Posts Tagged 'mollusks'

Subtle effect of ocean acidification on the larval development of the Nudibranch aeolidiella glauca (Nudibranchia, Gastropoda)

The body of knowledge on ocean acidification gives a better understanding of biological sensitivity to low pH. Key parameters such as life-history strategies or local adaptation were identified as keys to predict species sensitivity and resolve previously some of the unexplained species- and population-specific differences. Encapsulation has been suggested as one of these keys as it exposed the embryo to low pH conditions, or ontogenetic hypercapnia, leading to physiological adaptation. We tested this hypothesis on the nudibranch Aeolidiella glauca by exposing their egg-strings containing large number of eggs to two different pH (8.1 and 7.3). The fertilized eggs developed 1 egg-cell, over early cleavage up to morula, blastula, gastrula, rhomboid-shaped rotating gastrula, early rotating veliger larvae with developed shell, to free-swimming well developed veliger larvae. Despite a corrosive environment, the exposure to low pH had no significant effect on the developmental rate. The only significant effects were a slightly smaller and narrower shell in larvae raised at low pH as compared to the high pH. Our results showed a remarkable resilient to low pH in a calcifying mollusc and support the idea that ontogenic hypercapnia is leading to low sensitivity to ocean acidification.

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Impact of ocean acidification on shells of the abalone species Haliotis diversicolor and Haliotis discus hannai

Ocean acidification (OA) results from the absorption of anthropogenic CO2 emissions by the ocean and threatens the survival of many marine calcareous organisms including molluscs. We studied OA effects on adult shells of the abalone species Haliotis diversicolor and Haliotis discus hannai that were exposed to three pCO2 conditions (ambient, ∼880, and ∼1600 μatm) for 1 year. Shell periostracum corrosion under OA was observed for both species. OA reduced shell hardness and altered the nacre ultrastructure in H. diversicolor, making its shells more vulnerable to crushing force. OA exposure did not reduce the shell hardness of H. discus hannai and did not alter nacre ultrastructure. However, the reduced calcification also decreased its resistance to crushing force. Sr/Ca in the shell increased with rising calcification rate. Mg/Ca increased upon OA exposure could be due to a complimentary mechanism of preventing shell hardness further reduced. The Na/Ca distribution between the aragonite and calcite of abalone shells was also changed by OA. In general, both abalone species are at a greater risk in a more acidified ocean. Their shells may not provide sufficient protection from predators or to transportation stress in aquaculture.

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Influence of seagrass on juvenile Pacific oyster growth in two US west coast estuaries with different environmental gradients

Ocean acidification threatens many marine organisms, including oysters. Seagrass habitat has been suggested as a potential refuge for oysters because it may ameliorate stressful carbonate chemistry and augment food availability. We conducted an in situ study to investigate whether eelgrass Zostera marina habitat affects the growth of juvenile Pacific oysters Crassostrea gigas and influences local carbonate chemistry or food quantity at sites where we expected contrasting conditions in two US west coast estuaries. Juvenile oysters were out-planted in typical intertidal on-bottom (just above sediment) and off-bottom (45 cm above sediment) culture positions and in adjacent eelgrass and unvegetated habitats from June to September 2019. Water quality was measured with sondes for 24 h periods each month, and discrete water samples were collected in conjuncture. Results show that eelgrass habitat did not alter average local carbonate chemistry (pH, pCO2, Ωcalcite), but consistently reduced available food (relative chlorophyll a). Eelgrass habitat had little to no effect on the shell or tissue growth of juvenile oysters but may have influenced their energy allocation; oysters displayed a 16% higher ratio of shell to tissue growth in eelgrass compared to unvegetated habitat when cultured on-bottom. At the seascape scale, average site-level pH was negatively correlated with shell to tissue growth but not with shell growth alone. Overall, these findings suggest that juvenile oysters may display a compensatory response and allocate more energy to shell than tissue growth under stressful conditions like acidic water and/or altered food supply due to reduced immersion or eelgrass presence.

