Assessing the influence of ocean acidification on the deterioration of coral reefs in Sri Lanka

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P.D.N. Thilakarathne, R. S.M. Samarasekara, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8136171/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 29 Apr, 2026 Read the published version in Water, Air, & Soil Pollution → Version 1 posted You are reading this latest preprint version Abstract Rising atmospheric CO 2 levels have significantly increased ocean acidification (OA), endangering coral reefs, and nutrient (nitrate (NO 3 − ), and phosphate (PO 4 3− )) pollution also weakens the coral reef resilience. Therefore, the study evaluates the prevailing OA level over the Sri Lankan coral reef areas using the aragonite saturation state (Ω Ar ) and assesses the nitrate (NO 3 − ), and phosphate (PO 4 3− ) concentrations over the coral sites. The study was conducted on coral reefs on the eastern coast (EC), southern coast (SC), northern coast (NC), and west coast (WC) of Sri Lanka from April to June 2024. A total of 63 seawater samples were collected around each coastal site for analysis. The Ω Ar were supersaturated (Ω Ar > 1) and ranged from 2.98 ± 0.04 to 4.92 ± 0.12. Throughout the study period, the study sites had Ω Ar values exceeding 2.92 ± 0.16, indicating that the nation's corals were resilient to deterioration, and the comparative analysis demonstrates that these sites were not vulnerable to OA. The NO 3 − concentrations of 2–5 µmol L − 1 , from human activities, may intensify coral bleaching during heat stress. Results showed that SC (2.19 ± 1.28 µmol L − 1 ) and WC (3.52 ± 1.48 µmol L − 1 ) had NO 3 − above the permissible range, which may be due to waste discharge and high runoff. The significantly higher PO 4 3− concentrations were reported in EC (0.35 ± 0.07 µmol L − 1 ). Coral bleaching hotspot (HS) identification emphasizes how spatially distributed HS are from January to June. The OA risk assessment confirmed that climate change brought high risk to the coral reef ecosystems, which impact on the ecology and economy of Sri Lanka. Coral Bleaching Hotspot Nutrient Pollution Ocean Acidification Sea Surface Temperature Risk Assessment: Sri Lanka Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction The oceans act as major sinks for increasing atmospheric carbon dioxide (CO 2 ). More than 2000 Gt of anthropogenic CO 2 have been emitted into the atmosphere since the Industrial Revolution (Friedlingstein et al., 2019 ). Studies emphasize that the ocean's yearly net absorption of CO 2 can reach 1.5 ± 0.5 Pg C (Sun et al., 2021 ), which makes up 30% of the average CO 2 released by anthropogenic activities (Gruber et al., 2019 ). However, the high concentrations of dissolved CO 2 also suggest that the ocean's chemical balance will eventually change, lowering its pH level. This phenomenon is known as OA, which is one of the major threats to coral reef ecosystems worldwide. The estimated decrease in OA using model outputs in the Indian Ocean basin was estimated to be 0.0675 (pH) during 1961–2010 (Ghosh et al., 2024 ). Due to the detrimental impact that OA has on a variety of marine creatures, including reduced survival, calcification, growth rate, development, and abundance, OA is currently the subject of extensive research (Omar et al., 2019 ). Coral ecosystems are vital, offering resources and ecological services for raw materials, fisheries, tourism, coastal protection, and many more purposes that are worth approximately $ 350,000/ha per year (Fezzi et al., 2023 ). Despite their importance, these ecosystems are among the most vulnerable on the planet. Globally, the combined effects of climate change and human pressure are producing an alarming rate of coral reef collapse (Rampino and Shen, 2021 ). As the ocean absorbs atmospheric CO 2 , its pH and carbonate ion concentration ([CO 3 2− ]) decrease, thereby decreasing the saturation state; (Ω Ar = [Ca 2+ ] [CO 3 2− ]/Ksp), Aragonite saturation state (Ω Ar ) is the product of the concentrations of Ca 2+ and CO 3 2− , divided by the solubility product constant (Ksp) for aragonite (Farfan et al., 2018 ). The studies of the Ω Ar in marine environments are typically conducted to determine the state of the carbonate system and the degree of OA (Sun et al., 2021 ). Seawaters are undersaturated with aragonite when Ω Ar < 1.0, which makes CaCO 3 shells and skeletons susceptible to disintegration. Determining the primary mechanisms governing Ω Ar is crucial in forecasting Ω Ar variations in the future due to rising atmospheric CO 2 concentrations (Choi et al., 2022 ). The utilization of seawater's Ω Ar has made it easier to estimate the OA level and net calcification rates of corals. In recent years, there has been an increase in data gathering for Ω Ar and OA-related investigations around the globe (Afdal et al., 2024; Jarníková et al., 2022 ; Kim et al., 2023 ). However, there are very limited studies related to the Ω Ar that have been reported in South Asia (Sridevi and Sarma, 2024 ). Moreover, as far as we know, no previous research has investigated OA studies using Ω Ar as a proxy around the Sri Lankan coastal area, and no study has been found related to the Ω Ar . The Sri Lankan coastal water hosts diverse and vibrant coral reefs around the country. Within this island current estimated number of coral species is approximately 245 species (Arulananthan et al., 2021 ; Rajasuriya, 2012). Although rising atmospheric CO 2 levels have significantly increased OA, posing a risk to coral reefs and those ecosystems that are highly vulnerable to OA. Therefore, assess the Ω Ar is essential for the identification of the prevalent OC level over the coral reef sites in Sri Lanka. Furthermore, there were no previous study has investigated OA in South Asia using Ω Ar as a proxy in conjunction with a comprehensive risk assessment for coral reefs. Also, studies investigating the relationship between carbon and OA in all the coastal zones of Sri Lanka are few and far between. The OA risk assessment has never been conducted and it is essential to the decision-making processes and policy development in Sri Lanka, which are shows the significant knowledge gap. Therefore, this study conduted the addressed this essential data gaps by assessing the Ω Ar and conducting the OA risk assessment of the coral reef ecosystems around Sri Lanka. In this study, we have assessed the degree of OA in the coastal regions of Sri Lanka using Ω Ar as an indicator (or proxy). Moreover, the study contributes to baseline data for spatial variation in Ω Ar across the coral reef ecosystems in Sri Lanka. It is crucial to anticipate the emerging trends of OA's impact and devise suitable mitigation strategies in coastal waterways. 2. Methodology 2.1. Study Area The Sri Lankan coral reefs are predominantly located along the north, northwest, east, and southern coasts (Thilakarathne et al., 2024 ; Thilakarathne et al., 2023 ). The country faces two main monsoon patterns annually, which are: the northeast monsoon (November to February) and the southwest monsoon (May to September). The ocean circulation systems surrounding Sri Lanka significantly contribute to the connection between the Arabian Sea and the Bay of Bengal. This ocean current and monsoon promote the mixing and alteration of the sea surface dynamics surrounding the country (Schott and McCreary Jr, 2001 ). Due to monsoon patterns and ocean currents, two different sea conditions are observed around the country throughout the year (Sandamali et al., 2023 ). Therefore, this study was conducted to capture the spatial variation of Ω Ar across Sri Lanka under dynamic sea conditions along the south coast (SC), east coast (EC), west coast (WC), and northern coast (NC). Sampling was done in six sites on EC (Pasikudah, Kalkudah, Pigeon Island, Kayankerni, Adukkupar, and Salli Beach), six sites in the SC (Polhena, Mirissa, Talaramba, Weligama, Unawatuna, and Hikkaduwa), three sites in WC (Colombo, Negombo, and Uswetakeiywa), and six sites in NC (Kankesanthurai, Palali, Thondamanaru River Mouth, Thondamanaru, Inbarsitty, and Point Pedro) (Fig. 1 ) within the April to June period of 2024. Selection of the single, dynamic transition window minimizes the temporal heterogeneity among the sites it was allowed robust spatial comparisons. 2.2. Sample collection For quantification of the Ω Ar , two sets of seawater samples were collected from the ocean surface beyond the 10–15 m coastline and directly above the shallow coral reef habitat. Samples were collection was performed using 250 ml high densitypoly ethylene (HDPE) plastic bottles, ensuring no headspace. Those samples were taken from three locations of each coral reef site. The selected distance ensured sampling over the active reef zone while minimizing terrestrial freshwater influences, and sampling was performed in daytime conditions around mid tide. One set of samples was analyzed within the site, and the other set was immediately stored in a dark and low temperature (< 4 o C) until samples were analyzed in the laboratory. 2.3. Sample analysis Salinity (PSU), pH (in total scale), and temperature (°C) were measured using the HANNA H19829 multiparameter at the sites. The multiparameter probes were calibrated according to the National Institute of Standards and Technology (NIST) standard references approximately every fifteen samples to obtain the right measurement accuracy (Precision levels of salinity = ± 0.01 PSU, pH = ± 0.01, and temperature = ± 0.01°C). The laboratory-bought sample set was analyzed immediately for Total Alkalinity (TA,µmol Kg − 1 ), NO 3 − (µmol L − 1 ), and PO 4 3− (µmol L − 1 ) concentrations. HANNA (HI931) automatic potentiometric titrator was used for the measurement of TA. Standardized 0.1 mol/L HCl was employed to titrate the seawater samples. An Agilent Cary 60 UV-Vis spectrophotometer was used to measure NO 3 − and PO 4 3− concentrations. Temperature, TA, salinity, and pH were plotted into the Seacarb v3.3.2 package in the R 4.3.1 environment for data processing and subsequent Ω Ar calculation. For this calculation, the K1 and K2 acidity constants proposed by Millero ( 2010 ), the HSO 4 − constant of Khoo et al. ( 1977 ), the total boron constant of Lee et al. ( 2010 ), and the Constant for HF proposed by Perez and Fraga ( 1987 ) were used. Phosphate concentrations were also fed into the R calculations. During the calculation, silicate concentrations were assumed to be null. Around the Sri Lankan coastline, silicate concentration is lower ( < 10 µmol L − 1 , respectively) (Wimalasiri et al., 2020 ), there for ignoring these silicate concentrations induces minor errors in pHT (~ 0.003) and Ω Ar (~ 0.01) values (Li and Zhai, 2021 ). 2.4. Statistical Analysis Shapiro-Wilk tests were used to assess the normality of the data. Log transformation, Yeo-Johnson transformation, and reciprocal transformation were used to convert the not-normally distributed data to normally distributed data. For eligible data, one-way analysis of variance (One-way ANOVA) was conducted separately for the Ω Ar , NO 3 - , and PO 4 3- concentrations. All statistical analyses were performed using R version 4.3.2. 