Archive for the 'Science' Category

Impacts of rising temperatures and water acidification on the oxidative status and immune system of aquatic ectothermic vertebrates: a meta-analysis


  • CO2 emissions are driving increase in temperature and water acidification.
  • Meta-analysis implemented to assess impacts of CO2-stressors on ectotherms physiology.
  • High temperature and water acidification induce higher oxidative damage in ectotherms.
  • Early life stages are more capable than adults to upregulate antioxidant enzymes.
  • Oxidative status regulation underlies thermal acclimation.


Species persistence in the Anthropocene is dramatically threatened by global climate change. Large emissions of carbon dioxide (CO2) from human activities are driving increases in mean temperature, intensity of heatwaves, and acidification of oceans and freshwater bodies. Ectotherms are particularly sensitive to CO2-induced stressors, because the rate of their metabolic reactions, as well as their immunological performance, are affected by environmental temperatures and water pH. We reviewed and performed a meta-analysis of 56 studies, involving 1259 effect sizes, that compared oxidative status or immune function metrics between 42 species of ectothermic vertebrates exposed to long-term increased temperatures or water acidification (≥48 h), and those exposed to control parameters resembling natural conditions. We found that CO2-induced stressors enhance levels of molecular oxidative damages in ectotherms, while the activity of antioxidant enzymes was upregulated only at higher temperatures, possibly due to an increased rate of biochemical reactions dependent on the higher ambient temperature. Differently, both temperature and water acidification showed weak impacts on immune function, indicating different direction (increase or decrease) of responses among immune traits. Further, we found that the intensity of temperature treatments (Δ°C) and their duration, enhance the physiological response of ectotherms, pointing to stronger effects of prolonged extreme warming events (i.e., heatwaves) on the oxidative status. Finally, adult individuals showed weaker antioxidant enzymatic responses to an increase in water temperature compared to early life stages, suggesting lower acclimation capacity. Antarctic species showed weaker antioxidant response compared to temperate and tropical species, but level of uncertainty in the antioxidant enzymatic response of Antarctic species was high, thus pairwise comparisons were statistically non-significant. Overall, the results of this meta-analysis indicate that the regulation of oxidative status might be one key mechanism underlying thermal plasticity in aquatic ectothermic vertebrates.

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Common sea star (Asterias rubens) coelomic fluid changes in response to short-term exposure to environmental stressors

Common sea stars (Asterias rubens) are at risk of physiological stress and decline with projected shifts in oceanic conditions. This study assessed changes in coelomic fluid (CF) blood gases, electrolytes, osmolality, and coelomocyte counts in adult common sea stars after exposure to stressors mimicking effects from climate change for 14 days, including decreased pH (−0.4 units, mean: 7.37), hypoxia (target dissolved oxygen ~1.75 mg O2/L, mean: 1.80 mg O2/L), or increased temperature (+10 °C, mean: 17.2 °C) and compared sea star CF electrolytes and osmolality to tank water. Changes in CF blood gases, electrolytes, and/or coelomocyte counts occurred in all treatment groups after stressor exposures, indicating adverse systemic effects with evidence of increased energy expenditure, respiratory or metabolic derangements, and immunosuppression or inflammation. At baseline, CF potassium and osmolality of all groups combined were significantly higher than tank water, and, after exposures, CF potassium was significantly higher in the hypoxia group as compared to tank water. These findings indicate physiological challenges for A. rubens after stressor exposures and, given increased observations of sea star wasting events globally, this provides evidence that sea stars as a broad group are particularly vulnerable to changing oceans.

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Tidal restrictions in a central Californian estuarine system are associated with higher mean pH, but increased low-pH exposure

Coastal acidification is an emerging concern in estuaries impaired by nutrient pollution. In addition to rising levels of atmospheric CO2 which drives ocean acidification, high nutrient inputs to coastal areas can amplify heterotrophic metabolism, raise water column CO2 levels, and exacerbate pH declines. This study focuses on how a third anthropogenic stressor, tidal restriction, shapes effects of coastal acidification. Tidal restrictions associated with installation of gates that reduce tidal flow to a portion of an estuary are a common impact to coastal landscapes and can negatively affect water quality. This study examined pH in locations subject to varying levels of tidal restriction across a series of interconnected central California estuaries, whose waters are nutrient-impaired due to surrounding agriculture, and where 50% of the system is affected by tidal restrictions. Mean and variance of pH differed based on the level of tidal restriction. Sites lacking tidal restrictions had the lowest mean pH (7.98) but the least pH variance (0.07), and the most infrequent exposure to low pH (<7.0) conditions. In contrast, sites with minimal tidal exchange had the most exposure to low pH conditions, although mean pH levels were greater (8.08), because they also saw greater pH variance (0.46). Our results suggest that tidal restrictions alter pH levels and affect the resilience of estuaries to coastal acidification.

