ALBERT

Description: Hypoxia often intensifies with rising dissolved CO2, but the concurrent effects of hypoxia and acidification on bivalves are largely unknown. In this study, immune responses of hemocytes in the mussel Mytilus coruscus were examined under six combinations of pH (7.3, 7.7 and 8.1) and dissolved oxygen (DO) concentrations (2 mg/ L, 6 mg/L) for 72 h. Generally, total hemocyte account, phagocytosis, esterase and lysosomal content were reduced under low DO and pH conditions, whereas hemocyte mortality and reactive oxygen species production increased under low DO and pH. Both hypoxia and low pH have negative effects on mussels, but the effects of pH are not as strong as DO. Moreover, significant interactions between DO and pH occurred. However, acidification generally doesn't aggravate the effects induced by hypoxia. Acidification and hypoxia may increase disease risk and impact the aquaculture of this species.

Description: Ocean acidification and hypoxia, both caused by anthropogenic activities, have showed deleterious impacts on marine animals. However, their combined effect on the mussel's defence to its predator has been poorly understood, which hinders us to understand the prey-predator interaction in marine environment. The thick shell mussel Mytilus coruscus and its predator, the Asian paddle crab Charybdis japonica were exposed to three pH levels (7.3, 7.7, 8.1) at two concentrations of dissolved oxygen (2.0 mg/L, 6.0 mg/L) seawater. The anti-predatory responses of mussels, in terms of byssus thread production were analysed after 72 h exposure. During the experiment, frequency of shedding stalks (mussels shed their byssal stalks to release themselves from attachment and allow locomotion) and number of byssus threads increased with time, were significantly reduced by hypoxia and low pH levels, and some interactions among time, predator, DO and pH were observed. As expected, the presence of the crab induced an anti-predator response in M. coruscus (significant increases in most tested parameters except the byssus thread length). Acidification and hypoxia significantly reduced byssus thread diamter at the end of the experiment, but not the byssus thread length. Cumulative byssus thread length and volume were significantly impaired by hypoxia and acidification. Our results highlight the significance of anti-predatory responses for adult mussel M. coruscus even under a stressful environment in which stress occurs through ocean acidification and hypoxia. By decreasing the strength of byssus attachment, the chance of being dislodged and consumed by crabs is likely increased. Our data suggest that there are changes in byssus production induced by hypoxia and acidification, which may affect predation rates on M. coruscus in the field.

Description: Anthropogenic CO2 emissions have caused seawater temperature elevation and ocean acidification. In view of both phenomena are occurring simultaneously, their combined effects on marine species must be experimentally evaluated. The purpose of this study was to estimate the combined effects of seawater acidification and temperature increase on the energy budget of the thick shell mussel Mytilus coruscus. Juvenile mussels were exposed to six combined treatments with three pH levels (8.1, 7.7 and 7.3) * two temperatures (25 °C and 30 °C) for 14 d. We found that clearance rates (CRs), food absorption efficiencies (AEs), respiration rates (RRs), ammonium excretion rates (ER), scope for growth (SFG) and O:N ratios were significantly reduced by elevated temperature sometimes during the whole experiments. Low pH showed significant negative effects on RR and ER, and significantly increased O:N ratios, but showed almost no effects on CR, AE and SFG of M. coruscus. Nevertheless, their interactive effects were observed in RR, ER and O:N ratios. PCA revealed positive relationships among most physiological indicators, especially between SFG and CR under normal temperatures compared to high temperatures. PCA also showed that the high RR was closely correlated to an increasing ER with increasing pH levels. These results suggest that physiological energetics of juvenile M. coruscus are able to acclimate to CO2 acidification with a little physiological effect, but not increased temperatures. Therefore, the negative effects of a temperature increase could potentially impact the ecophysiological responses of M. coruscus and have significant ecological consequences, mainly in those habitats where this species is dominant in terms of abundance and biomass.