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Energy metabolism of Mytilus galloprovincialis under low seawater pH (in Russian)

The problem of acidification of the World Ocean and predicting the consequences for its inhabitants is becoming more and more relevant every year. The effect of short-term pH fluctuations in coastal ecosystems on the physiology of calcifying organisms—bivalves—remains poorly understood. The energy metabolism of the Black Sea mussel Mytilus galloprovincialis was investigated for the marine environment in a wide pH range, from 8.2 to 6.65. Lowering the pH to 7.0–7.5 led to a 20–25 % reduction in oxygen consumption by molluscs. At lower pH (6.54–6.7), aerobic respiration sharply decreased by 85–90 %, down to the minimum values (2.12–2.62 µgO2 /g dry/h), and the organisms transitioned to anaerobic metabolism. The metabolic response of the mussels subjected to short-term pH changes (8.2→6.65→7.2) has been investigated. The oxygen consumption of molluscs exposed at the same pH of 7.2 depended on the direction of the change in pH. Thus, in the case of pH 6.65→7.2, the respiration intensity was 30 % higher compared to the values obtained under the acidification pH 8.2→7.2. The Black Sea mussel M. galloprovincialis is shown to have the capacity for survival in the marine environment characterized by the rapid fluctuations in pH that occur during the upwelling events in the coastal areas of the Black Sea.

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Seasonality of marine calcifiers in the northern Barents Sea: spatiotemporal distribution of planktonic foraminifers and shelled pteropods and their contribution to carbon dynamics


  • In the northern Barents Sea there is a seasonal pattern of production and size distribution of planktonic foraminifers and pteropods, increasing from winter (March) to summer (July–August) and late autumn (December).
  • In general, pteropods dominate over planktonic foraminifera in the Arctic influenced stations.
  • In the study area, pteropods contribute the most (>80%) to carbon standing stocks and export production.
  • The highest values of carbon standing stocks and export production were found in the seasonal ice zone during all seasons.


The Barents Sea is presently undergoing rapid warming and the sea-ice edge and the productive zones are retreating northward at accelerating rates. Planktonic foraminifers and shelled pteropods are ubiquitous marine calcifiers that play an important role in the carbon budget and being particularly sensitive to ocean biogeochemical changes and ocean acidification. Their distribution at high latitudes have rarely been studied, and usually only for the summer season. Here we present results of their distribution patterns in the upper 300 m in the water column (individuals m−3), protein content and size distribution on a seasonal basis to estimate their inorganic and organic carbon standing stocks (µg m−3) and export production (mg m−2 d−1). The study area constitutes a latitudinal transect in the northern Barents Sea from 76˚ N to 82˚ N including seven stations through both Atlantic, Arctic, and Polar surface water regimes and the marginal and seasonal sea-ice zones. The transect was sampled in 2019 (August and December) and 2021 (March, May, and July). The highest carbon standing stocks and export production were found at the Polar seasonally sea-ice covered shelf stations with the contribution from shelled pteropods being significantly higher than planktonic foraminifers during all seasons. We recorded the highest production of foraminifers and pteropods in summer (August 2019 and July 2021) and autumn (December 2019) followed by spring (May 2021), and the lowest in winter (March 2021).

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Differential reaction norms to ocean acidification in two oyster species from contrasting habitats

Ocean acidification (OA), a consequence of the increase in anthropogenic emissions of carbon dioxide, causes major changes in the chemistry of carbonates in the ocean with deleterious effects on calcifying organisms. The pH/pCO2 range to which species are exposed in nature is important to consider when interpreting the response of coastal organisms to OA. In this context, emerging approaches, which assess the reaction norms of organisms to a wide pH gradient, are improving our understanding of tolerance thresholds and acclimation potential to OA. In this study, we decipher the reaction norms of two oyster species living in contrasting habitats: the intertidal oyster Crassostrea gigas and the subtidal flat oyster Ostrea edulis, which are two economically and ecologically valuable species in temperate ecosystems. Six-month-old oysters of each species were exposed in common garden for 48 days to a pH gradient ranging from 7.7 to 6.4 (total scale). Both species are tolerant down to a pH of 6.6 with high plasticity in fitness-related traits such as survival and growth. However, oysters undergo remodelling of membrane fatty acids to cope with decreasing pH along with shell bleaching impairing shell integrity and consequently animal fitness. Finally, our work reveals species-specific physiological responses and highlights that intertidal C. gigas seems to have a better acclimation potential to rapid and extreme OA changes than O. edulis. Overall, our study provides important data about the phenotypic plasticity and its limits in two oyster species, which is essential for assessing the challenges posed to marine organisms by OA.

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Effects of pH and salinity on survival, growth, and enzyme activities in juveniles of the sunray surf clam (Mactra chinensis Philippi)


  • Salinity and pH tolerance ranges were identified for Mactra chinensis Philippi juveniles in laboratory tests.
  • Survival rates were significantly reduced at extreme pH and salinity.
  • Low pH and salinity induced oxidative stress, decreasing antioxidant enzyme activities.