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Fresh and saline submarine groundwater discharge as sources of carbon and nutrients to the Japan Sea


  • Fresh groundwater was comparable to the discharge from rivers and the main source of carbon, phosphate, and nitrate to coastal waters.
  • Groundwater-derived alkalinity fluxes were 7 times greater than river inputs, buffering the coastal ocean.
  • Nutrient and chlorophyll observations revealed the strong influence of groundwater discharge on primary productivity.


Submarine groundwater discharge (SGD) is an important pathway for carbon and nutrients to the coastal ocean, sometimes exceeding river inputs. SGD fluxes can have implications for long-term carbon storage, ocean acidification and nutrient dynamics. Here, we used radium (223Ra and 226Ra) isotopes to quantify SGD-derived fluxes of dissolved inorganic (DIC) and organic (DOC) carbon, nitrate (NO3), nitrite (NO2), ammonium (NH4+) and phosphate (PO43−) in a spring-fed coastal bay in the Japan Sea. The average coastal water residence times using 223Ra/226Ra ratios was 32.5 ± 17.9 days. Fresh and saline SGD were estimated using a radium mixing model with short- and long-lived isotopes. The volume of fresh SGD entering the bay (4.6 ± 4.6 cm day−1) was more than twice that of the volume of saline SGD (1.9 ± 2.1 cm day−1). Fresh SGD (mmol m2 day−1) was the main source of DOC (2.7 ± 2.6), DIC (13.9 ± 13.7), PO43− (0.3 ± 0.3) and NO3 (6.6 ± 6.5) to the coastal ocean, whereas saline SGD was the main source of NH4+ (0.2 ± 0.2). Total SGD-derived carbon and nutrient fluxes were 4 – 7 and 2–16 times greater than local river inputs. Positive correlations between chlorophyll-a, 226Ra and δ13C-DIC indicate that SGD significantly (p < 0.05) enhances primary productivity nearshore. Overall, fresh SGD of nitrogen and carbon to seawater drove chlorophyll-a, decreased DIC/Alkalinity ratios, and modified the carbonate biogeochemistry of the coastal ocean.

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Effect of seagrass cover loss on seawater carbonate chemistry: implications for the potential of seagrass meadows to mitigate ocean acidification

Seagrass meadows are important marine ecosystems for mitigating ocean acidification because of their ability to raise the pH of seawater during the day. This ability may decrease as a result of the loss of these meadows, which is primarily caused by human activities and climate change. Here, we test the effect of seagrass cover loss on seawater carbonate chemistry to understand how the loss of seagrass meadows affects their ability to mitigate ocean acidification. pH, dissolved inorganic carbon (DIC), partial pressure of carbon dioxide (pCO2), and aragonite saturation state (ΩAr) were measured in experimental tidal pools with varying proportions of seagrass coverage: 0% (mimicking a complete loss of seagrass meadows); 1%–29% (mimicking the greatest loss of seagrass meadows); 30%–59% (mimicking a moderate loss of seagrass meadows); and 60%–100% (mimicking the lowest loss of seagrass meadows). It was found that as seagrass cover decreased, pH and ΩAr levels in seawater decreased proportionally during the day, while pCO2 and DIC increased. Additionally, correlation analysis showed a strong significant positive correlation between the seagrass cover and pH (rs = 0.9096, p < 0.0001) and ΩAr (rs = 0.9031, p < 0.0001), as well as a strong significant negative correlation between the seagrass cover and pCO2 (rs = −0.9068, p < 0.0001) and DIC (rs = −0.8947, p < 0.0001). These results imply that the 7% annual global loss in seagrass meadows may limit seagrass meadows’ ability to raise the pH of their surrounding seawater during the day, reducing their potential to mitigate ocean acidification. The study recommends that management strategies that minimize anthropogenic activities that cause seagrass loss be implemented in order for seagrass meadows to continue mitigating ocean acidification within their ecosystem and nearby ecosystems.

