern models: (i). The facilitation model indicates the presence of earlier species facilitates the colonization and growth of later species; (ii). The inhibition model indicates later species can colonize and grow only when earlier species disappear; (iii). In the tolerance model, later species can colonize and grow in the presence of earlier species (Connell and Slatyer 1977; Connell et al. 1987).\u003c/p\u003e\n\u003cp\u003eA limited number of studies have compared the artificial and natural reefs (e.g., Badalamenti et al. 2002; Douke et al. 2004; Oyamada et al. 2008). Regarding the artificial reef that we have been interested in, there are two research questions: (i) will the vegetation on an artificial reef approach that on a neighboring natural reef everywhere? and (ii) can it be said that the vegetation on a natural reef has reached the climax without any change?\u003c/p\u003e\n\u003cp\u003eMatsui (unpublished) reported that\u0026nbsp;seaweed species composition and coverage on an artificial reef had not caught up with those on a natural reef\u0026nbsp;in 3 years after the reef construction.\u0026nbsp;The\u0026nbsp;seaweed\u0026nbsp;on the artificial reef\u0026nbsp;is thus considered to be in the vegetation succession process, which\u0026nbsp;has not reached the climax condition, while the natural reef almost reached the climax phase.\u0026nbsp;On the other hand, Douke et al. (2004) reported that the vegetation on the artificial reef became close to that of the neighboring natural reef in 3 years after artificial reef construction. However, Douke et al. (2004) did not statistically verify the difference between artificial and natural reefs. Therefore, the vegetation on the artificial reef reported by Douke et al. (2004) may not statistically match that on the natural reef.\u003c/p\u003e\n\u003cp\u003eThen, we have been interested in a research question: how many years will it take for the seaweed species composition and coverage on the artificial reef to catch up with those on the natural reef? Thus, to address the above research questions, the objective of this study is to monitor and compare the brown seaweed, especially the \u003cem\u003eSargassum\u003c/em\u003e and \u003cem\u003eMyagropsis\u003c/em\u003e species distribution and coverage multi-temporally at four points, as well as to investigate their succession over the observation times (years 2 and 4) on the artificial reef constructed in Wakasa Bay, Japan, and to compare them to the natural reef.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003e\u0026nbsp;\u003cem\u003eSurvey sites\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe artificial reefs were constructed in Wakasa Bay (Fig. 1). This bay is located in the Japan Sea at Honshu Island between the Cape Echizen at the east and the Cape Kyoga at the west. The artificial reef was installed to northwest of fishing port in the east part of the bay near the natural reef. Table 1 provides the coordinates (latitude/longitude) at each survey site. The distance between the artificial and the natural reefs is approximately 50 m. The total area of the artificial reef was 1.8 ha; 1.5 ha on the east side and 0.3 ha on the west side. The construction was started in April 2017 and was completed in November 2017. The water depth on the east side (Stns. E-1 to E-4) is approximately 8\u0026ndash;10 m and that on the west side (Stn. W-1) is approximately 6\u0026ndash;8 m, and the bottom sediment is sand. There is a natural reef extending from the artificial reef toward the land side. The water depth on the natural reef is approximately 5\u0026ndash;6 m, and the bottom sediment is greenstone (Nakae et al. 2002).\u003c/p\u003e\n\u003cp\u003eThe structure on the artificial reef consists of paving stones on the seabed and X-blocks on the top (Fig. 2). The type of paving stone is granite from Tsuruga City, Fukui Prefecture. The paving stone weight is approximately 50\u0026ndash;200 kg, while X-Block weight is approximately 2,000 kg. The paving stones were placed at 5.3-m intervals.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eSurvey period and method\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe first and second monitoring studies were conducted in May and October 2019 in 2 years after artificial reef construction. The third and fourth monitoring studies were performed in June and October 2021 in 4 years after artificial reef construction. As part of each monitoring study, we investigated the seaweed species composition and coverage to determine whether those on the artificial reef approached those on the natural reef. The seaweed species composition and coverage were observed visually and recorded by scuba divers. The scuba divers who use underwater lights are expert persons and can identify seaweed at the species level by direct visualization. If the species name was unknown, the scuba divers brought back the seaweed to the laboratory and identified based on the reference books of Tanaka and Nakamura (2004) and Yoshida et al. (2015).