Posts Tagged 'mollusks'

Impact of climate change on direct and indirect species interactions

Recent marine climate change research has largely focused on the response of individual species to environmental changes including warming and acidification. The response of communities, driven by the direct effects of ocean change on individual species as well the cascade of indirect effects, has received far less study. We used several rocky intertidal species including crabs, whelks, juvenile abalone, and mussels to determine how feeding, growth, and interactions between species could be shifted by changing ocean conditions. Our 10 wk experiment revealed many complex outcomes which highlight the unpredictability of community-level responses. Contrary to our predictions, the largest impact of elevated CO2 was reduced crab feeding and survival, with a pH drop of 0.3 units. Surprisingly, whelks showed no response to higher temperatures or CO2 levels, while abalone shells grew 40% less under high CO2 conditions. Massive non-consumptive effects of crabs on whelks showed how important indirect effects can be in determining climate change responses. Predictions of species outcomes that account solely for physiological responses to climate change do not consider the potentially large role of indirect effects due to species interactions. For strongly linked species (e.g. predator-prey or competitor relationships), the indirect effects of climate change are much less known than direct effects, but may be far more powerful in reshaping future marine communities.

Continue reading ‘Impact of climate change on direct and indirect species interactions’

Effects of current and future coastal upwelling conditions on the fertilization success of the red abalone (Haliotis rufescens)

Acidification, deoxygenation, and warming are escalating changes in coastal waters throughout the world ocean, with potentially severe consequences for marine life and ocean-based economies. To examine the influence of these oceanographic changes on a key biological process, we measured the effects of current and expected future conditions in the California Current Large Marine Ecosystem on the fertilization success of the red abalone (Haliotis rufescens). Laboratory experiments were used to assess abalone fertilization success during simultaneous exposure to various levels of seawater pH (gradient from 7.95 to 7.2), dissolved oxygen (DO) ($60 and 180 mm. kg SW) and temperature (9, 13, and 18 C). Fertilization success declined continuously with decreasing pH but dropped precipitously below a threshold near pH 7.55 in cool (9 C—upwelling) to average (13 C) seawater temperatures. Variation in DO had a negligible effect on fertilization. In contrast, warmer waters (18 C) often associated with El Nino Southern Oscillation conditions in central California acted antagonistically with decreasing pH, largely reducing the strong negative influence below the pH threshold. Experimental approaches that examine the interactive effects of multiple environmental drivers and also strive to characterize the functional response of organisms along gradients in environmental change are becoming increasingly important in advancing our understanding of the real-world consequences of changing ocean conditions.

Continue reading ‘Effects of current and future coastal upwelling conditions on the fertilization success of the red abalone (Haliotis rufescens)’

Ocean acidification in the Baltic Sea : implications for the bivalve Macoma balthica

The Baltic Sea is one of the most human-impacted sea areas in the world and its ecosystems are exposed to a variety of stressors of anthropogenic origin. Large changes in the environmental conditions, species and communities of the Baltic Sea are predicted to occur due to global climate change, but the extent and magnitude of the future changes are challenging to estimate due to the multiple stressors simultaneously impacting the system. As an additional threat, future ocean acidification will play a role in modifying the environmental conditions, and these CO2-induced changes are predicted to be fast in the Baltic Sea. This is especially of concern for the species-poor, but functionally essential benthic communities where key species such as bivalve Macoma balthica live at the limits of their tolerance range, and are already regularly disturbed by environmental stressors such as hypoxia. Currently, only very limited knowledge about the effects of future ocean acidification exists for this species.

The overall aim of my thesis was to develop an understanding of the effects of CO2 increase on the vulnerability of Baltic Sea key species, and how this is related to other effects of climate change, e.g. an increase in bottom-water hypoxia. Specifically, I investigated how different life stages of the infaunal bivalve M. balthica could be affected by future ocean acidification. Survival, growth, behaviour and physiological responses were assessed in a combination of laboratory and mesocosm experiments by exposing different life stages of M. balthica to different pH levels over different time periods depending on the life stage in question. While some life stage-based differences in vulnerability and survival were found, the results indicate that reduced pH has a negative effect on all life stages. In larval M. balthica, even a slight pH decrease was found to cause significant negative changes during that delicate life stage, both by slowing growth and by decreasing survival. Other observed impacts included delayed settling of the post-larvae and increasing energetic demand of adult bivalves.

