The effects of chronic habitat degradation on the physiology and metal accumulation of eastern oysters (Crassostrea virginica) in the Hudson Raritan Estuary

The Hudson Raritan Estuary (HRE) was once home an abundant population of the eastern oyster, Crassostrea virginica. Years of habitat degradation, via removal of habitat and shell substrate, overfishing of the population, and inputs of organic and inorganic contaminants, all led to the decline of this previous keystone species. The HRE today is a highly eutrophic environment, with increased sediment inputs, periods of low dissolved oxygen, algal blooms, and hotspots of contaminants throughout. The current study was designed to understand how a chronically degraded habitat, as is present in the HRE now, affects both juvenile and adult oyster physiology. There are three parts to this study: in the first, a large scale field transplant study was deployed to determine how juvenile oyster health and subcellular physiology are altered over a continuum of sites across the HRE, and if subcellular metal accumulation related to alterations in physiology. Using eight sites across the HRE, it was apparent that there are many site-specific factors that affect oyster physiology, and the synergistic effects of these abiotic and biotic factors together influence oyster physiology the most. There was no one factor that could be isolated as a key parameter to determine future oyster restoration. The second part used a field transplant study to examine the role of a degraded habitat on adult oysters and reproduction. Using Vitellogenin protein and energy expenditures to estimate oyster reproduction, it was seen that adult oysters respond much slower than juveniles and no differences were seen between highly degraded habitats and less degraded habitats. Thirdly, both juveniles and adults were observed to accumulate non-essential metals (Cd and Hg) in the field. In order to determine if metal accumulation is the sole cause of physiological alterations, a laboratory exposure was designed to determine if changes in subcellular physiology could be correlated specifically to subcellular accumulation of Cd or Hg, when no other abiotic factors are able to influence oyster health. It was observed that Cd accumulation lead to physiological changes, but Hg accumulation did not. Using this information about the site-specific nature of oyster physiology and how metal accumulation can alter physiology will allow researchers to choose future restoration sites and set up projects that will allow for maximum growth and survival.