Description: Hypoxia and ocean acidification are two consequences of anthropogenic activities. These global trends occur on top of natural variability. In environments such as estuarine areas, short-term acute pH and O2 fluctuations are occurring simultaneously. The present study tested the combined effects of short-term seawater acidification and hypoxia on the physiology and energy budget of the thick shell mussel Mytilus coruscus. Mussels were exposed for 72 h to six combined treatments with three pH levels (8.1, 7.7 and 7.3) and two dissolved oxygen (DO) levels (2 mg/L, 6 mg/L). Clearance rate (CR), food absorption efficiency (AE), respiration rate (RR), ammonium excretion rate (ER), O:N ratio and scope for growth (SFG) were significantly reduced, and faecal organic dry weight ratio (E) was significantly increased at low DO. Low pH did not lead to a reduced SFG. Interactive effects of pH and DO were observed for CR, E and RR. Principal component analysis (PCA) revealed positive relationships among most physiological indicators, especially between SFG and CR under normal DO conditions. These results demonstrate that Mytilus coruscus was sensitive to short-term (72 h) exposure to decreased O2 especially if combined with decreased pH levels. In conclusion, the short-term oxygen and pH variation significantly induced physiological changes of mussels with some interactive effects.

Description: Ocean acidification (OA) and hypoxic events are increasing worldwide problems, their interactive effects have not been well clarified, although their co-occurrence is prevalent. The East China Sea (the Yangtze River estuary area) suffers from not only coastal hypoxia but also pH fluctuation, representing an ideal study site to explore the combined effect of OA and hypoxia on marine bivalves. We experimentally evaluated the antioxidant response of the mussel Mytilus coruscus exposed to three pH levels (8.1, 7.7 and 7.3) at two dissolved oxygen (DO) levels (2.0 mg/L and 6.0 mg/L) for 72h. Activities of superoxide dismutase, catalase, glutathione peroxidase, acid phosphatase, and alkaline phosphatase and levels of malondialdehyde were measured in gills and hemolymph. All enzymatic activities in hemolymph and gills followed a similar pattern throughout the experiment duration. Generally, low DO showed greater effects on enzyme activities than elevated CO2. Significant interactions between DO, pH and time were only observed at superoxide dismutase and catalase in both tissues. PCA revealed positive relationships between most enzyme activities in both gills and hemolymph with the exception of alkaline phosphatase activity and the level of malondialdehyde in the hemolymph. Overall, our results suggested that decreased pH and low DO induced similar antioxidant responses in the hard shelled mussel, and showed an additive effect on most enzyme activities. The evaluation of multiple environmental stressors, a more realistic scenario than single ones, is crucial to predict the effect of future global changes on coastal species and our results supply some insights on the potential combined effects of reduced pH and DO on marine bivalves.

Description: Hypoxia and ocean acidification are two consequences of anthropogenic activities. These global trends occur on top of natural variability. In environments such as estuarine areas, short-term acute pH and O2 fluctuations are occurring simultaneously. The present study tested the combined effects of short-term seawater acidification and hypoxia on the physiology and energy budget of the thick shell mussel Mytilus coruscus. Mussels were exposed for 72 h to six combined treatments with three pH levels (8.1, 7.7 and 7.3) and two dissolved oxygen (DO) levels (2 mg L−1, 6 mg L−1). Clearance rate (CR), food absorption efficiency (AE), respiration rate (RR), ammonium excretion rate (ER), O:N ratio and scope for growth (SFG) were significantly reduced, and faecal organic dry weight ratio (E) was significantly increased at low DO. Low pH did not lead to a reduced SFG. Interactive effects of pH and DO were observed for CR, E and RR. Principal component analysis (PCA) revealed positive relationships among most physiological indicators, especially between SFG and CR under normal DO conditions. These results demonstrate that Mytilus coruscus was sensitive to short-term (72 h) exposure to decreased O2 especially if combined with decreased pH levels. In conclusion, the short-term oxygen and pH variation significantly induced physiological changes of mussels with some interactive effects.