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A study of hypoxia and ocean acidification related physico-chemical parameters in selected coastal waters around Mauritius

Sea water samples were collected at five stations around Mauritius namely Flic-en-Flac, Albion, Mont Choisy, Trou-d’Eau-Douce and La Cambuse over 12 months from July 2021 to June 2022 for the analysis of dissolved oxygen (D.O), pHT and Total alkalinity (AT). Albion was the only open water system whereas the others were lagoons. Summer was from November 2021 to April 2022 while the period from July 2021 to October 2021, May 2022 and June 2022 were considered to be winter. The summer mean values of sea surface temperature (SST), D.O, pHT and AT varied from 28.2 ± 1.3 °C to 29.8 ± 2.2 °C, from 6.60 ± 1.15 mgL−1 to 8.11 ± 0.51 mgL−1, from 8.10 ± 0.09 to 8.20 ± 0.12 and from 2324.5 ± 110.6 μmol kg−1 to 2384.8 ± 118.6 μ mol kg−1, respectively. The winter mean values of these parameters varied from 24.7 ± 1.1 °C to 26.1 ± 1.4 °C, from 6.55 ± 1.21 mgL−1 to 8.26 ± 0.67 mgL−1, from 8.00 ± 0.08 to 8.13 ± 0.14 and from 2397.2 ± 84.9 μmol kg−1 to 2448.7 ± 108.5 μmol kg−1, respectively. The Two-way measures ANOVA and the post hoc analysis revealed that (1) the only two stations having a comparable mean pHT variability in the two seasons were Albion and La Cambuse, despite having opposite bearings and morphology, but their mean D.O variability was the contrary (2) the mean temporal variability in D.O and pHT at Mont Choisy were not significant due to the presence of sea grasses.

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Potential effects of climate change on the growth response of the toxic dinoflagellate Karenia selliformis from Patagonian waters of Chile

Northern Patagonia (41–44°S) is affected by climatic, hydrological and oceanographic anomalies, which in synergy with processes such as global warming and acidification of the coastal oceans may affect the frequency and intensity of harmful algal blooms (HABs). Greater frequency of HABs has been reported in the southeastern Pacific Ocean, including blooms of the toxic dinoflagellate Karenia selliformis, causing massive mortality of marine fauna in the oceanic and coastal areas of Patagonia. The objective of this study was to determine the effects of temperature and pH interaction on the growth of K. selliformis (strain CREAN_KS02), since these factors have wide seasonal fluctuations in the Patagonian fjord ecosystem. The CREAN_KS02 strain isolated from the Aysén Region (43°S) was used in a factorial experiment with five pH levels (7.0, 7.4, 7.7, 8.1 and 9.0) and two temperatures (12 and 17 °C) during a period of 18–21 days. Results indicated a significant effect of temperature and pH interaction on growth rate (range 0.22 ± 0.00 to 0.08 ± 0.01 d−1) and maximum density (range 13,710 ± 2,616 to 2,385 ± 809 cells mL−1) of K. selliformis. The highest density and growth of K. selliformis was found at 12 °C with a reduced pH (7.0–7.7). The results suggest that the current environmental conditions of coastal Patagonia, waters of low temperature and relatively low pH, may be favorable for the development of blooms of this species during autumn. We suggest that there is natural plasticity of K. selliformis in a wide pH range (7.0–8.1) but in a narrow low temperature range (10.6–12.9 °C), values that are typically recorded in the oceanic region of northern Patagonia. In contrast, in an extreme climate change scenario (ocean warming and coastal acidification) in northern Patagonia, a negative effect on the growth of K. selliformis may be expected due to amplification of the acidification effects caused by the thermal stress of high temperature water.

