Metabolic responses of the common mussel Mytilus edulis to hypoxia and anoxia

Chuang

Enviro Toxic and Chemistry

2005

Coupled respirometric and radiotracer techniques were applied to simultaneously measure the rates of oxygen and metal uptake in the green mussel Perna viridis. This was performed under different metabolic conditions by varying the ambient oxygen partial pressure (P(O2)), temperature, air exposure, and body size. When the mussels were tested under different hypoxic and anoxic conditions, Cd and Zn uptake decreased with decreasing P(O2), accompanied by a decrease in the ventilation activity of mussels. Significant reduction in metal uptake was observed at a P(O2) level of 3 kPa. Under anoxic conditions, the uptake of Cd and Zn was 1.6 to 2.7 times and 2.8 times, respectively, lower than those measured under normoxia. In contrast, both the absorption efficiencies of Cd and Zn and the oxygen extraction efficiency increased significantly with decreasing P(O2). There were significant correlations between the rates of Cd/Zn and O2 uptake by the mussels when quantified under various P(O2) levels. The uptake of Cd and Zn was temperature dependent and increased with temperature over a range of 15 to 30 degrees C. Significant correlations between the rates of Cd/Zn and O2 uptake were also found in the temperature experiments. With reimmersion of mussels after aerial exposure, the mussels experienced an apparent O2 debt. Metal uptake also increased within the first 15 min followed by gradual recovery to the control levels. Similarly, the quantified uptake rates of Zn were significantly correlated with the O2 uptake in experiments with different sizes of mussels. These results strongly suggest that Cd and Zn uptake are coupled with oxygen uptake in the mussels; thus, physiological processes need to be considered in studying metal accumulation.

Section: Resultssupporting

confidence: 87%

Metal and oxygen uptake in the green mussel Perna viridis under different metabolic conditions

Chuang

Enviro Toxic and Chemistry

2005

“…Effects of hypoxia through reduced growth and mortality of individual mussels had implications for the ecosystem level function of water column filtration and benthic-pelagic coupling. Decreased growth indicates that hypoxia suppressed productivity of mussels and inhibited energy transfer from the water column to the benthos at the individual level, as is expected by the negative correlation between DO concentration and feeding rate in Mytilus edulis (Wang and Widdows 1993). The overall result at the population level was that seven of the nine reefs (all but M and Q) showed no increase in average size over the hypoxic summer (Appendix B: Fig.…”

Section: Significance Of Hypoxia On Mussels: An Integrated Perspectivementioning

confidence: 81%

“…Reduced mussel growth due to hypoxia has not been detected prior to our study. This probably results from a reduction in feeding rates, which are negatively correlated with concentrations of dissolved oxygen in laboratory conditions (Wang and Widdows 1993).…”

Section: Impact Of Hypoxia On Musselsmentioning

confidence: 99%

Local Extinction of a Foundation Species in a Hypoxic Estuary: Integrating Individuals to Ecosystem

Altieri

Witman

2006

Ecology

We integrated across individual, population, community, and ecosystem levels to understand the impact of environmental stress by tracking the foundation species Mytilus edulis in the hypoxic estuary Narragansett Bay, Rhode Island, USA. Our initial surveys revealed that the mussels occurred in nine extensive (2-28 ha) dense (814-9943 individuals/m2) subtidal reefs that attracted a diverse suite of predators (sea stars, crabs, gastropods). Hypoxia occurred in the summer of 2001, and a mussel transplant experiment revealed overall reduced growth rates of individuals, and higher mortality rates among larger mussels. At the population level, large decreases in densities and cover of mussels were correlated with dissolved oxygen concentrations, leading to extinction at one site and reductions of over an order of magnitude at others. Within one year, seven of the eight remaining populations were edged to extinction, and the previously extinct population was recolonized. At the community level, a predator exclusion experiment indicated that predation was an unimportant source of mussel mortality during the hypoxic period, in part due to the emigration of sea stars, as predicted by the Consumer Stress Model. However, mussels were too intolerant to hypoxia to have a net benefit from the predation refuge. The seasonal (summer) occurrence of hypoxia allowed sea stars to return following a lag, as predicted by a stress return time model, and the resumption of predation contributed to the subsequent extinction of mussel populations. At the ecosystem level, the initial filtration rate of the mussel reefs was estimated at 134.6 x 10(6) m3/d, equivalent to filtering the volume of the bay 1.3 times during the 26-d average residence time. That function was reduced by >75% following hypoxia. The effect of hypoxia on each level of organization had consequences at others. For example, size-specific mortality and decreased growth of individuals, and reduced filtration capacity of reefs, indicated a loss of the ability of mussels to entrain planktonic productivity and potential to control future eutrophication and hypoxia. Our study quantified patterns of loss and identified pathways within an integrative framework of feedbacks, summarized in a conceptual model that is applicable to similar foundation species subjected to environmental stress.

“…Thus, it is possible that at pCO 2 [ 405 Pa, a downregulation of MO 2 may be encountered. During prolonged emersion or in a hypoxic/ anoxic environment, extracellular pCO 2 values in bivalve extracellular fluids rise and are coupled with decreases in pO 2 in the seawater encased by the closed shell valves (Famme 1980;Wang and Widdows 1993). Therefore, downregulation of energy demand and aerobic metabolism at very high pCO 2 may result from evolutionary adaptation of mussels to fluctuating pCO 2 in intertidal habitats.…”

Section: Discussionmentioning

confidence: 99%

Moderate seawater acidification does not elicit long-term metabolic depression in the blue mussel Mytilus edulis

2010

Marine organisms are exposed to increasingly acidic oceans, as a result of equilibration of surface ocean water with rising atmospheric CO 2 concentrations. In this study, we examined the physiological response of Mytilus edulis from the Baltic Sea, grown for 2 months at 4 seawater pCO 2 levels (39, 113, 243 and 405 Pa/385, 1,120, 2,400 and 4,000 latm). Shell and somatic growth, calcification, oxygen consumption and NH þ 4 excretion rates were measured in order to test the hypothesis whether exposure to elevated seawater pCO 2 is causally related to metabolic depression. During the experimental period, mussel shell mass and shell-free dry mass (SFDM) increased at least by a factor of two and three, respectively. However, shell length and shell mass growth decreased linearly with increasing pCO 2 by 6-20 and 10-34%, while SFDM growth was not significantly affected by hypercapnia. We observed a parabolic change in routine metabolic rates with increasing pCO 2 and the highest rates (?60%) at 243 Pa. NH þ 4 excretion rose linearly with increasing pCO 2 . Decreased O:N ratios at the highest seawater pCO 2 indicate enhanced protein metabolism which may contribute to intracellular pH regulation. We suggest that reduced shell growth under severe acidification is not caused by (global) metabolic depression but is potentially due to synergistic effects of increased cellular energy demand and nitrogen loss.