Date Awarded


Document Type


Degree Name

Master of Science (M.Sc.)


Virginia Institute of Marine Science


Ryan B. Carnegie

Committee Member

Andrew R. Wargo

Committee Member

Roger Mann

Committee Member

David Bushek


The Chesapeake Bay region values oysters for the ecosystem services, lucrative fishery, and historical significance that the species embodies; however, over the last half century, oyster abundances have been reduced to historical lows. Two protozoan parasites, Perkinsus marinus and Haplosporidium nelsoni, have been major influences on oyster populations, especially in high-salinity regions. Today, the population is recovering; catches have increased and oysters have expanded spatially. to investigate the cause of the recovery, three measurements were made on slides of oysters from a histological archive collected during summer at Wreck Shoal in the James River from 1988–2017: oocyte diameter, oocyte density, and gonad area fraction. Gametogenic investment served as a proxy for the fitness of oysters; it was hypothesized that an outbreak of P. marinus in the 2000s led to a tolerance response that can be detected as an increase in reproduction. Oocyte diameter has remained variable yet steady overall, except for a decrease in 2001 and 2002. Oocyte density and gonad area fraction increased sharply around 2003. Mean oocyte densities increased by a factor of 2.05 and gonad area fraction by a factor of 2.04. Oocyte density has been maintained at these higher counts in recent years. The increase in gonadal area ratio is presently decreasing slowly yet significantly (p=0.00429). The cause of the increase is still not well understood, as a variety of environmental variables were significant predictors of reproduction as well as the hypothesized cause, P. marinus weighted prevalence. Regardless of the cause, changes in reproductive patterns signify a positive change on the part of the oyster. The ability of the wild oyster population to adapt supports management strategies that protect old oysters, like sanctuaries and slot fisheries. These strategies allow fit oysters to grow to old age and pass on their beneficial traits to future generations. in the face of doubts about the efficacy of restoration, conservation emerges as a path forward.



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