2.5. Coral bleaching hotspot identification Maximum monthly mean (MMM) SST was employed for the identification of the coral bleaching Hot Spot (HP). The MMM of SST climatology is estimated using nightly SST data obtained from NOAA. To counteract the effects of solar glare and lessen the variance in SST brought on by daytime heating, pictures taken at night were employed. Corals are more vulnerable to bleaching when the SST exceeds the temperatures they usually experience in the hottest month. The coral bleaching HS demonstrates this by highlighting areas where the present SST is warmer than the highest monthly maximum mean of SST. A temperature difference of above 1.0°C was considered to be a threshold for thermal stress that would cause coral bleaching classified as a “Warning”, values 0–1.0°C were classified as a "watch" condition, and values less than or equal to zero were classified as a "No Stress" state. The discrepancy between the MMM SST climatology and the measured near-real-time SST, as provided by the equation, is represented by the value of HS. \(\:\text{H}\text{o}\text{t}\text{s}\text{p}\text{o}\text{t}\:(^\circ\:\text{C})\:=\:\text{S}\text{S}\text{T}\:-\:\left(\text{M}\text{M}\text{M}\:\text{S}\text{S}\text{T}\:\text{C}\text{l}\text{i}\text{m}\text{a}\text{t}\text{o}\text{l}\text{o}\text{g}\text{y}\right)\) The heat stress distribution and incidence that lead to coral bleaching are represented by the HS, and only positive values were used for the illustration (INCOIS, 2023 ). 2.6. Risk Assessment of the Ocean Acidification Effect on the Coral Reef Ecosystems in Sri Lanka Through employing a consistent approach, OA risk evaluations provide an opportunity to recognize and prioritize risks across coral reef ecosystems, emphasizing the regions' coral reefs that require mitigation plans most urgently. The risk assessment method we used here comprises four steps (Warren et al., 2018 ); (1) Determine the drivers of OA in the Sri Lankan coastal regions; (2) Identify the risk imposed by OA to the coral ecosystems; (3) Score individual risks; (4) Rank and prioritize risks. 2.6.1. Rank and prioritize risks After ranking the risk, it was ranked from highest to lowest based on the overall score. This was facilitated to identify the most important prioritized risk to the Sri Lankan coral ecosystems. Due to there was little variety in the overall risk ratings. The risks were divided into three categories: "Low" (score from 8 to 17), "Moderate" (score from 25 to 50), and "Severe" (score from 67 to 100). Severe scores were characterized by a "now" proximity and a "medium" magnitude (Maltby et al., 2022 ). However, the confidence level was assigned based on the IPCC matrix (Fig. 2 ). The supporting information provides detailed descriptions of determining the drivers of OA in the Sri Lankan coastal region (See S1) and identifying risks imposed by OA on coral ecosystems (See S2). The discussion section is a complete scoring and ranking of the risks relevant to coral reefs in Sri Lankan waters. 3. Results and Discussion 3.1. Aragonite saturation status around coral sites During the sampling period, a bleached coral cover was observed (Fig. 3 ). The bleached coral covers around Sri Lanka indicate that the global fourth massive coral bleaching event (2023–2024) impacted the coral reefs of Sri Lanka. This bleaching event was confirmed by the National Oceanic and Atmospheric Administration (NOAA) and the International Coral Reef Initiative (ICRI) (ICRI, 2024 ). Unfortunately, no data is available within the country regarding how much coral cover declined due to this bleaching event. Even though coral bleaching does not necessarily result in coral mortality, corals can recover and continue to offer the ecosystem services that people rely on while preserving their biodiversity (Schoepf et al., 2020 ), it is still important to record these events and monitor the degree of bleaching such that a warning system can be brought in place when the coral population reaches a critical stage. Zhou et al. ( 2020 ) showed that there exists a sensitive area of El Niño predictions in the tropical Indian Ocean, which mainly dominates in the subsurface of the eastern Indian Ocean, ranging from 60°E to 100°E, from the sea surface to 200 m underneath. This explains the climate-related warming and rise in sea temperature around Sri Lanka, which lies near ~ 80°E. During the study period, the mean values of the Ω Ar, NO 3 −, and PO 4 3− concentrations in each coral site are shown in Fig. 4 . The effect that OA will have on the net carbonate accretion of coral reefs is determined by the circumstances of the reef's saltwater. When the seawater Ω Ar reaches 2.92 ± 0.16, coral reef sands go from net precipitating to net dissolving (Eyre et al., 2018 ). According to the observed data around the country, Ω Ar was supersaturated (> 1), and all sites had Ω Ar above the threshold level (Table 1 ). This shows that the sample sites’ Ω Ar and pH lay between 3.0-4.92 and 8.05–8.35, respectively. However, a somewhat reduced level of Ω Ar was observed in the NC region compared to the other coastal areas due to a low level of pH (Table 1 ). The NC region is a heavily agriculturally dependent area (mainly paddy cultivation), mainly the Jaffna peninsula, which is the nearest place to the sample locations (Gopalakrishnan and Kumar, 2021 ). For those practices, farmers frequently use fertilizers and pesticides on their crops. Therefore, runoff from this area containing a huge amount of these fertilizers and pesticides can contribute to eutrophication. Conducted studies show that the Jaffna peninsula groundwater is also contaminated with excessive nitrate due to agricultural runoff (Jeyaruba and Thushyanthy, 2009 ; Vithanage et al., 2014 ). The breakdown of organic debris from these blooms depletes oxygen and emits CO 2 , resulting in a localized low pH level. This can be a contributing factor to the reduction in pH levels at the NC sampling sites. During the study period, Sri Lankan coral reef areas' ocean surface comprised higher Ω Ar when compared to the world's most acidified ocean region (Table 1 ). The Bering Sea, situated in the high latitudes of the Northern Hemisphere, is one of the most acidified regions in the world (Wiese et al., 2012 ). However, with the cold water temperatures there, the Bering Sea is especially vulnerable to OA (Sun et al., 2021 ). Therefore, a reduced level of annual Ω Ar (2.25 ± 0.51) was reported in the Bering Sea. In addition to that Gulf of Cádiz, the SW Iberian Peninsula, the Northern North Sea, the Western Arctic Ocean (Chukchi marginal area), and the Gulf of California-Cabo Pulmo identified the same situation. Table 1 The (Mean ± SD) Aragonite saturation status (Ω Ar ) and pH level in the study area and some selected most acidified oceans. Ocean Region Aragonite saturation status (Ω Ar ) pH References Bering Sea (Annual) 2.25 ± 0.51 N/A Sun et al. ( 2021 ) Gulf of Cádiz, SW Iberian Peninsula (Annual) 2.68 ± 0.30 8.01 ± 0.05 Jiménez-López et al. ( 2021 ) Northern North Sea (Winter) 1.96 ± 0.05 8.17 ± 0.01 Omar et al. ( 2019 ) Western Arctic Ocean (Chukchi marginal area) (Annual) 1.07 ± 0.14 (Ranged from 0.86 to 1.77) 8.11 ± 0.10 Kim et al. ( 2021 ) Gulf of California-Cabo Pulmo (December to March) 2.8 ± 0.11 7.93 ± 0.02 Norzagaray-López et al. ( 2017 ) North Coast of Sri Lanka 3.2 ± 0.64 * 8.11 ± 0.05 * This Study East Coast of Sri Lanka 4.44 ± 0.29 * 8.26 ± 0.04 * South Coast of Sri Lanka 4.21 ± 0.43 * 8.31 ± 0.03 * West Coast of Sri Lanka 4.39 ± 0.42 * 8.24 ± 0.05 * Note - N/A- Not available, *Mean ± SD values calculated from six sampling locations along; East, North, and South coasts and three locations on the West coast of Sri Lanka. The highest Ω Ar was reported within the Negombo reef area (4.92 ± 0.12), although it was compressed with a pH level of 8.29 ± 0.01. The highest pH level (8.35 ± 0.02) was observed in the Thal Aramba reef (Fig. 1 ) area, also this area was compressed with the Ω Ar 4.47 ± 0.24. These differences occurred due to the variation of the TA at each study location. Thal Aramba reef and Negombo reef TA were reported as 2288.588 ± 57.275 and 2531.549 ± 25.827, respectively. The lowest Ω Ar recorded in the Inbrasity coral site in NC (2.98 ± 0.04), due to the low level of pH (8.05 ± 0.01). Figures (b) and (c) show the pH and TA variation within each coral reef. However, the mean Ω Ar in NC sites showed somewhat lower values compared to the other coastal areas' coral sites, including Thondaimanaru, Inbarsitty, Palaali, and Point Pedro (3.3 ± 0.1, 2.98 ± 0.04, 3.22 ± 0.09, and 3.06 ± 0.17). In SC lowest Ω Ar was observed within the Polhena reef area (3.47 ± 0.19), mainly due to the location of the reef, which is located near the Nilwala River mouth and has a high freshwater inflow. During the study period, sea surface temperature lies between 28.71–32.82 ̊C. Figure 5 a emphasizes the Ω Ar variation in each coral reef around Sri Lanka with sea surface temperature (̊C) and salinity (PSU). No coral reef in the study areas suffered dissolution, and the Ω Ar level did not reach the 2.92 ± 0.16 level during the study period. When comparing Ω Ar of areas mentioned in Table 1 with Sri Lankan coral areas surface Ω Ar , it clearly emphasizes the reduced level of OA over the coral reefs in Sri Lanka. 3.2. Nitrate (NO 3 – ) and Phosphate (PO 4 3– ) concentrations The majority of coral reefs grow and endure in oligotrophic, tropical, and subtropical seas with extremely low levels of phosphate (PO 4 3– ) and nitrate (NO 3 – ). However, one of the main causes of global warming is nutrient pollution, which has grown over the past century (Bennett and Bennett, 2001 ; Burkepile et al., 2019 ). Local human influence is another stressor that coral reefs experience, in addition to those posed by global change. These consist of upwelling incidents (Richardson et al., 2020 ) and coastal seawater's nutrient enrichment due to land runoff, farming, and urban wastewater (Fabricius, 2011 ). The quantities of inorganic nitrogen (N) and phosphorus (P) can be significantly greater under these circumstances (up to 4 µM N and 0.5 µM P) (Blanckaert et al., 2021 ; Govers et al., 2014 ; Naumann et al., 2015 ). The usual levels of N and P concentrations on coral reefs are 0.5 µM and 0.1 µM (Lomas et al., 2006 ; Meeder et al., 2012 ). Recent research has demonstrated that NO 3 – concentrations of 2 to 5 µM, which are primary nitrogen molecules generated from human activity, can intensify coral bleaching during heat stress (Burkepile et al., 2019 ; Ezzat et al., 2016 ; Marangoni et al., 2022 ; Rosset et al., 2017 ). According to the observed data, emphasis on higher NO 3 – concentration was reported on the WC (3.52 ± 1.48 µmol L − 1 ) surface water may be due to high terrestrial runoff, urban wastewater, and anthropogenic activities. The WC is a highly urbanized region in the country with high population density, representing this region. This may be the main reason for the observed elevated NO 3 – concentration. The location in Colombo had the highest NO 3 – concentration (5.24 ± 0.13 µmol L − 1 ) among all coral reef sites due to high waste discharge and anthropogenic activities (Manage et al., 2022 ). Weligama, Polhena, Kankasanthure, Negombo, Colombo, and Uswetakeiywa (2.24 ± 1.2, 4.35 ± 0.22, 2.22 ± 0.47, 2.23 ± 0.15, 5.24 ± 0.13, and 3.14 ± 1.67 µmol L − 1 ) coral reef areas had high NO 3 – concentrations, which reached the 2 to 5 µM. This NO 3 – concentatration may contribute to coral bleaching during the heat stress. The PO 4 3– concentrations of all the study sites were below 0.94 ± 0.37, the highest concentration reported in the Weligama reef due to freshwater inflow and anthropogenic activities. The Weligama reef, situated inside the Weligama Bayis one of the rocky shorelines along the Sri Lankan coastline. The Polwatta River, being the river that flows into the bay from the southern section of the bay carries nutrients to the bay (Amarathunga et al., 2013 ). And this site is located near the Weligama fisheries harbor, therefore pollution level was high in this area. Those were the main reasons for the observed higher PO 4 3– concentrations in this area. 3.3. Statistical Analysis One-way ANOVA confirmed that there were significant differences (P > 0.05) of Ω Ar in NC (3.2 ± 0.64 µmol L − 1 ) compared to other coastal sites and no significant differences (P < 0.05) between EC and SC, SC and WC, and EC and WC. There were significant differences in NO 3 − concentrations between NC and WC, EC and SC, and WC and EC. Collected data confirms that there are significant differences in PO 4 3− concentrations in EC (0.35 ± 0.07 µmol L − 1 ) when compared to other coastal areas. 