\u003c/p\u003e\n\u003cp\u003eThe species identification and coverage counting of seaweeds on the artificial and natural areas were recorded by the divers using two-3.2 m scale bares, which cover observation areas of 3.2 m\u0026nbsp;by\u0026nbsp;3.2 m (10.24 m\u003csup\u003e2\u003c/sup\u003e). The seaweed coverage was then estimated using the percentage coverage; the seaweed coverage is 100% when seaweeds cover the entire square (Braun-Blanquet, 1964). When seaweeds are scarce, they are indicated as +, and the coverage is assumed to be 1% (see Table S1 in the online Supplementary Material).\u003c/p\u003e\n\u003cp\u003eWe measured the seaweed growing environment at each monitoring site in the four monitoring studies (May 2019, October 2019, June 2021, and October 2021). We measured environmental parameters (water depth, water temperature, pH, dissolved oxygen (DO) concentration, salinity, and turbidity) using a portable multi-item water quality meter (WQC-24, DKK-TOA Corp., Tokyo) once at each survey site and during the monitoring campaign. A self-recording water temperature logger (Thermochron SL-type, KN Laboratories, Inc., Osaka) that was set to record at 3-hour intervals was placed on the seabed near the artificial reef and left there for 9 months from June 2021 to February 2022 (Fig. 1).\u003c/p\u003e\n\u003cp\u003eWe investigated the water temperatures at Hiruga and Shitsumi offings in Wakasa Bay over the past 15 years (2006-2020). Hiruga offing is in the present study area and Shitsumi offing is in the previous study area where the seaweed species that have dominated on the natural reef was \u003cem\u003eS\u003c/em\u003e. \u003cem\u003epatens\u003c/em\u003e/\u003cem\u003eS\u003c/em\u003e. \u003cem\u003emacrocarpum\u003c/em\u003e. To understand the water pollution situation in public water areas, we used online data based on the Water Pollution Control Law in Fukui Prefecture (Fukui Prefecture). The water temperature was recorded in May, August, November, and March.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eAnalysis method\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eWe investigated the difference in the average brown seaweed coverage between the first (May 2019), second\u0026nbsp;(October 2019), third (June 2021), and fourth (October 2021) monitoring studies and between the artificial and natural reefs.\u003c/p\u003e\n\u003cp\u003eWe compared eight groups corresponding to the two reef types (Artificial VS Natural reefs) and four observation times (First, Second, Third, and fourth monitoring times) and then examined the normality of the survey data by the Kolmogorov‒Smirnov test. When normality was confirmed, paired two-way analysis of variance (ANOVA) was performed. Additionally, we performed a Wilcoxon\u0026apos;s rank sum test for the seaweed growing environment. These analyses were performed by the statistical software EZR (version 2.7-1) (Kanda 2013).\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cem\u003eSeaweed species composition\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;Forty-three species were successfully identified in the four monitoring studies conducted in May 2019 (the first monitoring study), October 2019 (the second monitoring study), June 2021 (the third monitoring study), and October 2021 (the fourth monitoring study) (Table S1 in the online Supplementary Material). Regarding species diversity, ten species of large brown seaweed of \u003cem\u003eSargassum\u003c/em\u003e and \u003cem\u003eMyagropsis\u003c/em\u003e were confirmed as \u003cem\u003eS\u003c/em\u003e. \u003cem\u003econfusum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehemiphyllum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehorneri\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003emacrocarpum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003emicracanthum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003epatens\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003epiluliferum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003eringgoldianum\u003c/em\u003e ssp. \u003cem\u003eCoreanum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003esiliquastrum\u003c/em\u003e, and \u003cem\u003eMyagropsis\u003c/em\u003e\u003cem\u003emyagroides\u003c/em\u003e (Table S1). Based on Table S1, the ranges of large brown seaweed observed at the five artificial reef sites (Stns. E-1 to E-4, W-1) were 5 to 7 species (\u003cem\u003eS\u003c/em\u003e. \u003cem\u003econfusum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehemiphyllum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehorneri\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003emacrocarpum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003epatens\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003epiluliferum\u003c/em\u003e,\u003cem\u003e\u0026nbsp;S\u003c/em\u003e. \u003cem\u003eringgoldianum\u003c/em\u003e ssp. \u003cem\u003eCoreanum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003esiliquastrum\u003c/em\u003e, and \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e), 4 to 9 species (\u003cem\u003eS\u003c/em\u003e. \u003cem\u003econfusum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehemiphyllum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehorneri\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003emacrocarpum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003epatens\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003epiluliferum\u003c/em\u003e,\u003cem\u003e\u0026nbsp;S\u003c/em\u003e. \u003cem\u003eringgoldianum\u003c/em\u003e ssp. \u003cem\u003eCoreanum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003esiliquastrum\u003c/em\u003e, and \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e), 4 to 6 species (\u003cem\u003eS\u003c/em\u003e. \u003cem\u003econfusum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehemiphyllum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehorneri\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003emacrocarpum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003epatens\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003epiluliferum\u003c/em\u003e,\u003cem\u003e\u0026nbsp;S\u003c/em\u003e. \u003cem\u003esiliquastrum\u003c/em\u003e, and \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e), and 5 to 7 species (\u003cem\u003eS\u003c/em\u003e. \u003cem\u003econfusum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehemiphyllum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehorneri\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003emacrocarpum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003emicracanthum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003epatens\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003epiluliferum\u003c/em\u003e,\u003cem\u003e\u0026nbsp;S\u003c/em\u003e. \u003cem\u003esiliquastrum\u003c/em\u003e, and \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e) with an average of 6.2, 6.0, 5.4, and 6.0 species for the first, second, third, and fourth monitoring studies, respectively. At the one natural reef sites (Stn. N-1), the ranges were 3 to 6 species (\u003cem\u003eS\u003c/em\u003e. \u003cem\u003econfusum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehemiphyllum\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehorneri\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003epatens\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003epiluliferum\u003c/em\u003e,\u003cem\u003e\u0026nbsp;S\u003c/em\u003e. \u003cem\u003esiliquastrum\u003c/em\u003e, and \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e).\u003c/p\u003e\n\u003cp\u003eRegarding seaweed coverage of all seaweed species, on the artificial reef, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehorneri\u003c/em\u003e was confirmed in the first monitoring study, however \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehorneri\u003c/em\u003e decreased and \u003cem\u003eS\u003c/em\u003e. \u003cem\u003econfusum\u003c/em\u003e increased in the second monitoring study. After that, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003econfusum\u003c/em\u003e decreased and \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e increased in the third and fourth monitoring studies. On the natural reef, \u003cem\u003eS.\u0026nbsp;patens\u003c/em\u003e dominated in the first and second monitoring studies. And then, \u003cem\u003eS.\u0026nbsp;patens\u003c/em\u003e decreased and\u003cem\u003e\u0026nbsp;M\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e increased in the third and fourth monitoring studies (Fig. 3).