The study investigated the impact of salinity and pH changes on the survival, growth, and antioxidant enzyme activity in Mactra chinensis Philippi (1.00 ± 0.10 cm shell length, 0.75±0.04 cm shell height), a marine clam species. Juveniles were exposed to various pH levels (5.4 – 9.6) and salinities (5 – 35 psu) for up to 20 days at 19 ± 0.5 ˚C. The individual effect of salinity and pH on juveniles were evaluated under pH 8.0 and salinity 30 psu, respectively. The results indicated that the highest survival rates were observed at pH 8.0 (85%, salinity = 30 psu) and salinity 30 psu (95%, pH = 8.0). The survival rates were significantly reduced at extreme pH (≤ 7.2; ≥ 8.4) and salinities (≤ 15; 35 psu). Additionally, oxidative stress was observed in clams exposed to low pH and salinity as indicated by the decreased activities of the antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD). Notably, no significant difference in relative growth rates was observed between salinity 25 and 30 psu, between pH 7.8/8.4 and pH 8.0. Our results provide information on potential impact of pH and salinity changes on economically important bivalve species and may be used to optimize pH and salinity in aquaculture.

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Effects of ocean acidification on Lottia scutum settlement

The effects of ocean acidification on calcifying marine organisms are becoming more pronounced as atmospheric CO2 levels have increased due to anthropogenic carbon emissions (Etheridge et al., 1996). Studies on these effects have also increased over time. Ocean acidification (OA) has been shown to affect the feeding behavior and metabolic rates of larvae in a number of species (Vargas et al., 2013; Pan et al., 2015). Metabolic changes can significantly influence developmental rates, but little is still known about consequences of OA for non-feeding marine invertebrate larvae. In this study, we focus on the effects of OA conditions on the larval stage of Lottia scutum, a Pacific rocky intertidal limpet species that ranges from Alaska to southern California. Larvae were exposed to OA conditions (pH 7.3) at competency stage and monitored for settlement behavior and metamorphosis. Our results indicate that L. scutum larvae were able to successfully settle in OA and ambient seawater treatments. We did not find a negative effect of the specific OA conditions used in this study on the settlement of L. scutum. These findings provide insight into how environmental stress might affect early life stages, as well as how marine invertebrate larvae from regularly low pH environments fare in OA conditions.

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Molecular responses in an Antarctic bivalve and an ascidian to ocean acidification


  • The non-calcifying species Cnemidocarpa verrucosa sp. A showed a greater number of differentially expressed genes than the calcifying Aequiyoldia eightsii.
  • The Ocean Acidification caused an upregulation of genes involved in the immune system and antioxidant response in the ascidian Cnemidocarpa verrucosa sp. A.
  • The abundance of the key marine organisms (such as Cnemidocarpa verrucosa), could be affected by Ocean Acidification if pH predictions for polar regions come true.
  • Contrary to expected, Ocean Acidification could not affect the mollusk Aequiyoldia eightsii compared to the non-calcifying species.


Southern Ocean organisms are considered particularly vulnerable to Ocean acidification (OA), as they inhabit cold waters where calcite-aragonite saturation states are naturally low. It is also generally assumed that OA would affect calcifying animals more than non-calcifying animals. In this context, we aimed to study the impact of reduced pH on both types of species: the ascidian Cnemidocarpa verrucosa sp. A, and the bivalve Aequiyoldia eightsii, from an Antarctic fjord. We used gene expression profiling and enzyme activity to study the responses of these two Antarctic benthic species to OA. We report the results of an experiment lasting 66 days, comparing the molecular mechanisms underlying responses under two pCO2 treatments (ambient and elevated pCO2). We observed 224 up-regulated and 111 down-regulated genes (FC ≥ 2; p-value ≤ 0.05) in the ascidian. In particular, the decrease in pH caused an upregulation of genes involved in the immune system and antioxidant response. While fewer differentially expressed (DE) genes were observed in the infaunal bivalve, 34 genes were up-regulated, and 69 genes were downregulated (FC ≥ 2; p-value ≤ 0.05) in response to OA. We found downregulated genes involved in the oxidoreductase pathway (such as glucose dehydrogenase and trimethyl lysine dioxygenase), while the heat shock protein 70 was up-regulated. This work addresses the effect of OA in two common, widely distributed Antarctic species, showing striking results. Our major finding highlights the impact of OA on the non-calcifying species, results that differ from the general trend, in which one remarks the higher impact on calcifying species. Our result proposes a deep discussion about the potential effect on non-calcifying species, such as ascidians, a diverse and abundant group, that form extended three-dimensional clusters in the shallow waters and shelf areas along the Southern Ocean.