3.4. Coral Bleaching Hotspot Corals are vulnerable to bleaching when the SST exceeds the temperatures they usually experience in the hottest month. The HS product on coral bleaching demonstrates this by highlighting areas where the present SST is warmer than the highest monthly maximum mean of SST. This HS identification was carried out bi-weekly analysis from the 3rd of January 2024 to the 19th of June 2024 around Sri Lanka. Only one map from January and February is included in Fig. 6 due to a lack of differences between these two months. It clearly shows that increasing the warning areas from e to g due to the peak of the El Niño condition, in this period, most of the coral areas around the country suffer from heat stress and are more vulnerable to coral bleaching. Then from g to j, reducing the warning areas around Sri Lanka, due to reduce the effect of El Niño condition. 3.5. Risks to coral reefs A wide range of OA risks for coral reef ecosystems was identified that might impact key species, coral habitats, and society in Sri Lanka. Lowering the coral calcification rate and reproduction, and damaging the breeding ground of the coral-associated species are the most prioritized OA risks to the coral reefs. Low risk associated with reducing the coral reef biodiversity, lowering the reef fishery, altering the coral competition, and increasing the susceptibility of coral diseases; therefore, these were categorized under the low-risk category (Table 2 ). The most well-known hazard to corals is the effect of OA on calcification, and many studies indicate that calcification declines with OA (Chan and Connolly, 2013 ; Erez et al., 2011 ; Kornder et al., 2018 ), however, some observations emphasize no significant effect of OA on coral reef calcification (Carbonne et al., 2021 ). The impact of acidity on reproduction metrics varies as well. Overall, acidification does not seem to significantly impact the early phases of reproduction, including gamete generation, fertilization, larval development, growth, and survival (Pitts et al., 2020 ; Rivest et al., 2018 ). On the other hand, the consequences of reproduction are more persistent at the later stages (settlement, metamorphosis, recruit growth, and survival) (Jiang et al., 2018 ; Yuan et al., 2018 ), indicating that compared to gametes or larvae, recruits are more susceptible to acidity. This is concerning since it was projected that a modest (20%) loss in recruitment would result in a 15% reduction in coral cover over a seven-year timeframe (Evensen et al., 2021 ). The coral reefs of Sri Lanka are home to a wide variety of invertebrate species, including seagrass and algae. The various creatures that live on reefs and form shells, including mussels, clams, urchins, and other calcifying organisms, are adversely affected by ocean acidification (Kurihara, 2008 ). In addition to the decrease in calcification, behavioral modifications, and interference with numerous physiological functions like nutrition and reproduction. However, research reveals a wide range in the sensitivity of different organisms (Allemand and Osborn, 2019 ). The OA affects the corals, and it alters the habitat around the area, hence altering their breeding ground. There is little data on coral disease under acidification, although there are some signs that pathogen virulence and abundance, and coral susceptibility, may be altered. It has been observed experimentally that the coral microbiome has higher abundances of microorganisms related to diseases (Grottoli et al., 2018 ; Vega Thurber et al., 2020). The innate immune system of corals is comparatively advanced. It can identify microorganisms, initiate signaling reactions, and mount a response downstream to control the coral's health (Quistad and Traylor-Knowles, 2016 ). The physiological cost of competition under OA could be larger under acidified environments, if they reduce the costs of development of the corals by devoting their energy to winning competitive encounters (Evensen et al., 2018 ). Ocean acidification affects the distribution of energy among the main life processes, including growth, fecundity, regenerative capacity, and overall coral fitness (Horwitz and Fine, 2014 ; Horwitz et al., 2017 ). This risk assessment gives a comprehensive overview of OA risks to Sri Lankan coral reefs. It provides a detailed report on how frequently we need to take action the protect these ecosystems. Table 2 Rank and prioritized ocean acidification (OA) risks to coral reefs in Sri Lanka. OA-driven Risk Proximity Magnitude Risk score Risk category Confidence level Lower the coral calcification and reproduction 2 3 50 Severe Medium Damage to the breeding ground 2 3 50 Severe Medium Reduce the coral reef biodiversity 2 2 33.33 Low Medium Lowering the reef fishery 2 2 33.33 Low Medium Alter the coral competition 2 2 33.33 Low Medium Increase the susceptibility of coral diseases 1 2 16.67 Low Medium 4. Conclusion Ocean acidification contributes to the decrease in the surface Ω Ar . During the study period, the studied coral reef areas Ω Ar were supersaturated (> 1), and coral reefs were not susceptible to dissolution. Even though Sri Lanka is a small country, this study demonstrates that the coastal areas have a substantial spatial variation of Ω Ar . However, the NC of Sri Lanka is associated with the lowest Ω Ar (3.2 ± 0.64) due to the low level of pH. Due to agricultural practices in NC, runoff contains high quantities of fertilizers and pesticides, which contribute to eutrophication. This eutrophication condition makes it easier to deliver low-pH water to coastal areas, which can lower the pH level of the coastal water. The NO 3 − concentrations of 2–5 µmol L − 1 were generated from human activities, which may intensify coral bleaching during heat stress. The current result showed that SC (2.19 ± 1.28) and WC (3.52 ± 1.48) had mean NO 3 − concentration higher than the above range. The observed data suggest that the Sri Lankan coral reefs are not susceptible to OA. Although coral reefs are one of the world's most vulnerable ecosystems to OA, it affects the economic, social, and ecological aspects of coral ecosystems. Seasonal variation of Ω Ar is important to get a clear picture of the vulnerable ecosystems throughout the year. However, changes in climate, anthropogenic activities, and related changes in ocean conditions may alter these conditions around Sri Lanka. Therefore, the conducted risk assessment emphasized a wide range of OA risks for coral reef ecosystems that impact key species, coral habitats, and society in Sri Lanka. Lowering the coral calcification rate and reproduction, and damaging the breeding ground of the coral-associated species are the most prioritized OA risks to the country. Sri Lankan coral reefs are at risk of OA events due to anthropogenically driven climate change in the future. Therefore, frequently monitoring OA around Sri Lanka will require more research focusing on the carbonate chemistry in these waters to protect the country's vulnerable ecosystems. Urgent actions need to be taken to mitigate climate change and protect these ecosystems. Developing countries, including Sri Lanka, also need more support for the preservation and rebuilding of coral reefs since there is a lack of finance and technology available for continuing conservation and restoration activities. Declarations Ethical Approval No ethical approval is needed Funding This study was funded by the Centre for Environment, Fisheries and Aquaculture Science (CEFAS). Data availability Data will be made available on request. Acknowledgements The authors extend their heartfelt gratitude to Mr. Upul Liyanage, Senior Scientist at the National Aquatic Resources Research and Development Agency (NARA), and Dr. Gunaalan Kuddithamby, Senior Lecturer at the Department of Fisheries Science, University of Jaffna, for their invaluable assistance during the sampling process. CRediT authorship contribution statement Praveen Abhishek was responsible for the data analysis and manuscript writing. E.P.D.N. Thilakarathne contributed to supervising the work, methodology, and review and editing process. R.S.M. Samarasekara contributed supervision of the work, and participated in the review and editing process. Piyali Chowdhury: Provided supervision and contributed to reviewing and editing the manuscript. K. Reinursha: Supported data curation and formal analysis. Meththika Vithanage: Conceptualization, methodology, supervision, review, and editing. References Afdal, Bengen, D.G., Wahyudi, A.a.J., Rastina, Prayitno, H.B., Hamzah, F., Koropitan, A.F., 2024. Spatial variability of aragonite saturation state (Ωarag) in Indonesian coastal waters. Marine environmental research 195, 106377.0141-1136.https://doi.org/10.1016/j.marenvres.2024.106377 Allemand, D., Osborn, D., 2019. Ocean acidification impacts on coral reefs: From sciences to solutions. 