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Effects of global environmental change on microalgal photosynthesis, growth and their distribution

Global climate change (GCC) constitutes a complex challenge posing a serious threat to biodiversity and ecosystems in the next decades. There are several recent studies dealing with the potential effect of increased temperature, decrease of pH or shifts in salinity, as well as cascading events of GCC and their impact on human-environment systems. Microalgae as primary producers are a sensitive compartment of the marine ecosystems to all those changes. However, the potential consequences of these changes for marine microalgae have received relatively little attention and they are still not well understood. Thus, there is an urgent need to explore and understand the effects generated by multiple climatic changes on marine microalgae growth and biodiversity. Therefore, this review aimed to compare and contrast mechanisms that marine microalgae exhibit to directly respond to harsh conditions associated with GCC and the potential consequences of those changes in marine microalgal populations. Literature shows that microalgae responses to environmental stressors such as temperature were affected differently. A stress caused by salinity might slow down cell division, reduces size, ceases motility, and triggers palmelloid formation in microalgae community, but some of these changes are strongly species-specific. UV irradiance can potentially lead to an oxidative stress in microalgae, promoting the production of reactive oxygen species (ROS) or induce direct physical damage on microalgae, then inhibiting the growth of microalgae. Moreover, pH could impact many groups of microalgae being more tolerant of certain pH shifts, while others were sensitive to changes of just small units (such as coccolithophorids) and subsequently affect the species at a higher trophic level, but also total vertical carbon transport in oceans. Overall, this review highlights the importance of examining effects of multiple stressors, considering multiple responses to understand the complexity behind stressor interactions.

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Oregon shellfish farmers: perceptions of stressors, adaptive strategies, and policy linkages


  • Interviews were conducted with fifteen (79%) of oyster farmers in Oregon.
  • Farmers are most impacted by environmental, economic, and regulatory stressors.
  • Shellfish farmers had matching adaptive strategies to address these stressors.
  • Flexible aquaculture policies can help support these strategies.


In the United States, domestic oyster aquaculture production is insufficient to meet national demand, thus creating a reliance on international oyster imports for consumption. West coast shellfish farmers are threatened by climate change, including ocean acidification as well as socioeconomic challenges such as labor availability. To expand and enhance United States oyster production, and support domestic food security and livelihoods, a better understanding of the limitations that oyster farmers’ experience, and corresponding pathways forward for adaptation is needed. Through semi-structured interviews conducted with commercial Oregon shellfish farmers, we assess the environmental, economic, social and regulatory stressors impacting oyster growing operations, and the corresponding adaptive strategies employed or envisioned by aquaculture farmers. We find farmers are most impacted by environmental stressors (nuisance species that interact with oysters or oyster habitat negatively), followed by regulatory and economic stressors (permitting and regulations and labor availability). Farmers perceived ocean acidification as a risk, but primarily at the oyster larva stage rather than the juvenile or adult grow-out stage. Examples of farmer-identified adaptive strategies included streamlining permitting and regulations, incentivizing employee retention, and having flexibility in culture type to avoid nuisance species and other environmental stressors. An increase in targeted outreach related to aquaculture policies and engagement with industry, scientists, managers, and policy-makers could facilitate policies that support these and other adaptive strategies.

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Spatial distribution of seawater carbonate chemistry and hydrodynamic controls in a low-inflow estuary


  • Hydrodynamic exchange in low-inflow estuaries influences local carbonate chemistry.
  • Large tidal differences in alkalinity due to hypersaline conditions near bay head.
  • Flushing time largely explains spatial trends in carbonate chemistry.
  • Diel cycles and long flushing times minimized tidal differences in dissolved CO2.


Coastal and estuarine systems play an important role in the global carbon cycle and often have complex carbonate chemistry dynamics due to a multitude of biogeochemical and physical drivers. Compared to classic estuaries, mechanisms driving the distribution of carbonate parameters in low-inflow estuaries are understudied. The spatial distribution of carbonate chemistry and hydrodynamic parameters were characterized in Morro Bay, a short and seasonally hypersaline estuary on the Central California Coast, during the dry, low-inflow season to better understand in situ modifications. Sampling transects were completed in the main channel in June, August, and September of 2018, bracketing both a high and low tide on each date. Temperature, salinity, total alkalinity, and dissolved inorganic carbon all increased from the mouth to the back of the estuary, with larger values observed during the low tide. pH values decreased towards the back of the bay, and had little variation between high and low tide for June and August transects. Flushing times (estimated using a salt-budget model approach) also increased toward the back of the bay which led to hypersaline conditions. Salinity alone only explained 20–33% of observed changes in total alkalinity and 13–22% of observed changes in dissolved inorganic carbon throughout the bay. The remaining changes in total alkalinity and dissolved inorganic carbon were likely driven by biogeochemical modifications enhanced by extended flushing times, particularly in the back bay. Prior to this project, Morro Bay experienced a recent, rapid collapse of eelgrass, the major biogenic habitat. In the last four years eelgrass in Morro Bay appears to be on a recovery trajectory; therefore, this study provides a baseline whereby future studies can evaluate carbonate chemistry changes associated with potential eelgrass recovery and expansion. This study highlights the unique hydrodynamic exchange in seasonally low-inflow estuaries and its potentially large role in influencing local carbonate chemistry and ocean acidification.

