Date of Award

Spring 2022

Project Type

Thesis

Program or Major

Biological Sciences

Degree Name

Master of Science

First Advisor

Bonnie Brown

Second Advisor

Elizabeth Harvey

Third Advisor

Raymond Grizzle

Abstract

Eastern oyster, Crassostrea virginica, populations have been declining steadily over the past several decades across the North American east coast. Great Bay Estuary (GBE), located in New Hampshire, is experiencing this loss and restoration efforts have been put into effect. This work addresses restoration needs by characterizing abundances of settled spat and two early stages of C. virginica, D-hinge and veliger, in GBE from June 2020 through November 2020. Abundances are compared based on the collection site and the physicochemical data recorded on each sampling date. It was found that there were no differences in larval abundance at different sites in GBE. Although physicochemical factors are known to play a role in larval abundance, very little significance was found, suggesting future study may need to be modified to include a broader range of sampling. This study indicates that both D-hinge, veliger, and spat settlement occur in GBE prior to the time when sampling traditionally has started (June), suggesting an earlier than previously thought first spawn of C. virginica in GBE. This finding can be used to enhance restoration efforts as it suggests that spat for restoration are present earlier in the season and that recruitment devices should be deployed before the previously thought first spawn of each season.

Disease analysis was performed on eastern oysters as diseases are currently contributing greatly to the decline of eastern oysters in GBE. Presence of Haplosporidium nelsoni and Perkinsus marinus, organisms that cause MSX and Dermo (respectively) was examined in the water column, and it was found there were no significant differences between abundances of these disease-causing organisms at oyster farms and oyster reefs. A molecular diagnostic test, QCPCR, was compared to histological classifications of MSX and Dermo and it was found that MSX could be identified and quantified as well using QCPCR as with histology, but work remains to be done on the Dermo method to improve accuracy. Both MSX and Dermo levels were compared in farmed and wild oysters (as farmed oysters are thought to be MSX-tolerant). This study showed that MSX levels were significantly lower in aquacultured oysters than wild oysters, but that Dermo levels were comparable between the two. Although there were varying levels of disease in eastern oysters in GBE (especially between wild and aquacultured oysters), similar amounts of the infectious agents were found throughout GBE waters, indicating that location does not have an impact on disease susceptibility.

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