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13:53:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8136171/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8136171/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11270-026-09452-x","type":"published","date":"2026-04-29T15:57:32+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":97148388,"identity":"a6b3aafe-c3d4-47f5-9994-de3c4790aace","added_by":"auto","created_at":"2025-12-01 10:17:50","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":3504573,"visible":true,"origin":"","legend":"","description":"","filename":"AbhisheketalManuscriptOA.docx","url":"https://assets-eu.researchsquare.com/files/rs-8136171/v1/b82f828b19d0532485cb4abf.docx"},{"id":97148413,"identity":"8ec5aacb-d111-48e2-bc30-cd72a22ac1ca","added_by":"auto","created_at":"2025-12-01 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10:17:54","extension":"html","order_by":17,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":177036,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8136171/v1/88e3821e93df592d70440c78.html"},{"id":97148393,"identity":"2069be4b-a691-43a2-8531-3486b5d480fe","added_by":"auto","created_at":"2025-12-01 10:17:51","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":142324,"visible":true,"origin":"","legend":"\u003cp\u003eLocation of sample collection along the coast of Sri Lanka (north, east, west, and south coast).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8136171/v1/bf7d65907ce406041c4e4511.png"},{"id":97148390,"identity":"fba93197-b818-422d-b492-10b9c914abc7","added_by":"auto","created_at":"2025-12-01 10:17:50","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":74657,"visible":true,"origin":"","legend":"\u003cp\u003eThe IPCC matrix used to score risks qualitatively\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8136171/v1/9b6e3c629be46729ee906bd8.png"},{"id":97148407,"identity":"3810c1aa-93db-45d7-b6da-9235127a9508","added_by":"auto","created_at":"2025-12-01 10:17:52","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":654177,"visible":true,"origin":"","legend":"\u003cp\u003eBleached corals on the eastern coast (EC) of Sri Lanka during May 2024, when the fourth massive coral bleaching event occurred (Images were taken by Mr. E.P.D.N. Thilakarathne).\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8136171/v1/90b3f5a2cba1c6c6fe261dd9.png"},{"id":97148389,"identity":"19a3d9a7-6474-461c-a559-8c5de8c30dfd","added_by":"auto","created_at":"2025-12-01 10:17:50","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":121537,"visible":true,"origin":"","legend":"\u003cp\u003ea; Mean aragonite saturation state (Ω\u003csub\u003eAr\u003c/sub\u003e), b; Mean nitrate (NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e) (µmol L\u003csup\u003e-1\u003c/sup\u003e), and phosphate (PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e) (µmol L\u003csup\u003e-1\u003c/sup\u003e) concentrations over the coral reef sites in the northern coast (NC), east coast (EC), south coast (SC), and west coast (WC) of Sri Lanka.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8136171/v1/1024ef70a3b6c169e875a5f3.png"},{"id":97148430,"identity":"9427352a-6d58-427e-a5a9-56790db79374","added_by":"auto","created_at":"2025-12-01 10:17:57","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":202450,"visible":true,"origin":"","legend":"\u003cp\u003ea: Mean Aragonite Saturation Level (Ω\u003csub\u003eAr\u003c/sub\u003e) variation with temperature (̊C) and salinity (PSU), b: Mean pH variation, c: Mean Total Alkalinity (TA) (µmol Kg\u003csup\u003e-1\u003c/sup\u003e) variation over the coral reef sites in the Northern Coast (NC), East Coast (EC), South Coast (SC), and West Coast (WC) of Sri Lanka\u003cem\u003e.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8136171/v1/507aa5fc1949ef0b4ba28cf3.png"},{"id":97148423,"identity":"24720b4d-f3e0-4219-b000-210a5abf0135","added_by":"auto","created_at":"2025-12-01 10:17:56","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":195266,"visible":true,"origin":"","legend":"\u003cp\u003eIdentification of the spatial distribution of coral bleaching Hotspots (HP) around Sri Lanka. This HS identification was carried out bi-weekly analysis from the 3\u003csup\u003erd\u003c/sup\u003e of January 2024 to the 19\u003csup\u003eth\u003c/sup\u003e of June 2024 (a: Jan 3, b: Feb 14, c: Mar 13, d: Mar 27, e: Apr 10, f: Apr 24, g: May 8, h: May 22, i: Jun 5, j: Jun 19). Only one map from January and February is included due to a lack of differences between these two months.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8136171/v1/762079549575c866a5c0716f.png"},{"id":108439282,"identity":"34b52d61-b730-49bb-bb44-550f9cc4ebc6","added_by":"auto","created_at":"2026-05-04 16:19:41","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1779792,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8136171/v1/fd5fa96a-ef8b-4386-bd59-e93b6088dadf.pdf"},{"id":97248578,"identity":"535bf7c2-c53b-4508-8d33-1c2680ea04e7","added_by":"auto","created_at":"2025-12-02 13:03:40","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":29513,"visible":true,"origin":"","legend":"","description":"","filename":"AbhisheketalSupplementaryDocument.docx","url":"https://assets-eu.researchsquare.com/files/rs-8136171/v1/63c7e1daa723fed63f8a8675.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Assessing the influence of ocean acidification on the deterioration of coral reefs in Sri Lanka","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe oceans act as major sinks for increasing atmospheric carbon dioxide (CO\u003csub\u003e2\u003c/sub\u003e). More than 2000 Gt of anthropogenic CO\u003csub\u003e2\u003c/sub\u003e have been emitted into the atmosphere since the Industrial Revolution (Friedlingstein et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Studies emphasize that the ocean's yearly net absorption of CO\u003csub\u003e2\u003c/sub\u003e can reach 1.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 Pg C (Sun et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), which makes up 30% of the average CO\u003csub\u003e2\u003c/sub\u003e released by anthropogenic activities (Gruber et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). However, the high concentrations of dissolved CO\u003csub\u003e2\u003c/sub\u003e also suggest that the ocean's chemical balance will eventually change, lowering its pH level. This phenomenon is known as OA, which is one of the major threats to coral reef ecosystems worldwide. The estimated decrease in OA using model outputs in the Indian Ocean basin was estimated to be 0.0675 (pH) during 1961\u0026ndash;2010 (Ghosh et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Due to the detrimental impact that OA has on a variety of marine creatures, including reduced survival, calcification, growth rate, development, and abundance, OA is currently the subject of extensive research (Omar et al., \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eCoral ecosystems are vital, offering resources and ecological services for raw materials, fisheries, tourism, coastal protection, and many more purposes that are worth approximately \u003cspan\u003e$\u003c/span\u003e350,000/ha per year (Fezzi et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Despite their importance, these ecosystems are among the most vulnerable on the planet. Globally, the combined effects of climate change and human pressure are producing an alarming rate of coral reef collapse (Rampino and Shen, \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). As the ocean absorbs atmospheric CO\u003csub\u003e2\u003c/sub\u003e, its pH and carbonate ion concentration ([CO\u003csub\u003e3\u003c/sub\u003e \u003csup\u003e2\u0026minus;\u003c/sup\u003e]) decrease, thereby decreasing the saturation state; (Ω\u003csub\u003eAr\u003c/sub\u003e= [Ca\u003csup\u003e2+\u003c/sup\u003e] [CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e]/Ksp), Aragonite saturation state (Ω\u003csub\u003eAr\u003c/sub\u003e) is the product of the concentrations of Ca\u003csup\u003e2+\u003c/sup\u003e and CO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e, divided by the solubility product constant (Ksp) for aragonite (Farfan et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The studies of the Ω\u003csub\u003eAr\u003c/sub\u003e in marine environments are typically conducted to determine the state of the carbonate system and the degree of OA (Sun et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Seawaters are undersaturated with aragonite when Ω\u003csub\u003eAr\u003c/sub\u003e\u0026thinsp;\u0026lt;\u0026thinsp;1.0, which makes CaCO\u003csub\u003e3\u003c/sub\u003e shells and skeletons susceptible to disintegration. Determining the primary mechanisms governing Ω\u003csub\u003eAr\u003c/sub\u003e is crucial in forecasting Ω\u003csub\u003eAr\u003c/sub\u003e variations in the future due to rising atmospheric CO\u003csub\u003e2\u003c/sub\u003e concentrations (Choi et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The utilization of seawater's Ω\u003csub\u003eAr\u003c/sub\u003e has made it easier to estimate the OA level and net calcification rates of corals.\u003c/p\u003e\u003cp\u003eIn recent years, there has been an increase in data gathering for Ω\u003csub\u003eAr\u003c/sub\u003e and OA-related investigations around the globe (Afdal et al., 2024; Jarn\u0026iacute;kov\u0026aacute; et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Kim et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). However, there are very limited studies related to the Ω\u003csub\u003eAr\u003c/sub\u003e that have been reported in South Asia (Sridevi and Sarma, \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Moreover, as far as we know, no previous research has investigated OA studies using Ω\u003csub\u003eAr\u003c/sub\u003e as a proxy around the Sri Lankan coastal area, and no study has been found related to the Ω\u003csub\u003eAr\u003c/sub\u003e. The Sri Lankan coastal water hosts diverse and vibrant coral reefs around the country. Within this island current estimated number of coral species is approximately 245 species (Arulananthan et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Rajasuriya, 2012). Although rising atmospheric CO\u003csub\u003e2\u003c/sub\u003e levels have significantly increased OA, posing a risk to coral reefs and those ecosystems that are highly vulnerable to OA. Therefore, assess the Ω\u003csub\u003eAr\u003c/sub\u003e is essential for the identification of the prevalent OC level over the coral reef sites in Sri Lanka.\u003c/p\u003e\u003cp\u003eFurthermore, there were no previous study has investigated OA in South Asia using Ω\u003csub\u003eAr\u003c/sub\u003e as a proxy in conjunction with a comprehensive risk assessment for coral reefs. Also, studies investigating the relationship between carbon and OA in all the coastal zones of Sri Lanka are few and far between. The OA risk assessment has never been conducted and it is essential to the decision-making processes and policy development in Sri Lanka, which are shows the significant knowledge gap. Therefore, this study conduted the addressed this essential data gaps by assessing the Ω\u003csub\u003eAr\u003c/sub\u003e and conducting the OA risk assessment of the coral reef ecosystems around Sri Lanka. In this study, we have assessed the degree of OA in the coastal regions of Sri Lanka using Ω\u003csub\u003eAr\u003c/sub\u003e as an indicator (or proxy). Moreover, the study contributes to baseline data for spatial variation in Ω\u003csub\u003eAr\u003c/sub\u003e across the coral reef ecosystems in Sri Lanka. It is crucial to anticipate the emerging trends of OA's impact and devise suitable mitigation strategies in coastal waterways.