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eSeaweed coverage\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe average seaweed coverage of all seaweed species on the artificial reef was 83%, 84%, 94%, and 86% \u0026nbsp;in the first, second, third, and fourth monitoring studies, respectively. Similarly, that on the natural reef was 85%, 90%, 90%, and 90% in the first, second, third, and fourth monitoring studies, respectively (Fig. 4).\u003c/p\u003e\n\u003cp\u003eStatistical analysis (ANOVA) showed that there were not significant differences in the average seaweed coverage for all seaweed species, including green algae, brown algae, and red algae. A significant difference was not confirmed for reef types (Artificial VS Natural reefs), observation times (First, Second, Third, and fourth monitoring times), and the interaction of these two factors.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eGrowing environment for all seaweeds\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;As a result of Wilcoxon\u0026apos;s rank sum test for water depth, water temperature, pH, DO concentration, salinity, and turbidity, a significant difference was confirmed between the artificial and natural reefs only in water depth (p=0.002) (Table 2).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;Regarding the water temperature for 9 months, the maximum value was 30.0\u0026deg;C (July 31, 2021), and the minimum value was 7.2\u0026deg;C (February 23, 2022) in the present study area. Seasonal changes in water temperature in the Hiruga and Shitsumi offings are shown in Fig. 5. The water temperature in the Hiruga offing is higher than that in the Shitsumi offing throughout the season. Particularly, the results of Wilcoxon\u0026rsquo;s rank sum test on the seasonal changes in water temperature in the two offings showed a significant difference in March (p = 0.051).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003e\u003cem\u003eBrown seaweeds in 4 years after artificial reef construction\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe seaweed coverage of \u003cem\u003eSargassum\u003c/em\u003e and \u003cem\u003eMyagropsis\u003c/em\u003e species on the artificial reef approached that on the natural reef in 2 years after construction. However, the seaweed species composition of brown seaweeds differs between the artificial and natural reefs in 2 years after construction. The results of the first monitoring study on the artificial reef showed that nine species of \u003cem\u003eSargassum\u003c/em\u003e and one species of \u003cem\u003eMyagropsis\u003c/em\u003e existed, but only two species of \u003cem\u003eS\u003c/em\u003e.\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003cem\u003ehorneri\u003c/em\u003e/\u003cem\u003eS\u003c/em\u003e.\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003cem\u003econfusum\u003c/em\u003e dominated the \u003cem\u003eSargassum\u003c/em\u003e community, with a percent cover of 55% and 22%, respectively; nine species in the second monitoring study, but only one species of \u003cem\u003eS\u003c/em\u003e.\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003cem\u003econfusum\u003c/em\u003e dominated the \u003cem\u003eSargassum\u003c/em\u003e community, with a percent cover of 64%. In the third monitoring study, eight species were found but dominated by only two species of \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e/\u003cem\u003eS\u003c/em\u003e.\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003cem\u003econfusum\u003c/em\u003e with a percent cover of 56% and 32%, respectively; nine species in the fourth monitoring study, but only three species of \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e/\u003cem\u003eS\u003c/em\u003e.\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003cem\u003epatens\u003c/em\u003e/\u003cem\u003eS\u003c/em\u003e.\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003cem\u003econfusum\u003c/em\u003e dominated with a percent cover of 35%, 15%, and 13%, respectively (Fig. 6a). Meanwhile, on the natural reef, six species existed in the first monitoring study, with a high percent cover of \u003cem\u003eS\u003c/em\u003e. \u003cem\u003epatens\u003c/em\u003e of 70%, while six species in the second monitoring study, but only \u003cem\u003eS\u003c/em\u003e.\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003cem\u003epatens\u003c/em\u003e/\u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e dominated with a percent cover of 55% and 20%, respectively. However, in the third and fourth monitoring studies, only one species of \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e dominated with a percent cover of 80% and 50%, respectively (Fig. 6b). Since both the artificial and natural reefs were dominated by only one species of \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e, it could be assumed that \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e may be the climax-forming species in this region (Fig. 6).