The results suggest consistent negative effects at all life stages with potential major implications for the resilience of M. Balthica populations, which are currently under threat from a range of anthropogenic stressors such as increasing hypoxia. The kind of experimental studies conducted in this thesis are useful for pinpointing mechanisms, but they are always simplifications of reality, however, and are usually conducted over time scales that are short in relation to the time scales over which ocean acidification is affecting populations, communities and ecosystems. To fully understand and to be able to estimate how the complex ecosystems are about to change in the future, incorporating more of the biotic interactions, impacting stressors and relevant environmental conditions are needed for increasing the level of realism in the experiments.

Continue reading ‘Ocean acidification in the Baltic Sea : implications for the bivalve Macoma balthica’

Soluble adenylyl cyclase mediates mitochondrial pathway of apoptosis and ATP metabolism in oyster Crassostrea gigas exposed to elevated CO2

Ocean acidification (OA) has deleterious impacts on immune response and energy homeostasis status of Mollusca. In the present study, the apoptosis ratio of hemocytes and the adenosine triphosphate (ATP) allocation in gill tissues were determined after Pacific oysters Crassostrea gigas were exposed to elevated CO2 environment (pH = 7.50) for 16 days. The apoptosis ratio in CO2 exposure group (35.2%) was significantly higher (p < 0.05) than that in the control group, and the increased apoptosis ratio induced by elevated CO2 could be significantly inhibited (p < 0.05) by KH7, a specific inhibitor of a bicarbonate sensor soluble adenylyl cyclase (sAC). After CO2 exposure, sAC in oyster (CgsAC) was found to be clustered with mitochondria in the cytoplasm, and the pro-caspase-3 was cleaved into two small fragments. Moreover, the activities of caspase-3 and caspase-9 also increased post CO2 exposure and these increases could be inhibited by KH7. However, the activities of caspase-8 did not change significantly compared with that in the control group. After CO2 exposure, the ATP content in the gill increased significantly (p < 0.05) and such increase could also be inhibited by KH7. The ATP content in purified gill mitochondria decreased significantly (p < 0.05) after CO2 exposure, which was also inhibited by KH7. These results implied that the elevated CO2 could activate the mitochondria-CgsAC pathway of apoptosis and ATP metabolism in oyster, and this pathway played essential roles in maintaining the homeostasis and the balance of energy metabolism in response to OA.

Continue reading ‘Soluble adenylyl cyclase mediates mitochondrial pathway of apoptosis and ATP metabolism in oyster Crassostrea gigas exposed to elevated CO2’

Naturally acidified habitat selects for ocean acidification–tolerant mussels

Ocean acidification severely affects bivalves, especially their larval stages. Consequently, the fate of this ecologically and economically important group depends on the capacity and rate of evolutionary adaptation to altered ocean carbonate chemistry. We document successful settlement of wild mussel larvae (Mytilus edulis) in a periodically CO2-enriched habitat. The larval fitness of the population originating from the CO2-enriched habitat was compared to the response of a population from a nonenriched habitat in a common garden experiment. The high CO2–adapted population showed higher fitness under elevated PCO2 (partial pressure of CO2) than the non-adapted cohort, demonstrating, for the first time, an evolutionary response of a natural mussel population to ocean acidification. To assess the rate of adaptation, we performed a selection experiment over three generations. CO2 tolerance differed substantially between the families within the F1 generation, and survival was drastically decreased in the highest, yet realistic, PCO2 treatment. Selection of CO2-tolerant F1 animals resulted in higher calcification performance of F2 larvae during early shell formation but did not improve overall survival. Our results thus reveal significant short-term selective responses of traits directly affected by ocean acidification and long-term adaptation potential in a key bivalve species. Because immediate response to selection did not directly translate into increased fitness, multigenerational studies need to take into consideration the multivariate nature of selection acting in natural habitats. Combinations of short-term selection with long-term adaptation in populations from CO2-enriched versus nonenriched natural habitats represent promising approaches for estimating adaptive potential of organisms facing global change.