\u003c/p\u003e"},{"header":"2. Methodology","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1. Study Area\u003c/h2\u003e\n \u003cp\u003eThe Sri Lankan coral reefs are predominantly located along the north, northwest, east, and southern coasts (Thilakarathne et al., \u003cspan class=\"CitationRef\"\u003e2024\u003c/span\u003e; Thilakarathne et al., \u003cspan class=\"CitationRef\"\u003e2023\u003c/span\u003e). The country faces two main monsoon patterns annually, which are: the northeast monsoon (November to February) and the southwest monsoon (May to September). The ocean circulation systems surrounding Sri Lanka significantly contribute to the connection between the Arabian Sea and the Bay of Bengal. This ocean current and monsoon promote the mixing and alteration of the sea surface dynamics surrounding the country (Schott and McCreary Jr, \u003cspan class=\"CitationRef\"\u003e2001\u003c/span\u003e). Due to monsoon patterns and ocean currents, two different sea conditions are observed around the country throughout the year (Sandamali et al., \u003cspan class=\"CitationRef\"\u003e2023\u003c/span\u003e). Therefore, this study was conducted to capture the spatial variation of Ω\u003csub\u003eAr\u003c/sub\u003e across Sri Lanka under dynamic sea conditions along the south coast (SC), east coast (EC), west coast (WC), and northern coast (NC). Sampling was done in six sites on EC (Pasikudah, Kalkudah, Pigeon Island, Kayankerni, Adukkupar, and Salli Beach), six sites in the SC (Polhena, Mirissa, Talaramba, Weligama, Unawatuna, and Hikkaduwa), three sites in WC (Colombo, Negombo, and Uswetakeiywa), and six sites in NC (Kankesanthurai, Palali, Thondamanaru River Mouth, Thondamanaru, Inbarsitty, and Point Pedro) (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e) within the April to June period of 2024. Selection of the single, dynamic transition window minimizes the temporal heterogeneity among the sites it was allowed robust spatial comparisons.\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003e2.2. Sample collection\u003c/h2\u003e\n \u003cp\u003eFor quantification of the Ω\u003csub\u003eAr\u003c/sub\u003e, two sets of seawater samples were collected from the ocean surface beyond the 10\u0026ndash;15 m coastline and directly above the shallow coral reef habitat. Samples were collection was performed using 250 ml high densitypoly ethylene (HDPE) plastic bottles, ensuring no headspace. Those samples were taken from three locations of each coral reef site. The selected distance ensured sampling over the active reef zone while minimizing terrestrial freshwater influences, and sampling was performed in daytime conditions around mid tide. One set of samples was analyzed within the site, and the other set was immediately stored in a dark and low temperature (\u0026lt;\u0026thinsp;4 \u003csup\u003eo\u003c/sup\u003eC) until samples were analyzed in the laboratory.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003e2.3. Sample analysis\u003c/h2\u003e\n \u003cp\u003eSalinity (PSU), pH (in total scale), and temperature (\u0026deg;C) were measured using the HANNA H19829 multiparameter at the sites. The multiparameter probes were calibrated according to the National Institute of Standards and Technology (NIST) standard references approximately every fifteen samples to obtain the right measurement accuracy (Precision levels of salinity\u0026thinsp;=\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01 PSU, pH\u0026thinsp;=\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01, and temperature\u0026thinsp;=\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01\u0026deg;C). The laboratory-bought sample set was analyzed immediately for Total Alkalinity (TA,\u0026micro;mol Kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e (\u0026micro;mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e (\u0026micro;mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) concentrations. HANNA (HI931) automatic potentiometric titrator was used for the measurement of TA. Standardized 0.1 mol/L HCl was employed to titrate the seawater samples. An Agilent Cary 60 UV-Vis spectrophotometer was used to measure NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e and PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e concentrations. Temperature, TA, salinity, and pH were plotted into the Seacarb v3.3.2 package in the R 4.3.1 environment for data processing and subsequent Ω\u003csub\u003eAr\u003c/sub\u003e calculation. For this calculation, the K1 and K2 acidity constants proposed by Millero (\u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e), the HSO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e constant of Khoo et al. (\u003cspan class=\"CitationRef\"\u003e1977\u003c/span\u003e), the total boron constant of Lee et al. (\u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e), and the Constant for HF proposed by Perez and Fraga (\u003cspan class=\"CitationRef\"\u003e1987\u003c/span\u003e) were used. Phosphate concentrations were also fed into the R calculations. During the calculation, silicate concentrations were assumed to be null. Around the Sri Lankan coastline, silicate concentration is lower (\u003cem\u003e\u0026lt;\u003c/em\u003e\u0026thinsp;10 \u0026micro;mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively) (Wimalasiri et al., \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e), there for ignoring these silicate concentrations induces minor errors in pHT (~\u0026thinsp;0.003) and Ω\u003csub\u003eAr\u003c/sub\u003e (~\u0026thinsp;0.01) values (Li and Zhai, \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n \u003ch2\u003e2.4. Statistical Analysis\u003c/h2\u003e\n \u003cp\u003eShapiro-Wilk tests were used to assess the normality of the data. Log transformation, Yeo-Johnson transformation, and reciprocal transformation were used to convert the not-normally distributed data to normally distributed data. For eligible data, one-way analysis of variance (One-way ANOVA) was conducted separately for the Ω\u003csub\u003eAr\u003c/sub\u003e, NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e, and PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3-\u003c/sup\u003e concentrations. All statistical analyses were performed using R version 4.3.2.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n \u003ch2\u003e2.5. Coral bleaching hotspot identification\u003c/h2\u003e\n \u003cp\u003eMaximum monthly mean (MMM) SST was employed for the identification of the coral bleaching Hot Spot (HP). The MMM of SST climatology is estimated using nightly SST data obtained from NOAA. To counteract the effects of solar glare and lessen the variance in SST brought on by daytime heating, pictures taken at night were employed. Corals are more vulnerable to bleaching when the SST exceeds the temperatures they usually experience in the hottest month. The coral bleaching HS demonstrates this by highlighting areas where the present SST is warmer than the highest monthly maximum mean of SST. A temperature difference of above 1.0\u0026deg;C was considered to be a threshold for thermal stress that would cause coral bleaching classified as a \u0026ldquo;Warning\u0026rdquo;, values 0\u0026ndash;1.0\u0026deg;C were classified as a \u0026quot;watch\u0026quot; condition, and values less than or equal to zero were classified as a \u0026quot;No Stress\u0026quot; state. The discrepancy between the MMM SST climatology and the measured near-real-time SST, as provided by the equation, is represented by the value of HS.\u003c/p\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{H}\\text{o}\\text{t}\\text{s}\\text{p}\\text{o}\\text{t}\\:(^\\circ\\:\\text{C})\\:=\\:\\text{S}\\text{S}\\text{T}\\:-\\:\\left(\\text{M}\\text{M}\\text{M}\\:\\text{S}\\text{S}\\text{T}\\:\\text{C}\\text{l}\\text{i}\\text{m}\\text{a}\\text{t}\\text{o}\\text{l}\\text{o}\\text{g}\\text{y}\\right)\\)\u003c/span\u003e\u003c/span\u003e\u003cbr\u003e\u003cbr\u003eThe heat stress distribution and incidence that lead to coral bleaching are represented by the HS, and only positive values were used for the illustration (INCOIS, \u003cspan class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e2.6. Risk Assessment of the Ocean Acidification Effect on the Coral Reef Ecosystems in Sri Lanka\u003c/h2\u003e\n \u003cp\u003eThrough employing a consistent approach, OA risk evaluations provide an opportunity to recognize and prioritize risks across coral reef ecosystems, emphasizing the regions\u0026apos; coral reefs that require mitigation plans most urgently. The risk assessment method we used here comprises four steps (Warren et al., \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e);\u003c/p\u003e\n \u003cp\u003e(1) Determine the drivers of OA in the Sri Lankan coastal regions;\u003c/p\u003e\n \u003cp\u003e(2) Identify the risk imposed by OA to the coral ecosystems;\u003c/p\u003e\n \u003cp\u003e(3) Score individual risks;\u003c/p\u003e\n \u003cp\u003e(4) Rank and prioritize risks.\u003c/p\u003e\n \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\n \u003ch2\u003e2.6.1. Rank and prioritize risks\u003c/h2\u003e\n \u003cp\u003eAfter ranking the risk, it was ranked from highest to lowest based on the overall score. This was facilitated to identify the most important prioritized risk to the Sri Lankan coral ecosystems. Due to there was little variety in the overall risk ratings. The risks were divided into three categories: \u0026quot;Low\u0026quot; (score from 8 to 17), \u0026quot;Moderate\u0026quot; (score from 25 to 50), and \u0026quot;Severe\u0026quot; (score from 67 to 100). Severe scores were characterized by a \u0026quot;now\u0026quot; proximity and a \u0026quot;medium\u0026quot; magnitude (Maltby et al., \u003cspan class=\"CitationRef\"\u003e2022\u003c/span\u003e). However, the confidence level was assigned based on the IPCC matrix (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eThe supporting information provides detailed descriptions of determining the drivers of OA in the Sri Lankan coastal region (See S1) and identifying risks imposed by OA on coral ecosystems (See S2). The discussion section is a complete scoring and ranking of the risks relevant to coral reefs in Sri Lankan waters.