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThat is, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehorneri\u003c/em\u003e/\u003cem\u003eS\u003c/em\u003e. \u003cem\u003econfusum\u003c/em\u003e were dominant on the artificial reef and \u003cem\u003eS\u003c/em\u003e. \u003cem\u003epatens\u003c/em\u003e/\u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e were dominant on the natural reef in 2 years after construction. After that, \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e dominated on both the artificial and natural reefs in 4 years after construction. It is thus estimated that the seaweed coverage on the artificial reef approaches that on the natural reef immediately, while the seaweed species composition takes time to approach that on the natural reef.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eSargassum\u003c/em\u003e \u003cem\u003econfusum\u003c/em\u003e is often the first species of brown algae of \u003cem\u003eSargassum\u003c/em\u003e to be colonized when an artificial reef is constructed, and \u003cem\u003eS\u003c/em\u003e. \u003cem\u003econfusum\u003c/em\u003e may have characteristics that other \u003cem\u003eSargassum\u003c/em\u003e seaweeds do not have, i.e., (\u003cem\u003ei\u003c/em\u003e) it attaches easily to new substrates, and (\u003cem\u003eii\u003c/em\u003e) it is difficult for phytophagous animals to eat the juvenile form of this seaweed (Kyoto Prefectural Agriculture, Forestry and Fisheries Technology Center, Fisheries Technology Department). A common feature of \u003cem\u003eS\u003c/em\u003e. \u003cem\u003econfusum\u003c/em\u003e is that it can adapt to unstable environments where other \u003cem\u003eSargassum\u003c/em\u003e seaweeds cannot grow. As time passes, species other than \u003cem\u003eS\u003c/em\u003e. \u003cem\u003econfusum\u003c/em\u003e will dominate (Douke et al. 2004). In the present study, as it changed from \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehorneri\u003c/em\u003e to \u003cem\u003eS\u003c/em\u003e. \u003cem\u003econfusum\u003c/em\u003e in 2 years after construction and from \u003cem\u003eS\u003c/em\u003e. \u003cem\u003econfusum\u003c/em\u003e to \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e in 4 years after construction, the seaweed species composition on the artificial reef was consistent with previous studies. Regarding the reason for the decrease in \u003cem\u003eS\u003c/em\u003e. \u003cem\u003econfusum\u003c/em\u003e and the increase in \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e on the artificial reef, it is considered that the fact that \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e covers the upper part of \u003cem\u003eS\u003c/em\u003e. \u003cem\u003econfusum\u003c/em\u003e is advantageous in terms of competition for light (Yatsuya et al. 2005). Therefore, these changes are considered to be a process of vegetation succession.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eVegetation succession: Further research challenges\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eSargassum\u003c/em\u003e \u003cem\u003ehorneri\u003c/em\u003e has been reported to appear only in 1 year after artificial reef construction. That is, annual seaweeds settle in the first year, and perennial seaweeds follow (Douke et al. 2004; Yatsuya et al. 2008; Endo et al. 2019). In the present study, \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehorneri\u003c/em\u003e was dominant in the first monitoring study on the artificial reef, but it was hardly confirmed in the other three monitoring studies on both the artificial and natural reefs. Thus, these results coincided with those of previous studies. Additionally, it is estimated that the reason why \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehorneri\u003c/em\u003e appeared even 2 years after construction instead of 1 year after construction was that the seaweed did not grow in time for the following spring because the construction was completed in November 2017.\u003c/p\u003e\n\u003cp\u003ePrevious studies have determined that natural reefs are in a state of climax (Douke et al. 2004). On the other hand, the present findings did not advocate the previous studies because \u003cem\u003eS\u003c/em\u003e. \u003cem\u003epatens\u003c/em\u003e was dominant in 2 years after construction, while \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e dominated in 4 years after construction on the natural reef. Further vegetation succession research can be expected to establish whether this change is simply an annual variation or constitutes vegetation succession.