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A carbonic anhydrase serves as an important acid-base regulator in Pacific oyster Crassostrea gigas exposed to elevated CO2: implication for physiological responses of mollusk to ocean acidification

Carbonic anhydrases (CAs) have been demonstrated to play an important role in acid-base regulation in vertebrates. However, the classification and modulatory function of CAs in marine invertebrates, especially their responses to ocean acidification remain largely unknown. Here, a cytosolic α-CA (designated as CgCAII-1) was characterized from Pacific oyster Crassostrea gigas and its molecular activities against CO2 exposure were investigated. CgCAII-1 possessed a conserved CA catalytic domain, with high similarity to invertebrate cytoplasmic or mitochondrial α-CAs. Recombinant CgCAII-1 could convert CO2 to HCO3− with calculated activity as 0.54 × 103 U/mg, which could be inhibited by acetazolamide (AZ). The mRNA transcripts of CgCAII-1 in muscle, mantle, hepatopancreas, gill, and hemocytes increased significantly after exposure to elevated CO2. CgCAII-1 could interact with the hemocyte membrane proteins and the distribution of CgCAII-1 protein became more concentrated and dense in gill and mantle under CO2 exposure. The intracellular pH (pHi) of hemocytes under CO2 exposure increased significantly (p < 0.05) and CA inhibition reduced the pHi value. Besides, there was no increase in CA activity in gill and mantle after CO2 exposure. The impact of CO2 exposure on CA activity coupled with the mRNA expression level and protein translocation of CgCAII-1 provided evidences that CgCAII-1 could respond to ocean acidification and participate in acid-base regulation. Such cytoplasmic CA-based physiological regulation mechanism might explain other physiological responses of marine organisms to OA.

Continue reading ‘A carbonic anhydrase serves as an important acid-base regulator in Pacific oyster Crassostrea gigas exposed to elevated CO2: implication for physiological responses of mollusk to ocean acidification’

Elevated temperature has adverse effects on GABA-mediated avoidance behaviour to sediment acidification in a wide-ranging marine bivalve

Sediment acidification is known to influence the burrowing behaviour of juvenile marine bivalves. Unlike the alteration of behaviour by ocean acidification (OA) observed in many marine organisms, this burrowing response to present-day variation in sediment pH is likely adaptive in that it allows these organisms to avoid shell dissolution and mortality. However, the consequences of global climate stressors on these burrowing responses have yet to be tested. Further, while neurotransmitter interference appears to be linked to the alteration of behaviour by OA in marine vertebrates, the mechanism(s) controlling the burrowing responses of juvenile bivalves in response to present-day variation in sediment acidification remain unknown. We tested the interactive effects of elevated seawater temperature and sediment acidification on juvenile soft-shell clam burrowing behaviour (measured as the proportion of clams burrowed into sediment) to test for effects of elevated temperature on bivalve burrowing responses to sediment acidification. We also examined whether GABAA-like receptor interference could act as a potential biological mechanism underpinning the burrowing responses of these clams to present-day variation in sediment acidification. Results showed that both elevated temperature and gabazine administration reduced the proportion of clams that avoided burrowing into low pH sediment. These results suggest that CO2 effects on neurophysiology (GABAA receptors) can act to mediate adaptive behaviours in juvenile marine bivalves to elevated CO2, but that these behaviours may be adversely affected by elevated temperature.

Continue reading ‘Elevated temperature has adverse effects on GABA-mediated avoidance behaviour to sediment acidification in a wide-ranging marine bivalve’


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Ocean acidification in the IPCC AR5 WG II

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