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.1. Aragonite saturation status around coral sites\u003c/h2\u003e\u003cp\u003eDuring the sampling period, a bleached coral cover was observed (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The bleached coral covers around Sri Lanka indicate that the global fourth massive coral bleaching event (2023\u0026ndash;2024) impacted the coral reefs of Sri Lanka. This bleaching event was confirmed by the National Oceanic and Atmospheric Administration (NOAA) and the International Coral Reef Initiative (ICRI) (ICRI, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eUnfortunately, no data is available within the country regarding how much coral cover declined due to this bleaching event. Even though coral bleaching does not necessarily result in coral mortality, corals can recover and continue to offer the ecosystem services that people rely on while preserving their biodiversity (Schoepf et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), it is still important to record these events and monitor the degree of bleaching such that a warning system can be brought in place when the coral population reaches a critical stage. Zhou et al. (\u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) showed that there exists a sensitive area of El Ni\u0026ntilde;o predictions in the tropical Indian Ocean, which mainly dominates in the subsurface of the eastern Indian Ocean, ranging from 60\u0026deg;E to 100\u0026deg;E, from the sea surface to 200 m underneath. This explains the climate-related warming and rise in sea temperature around Sri Lanka, which lies near ~\u0026thinsp;80\u0026deg;E. During the study period, the mean values of the Ω\u003csub\u003eAr,\u003c/sub\u003e NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;,\u003c/sup\u003e and PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003econcentrations in each coral site are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe effect that OA will have on the net carbonate accretion of coral reefs is determined by the circumstances of the reef's saltwater. When the seawater Ω\u003csub\u003eAr\u003c/sub\u003e reaches 2.92\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16, coral reef sands go from net precipitating to net dissolving (Eyre et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). According to the observed data around the country, Ω\u003csub\u003eAr\u003c/sub\u003e was supersaturated (\u0026gt;\u0026thinsp;1), and all sites had Ω\u003csub\u003eAr\u003c/sub\u003e above the threshold level (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). This shows that the sample sites\u0026rsquo; Ω\u003csub\u003eAr\u003c/sub\u003e and pH lay between 3.0-4.92 and 8.05\u0026ndash;8.35, respectively. However, a somewhat reduced level of Ω\u003csub\u003eAr\u003c/sub\u003e was observed in the NC region compared to the other coastal areas due to a low level of pH (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The NC region is a heavily agriculturally dependent area (mainly paddy cultivation), mainly the Jaffna peninsula, which is the nearest place to the sample locations (Gopalakrishnan and Kumar, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). For those practices, farmers frequently use fertilizers and pesticides on their crops. Therefore, runoff from this area containing a huge amount of these fertilizers and pesticides can contribute to eutrophication. Conducted studies show that the Jaffna peninsula groundwater is also contaminated with excessive nitrate due to agricultural runoff (Jeyaruba and Thushyanthy, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Vithanage et al., \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The breakdown of organic debris from these blooms depletes oxygen and emits CO\u003csub\u003e2\u003c/sub\u003e, resulting in a localized low pH level. This can be a contributing factor to the reduction in pH levels at the NC sampling sites.\u003c/p\u003e\u003cp\u003eDuring the study period, Sri Lankan coral reef areas' ocean surface comprised higher Ω\u003csub\u003eAr\u003c/sub\u003e when compared to the world's most acidified ocean region (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The Bering Sea, situated in the high latitudes of the Northern Hemisphere, is one of the most acidified regions in the world (Wiese et al., \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). However, with the cold water temperatures there, the Bering Sea is especially vulnerable to OA (Sun et al., \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Therefore, a reduced level of annual Ω\u003csub\u003eAr\u003c/sub\u003e (2.25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.51) was reported in the Bering Sea. In addition to that Gulf of C\u0026aacute;diz, the SW Iberian Peninsula, the Northern North Sea, the Western Arctic Ocean (Chukchi marginal area), and the Gulf of California-Cabo Pulmo identified the same situation.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eThe (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD) Aragonite saturation status (Ω\u003csub\u003eAr\u003c/sub\u003e) and pH level in the study area and some selected most acidified oceans.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eOcean Region\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eAragonite saturation status (Ω\u003csub\u003eAr\u003c/sub\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003epH\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eReferences\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eBering Sea (Annual)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e2.25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.51\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eN/A\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSun et al. (\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2021\u003c/span\u003e)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGulf of C\u0026aacute;diz, SW Iberian Peninsula (Annual)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e2.68\u0026thinsp;\u0026plusmn;\u0026thinsp;0.30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e8.01\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eJim\u0026eacute;nez-L\u0026oacute;pez et al. (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2021\u003c/span\u003e)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNorthern North Sea (Winter)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e1.96\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e8.17\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eOmar et al. (\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2019\u003c/span\u003e)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eWestern Arctic Ocean (Chukchi marginal area) (Annual)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e1.07\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14\u003c/p\u003e\u003cp\u003e(Ranged from 0.86 to 1.77)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e8.11\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eKim et al. (\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGulf of California-Cabo Pulmo (December to March)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e2.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e7.93\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eNorzagaray-L\u0026oacute;pez et al. (\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2017\u003c/span\u003e)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNorth Coast of Sri Lanka\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e3.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.64\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e8.11\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\" morerows=\"3\" rowspan=\"4\"\u003e\u003cp\u003eThis Study\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEast Coast of Sri Lanka\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e4.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.29\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e8.26\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSouth Coast of Sri Lanka\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e4.21\u0026thinsp;\u0026plusmn;\u0026thinsp;0.43\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e8.31\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eWest Coast of Sri Lanka\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e4.39\u0026thinsp;\u0026plusmn;\u0026thinsp;0.42\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e8.24\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"4\"\u003e\u003cb\u003eNote\u003c/b\u003e\u003cem\u003e-\u003c/em\u003eN/A- Not available, *Mean\u0026thinsp;\u003cb\u003e\u0026plusmn;\u003c/b\u003e\u0026thinsp;SD values calculated from six sampling locations along; East, North, and South coasts and three locations on the West coast of Sri Lanka.\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe highest Ω\u003csub\u003eAr\u003c/sub\u003e was reported within the Negombo reef area (4.92\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12), although it was compressed with a pH level of 8.29\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01. The highest pH level (8.35\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02) was observed in the Thal Aramba reef (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) area, also this area was compressed with the Ω\u003csub\u003eAr\u003c/sub\u003e 4.47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.24. These differences occurred due to the variation of the TA at each study location. Thal Aramba reef and Negombo reef TA were reported as 2288.588\u0026thinsp;\u0026plusmn;\u0026thinsp;57.275 and 2531.549\u0026thinsp;\u0026plusmn;\u0026thinsp;25.827, respectively. The lowest Ω\u003csub\u003eAr\u003c/sub\u003e recorded in the Inbrasity coral site in NC (2.98\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04), due to the low level of pH (8.05\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01). Figures (b) and (c) show the pH and TA variation within each coral reef. However, the mean Ω\u003csub\u003eAr\u003c/sub\u003e in NC sites showed somewhat lower values compared to the other coastal areas' coral sites, including Thondaimanaru, Inbarsitty, Palaali, and Point Pedro (3.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1, 2.98\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04, 3.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09, and 3.06\u0026thinsp;\u0026plusmn;\u0026thinsp;0.17). In SC lowest Ω\u003csub\u003eAr\u003c/sub\u003e was observed within the Polhena reef area (3.47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.19), mainly due to the location of the reef, which is located near the Nilwala River mouth and has a high freshwater inflow. During the study period, sea surface temperature lies between 28.71\u0026ndash;32.82 ̊C. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea emphasizes the Ω\u003csub\u003eAr\u003c/sub\u003e variation in each coral reef around Sri Lanka with sea surface temperature (̊C) and salinity (PSU). No coral reef in the study areas suffered dissolution, and the Ω\u003csub\u003eAr\u003c/sub\u003e level did not reach the 2.92\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16 level during the study period. When comparing Ω\u003csub\u003eAr\u003c/sub\u003e of areas mentioned in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e with Sri Lankan coral areas surface Ω\u003csub\u003eAr\u003c/sub\u003e, it clearly emphasizes the reduced level of OA over the coral reefs in Sri Lanka.