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Physiological responses of scallops and mussels to environmental variability: implications for future shellfish aquaculture


  • High acclimatization capability in mussels and scallops
  • Growth rates, δ13C, δ15N, and shell strength differed between seasons and depths.
  • Mussels and scallops had higher growth rates at 5 m than 30 m.
  • Shell strength changed with depth in mussels but not in the scallops.
  • Differences in nutritional sources between depths are higher in winter than spring.


Puget Sound (Washington, USA) is a large estuary, known for its profitable shellfish aquaculture industry. However, in the past decade, scientists have observed strong acidification, hypoxia, and temperature anomalies in Puget Sound. These co-occurring environmental stressors are a threat to marine ecosystems and shellfish aquaculture. Our research assesses how environmental variability in Puget Sound impacts two ecologically and economically important bivalves, the purple-hinge rock scallop (Crassodoma gigantea) and Mediterranean mussel (Mytilus galloprovincialis). Our study examines the effect of depth and seasonality on the physiology of these two important bivalves to gain insight into ideal grow-out conditions in an aquaculture setting, improving the yield and quality of this sustainable protein source. To do this, we used Hood Canal (located in Puget Sound) as a natural multiple-stressor laboratory, which allowed us to study acclimatization capacity of shellfish in their natural habitat and provide the aquaculture industry information about differences in growth rate, shell strength, and nutritional sources across depths and seasons. Bivalves were outplanted at two depths (5 and 30 m) and collected after 3.5 and 7.5 months. To maximize mussel and scallop growth potential in an aquaculture setting, our results suggest outplanting at 5 m depth, with more favorable oxygen and pH levels. Mussel shell integrity can be improved by placing out at 5 m, regardless of season, however, there were no notable differences in shell strength between depths in scallops. For both species, δ13C values were lowest at 5 m in the winter and δ15N was highest at 30 m regardless of season. Puget Sound’s combination of naturally and anthropogenically acidified conditions is already proving to be a challenge for shellfish farmers. Our study provides crucial information to farmers to optimize aquaculture grow-out as we begin to navigate the impacts of climate change.

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From individual to ecosystem: multi-stressor effects of acidification and warming on the physiological responses of coastal marine invertebrates

Climate change is directly impacting the services humans derive from the sea at an accelerated rate. Ocean warming and acidification (i.e., a decrease in ocean pH) are leading to modifications in population sizes and ecosystem functioning. The observed shifts in these higher order processes are a direct result of individuals’ responses (i.e., physiology, including metabolism, growth, calcification, and survival) occurring within communities. Natural variation in past environmental exposure experienced by individuals may lead to greater population resilience, or it may push individuals past physiological thresholds leading to increased sensitivity and vulnerability to climate change. Thus, we need to determine how individual-level physiological responses to climate change scale up to influence marine ecosystems. Rocky intertidal habitats are an ideal study system for evaluating the relationships between individual physiological responses, ecosystem functioning, and climate change. Tide pools possess unique thermal and pH environments and can be monitored under natural conditions or manipulated with field-experiments over daily and seasonal time scales, creating natural “experimental mesocosms”. In addition, many species within rocky intertidal habitats are exposed to environmental conditions close to their tolerance limits, increasing their potential vulnerability to climate change. In Chapter 1, by utilizing the unique thermal environments of tide pools, I showed that across small spatial scales (pools), thermal history influences thermal sensitivity of marine invertebrates for short-term time intervals (1-week and 1-day) and that this relationship differs seasonally and between species with differing traits, including mobility. This suggests that variability in thermal responses among individuals may allow for a natural buffer at a population level in response to climate change. Multiple stressors may affect individuals independently or interactively, amplifying or mitigating effects. Thus, to determine the impacts of climate change, in Chapter 2, I used a 6-month long field manipulation of ocean warming and acidification in tide pools. I examined the combined effects of warming and acidification on the shell structure (shell thickness and corrosion) and functional properties (shell strength) of the ecologically critical species, the Pacific blue mussel (Mytilus trossulus). Acidification led to thinner, weaker, and more corroded shells whereas combined warming and acidification resulted in an increase in shell strength. My results suggest that to some degree, warming may mitigate the negative impacts of acidification on this mollusk species. Lastly, in Chapter 3, I characterize how warming and acidification, individually and interactively, impact net ecosystem calcification and the individual and population-level mechanisms driving impacts on net ecosystem calcification. Net ecosystem calcification tended to increase during the day and decrease at night; however, addition of CO2 during the hottest months led to decreased net ecosystem calcification and increased dissolution during both day and night. I found that individual mussel metabolic rates increased significantly in the presence of elevated CO2 and increased daily maximum of pool temperatures. Through this individual-level pathway, pH and temperature had a strong impact on the metabolic rates of individuals ultimately resulting in changes in net ecosystem calcification. On the other hand, greater mussel abundance was associated with increased net ecosystem calcification. Yet, with the addition of CO2, calcification decreased even in pools with the highest abundance of mussels, indicating that there are other pathways by which changes in pH can drive alterations in net ecosystem calcification. My dissertation reveals how species’ traits and natural thermal variation from short-term to seasonal time scales influence metabolic sensitivity to future warming among individuals (Ch. 1), independent climate stressors can negatively impact shellfish in situ, whereas the combined interactive effects between multiple stressors can lead to mitigation of the negative impacts of a single stressor alone (Ch. 2), and that ecosystem-level consequences of climate change are mediated by the abundance of dominant calcifiers and that this effect is dependent on the magnitude of acidification and warming (Ch. 3).