\u003c/p\u003e\n\u003cp\u003eThe seaweed species that have dominated on the natural reef has differed among the perennials of \u003cem\u003eSargassum\u003c/em\u003e: \u003cem\u003eS\u003c/em\u003e. \u003cem\u003efulvellum\u003c/em\u003e (Douke et al. 2004), \u003cem\u003eS\u003c/em\u003e. \u003cem\u003epatens\u003c/em\u003e/\u003cem\u003eS\u003c/em\u003e. \u003cem\u003epiluliferum\u003c/em\u003e (Yatsuya et al. 2008; Endo et al. 2019), \u003cem\u003eS\u003c/em\u003e. \u003cem\u003epatens\u003c/em\u003e/\u003cem\u003eS\u003c/em\u003e. \u003cem\u003emacrocarpum\u003c/em\u003e at Shitsumi offing in the previous study, and \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e at Hiruga offing in the present investigation. The survey sites used by Douke et al. (2004) are located outside Wakasa Bay, whereas Wakasa Bay sites were examined by Yatsuya et al. (2008), Endo et al. (2019), the previous study, and the present investigation. The survey sites evaluated in the Yatsuya and Endo studies are located in western Wakasa Bay, and Shitsumi offing and Hiruga offing are located in the center of Wakasa Bay. It seems likely that the water temperature varies slightly depending on the survey sites (Matsui et al. 2023). Therefore, the water temperature varies at each location within Wakasa Bay, and it is estimated that seaweed growth depends on the water temperature. The upper limit temperature for the growth of \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e is 30\u0026deg;C (Haraguchi et al. 2005), it is possible that this study area, where the water temperature does not exceed 30\u0026deg;C, is suitable for the growth of \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e. In addition, the maturity period of \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e and \u003cem\u003eS\u003c/em\u003e. \u003cem\u003emacrocarpum\u003c/em\u003e/\u003cem\u003eS\u003c/em\u003e. \u003cem\u003epatens\u003c/em\u003e is February-March and May-June, respectively (Kyoto Prefectural Agriculture, Forestry and Fisheries Technology Center, Fisheries Technology Department 2009). It encourages \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e to grow such that the water temperature at Hiruga offing is higher than that at Shitsumi offing in March.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eAn artificial reef was constructed in Wakasa Bay, Japan, and we monitored the reef in 2 years and 4 years after the construction was completed. We set up five sites on the artificial reef as a treatment area and one site on the natural reef as a control area and then identified the seaweed species composition of the \u003cem\u003eSargassum\u003c/em\u003e and \u003cem\u003eMyagropsis\u003c/em\u003e communities and their coverage on each reef.\u003c/p\u003e\n\u003cp\u003eThe seaweed coverage on the artificial reef was already close to that on the natural reef in 2 years after construction. However, the dominant species on the artificial reef was not conformable to that on the natural reef in 2 years after construction. Especially, on the artificial reef, the presence of \u003cem\u003eS\u003c/em\u003e.\u0026nbsp;\u003cem\u003ehorneri\u003c/em\u003e/\u003cem\u003eS\u003c/em\u003e.\u0026nbsp;\u003cem\u003econfusum\u003c/em\u003e was dominant in 2 years after construction and that of \u003cem\u003eM\u003c/em\u003e.\u0026nbsp;\u003cem\u003emyagroides\u003c/em\u003e was dominant in 4 years after construction. Whereas on the natural reef, the presence of \u003cem\u003eS\u003c/em\u003e.\u0026nbsp;\u003cem\u003epatens\u003c/em\u003e dominated in 2 years after construction and that of \u003cem\u003eM\u003c/em\u003e.\u0026nbsp;\u003cem\u003emyagroides\u003c/em\u003e dominated in 4 years after construction. That is, the species composition on the artificial reef was close to that on the natural reef in 4 years after construction. Thus, the recovery of species composition takes longer than that of seaweed coverage on the artificial reef.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthors contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAM wrote the main manuscript text, figures 1-6, and Tables 1-2. MK, SN, and MT are scuba divers. They observed visually and recorded the seaweed species composition and coverage. NI is a research assistant.