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OA-ICC bibliographic database updated

An updated version of the OA-ICC bibliographic database is available online.

The database currently contains 10,040 references and includes citations, abstracts and assigned keywords. Updates are made every month.

The database is available as a group on Zotero. Subscribe online or, for a better user experience, download the Zotero desktop application and sync with the group OA-ICC in Zotero. Please see the “User instructions” for further details.

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Groundwater discharge and streams drive spatial alkalinity and pCO2 dynamics in two contrasting tropical lagoons

Coral reef lagoons are areas of complex carbon cycling, however, regional (e.g. land use) and global (e.g. climate) factors, including land runoff and ocean acidification, are adversely affecting carbonate-building coral reef systems. Coupled with this, surplus nutrients entering coastal waters can prompt excess algae growth, which can stimulate further carbon dioxide (CO2) production in the water column, thus enhancing coral/sediment dissolution. However, new inputs of alkalinity into coastal systems can buffer against acidification. By combining the natural groundwater tracer radon (222Rn) with carbonate chemistry in two contrasting Cook Island lagoons (the fringing Muri Lagoon on Rarotonga and the comparatively larger Aitutaki near-atoll lagoon), we were able to identify multiple drivers of coral reef acidification and regulation. Despite the lagoons having similar rates of submarine groundwater discharge (3.1 to 3.3 cm d−1; although the rate in Aitutaki is a maximum rate based on an assumed 100 m seepage face), groundwater inputs of CO2 and alkalinity were primarily driven by different sources (discrete offshore seeps in Muri Lagoon and dredged channels in Aitutaki Lagoon). Streams delivered low alkalinity water to both lagoons, but high pCO2 waters to the Aitutaki Lagoon in contrast to Muri Lagoon. Aragonite saturation states (ΩAr) ranged between 2.2 and 5.2, with areas of low ΩAr corresponding to areas of high radon and excess algal growth in Muri Lagoon, and areas that receive low alkalinity surface water in Aitutaki. Time-series sampling indicated that tidal heights and the ability of seawater to overtop the fringing reef influenced groundwater dynamics, lagoon hydrodynamics and carbonate chemistry. Groundwater discharge and stream flows were a significant freshwater source of new geologic CO2 and alkalinity to each lagoon, while recirculated seawater is likely a significant source of biologic CO2 driven by microbial respiration in sediments. The study found that while groundwater inputs of alkalinity may reduce acidification, they do not fully counteract ongoing acidification and CO2 inputs. This study also highlighted the need for future studies to undertake detailed spatial measurements to accurately characterise tropical island carbon dynamics due to the heterogeneous nature of these environments.

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Dissolved CO2 and oxygen dynamics on coral reefs: from natural variability and impacts on calcification to projections under warming

