EXPLORING LARVAL SETTLEMENT OF THE EASTERN OYSTER (CRASSOSTREA VIRGINICA) IN ATLANTIC CANADA

Abstract

An ongoing issue for the Nova Scotia oyster aquaculture industry is the lack of reliable seed sources, which primarily relies on collecting wild seed. This thesis focuses on understanding and predicting the timing of settlement of the eastern oyster Crassostrea virginica in response to environmental drivers, which aims to help farmers and managers optimize spat collection and plan for future climate scenarios. The Growing Degree Day (GDD) framework is used to leverage the dominant effect of temperature on larval development and predict the timing of settlement. The model is calibrated with existing literature data and validated with field data collected from June to September 2022 across four estuaries in Nova Scotia. The validated GDD model could be implemented as an operational tool for farmers as the only required input is temperature, which is often already being monitored. Expanding upon the GDD model, temperature predictions from a regional climate model are incorporated to simulate conditions from three distinct timeframes: Past (1991-1995, Present (2021-2025), and Future (2051-2055). Findings suggest that rising ocean temperatures may lead to habitat expansion and earlier settlement for C. virginica in Atlantic Canada. However, the asynchronous phenological shift between oyster larvae and their food resources, represented by Chlorophyll-a, indicates a potential trophic mismatch that could pose challenges for predicting settlement. Outcomes from this research reaffirm our understanding of major biological drivers such as temperature and highlight avenues for further investigation of causal relationships associated with other environmental parameters, particularly potential trophic mismatch between larval presence and food availability.