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Date of Graduation
Master of Science (MS)
Department of Biology
The eastern oyster, Crassostrea virginica, is a keystone species that has undergone a large (> 95%) population decline due to overharvest, pollution, and disease. Restoration efforts focus on alternative larval attachment substrates such as concrete, to supplement the loss of natural oyster shell. Magnesium is a component of bivalve shells and its presence in the environment has shown to be important to the growth of mussels, but the same relationship has not been studied in oysters. Assuming that magnesium can be assimilated from the substrate on which the organism is growing, or that ions of magnesium are leached into the water, magnesium supplements to concrete could have a similar benefit. Supplements in the form of magnesium carbonate can be incorporated into cement. A site in the northern neck of the Chesapeake Bay was used to test the effect of different artificial substrates (natural shell, concrete, and concrete enriched with magnesium carbonate) on mortality, growth, and recruitment exhibited by larval oysters and spat. Shell substrate types were tested for their effects on water chemistry in aquaria over the course of 8 weeks to understand the potential for leeching of nutrients into the environment. Spat on magnesium enriched substrates were not found to have a significant statistical difference from other spat for mortality, growth, or recruitment after running Kruskal-Wallis, ANOVA, and Poisson ANOVA analyses respectively (all p val > 0.05). Magnesium supplemented shells in aquaria impacted the pH (-0.14 pH units), alkalinity (+9 ppm CaCO₃), and magnesium (+36 ppm) concentrations in water chemistry over 8 weeks. Spat on all substrates were found to have grown to average sizes larger than expected for the region of the Chesapeake the study was conducted (33-37 mm compared to 24 mm in previous observations), but within the range of growth seen throughout the entire Bay. Although magnesium enriched substrates did not have a significant impact on oysters’ recruitment, growth, and survival relative to other substrates, spat did show higher recruitment and growth, and lower mortality than spat attached to concrete, indicating potential biological significance. The potential exists that higher concentrations of magnesium incorporation into artificial substrates could have a greater impact on attached spat and should be examined in future research.
Elder, Matthew, "Efficacy of magnesium enriched artificial substrate for oyster restoration" (2018). Masters Theses. 574.