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Pacific oysters do not compensate growth retardation following extreme acidification events

Ocean acidification caused by anthropogenic carbon dioxide emissions alters the growth of marine calcifiers. Although the immediate effects of acidification from global ocean models have been well studied on calcifiers, their recovery capacity over a wide range of pH has never been evaluated. This aspect is crucial because acidification events that arise in coastal areas can far exceed global ocean predictions. However, such acidification events could occur transiently, allowing for recovery periods during which the effects on growth would be compensated, maintained or amplified. Here we evaluated the recovery capacity of a model calcifier, the Pacific oyster Crassostrea gigas. We exposed juveniles to 15 pH conditions between 6.4 and 7.8 for 14 days. Oyster growth was retarded below pH 7.1 while shells were corroded at pH 6.5. We then placed the oysters under ambient pH > 7.8 for 42 days. Growth retardation persisted at pH levels below pH 7.1 even after the stress was removed. However, despite persistent retardation, growth has resumed rapidly suggesting that the oysters can recover from extreme acidification. Yet we found that the differences in individual weight between pH conditions below 7.1 increased over time, and thus the growth retardation cannot be compensated and may affect the fitness of the bivalves.

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Short-term exposure to independent and combined acidification and warming elicits differential responses from two tropical seagrass-associated invertebrate grazers

Ocean acidification and warming could affect animal physiology, key trophic interactions and ecosystem functioning in the long term. This study investigates the effects of four pH−temperature combination treatments simulating ocean acidification (OA), ocean warming (OW) and combined OA and OW conditions (FUTURE) relative to ambient present-day conditions (PRESENT) on the grazing of the juveniles of two seagrass-associated invertebrates namely the sea cucumber Stichopus cf. horrens and topshell Trochus maculatus over a 5-day exposure period. Diel and feeding activity of both species increased under OW and FUTURE to some extent, while the nighttime activity of Trochus but not Stichopus decreased under OA relative to PRESENT during the first 2 days. Fecal production of Stichopus did not differ among treatments, while the lowest fecal production of Trochus was observed under OA during the first 24 h of grazing. These responses suggest that Trochus may be initially more sensitive to OA compared with Stichopus. Interestingly, fecal production of Trochus in FUTURE was significantly higher than OA, suggesting that warming may ameliorate the negative effect of acidification. Diel activity, feeding and fecal production after 5 days did not differ among treatments for both species, suggesting acclimation to the acute changes in temperature and pH after a few days, although Stichopus acclimated rapidly than Trochus. The ability of the two juvenile invertebrate grazers to rapidly acclimate to increased temperature and lowered pH conditions after short-term exposure may favor their survival under projected changes in ocean conditions.

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Using meta-analysis to explore the roles of global upwelling exposure and experimental design in bivalve responses to low pH


  • Meta-analysis was used to assess bivalve responses to low pH.
  • Strong upwelling regions may yield bivalves that are less sensitive to low pH.
  • Upwelling explains up to 49 % variability of bivalve metabolic responses to low pH.
  • Larger carbonate chemistry deltas in experiments yield stronger responses.