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.2. Nitrate (NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026ndash;\u003c/sup\u003e) and Phosphate (PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026ndash;\u003c/sup\u003e) concentrations\u003c/h2\u003e\u003cp\u003eThe majority of coral reefs grow and endure in oligotrophic, tropical, and subtropical seas with extremely low levels of phosphate (PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026ndash;\u003c/sup\u003e) and nitrate (NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026ndash;\u003c/sup\u003e). However, one of the main causes of global warming is nutrient pollution, which has grown over the past century (Bennett and Bennett, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Burkepile et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Local human influence is another stressor that coral reefs experience, in addition to those posed by global change. These consist of upwelling incidents (Richardson et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) and coastal seawater's nutrient enrichment due to land runoff, farming, and urban wastewater (Fabricius, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). The quantities of inorganic nitrogen (N) and phosphorus (P) can be significantly greater under these circumstances (up to 4 \u0026micro;M N and 0.5 \u0026micro;M P) (Blanckaert et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Govers et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Naumann et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). The usual levels of N and P concentrations on coral reefs are 0.5 \u0026micro;M and 0.1 \u0026micro;M (Lomas et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Meeder et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Recent research has demonstrated that NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026ndash;\u003c/sup\u003e concentrations of 2 to 5 \u0026micro;M, which are primary nitrogen molecules generated from human activity, can intensify coral bleaching during heat stress (Burkepile et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Ezzat et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Marangoni et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Rosset et al., \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). According to the observed data, emphasis on higher NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026ndash;\u003c/sup\u003e concentration was reported on the WC (3.52\u0026thinsp;\u0026plusmn;\u0026thinsp;1.48 \u0026micro;mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) surface water may be due to high terrestrial runoff, urban wastewater, and anthropogenic activities. The WC is a highly urbanized region in the country with high population density, representing this region. This may be the main reason for the observed elevated NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026ndash;\u003c/sup\u003e concentration. The location in Colombo had the highest NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026ndash;\u003c/sup\u003e concentration (5.24\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13 \u0026micro;mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) among all coral reef sites due to high waste discharge and anthropogenic activities (Manage et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Weligama, Polhena, Kankasanthure, Negombo, Colombo, and Uswetakeiywa (2.24\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2, 4.35\u0026thinsp;\u0026plusmn;\u0026thinsp;0.22, 2.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.47, 2.23\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15, 5.24\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13, and 3.14\u0026thinsp;\u0026plusmn;\u0026thinsp;1.67 \u0026micro;mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) coral reef areas had high NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026ndash;\u003c/sup\u003e concentrations, which reached the 2 to 5 \u0026micro;M. This NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026ndash;\u003c/sup\u003e concentatration may contribute to coral bleaching during the heat stress. The PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026ndash;\u003c/sup\u003e concentrations of all the study sites were below 0.94\u0026thinsp;\u0026plusmn;\u0026thinsp;0.37, the highest concentration reported in the Weligama reef due to freshwater inflow and anthropogenic activities. The Weligama reef, situated inside the Weligama Bayis one of the rocky shorelines along the Sri Lankan coastline. The Polwatta River, being the river that flows into the bay from the southern section of the bay carries nutrients to the bay (Amarathunga et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). And this site is located near the Weligama fisheries harbor, therefore pollution level was high in this area. Those were the main reasons for the observed higher PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026ndash;\u003c/sup\u003e concentrations in this area.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e3.3. Statistical Analysis\u003c/h2\u003e\u003cp\u003eOne-way ANOVA confirmed that there were significant differences (P\u0026thinsp;\u0026gt;\u0026thinsp;0.05) of Ω\u003csub\u003eAr\u003c/sub\u003e in NC (3.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.64 \u0026micro;mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) compared to other coastal sites and no significant differences (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05) between EC and SC, SC and WC, and EC and WC. There were significant differences in NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e concentrations between NC and WC, EC and SC, and WC and EC. Collected data confirms that there are significant differences in PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e concentrations in EC (0.35\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07 \u0026micro;mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) when compared to other coastal areas.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003e3.4. Coral Bleaching Hotspot\u003c/h2\u003e\u003cp\u003eCorals are vulnerable to bleaching when the SST exceeds the temperatures they usually experience in the hottest month. The HS product on coral bleaching demonstrates this by highlighting areas where the present SST is warmer than the highest monthly maximum mean of SST. This HS identification was carried out bi-weekly analysis from the 3rd of January 2024 to the 19th of June 2024 around Sri Lanka. Only one map from January and February is included in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e due to a lack of differences between these two months. It clearly shows that increasing the warning areas from e to g due to the peak of the El Ni\u0026ntilde;o condition, in this period, most of the coral areas around the country suffer from heat stress and are more vulnerable to coral bleaching. Then from g to j, reducing the warning areas around Sri Lanka, due to reduce the effect of El Ni\u0026ntilde;o condition.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\u003ch2\u003e3.5. Risks to coral reefs\u003c/h2\u003e\u003cp\u003eA wide range of OA risks for coral reef ecosystems was identified that might impact key species, coral habitats, and society in Sri Lanka. Lowering the coral calcification rate and reproduction, and damaging the breeding ground of the coral-associated species are the most prioritized OA risks to the coral reefs. Low risk associated with reducing the coral reef biodiversity, lowering the reef fishery, altering the coral competition, and increasing the susceptibility of coral diseases; therefore, these were categorized under the low-risk category (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe most well-known hazard to corals is the effect of OA on calcification, and many studies indicate that calcification declines with OA (Chan and Connolly, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Erez et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Kornder et al., \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), however, some observations emphasize no significant effect of OA on coral reef calcification (Carbonne et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The impact of acidity on reproduction metrics varies as well. Overall, acidification does not seem to significantly impact the early phases of reproduction, including gamete generation, fertilization, larval development, growth, and survival (Pitts et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Rivest et al., \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). On the other hand, the consequences of reproduction are more persistent at the later stages (settlement, metamorphosis, recruit growth, and survival) (Jiang et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Yuan et al., \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), indicating that compared to gametes or larvae, recruits are more susceptible to acidity. This is concerning since it was projected that a modest (20%) loss in recruitment would result in a 15% reduction in coral cover over a seven-year timeframe (Evensen et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe coral reefs of Sri Lanka are home to a wide variety of invertebrate species, including seagrass and algae. The various creatures that live on reefs and form shells, including mussels, clams, urchins, and other calcifying organisms, are adversely affected by ocean acidification (Kurihara, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). In addition to the decrease in calcification, behavioral modifications, and interference with numerous physiological functions like nutrition and reproduction. However, research reveals a wide range in the sensitivity of different organisms (Allemand and Osborn, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). The OA affects the corals, and it alters the habitat around the area, hence altering their breeding ground.\u003c/p\u003e\u003cp\u003eThere is little data on coral disease under acidification, although there are some signs that pathogen virulence and abundance, and coral susceptibility, may be altered. It has been observed experimentally that the coral microbiome has higher abundances of microorganisms related to diseases (Grottoli et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Vega Thurber et al., 2020). The innate immune system of corals is comparatively advanced. It can identify microorganisms, initiate signaling reactions, and mount a response downstream to control the coral's health (Quistad and Traylor-Knowles, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The physiological cost of competition under OA could be larger under acidified environments, if they reduce the costs of development of the corals by devoting their energy to winning competitive encounters (Evensen et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Ocean acidification affects the distribution of energy among the main life processes, including growth, fecundity, regenerative capacity, and overall coral fitness (Horwitz and Fine, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Horwitz et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). This risk assessment gives a comprehensive overview of OA risks to Sri Lankan coral reefs. It provides a detailed report on how frequently we need to take action the protect these ecosystems.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eRank and prioritized ocean acidification (OA) risks to coral reefs in Sri Lanka.