Coral reefs globally are facing impacts from ocean warming, acidification, and oxygen loss as a result of anthropogenic climate change. Understanding the spatiotemporal patterns of reef carbonate chemistry and oxygen variability, as well as how low pH or oxygen conditions might affect coral physiology, is key to predicting how global reefs will be impacted in the future. In this dissertation, I leveraged dissolved oxygen data from autonomous sensors deployed at 32 sites around the world to explore present-day oxygen variability and project changes in hypoxia exposure under modeled ocean warming. I show that hypoxia is pervasive on global coral reefs, with 84 % of the reef habitats surveyed experiencing weak to moderate hypoxia and 13 % experiencing severe hypoxia under present-day conditions. Calculations of reef oxygen loss under 5 warming scenarios reveal that warming will increase the duration, intensity, and severity of hypoxic events on reefs, leading to severely hypoxic conditions on more than a third of these reef habitats by 2100. In case studies of reefs in Bermuda and Taiwan, I examined multidimensional variability in carbonate chemistry and oxygen across a reef and assessed the potential for seagrass beds to serve as refugia for corals from ocean acidification and deoxygenation. In Bermuda, data from spatial seawater surveys and a suite of autonomous sensors at the surface and benthos revealed strong signals of both benthic and water column productivity that interacted with local geomorphology and hydrodynamics to create the observed patterns in carbonate chemistry and oxygen across the reef. In Taiwan, strong gradients in temperature, pH, and oxygen across the seagrass bed were associated with significant differences in coral skeletal extension rate, density, and ∂13C isotopic composition measured from coral cores. However, there was no evidence that the presence of seagrass significantly impacted coral calcification rates along this gradient. Altogether, this dissertation provides projections of coral reef oxygen loss under rapid climate change and highlights the contributions of local conditions to observed variability in seawater chemistry with complex impacts on coral growth.

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Proteomic and transcriptomic responses enable clams to correct the pH of calcifying fluids and sustain biomineralization in acidified environments

Seawater pH and carbonate saturation are predicted to decrease dramatically by the end of the century. This process, designated ocean acidification (OA), threatens economically and ecologically important marine calcifiers, including the northern quahog (Mercenaria mercenaria). While many studies have demonstrated the adverse impacts of OA on bivalves, much less is known about mechanisms of resilience and adaptive strategies. Here, we examined clam responses to OA by evaluating cellular (hemocyte activities) and molecular (high-throughput proteomics, RNASeq) changes in hemolymph and extrapallial fluid (EPF—the site of biomineralization located between the mantle and the shell) in M. mercenaria continuously exposed to acidified (pH ~7.3; pCO2 ~2700 ppm) and normal conditions (pH ~8.1; pCO2 ~600 ppm) for one year. The extracellular pH of EPF and hemolymph (~7.5) was significantly higher than that of the external acidified seawater (~7.3). Under OA conditions, granulocytes (a sub-population of hemocytes important for biomineralization) were able to increase intracellular pH (by 54% in EPF and 79% in hemolymph) and calcium content (by 56% in hemolymph). The increased pH of EPF and hemolymph from clams exposed to high pCO2 was associated with the overexpression of genes (at both the mRNA and protein levels) related to biomineralization, acid–base balance, and calcium homeostasis, suggesting that clams can use corrective mechanisms to mitigate the negative impact of OA.

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Combined effects of climate change stressors and predators with contrasting feeding-digestion strategies on a mussel species

Graphical abstract


  • Combined effects of climate change stressors and Predator Cues (PC) were evaluated.
  • Ocean Acidification (OA), Warming (OW) and PC affected mussel traits.
  • At the control temperature (15 °C), mussel byssal biogenesis increased with PC.
  • PC affected mussel size, wet mass and calcification rate.
  • The effects of starfish PC on some mussel traits were larger than those of snail PC.


We investigated the combined effects of Ocean Warming (OW), Acidification (OA) and predator cues (Non-Consumptive Effects; NCEs) of two predators with contrasting feeding-digestion strategies on the mussel Perumytilus purpuratus. We considered starfish-NCEs (partially external digestion) and snail-NCEs (internal digestion). Mussels were exposed for 13 weeks to cross-factored OA (~500 and ~1400 μatm, pCO2) and OW (~15 and ~20 °C) conditions, in the presence/absence of NCEs from one or both predators. Mussels exposed to both NCEs exhibited smaller length and buoyant weight growth than those under control or snail-NCEs conditions. Mussels exposed to starfish-NCEs exhibited smaller wet mass than control mussels. OW and starfish-NCEs in isolation or combined with snail-NCEs increased mussel oxygen consumption. Byssal biogenesis was affected by the three-factors interaction. Clearance rates were affected by the OW × OA interaction. We suggest that mainly starfish-NCEs, in isolation or interacting with OA or/and OW, can threat mussel traits and the associated community.

