A study of the eastern oyster, Crassostrea virginica: (1) Dermo tolerance, survival, growth, condition and Hsp70 expression in different geographic stocks; (2) Heat tolerance and effects of sublethal heat shock on survival and Hsp70 expression of infected and uninfected oysters

The diseases Dermo and MSX have devastated Chesapeake Bay populations of the eastern oyster, Crassostrea virginica. The protozoan Perkinsus marinus, which causes Dermo, is particularly problematic since it persists over a wide range of salinities and temperatures. An objective of this dissertation was to determine whether specific wild oyster stocks had developed natural resistance to Dermo and if several parameters (survival, growth, condition and energy reserves) were associated with resistance. Another objective was to characterize heat shock protein (hsp70) expression in the eastern oyster. Heat shock proteins such as hsp70 protect organisms from thermal stress and other stressors, and this function may play an important role in disease resistance in oysters. In field trials a F0 Chesapeake Bay stock from Tangier Sound (CTS) survived similarly to a disease resistant hatchery strain (XB). A Louisiana stock was also resistant to Dermo, but not MSX. Despite high mortality, a disease-susceptible stock (CRB) reached market size the fastest. Growth and condition index varied between stocks, but did not reflect Dermo resistance. Energy reserves were affected strongly by season, but not disease or stock. Results imply that Dermo resistant strains could be developed from these stocks but criteria for optimal strain selection for aquaculture and restoration may be divergent. Mortalities of F1 oysters (CRB, CTS and XB) were similar to F0 parents, demonstrating a genetic basis to Dermo resistance. Total hsp70 did not correlate with seasonal temperatures, while hsp70 isoforms (hsp69 and hsp72) varied inversely across seasons. Hsp70 did not vary significantly between strains, indicating a stronger environmental influence on hsp70 expression. In lab experiments hsp70 in oyster gills was elevated greater than two weeks after a sub-lethal heat shock. Thermal tolerance, but not hsp70, varied between CTS and Louisiana oyster stocks. Heat shock protected oysters experimentally infected with P. marinus and non-infected oysters from lethal heat stress. Infection alone induced expression of hsp70. Observed inherent and induced differences in thermal tolerance suggest that both genotype and phenotype may be manipulated to improve survival in cultured bivalves. The implications of this research for bivalve aquaculture as well as areas for future research are discussed

Quantifying Spatial and Temporal Trends of Microplastic Pollution in Surface Water and in the Eastern Oyster Crassostrea virginica for a Dynamic Florida Estuary

Microplastics (MPs) are a ubiquitous pollutant, emphasizing the need to understand their abundance and the factors that influence these patterns around the globe. In a prior study, high numbers of MPs were found in surface waters and tissues of the oyster Crassostrea virginica collected from one location in the Indian River Lagoon (IRL, FL, USA). To better understand spatial and temporal variability of MPs throughout the IRL, for one year, monthly surface water samples were collected from 35 sites, while oysters were collected quarterly from 12 sites. Microscopy and ATR-FTIR were used to quantify MP. In total, 3755 MPs were found in 44% of water samples (mean density ± CI: 1.47 ± 0.09 MP/L). South IRL water had the most MPs, likely associated with proximity to urbanization, inlets (MP sinks) and tributaries (MP sources). MP (n = 3181) were found in 70% of examined C. virginica (n = 1402). Abundances of MP in oysters were lower in the spring and in north IRL. The overall mean abundance was 2.26 ± 0.16 MP/oyster, and the density was 2.43 ± 0.52 MP/g wet tissue weight. Our results provide a more complete picture of MPs in the IRL, a subtropical, shallow-water estuarine system