TISSUE SPECIFIC RESPONSES OF THE ESTUARINE BIVALVE SPECIES CRASSOSTREA VIRGINICA AND GEUKENSIA DEMISSA TO HYPOXIA
1 online resource (133 pages) : PDF
University of North Carolina at Charlotte
Aquatic ecosystems are exposed to multiple stressors simultaneously. Many estuarine sites which show diurnal dissolved oxygen (DO) and pH fluctuations are also exposed to metals which can be toxic to marine organisms. Bivalve mollusks serve as good indicators of metal pollution and water quality parameters in estuarine ecosystems. In shallow-water coastal environments, DO levels can fluctuate diurnally or during low tide exposures between hypoxia and normoxia. Dissolved oxygen and pH shifts are important environmental variables in estuarine ecosystems that may contribute to oxidative stress and tissue injury, as well as affect microbial flora and bioavailability of metals. Therefore metal exposures can cause oxidative damage that may be exacerbated by hypoxia and pH. The overall purpose of our study is to investigate the effects of hypoxia on oxidative damage and antioxidant status, and consider the potential impacts on microbial flora and metal bioavailability in Eastern oysters, Crassostrea virginica and Atlantic ribbed marsh mussels, Geukensia demissa. It is known that oxidative stress caused by these environmental factors can affect the antioxidant status of the tissues in marine organisms. In this study, bivalves were exposed to different oxygen regimes using CO2 and N2 gas, and minisondes were used to record water quality parameters semi-continuously over the course of the exposures. Hepatopancreas tissues were dissected and used to measure total Glutathione as a marker of overall antioxidant status and Malondialdehyde concentration as a marker of tissue damage under various dissolved oxygen regimes. Bacterial concentrations were determined, and bacterial genomic techniques (ARISA - Automated Ribosomal Intergenic Spacer Analysis) were used to characterize microbial diversity in oyster hepatopancreas tissues. The study also included metal-contaminated sediment exposure under different dissolved oxygen regimes and metal concentrations were determined in gill and hepatopancreas tissues. Field samples were also collected from polluted and relatively clean sites and analyzed for tissue damage, antioxidant status, bacterial loads and tissue metal concentration. Differences in antioxidant and tissue damage levels in cyclic and continuous hypoxia treatments were observed, and the results indicate that reduced pH along with low DO was more damaging than low DO alone. These studies also suggest that low DO conditions can affect microbial concentrations and diversity as well as the metal bioavailability in bivalves. Increases in tissue metal concentrations were found in hypoxic regimes indicating that hypoxia plays a role in determining metal bioavailability and together these stressors can increase the susceptibility of these bivalves to oxidative stress. Species-and tissue-specific responses were observed in hypoxia as well as hypoxia combined with metal exposures. These differences emphasize the need for the use of multiple bioindicator species for overall habitat health assessment and to determine vulnerabilities of co-exisitng species. These studies suggest that the interactions between environmental stressors are important determinants of the health of bivalve populations in estuarine ecosystems.
Clinton, SandraClemens, MarkParrow, MatthewGagne, Sara
Thesis (Ph.D.)--University of North Carolina at Charlotte, 2015.
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