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Assessing annual nearshore carbonate chemistry trends in Alaska’s marginal seas

One of the consequences of anthropogenic carbon emissions is ocean acidification (OA). As atmospheric concentrations of carbon dioxide (CO₂) continue to rise, oceanic absorption of CO₂ changes the balance of dissolved inorganic carbon species (DIC) in seawater and alters marine carbonate chemistry. OA is predicted to be more pronounced in high-latitude environments, highlighting the importance of characterizing nearshore carbonate chemistry in polar and subpolar habitats, such as Alaska’s marginal seas. OA can have significant impacts on calcifying organisms (including pteropods, clams, mussels, and oysters), lowering the saturation of calcium carbonate minerals that are essential for shell formation in seawater. Despite the economic, subsistence, and cultural importance of vulnerable Alaskan marine biota, to date there are limited in situ data tracking the nearshore carbonate chemistry fluctuations of coastal Alaskan waters. To address this knowledge gap, this study’s research goal is to compare, in highfrequency resolution, the seasonal carbonate chemistry fluctuations in two representative nearshore Alaskan ecosystems: Kaktovik Lagoon (Arctic Ocean) and Kachemak Bay (Gulf of Alaska). Moored sensors detected pH, temperature, salinity, and O₂ data to characterize which physicochemical variables have the greatest average contributions to site-specific pH variability across one year (September 2018-August 2019) in these two regions. Analyses of the annual time series from both regions revealed interregional disparities, especially related to seasonality, biotic activity, and physicochemical fluctuations in the seawater. The pH dynamics of the Kachemak Bay mooring sites demonstrated a strong connection to a seasonal biotic signal, specifically through the push-pull effect of photosynthesis and respiration on DIC. Kaktovik’s pH dynamics suggested an interplay among salinity, biotic activity, and seasonal ice coverage. Both regions demonstrated high pH variability, with pH values shifting a maximum of 0.85 and 0.39 pH units over three hours in the two Kachemak Bay mooring sites, and 0.49 pH units over one hour in Kaktovik Lagoon. Forecast data for these regions project large declines in pH values over the coming century, with potentially deleterious impacts on local biota. Forecasted average monthly values based on 2018/2019 sampling reached pH < 7.5 for at least one month at all sites. Given the ocean change expectations for Alaskan marine environments, it is highly important that we establish seasonal carbonate chemistry baselines for Alaskan nearshore ecosystems.

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Elevated CO2 reduces copper accumulation and toxicity in the diatom Thalassiosira pseudonana

The projected ocean acidification (OA) associated with increasing atmospheric CO2 alters seawater chemistry and hence the bio-toxicity of metal ions. However, it is still unclear how OA might affect the long-term resilience of globally important marine microalgae to anthropogenic metal stress. To explore the effect of increasing pCO2 on copper metabolism in the diatom Thalassiosira pseudonana (CCMP 1335), we employed an integrated eco-physiological, analytical chemistry, and transcriptomic approach to clarify the effect of increasing pCO2 on copper metabolism of Thalassiosira pseudonana across different temporal (short-term vs. long-term) and spatial (indoor laboratory experiments vs. outdoor mesocosms experiments) scales. We found that increasing pCO2 (1,000 and 2,000 μatm) promoted growth and photosynthesis, but decreased copper accumulation and alleviated its bio-toxicity to T. pseudonana. Transcriptomics results indicated that T. pseudonana altered the copper detoxification strategy under OA by decreasing copper uptake and enhancing copper-thiol complexation and copper efflux. Biochemical analysis further showed that the activities of the antioxidant enzymes glutathione peroxidase (GPX), catalase (CAT), and phytochelatin synthetase (PCS) were enhanced to mitigate oxidative damage of copper stress under elevated CO2. Our results provide a basis for a better understanding of the bioremediation capacity of marine primary producers, which may have profound effect on the security of seafood quality and marine ecosystem sustainability under further climate change.