Description: Ocean acidification (OA) and hypoxic events are increasing worldwide problems, their interactive effects have not been well clarified, although their co-occurrence is prevalent. The East China Sea (the Yangtze River estuary area) suffers from not only coastal hypoxia but also pH fluctuation, representing an ideal study site to explore the combined effect of OA and hypoxia on marine bivalves. We experimentally evaluated the antioxidant response of the mussel Mytilus coruscus exposed to three pH levels (8.1, 7.7 and 7.3) at two dissolved oxygen (DO) levels (2.0 mg L−1 and 6.0 mg L−1) for 72 h. Activities of superoxide dismutase, catalase, glutathione peroxidase, acid phosphatase, and alkaline phosphatase and levels of malondialdehyde were measured in gills and hemolymph. All enzymatic activities in hemolymph and gills followed a similar pattern throughout the experiment duration. Generally, low DO showed greater effects on enzyme activities than elevated CO2. Significant interactions between DO, pH and time were only observed at superoxide dismutase and catalase in both tissues. PCA revealed positive relationships between most enzyme activities in both gills and hemolymph with the exception of alkaline phosphatase activity and the level of malondialdehyde in the hemolymph. Overall, our results suggested that decreased pH and low DO induced similar antioxidant responses in the hard shelled mussel, and showed an additive effect on most enzyme activities. The evaluation of multiple environmental stressors, a more realistic scenario than single ones, is crucial to predict the effect of future global changes on coastal species and our results supply some insights on the potential combined effects of reduced pH and DO on marine bivalves.

Description: This study evaluated the combined effects of seawater pH decrease and temperature increase on the activity of antioxidant enzymes in the thick shell mussel Mytilus coruscus, an ecological and economic bivalve species widely distributed along the East China Sea. Mussels were exposed to three pH levels (8.1, 7.7 and 7.3) and two temperatures (25 °C and 30 °C) for 14 days. Activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione (GSH), acid phosphatase (ACP), alkaline phosphatase (AKP) and glutamic-pyruvic transaminase (GPT) were measured in gills and digestive glands after 1, 3, 7 and 14 days of exposure. All enzymatic activities were significantly impacted by pH, temperature. Enzymatic activities at the high temperature were significantly higher than those at the low temperature, and the mussels exposed to pH 7.3 showed significantly higher activities than those under higher pH condition for all enzymes except ACP. There was no interaction between temperature and pH in two third of the measured activities suggesting similar mode of action for both drivers. Interaction was only consistently significant for GPX. PCA revealed positive relationships between the measured biochemical indicators in both gills and digestive glands. Overall, our results suggest that decreased pH and increased temperature induce a similar anti-oxidative response in the thick shell mussel.

Description: Hypoxia often intensifies with rising dissolved CO2, but the concurrent effects of hypoxia and acidification on bivalves are largely unknown. In this study, immune responses of hemocytes in the mussel Mytilus coruscus were examined under six combinations of pH (7.3, 7.7 and 8.1) and dissolved oxygen (DO) concentrations (2 mg L− 1, 6 mg L− 1) for 72 h. Generally, total hemocyte account, phagocytosis, esterase and lysosomal content were reduced under low DO and pH conditions, whereas hemocyte mortality and reactive oxygen species production increased under low DO and pH. Both hypoxia and low pH have negative effects on mussels, but the effects of pH are not as strong as DO. Moreover, significant interactions between DO and pH occurred. However, acidification generally doesn't aggravate the effects induced by hypoxia. Acidification and hypoxia may increase disease risk and impact the aquaculture of this species.

Description: Ocean acidification and hypoxia, both caused by anthropogenic activities, have showed deleterious impacts on marine animals. However, their combined effect on the mussel's defence to its predator has been poorly understood, which hinders us to understand the prey–predator interaction in marine environment. The thick shell mussel Mytilus coruscus and its predator, the Asian paddle crab Charybdis japonica were exposed to three pH levels (7.3, 7.7, 8.1) at two concentrations of dissolved oxygen (2.0 mg L−1, 6.0 mg L−1) seawater. The anti-predatory responses of mussels, in terms of byssus thread production were analyzed after 72 h exposure. During the experiment, frequency of shedding stalks (mussels shed their byssal stalks to release themselves from attachment and allow locomotion) and number of byssus threads increased with time, were significantly reduced by hypoxia and low pH levels, and some interactions among time, predator, DO and pH were observed. As expected, the presence of the crab induced an anti-predator response in M. coruscus (significant increases in most tested parameters except the byssus thread length). Acidification and hypoxia significantly reduced byssus thread diamter at the end of the experiment, but not the byssus thread length. Cumulative byssus thread length and volume were significantly impaired by hypoxia and acidification. Our results highlight the significance of anti-predatory responses for adult mussel M. coruscus even under a stressful environment in which stress occurs through ocean acidification and hypoxia. By decreasing the strength of byssus attachment, the chance of being dislodged and consumed by crabs is likely increased. Our data suggest that there are changes in byssus production induced by hypoxia and acidification, which may affect predation rates on M. coruscus in the field.