Low pH conditions, associated with ocean acidification, represent threats to many commercially and ecologically important organisms, including bivalves. However, there are knowledge gaps regarding factors explaining observed differences in biological responses to low pH in laboratory experiments. Specific sources of local adaptation such as upwelling exposure and the role of experimental design, such as carbonate chemistry parameter changes, should be considered. Linking upwelling exposure, as an individual oceanographic phenomenon, to responses measured in laboratory experiments may further our understanding of local adaptation to global change. Here, meta-analysis is used to test the hypotheses that upwelling exposure and experimental design affect outcomes of individual, laboratory-based studies that assess bivalve metabolic (clearance and respiration rate) responses to low pH. Results show that while bivalves generally decrease metabolic activity in response to low pH, upwelling exposure and experimental design can significantly impact outcomes. Bivalves from downwelling or weak upwelling areas decrease metabolic activity in response to low pH, but bivalves from strong upwelling areas increase or do not change metabolic activity in response to low pH. Furthermore, experimental temperature, exposure time and magnitude of the change in carbonate chemistry parameters all significantly affect outcomes. These results suggest that bivalves from strong upwelling areas may be less sensitive to low pH. This furthers our understanding of local adaptation to global change by demonstrating that upwelling alone can explain up to 49 % of the variability associated with bivalve metabolic responses to low pH. Furthermore, when interpreting outcomes of individual, laboratory experiments, scientists should be aware that higher temperatures, shorter exposure times and larger changes in carbonate chemistry parameters may increase the chance of suppressed metabolic activity.

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Estuarine shellfish and climate change

Over centuries, shellfish populations have directly and indirectly benefitted humans living in coastal communities by providing fisheries and ecosystem services. The naturally dynamic estuarine environment, home to many economically important shellfish populations is, however, also commonly subjected to anthropogenic pressure from exploitation, pollution, and the acceleration of climate change. Climate change alters the rate and direction of long-term biogeochemical change in the ocean, but also, in combination with large-scale climate oscillations and other factors, can modulate the frequency, persistence, and/or magnitude of extreme coastal events including estuarine heatwaves, coastal hypoxia, and coastal acidification. This chapter explores the dynamic variability of the estuarine environment and assesses the impacts of climate stressors in isolation and in combination with other climatic/anthropogenic stressors on estuarine shellfish species. Individually, warming temperatures can alter the rates of physiological processes and can result in changes in growth and reproduction, while extremes in temperature can elicit physiological stress, mortality, or even local extinctions. Range contractions or expansions resulting from shifts in temperature or salinity can have cascading effects on ecosystem functioning, as important functional roles associated with shellfish (i.e., suspension-feeding, habitat engineering, bioturbation, predation) are gained or lost. Since nearly all shellfish species produce calcified structures exposed to the external environment, increasing CO2 concentrations and extremes in CO2 can have negative consequences on calcification that may vary by life stage and may have fitness-related consequences. Low oxygen extremes, which may become more persistent or severe under warming temperatures, consistently yield negative effects on the growth, development, metabolism, reproduction, survival, and/or abundance of mollusks and crustaceans and, thus, can have disproportionate impacts on ecosystem functioning.Estuaries commonly host co-occurring extremes (e.g., hypoxia and acidification), forcing organisms to cope with multiple stressors. Multi-stressors, an emerging field of research, can have a range of additive, synergistic, and antagonistic effects on shellfish species, with additional stressors typically yielding more negative outcomes than single stressors. Still, there are many unknowns regarding the potential effects of climate change syndromes on coastal shellfish, particularly in dynamic estuarine environments, and examinations of the combined impacts of warming/hypoxia/acidification and/or harmful algal blooms have only just begun. Autonomous observing platforms and high-frequency sensor arrays are essential to generating long-term and fine-scale time series datasets to characterize the shifting biogeochemical patterns under climate change. It will also be critical to scale up physiological studies to assess impacts on populations, communities, and ecosystems. Finally, to protect and/or restore shellfish resources, continued collaboration between communities and researchers on adaptive strategies that mitigate harm to shellfish populations experiencing extremes in future change will be vital.