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Potential ecosystem regime shift resulting from elevated CO2 and inhibition of macroalgal recruitment by turf algae

Rising carbon dioxide (CO2) concentrations are predicted to cause an undesirable transition from macroalgae-dominant to turf algae-dominant ecosystems due to its effect on community structuring processes. As turf algae are more likely to proliferate due to the CO2 fertilization effect than macroalgae and often inhibit macroalgal recruitment, increased CO2 beyond certain levels may produce novel positive feedback loops that promote turf algae growth and thus can stabilize turf algae-dominant ecosystems. In this study, we built a simple competition model between macroalgae and turf algae in a homogeneous space to investigate the steady-state response of the ecosystem to changes in the partial pressure of CO2 (pCO2). We found that discontinuous regime shifts in response to pCO2 change can occur once turf algae coverage reaches a critical level capable of inhibiting macroalgal recruitment. The effect of localized turf algae density on the success rate of macroalgae recruitment was also investigated using a patch model that simulated a two-dimensional heterogeneous space. This suggested that in addition to the inhibitory effect by turf algae, a self-enhancing effect by macroalgae could also be important in predicting the potential discontinuous regime shifts in response to future pCO2 changes.

Continue reading ‘Potential ecosystem regime shift resulting from elevated CO2 and inhibition of macroalgal recruitment by turf algae’

Assessment of CO2 and O2 spatial variability in an indigenous aquaculture system for restoration impacts

Spatial variability in carbon dioxide (CO2) and oxygen (O2) was assessed within an Indigenous Hawaiian fishpond undergoing active ecosystem restoration. The brackish, tidal fishpond is located within Kāne‘ohe Bay, Hawai‘i. Following a year of monthly discrete sampling, a significant shift in DIC and percent O2 saturation was observed along the North-South axis within the pond. The south end of the pond was higher in DIC (+35 μmol·kg⁻¹) and lower in percent O2 saturation (-19%) than the north end, which exhibited values similar to those observed in water entering the fishpond from the bay. Water quality parameters and inequal proximity to water flux sites suggested that a difference in residence time may exist along the north-south axis. In addition, ΔTA/ΔDIC relationships revealed a respiration signal in south end of the pond, which was enhanced at depth. While physical processes strongly affect CO2 and O2 across various temporal scales, spatial patterns in biological processes may also affect variability within the fishpond. These findings demonstrate that changes in water chemistry within the fishpond are the result of ecosystem restoration efforts. In turn, future management decisions at the fishpond will play an important role in preserving its viability as a healthy habitat for the intended marine species.

Continue reading ‘Assessment of CO2 and O2 spatial variability in an indigenous aquaculture system for restoration impacts’

Clay-shielded estuarine gastropods are better protected against environmental acidification than unshielded individuals

Graphical abstract.


  • Acidified estuaries compromise building and threaten dissolution of gastropods shells.
  • Periostracum of Neripteron snails directs formation of an outer shell clay shield.
  • Shield constructed of the mineral illite is tightly chemically-bonded to the periostracum.
  • The more reflective unshielded shells showed a greater rate of dissolution.
  • Ecological and evolutionary constraints on carbonate shell building predict outer protection.


The effects of progressive global acidification on the shells of marine organisms is a topic of much current interest. Most studies on molluscan shell resistance to dissolution consider the carbonate mineral component, with less known about the protective role of the outer organic periostracum. Outer-shell resistance would seem especially important to gastropods living in carbonate-undersaturated and calcium-deficient estuarine waters that threaten shell dissolution and constrain CaCO3 production. We tested this prediction using gastropods from an acidified estuarine population (Neripteron violaceum) that form a clay shield outside the periostracum. Specifically, we aimed to show that the carbonate shell component lacks integrity, that the formation of the clay shield is directed by the organism, and that the clay shield functions to protect against shell dissolution. We found no evidence for any specific carbonate dissolution resistance strategy in the thin, predominantly aragonitic shells of these gastropods. Shield formation was directed by an ornamented periostracum which strongly bonded illite elements (e.g., Fe, Al and S), that become available through suspension in the water column. In unshielded individuals, CaCO3 erosion was initiated randomly across the shell (not age-related) and progressed rapidly when the periostracum was breached. A light reflectance technique showed qualitatively that shield consolidation is negatively-related to shell erosion. These findings support a conceptual framework for gastropod outer-shell responses to acidification that considers both environmental and evolutionary constraints on shell construction. We describe a novel strategy for shell protection against dissolution, highlighting the diversity of mechanisms available to gastropods facing extreme coastal acidification.

Continue reading ‘Clay-shielded estuarine gastropods are better protected against environmental acidification than unshielded individuals’

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