\u0026nbsp;All authors reviewed the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors did not receive support from any organization for the submitted work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available in the supplementary material of this article (Table S1).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no relevant financial or nonfinancial interests to disclose.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe would like to express our deepest gratitude to all of the following individuals. Shuhei Kajimura and Kazuyuki Miyanaga (Forestry and Fisheries Department, Reinan Promotion Bureau, Fukui Prefecture) agreed to publish the survey results and provided earlier reports. Dr. Hikaru Endo (Faculty of Fisheries, Department of Fisheries Science and Technology, Kagoshima University) provided research papers and useful advice on vegetation succession. Dr. Yoshitake Takada (Fisheries Technology Institute, Japan Fisheries Research and Education Agency) advised on how to analyze community compositions using the statistical software R.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eArkema KK, Reed DC, Schroeter SC (2009) Direct and indirect effects of giant kelp determine benthic community structure and dynamics. 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Environmental Biology of Fishes 106(8): 1755\u0026ndash;1766. https://doi.org/10.1007/s10641-023-01453-7\u003c/li\u003e\n\u003cli\u003eMinistry of the Environment (2021) About the results of seaweed bed survey (2018-2020) (in Japanese). https://www.biodic.go.jp/moba/1_4.html#1_4_1\u003c/li\u003e\n\u003cli\u003eNakae S, Komatsubara T, Naito K (2002) Geology of the Nishizu District, Quadrangle Series, 1:50,000 (in Japanese with English abstract). Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Ibaraki\u003c/li\u003e\n\u003cli\u003eOhno M (1993) Succession of seaweed communities on artificial reefs in Ashizuri, Tosa Bay, Japan. Algae 8(2): 191\u0026ndash;198.\u003c/li\u003e\n\u003cli\u003eOhno M, Arai S, Watanabe M (1990) Seaweed succession on artificial reefs on different bottom substrata. 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Ecology 65(3): 937\u0026ndash;948. https://doi.org/10.2307/1938066\u003c/li\u003e\n\u003cli\u003eSchroeter SC, Reed DC, Raimondi PT (2015) Effects of reef physical structure on development of benthic reef community: a large-scale artificial reef experiment. Marine Ecology Progress Series 540: 43\u0026ndash;55. https://doi.org/10.3354/meps11483\u003c/li\u003e\n\u003cli\u003eSmale DA (2020) Impacts of ocean warming on kelp forest ecosystems. New Phytologist 225(4): 1447\u0026ndash;1454. https://doi.org/10.1111/nph.16107\u003c/li\u003e\n\u003cli\u003eSteneck RS, Graham MH, Bourque BJ, Corbett D, Erlandson JM, Estes JA, Tegner MJ (2002) Kelp forest ecosystems: biodiversity, stability, resilience and future. Environmental Conservation 29(4): 436\u0026ndash;459. https://doi.org/10.1017/S0376892902000322\u003c/li\u003e\n\u003cli\u003eTanaka J, Nakamura T (2004) A photographic Guide; Japanese Seaweeds (in Japanese). Heibonsha Limited, Publishers, Tokyo\u003c/li\u003e\n\u003cli\u003eTerawaki T, Yoshikawa K, Yoshida G, Uchimura M, Iseki K (2003) Ecology and restoration techniques for Sargassum beds in the Seto Inland Sea, Japan. Marine Pollution Bulletin 47(1-6): 198\u0026ndash;201. https://doi.org/10.1016/S0025-326X(03)00054-7\u003c/li\u003e\n\u003cli\u003eTomiyama A (1981) Aquatic afforestation with \u003cem\u003eSargassum\u003c/em\u003e (in Japanese). In: The Japanese Society of Fisheries Science (ed) Seaweed beds. KOUSEISHA KOUSEIKAKU Co., Ltd., Tokyo, pp 142\u0026ndash;157\u003c/li\u003e\n\u003cli\u003eWatanuki A, Yamamoto A (1990) Settlement of seaweeds on coastal structures. Hydrobiologia 204(1): 275\u0026ndash;280. https://doi.org/10.1007/BF00040245\u003c/li\u003e\n\u003cli\u003eWernberg T, Krumhansl K, Filbee-Dexter K, Pedersen MF (2019) Status and trends for the world\u0026rsquo;s kelp forests. In: Sheppard C (ed) World Seas: An Environmental Evaluation: Ecological Issues and Environmental Impacts, 2nd edn. Academic Press, Massachusetts, pp 57\u0026ndash;78\u003c/li\u003e\n\u003cli\u003eYamauchi K (1984) The formation of Sargassum beds on artificial substrata by transplanting seedlings of \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehorneri\u003c/em\u003e (T\u003csub\u003eURNER\u003c/sub\u003e) C. A\u003csub\u003eGARDH\u003c/sub\u003e and \u003cem\u003eS\u003c/em\u003e. \u003cem\u003emuticum\u003c/em\u003e (Y\u003csub\u003eENDO\u003c/sub\u003e) F\u003csub\u003eENSHOLT\u003c/sub\u003e. Bulletin of the Japanese Society of Scientific Fisheries 50(7): 1115\u0026ndash;1123. https://doi.org/10.2331/suisan.50.1115\u003c/li\u003e\n\u003cli\u003eYatsuya K, Nishigaki T, Douke A, Itani M, Wada Y (2005) Succession of a Sargassaceae community on an artificially installed stone bed off Amino, Japan Sea Ⅱ Productive structure of Sargassaceae community and age composition of \u003cem\u003eSargassum\u003c/em\u003e \u003cem\u003econfusum\u003c/em\u003e. (in Japanese with English abstract). Bulletin of the Kyoto Institute of Oceanic and Fisheries Science 27: 19\u0026ndash;24.