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Responses of marine macroalgae to climate change drivers

Climate changes are progressively altering global ocean environments, leading to ocean acidification and warming, marine heatwaves, deoxygenation, and enhanced exposure of UV radiations within upper mixing layers. Marine macroalgae are affected by these environmental changes in coastal waters, where changing magnitudes of these drivers are usually larger than in open oceans. While macroalgae have developed physiological mechanisms to cope with these stressors, their responses to or tolerances to these stressors are species-specific and spatiotemporally variable. Fleshy macroalgal species are commonly capable of tolerating moderate decline of pH and diel fluctuations of pH, and their growth and photosynthesis can be enhanced by elevated CO2 concentrations in seawater and in the air during emersion at low tides. However, macroalgal calcifiers are especially sensitive to ocean acidification, with their calcification being reduced, which exacerbates the harm of solar UV radiation due to thinned protective calcareous layers. Marine warming and heatwaves, however, may endanger most macroalgal species as their seasonality of life cycle is temperature-dependent. Macroalgae either distributed in upper or lower intertidal zones are susceptible to UV radiation, which may have negative, neutral, or beneficial effects on them, depending on the levels of UV and other factors. UV-A (315–400 nm) can stimulate the photosynthesis of macroalgae under low to moderate levels of solar radiation; however, UV-B (280–315 nm) mainly causes negative effects. While the combined effects of elevated temperature, CO2, and UV radiation have rarely been documented, exposures to marine heatwaves and high levels of UV can be fatal to microscopic stages of macroalgae. Apart from the species found in estuaries, the physiology and community structure of macroalgae can be influenced by reduced salinity and pH associated with rainfall and/or terrestrial runoffs. Nevertheless, reduced O2 availability associated with ocean deoxygenation and/or hypoxia, promoted by eutrophication and ocean warming, may favor macroalgal carbon fixation because of suppressed photorespiration due to reduced O2 vs. CO2 ratios, although little documentation exists to support this possibility. While macroscopic stages of macroalgae are resilient or even benefit from some of the drivers, their microscopic stages and/or juveniles are susceptible to ocean climate changes, and the sustainability of their life cycles is endangered. In this chapter, we review and analyze the responses of different macroalgal groups and different life cycle stages to climate change drivers individually and/or jointly based on the literature surveyed, along with perspectives for future studies on the multifaceted effects of ocean climate changes.

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A bone morphogenetic protein regulates the shell formation of Crassostrea gigas under ocean acidification

Bone morphogenetic proteins (BMPs) are key factors controlling osteoblast differentiation, which have been proved to be involved in the hard tissue formation of marine mollusks. In the present study, a member of BMPs gene (CgBMP7) was identified from Pacific oyster Crassostrea gigas (C. gigas) with the aim to understand its possible role in the regulation of shell formation under ocean acidification (OA) conditions. The open reading frame (ORF) of CgBMP7 was of 1254 bp encoding a polypeptide of 417 amino acids. The deduced amino acid sequence of CgBMP7 was comprised of one signal peptide, one prodomain and one TGF-β domain, which shared 21.69%-61.10% identities with those from other species. The mRNA transcript of CgBMP7 was ubiquitously expressed in all the tested tissues of adult oysters with a higher expression level in mantle, notably highest in the middle fold of the three folds of mantle. The expression level of bone morphogenetic protein type I receptor (CgBMPR1B) mRNA was also highest in the MF and up-regulated dramatically post recombinant BMP7 protein (rCgBMP7) stimulation. After the blockage of BMPR1B with inhibitor LDN193189 (LDN), the mRNA expression level and phosphorylation level of CgSmad1/5/8 in mantle were decreased, and the mRNA expression level of CgCaM and Cgengrailed-1 were down-regulated significantly. During the oysters were exposed to acidified seawater for weeks, the expression levels of CgBMP7, CgBMPR1B and CgSmad1/5/8 in the middle fold of mantle decreased significantly (p < 0.01) at the 4th week, and CgCaM and Cgengrailed-1 also exhibited the same variable expression patterns as CgBMP7. In addition, the growth of shell in the treatment group (pH 7.8) was slower than that in the control group (pH 8.1). These results collectively indicated that BMP7 was able to trigger the BMPR-Smad signaling pathway and involved in controlling the formation of oyster calcified shell under OA conditions.