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eOA-driven Risk\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eProximity\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eMagnitude\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eRisk score\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eRisk category\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eConfidence level\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLower the coral calcification and reproduction\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eSevere\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003eMedium\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDamage to the breeding ground\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eSevere\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003eMedium\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eReduce the coral reef biodiversity\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e33.33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eLow\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003eMedium\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLowering the reef fishery\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e33.33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eLow\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003eMedium\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAlter the coral competition\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e33.33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eLow\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003eMedium\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eIncrease the susceptibility of coral diseases\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e16.67\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003eLow\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003eMedium\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eOcean acidification contributes to the decrease in the surface Ω\u003csub\u003eAr\u003c/sub\u003e. During the study period, the studied coral reef areas Ω\u003csub\u003eAr\u003c/sub\u003e were supersaturated (\u0026gt;\u0026thinsp;1), and coral reefs were not susceptible to dissolution. Even though Sri Lanka is a small country, this study demonstrates that the coastal areas have a substantial spatial variation of Ω\u003csub\u003eAr\u003c/sub\u003e. However, the NC of Sri Lanka is associated with the lowest Ω\u003csub\u003eAr\u003c/sub\u003e (3.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.64) due to the low level of pH. Due to agricultural practices in NC, runoff contains high quantities of fertilizers and pesticides, which contribute to eutrophication. This eutrophication condition makes it easier to deliver low-pH water to coastal areas, which can lower the pH level of the coastal water. The NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e concentrations of 2\u0026ndash;5 \u0026micro;mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e were generated from human activities, which may intensify coral bleaching during heat stress. The current result showed that SC (2.19\u0026thinsp;\u0026plusmn;\u0026thinsp;1.28) and WC (3.52\u0026thinsp;\u0026plusmn;\u0026thinsp;1.48) had mean NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e concentration higher than the above range. The observed data suggest that the Sri Lankan coral reefs are not susceptible to OA. Although coral reefs are one of the world's most vulnerable ecosystems to OA, it affects the economic, social, and ecological aspects of coral ecosystems. Seasonal variation of Ω\u003csub\u003eAr\u003c/sub\u003e is important to get a clear picture of the vulnerable ecosystems throughout the year. However, changes in climate, anthropogenic activities, and related changes in ocean conditions may alter these conditions around Sri Lanka. Therefore, the conducted risk assessment emphasized a wide range of OA risks for coral reef ecosystems that impact key species, coral habitats, and society in Sri Lanka. Lowering the coral calcification rate and reproduction, and damaging the breeding ground of the coral-associated species are the most prioritized OA risks to the country. Sri Lankan coral reefs are at risk of OA events due to anthropogenically driven climate change in the future. Therefore, frequently monitoring OA around Sri Lanka will require more research focusing on the carbonate chemistry in these waters to protect the country's vulnerable ecosystems. Urgent actions need to be taken to mitigate climate change and protect these ecosystems. Developing countries, including Sri Lanka, also need more support for the preservation and rebuilding of coral reefs since there is a lack of finance and technology available for continuing conservation and restoration activities.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthical Approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo ethical approval is needed\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was funded by the Centre for Environment, Fisheries and Aquaculture Science (CEFAS).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData will be made available on request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors extend their heartfelt gratitude to Mr. Upul Liyanage, Senior Scientist at the National Aquatic Resources Research and Development Agency (NARA), and Dr. Gunaalan Kuddithamby, Senior Lecturer at the Department of Fisheries Science, University of Jaffna, for their invaluable assistance during the sampling process.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCRediT\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eauthorship contribution statement\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePraveen Abhishek was responsible for the data analysis and manuscript writing. E.P.D.N. Thilakarathne contributed to supervising the work, methodology, and review and editing process.\u0026nbsp;R.S.M. Samarasekara contributed supervision of the work, and participated in the review and editing process. Piyali Chowdhury: Provided supervision and contributed to reviewing and editing the manuscript. K. Reinursha: Supported data curation and formal analysis. Meththika Vithanage: Conceptualization, methodology, supervision, review, and editing.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAfdal, Bengen, D.G., Wahyudi, A.a.J., Rastina, Prayitno, H.B., Hamzah, F., Koropitan, A.F., 2024. Spatial variability of aragonite saturation state (\u0026Omega;arag) in Indonesian coastal waters. Marine environmental research 195, 106377.0141-1136.https://doi.org/10.1016/j.marenvres.2024.106377\u003c/li\u003e\n \u003cli\u003eAllemand, D., Osborn, D., 2019. Ocean acidification impacts on coral reefs: From sciences to solutions. 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Journal of Oceanology and Limnology 38, 1602-1615.2523-3521.https://doi.org/10.1007/s00343-019-9062-4\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"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":"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":"Coral Bleaching Hotspot, Nutrient Pollution, Ocean Acidification, Sea Surface Temperature, Risk Assessment: Sri Lanka","lastPublishedDoi":"10.21203/rs.3.rs-8136171/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8136171/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eRising atmospheric CO\u003csub\u003e2\u003c/sub\u003e levels have significantly increased ocean acidification (OA), endangering coral reefs, and nutrient (nitrate (NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e), and phosphate (PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e)) pollution also weakens the coral reef resilience. Therefore, the study evaluates the prevailing OA level over the Sri Lankan coral reef areas using the aragonite saturation state (Ω\u003csub\u003eAr\u003c/sub\u003e) and assesses the nitrate (NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e), and phosphate (PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e) concentrations over the coral sites. The study was conducted on coral reefs on the eastern coast (EC), southern coast (SC), northern coast (NC), and west coast (WC) of Sri Lanka from April to June 2024. A total of 63 seawater samples were collected around each coastal site for analysis. The Ω\u003csub\u003eAr\u003c/sub\u003e were supersaturated (Ω\u003csub\u003eAr\u003c/sub\u003e\u0026thinsp;\u0026gt;\u0026thinsp;1) and ranged from 2.98\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04 to 4.92\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12. Throughout the study period, the study sites had Ω\u003csub\u003eAr\u003c/sub\u003e values exceeding 2.92\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16, indicating that the nation's corals were resilient to deterioration, and the comparative analysis demonstrates that these sites were not vulnerable to OA. The NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e concentrations of 2\u0026ndash;5 \u0026micro;mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, from human activities, may intensify coral bleaching during heat stress. Results showed that SC (2.19\u0026thinsp;\u0026plusmn;\u0026thinsp;1.28 \u0026micro;mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and WC (3.52\u0026thinsp;\u0026plusmn;\u0026thinsp;1.48 \u0026micro;mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) had NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e above the permissible range, which may be due to waste discharge and high runoff. The significantly higher PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e concentrations were reported in EC (0.35\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07 \u0026micro;mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Coral bleaching hotspot (HS) identification emphasizes how spatially distributed HS are from January to June. The OA risk assessment confirmed that climate change brought high risk to the coral reef ecosystems, which impact on the ecology and economy of Sri Lanka.\u003c/p\u003e","manuscriptTitle":"Assessing the influence of ocean acidification on the deterioration of coral reefs in Sri Lanka","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-01 10:10:25","doi":"10.21203/rs.3.rs-8136171/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":"958028e1-9f9f-425a-8b9a-259661e21b5a","owner":[],"postedDate":"December 1st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-05-04T16:19:35+00:00","versionOfRecord":{"articleIdentity":"rs-8136171","link":"https://doi.org/10.1007/s11270-026-09452-x","journal":{"identity":"water-air-and-soil-pollution","isVorOnly":false,"title":"Water, Air, \u0026 Soil Pollution"},"publishedOn":"2026-04-29 15:57:32","publishedOnDateReadable":"April 29th, 2026"},"versionCreatedAt":"2025-12-01 10:10:25","video":"","vorDoi":"10.1007/s11270-026-09452-x","vorDoiUrl":"https://doi.org/10.1007/s11270-026-09452-x","workflowStages":[]},"version":"v1","identity":"rs-8136171","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8136171","identity":"rs-8136171","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}