\u003c/li\u003e\n\u003cli\u003eYatsuya K, Nishigaki T, Shirafuji N, Takeno K (2008) Effect of drifting seaweeds captured by a floating rope on the supply of embryos to new substrata of an artificial reef area off Yoro-Oshima, and algal succession in this area (in Japanese with English abstract). Bulletin of the Kyoto Institute of Oceanic and Fisheries Science 30: 31\u0026ndash;37.\u003c/li\u003e\n\u003cli\u003eYoshida T, Suzuki M, Yoshinaga K (2015) Checklist of marine algae of Japan (Revised in 2015) (in Japanese). The Japanese Journal of Phycology 63(3): 129\u0026ndash;189.\u003c/li\u003e\n\u003cli\u003eYoshikawa K (1987) Studies on the formation of Sargassum beds-Ⅲ The formation of Sargassum beds by setting campus sheets for embryo to settle down effectively (in Japanese with English abstract). Bulletin of the Nansei Regional Fisheries Research Laboratory 21: 25\u0026ndash;35.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTables 1 and 2 are available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Artificial and natural reefs, Monitoring, Seaweed community succession, Seaweed coverage, Seaweed species composition, Wakasa Bay – Japan","lastPublishedDoi":"10.21203/rs.3.rs-4459311/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4459311/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe threat of declining seaweed beds has been a concern around the world. Seagrass and seaweed (brown algae) beds are essential habitats supporting fisheries. However, approximately 22% of these habitats have been lost in Japan due to increased coastal landfill sites and ports. This study aims to rehabilitate the depletion of these habitats by constructing an artificial reef in Wakasa Bay, Japan, and monitoring brown algae (\u003cem\u003eSargassum\u003c/em\u003e and \u003cem\u003eMyagropsis\u003c/em\u003e) succession in 2 years and 4 years after the construction was completed. In this study, we set up five sites on the artificial reef as a treatment area and one site on the natural reef as a control area and then identified the seaweed species composition of the \u003cem\u003eSargassum\u003c/em\u003e and \u003cem\u003eMyagropsis\u003c/em\u003e communities and their coverage on each reef using underwater visual observation by scuba divers. The seaweed coverage on the artificial reef was already close to that on the natural reef in 2 years after construction. However, the dominant species on the artificial reef was not conformable to that on the natural reef in 2 years after construction. The dominant species on the artificial reef changed to \u003cem\u003eS\u003c/em\u003e. \u003cem\u003ehorneri\u003c/em\u003e/\u003cem\u003eS\u003c/em\u003e. \u003cem\u003econfusum\u003c/em\u003e in 2 years after construction and \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e in 4 years after construction. On the other hand, the dominant species on the natural reef changed to \u003cem\u003eS\u003c/em\u003e. \u003cem\u003epatens\u003c/em\u003e in 2 years after construction and \u003cem\u003eM\u003c/em\u003e. \u003cem\u003emyagroides\u003c/em\u003e in 4 years after construction. That is, the species composition on the artificial reef was close to that on the natural reef in 4 years after construction. Thus, the recovery of species composition takes longer than that of seaweed coverage on the artificial reef.\u003c/p\u003e","manuscriptTitle":"Comparison of seaweed species composition and coverage of Sargassum and Myagropsis communities between artificial and natural reefs in Wakasa Bay, Japan","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-04 14:02:48","doi":"10.21203/rs.3.rs-4459311/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"ef93b64b-02e4-46d2-b27c-b6cf2930061e","owner":[],"postedDate":"June 4th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-06-23T07:29:19+00:00","versionOfRecord":[],"versionCreatedAt":"2024-06-04 14:02:48","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4459311","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4459311","identity":"rs-4459311","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}