Continue reading ‘A bone morphogenetic protein regulates the shell formation of Crassostrea gigas under ocean acidification’

Transcriptomic responses in the nervous system and correlated behavioural changes of a cephalopod exposed to ocean acidification

The nervous system is central to coordinating behavioural responses to environmental change, likely including ocean acidification (OA). However, a clear understanding of neurobiological responses to OA is lacking, especially for marine invertebrates. We evaluated the transcriptomic response of the central nervous system (CNS) and eyes of the two-toned pygmy squid ( Idiosepius pygmaeus ) to OA conditions, using a de novo transcriptome assembly created with long read PacBio ISO-sequencing data. We then correlated patterns of gene expression with CO treatment levels and OA-affected behaviours in the same individuals. OA induced transcriptomic responses within the nervous system related to various different types of neurotransmission, neuroplasticity, immune function and oxidative stress. These molecular changes may contribute to OA-induced behavioural changes, as suggested by correlations between gene expression profiles, CO treatment and OA-affected behaviours. This study provides the first molecular insights into the neurobiological effects of OA on a cephalopod and correlates molecular changes with whole animal behavioural responses, helping to bridge the gap in our knowledge between environmental change and animal responses.

Continue reading ‘Transcriptomic responses in the nervous system and correlated behavioural changes of a cephalopod exposed to ocean acidification’

Short-term exposure to combined condition of low salinity and pH affects ROS-mediated stress in disk abalone (Haliotis discus hannai)

Climate change due to global warming can alter the salinity and pH in aquatic ecosystems. Low salinity (LS) and ocean acidification (OA) are stressors involved in osmotic regulation and can alter the antioxidant capacity of the body. In this study, we observed Na+/K+-ATPase (NKA) expression and activity in disk abalone gill tissue and changes in hemolymph osmolarity in relation to osmotic regulation over a short period (5 days). To confirm the degree of oxidative stress caused by changes in salinity and pH, changes in H2O2 levels, reactive oxygen species (ROS) levels, antioxidant enzyme (superoxide dismutase [SOD] and catalase [CAT]) expression, and caspase-7 expression were investigated at the molecular level. The degree of DNA damage was evaluated using the comet assay. mRNA expression, activity of gill NKA, and osmolarity of the hemolymph were significantly decreased in the LS group. Nonetheless, no noteworthy distinction was observed in mRNA expression or NKA activity between the control group and OA group. Hemolymph H2O2 levels and mRNA expression of SOD, CAT, and caspase-7 were significantly higher under the LS + OA condition than under single conditions of LS and OA. Further, caspase-7 mRNA expression and DNA damage increased with increasing exposure time. The group exposed to LS + OA showed the highest levels of caspase-7 expression and DNA damage. These results indicate that a combination of low salinity and pH induces more stress than a single condition does. Unmanageable ROS-mediated stress caused by environmental changes can lead to cell death and DNA damage.

Continue reading ‘Short-term exposure to combined condition of low salinity and pH affects ROS-mediated stress in disk abalone (Haliotis discus hannai)’

Water quality and the CO2-carbonate system during the preconditioning of Pacific oyster (Crassostrea gigas) in a recirculating aquaculture system

The continued increase of the demand for seed of the Pacific oyster (Crassostrea gigas) has driven the aquaculture industry to produce land-based hatcheries using broodstock conditioning. This has led to the need to create closed systems to control the main factors involved in reproduction (temperature and food). Additionally, reproductive synchronization of broodstocks may be considered to ensure homogeneous maturation and spawning among the organisms. In this work, we synchronized the broodstock reproductive stage of Pacific oysters in a recirculating aquaculture system (RAS) using a “preconditioning” process and evaluated the effect of the water quality and the CO2-carbonate system on preconditioned broodstock. The oysters were kept at 12 °C for 45 days in a RAS containing a calcium reactor (C2) or without a calcium reactor (C1, control). Water quality parameters were measured daily, and the oyster’s condition and reproductive development were monitored using condition index, biometrics, and histology, on Days 0, 20, and 45. C1 and C2 systems kept the water quality within the ranges reported as favorable for bivalves. The calcium reactor kept the pH (8.03–8.10), alkalinity (200 mg/L as CaCO3), CO32− (≤ 80 µmol/kg), and Ω aragonite (≤ 1) closer to the ranges reported as optimal for bivalves. However, no significant differences were detected in the total weight and the condition index in C1 and C2. The preconditioning allowed to maintain the organisms in early reproductive development, allowing gametogenesis synchronization to start maturation.

Continue reading ‘Water quality and the CO2-carbonate system during the preconditioning of Pacific oyster (Crassostrea gigas) in a recirculating aquaculture system’

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