Environmental factors influencing annual Eastern oyster (Crassostrea virginica) spatfall in the Mullica River

Understanding relationships between water quality and marine organisms is important for understanding how these populations respond to environmental changes. The eastern oyster (Crassostrea virginica) goes through a larval and juvenile stage before reaching maturity. The juvenile or “spat” phase occurs as larvae from the water column settle onto a hard substrate and become fixed. The settlement of spat is affected by biotic and abiotic factors such as temperature and salinity. We compared these factors to annual spat settlement and recruitment indexes over a six year period (2014-2020). Indexes were calculated from biweekly spat bags (settlement) as well as seasonal bags (recruitment) from 10 sites within the Mullica River. Spat bags were deployed from June to September each year. Water quality data was obtained from the Chestnut Neck monitoring station within the Jacques Cousteau National Estuarine Research Reserve System (JCNERRS) and averaged monthly and daily from May to September each year. We compared the water quality data to the settlement and recruitment indexes using a multiple regression. It was determined that the spat index was not affected by salinity, however it was negatively affected by May temperature and positively affected July and August temperature. The seasonal recruitment index was similarly negatively affected by May temperature and positively influenced by June and August temperatures. Recruitment indexes additionally were negatively affected by July temperature and salinity. This suggests that temperature has a stronger influence over salinity in affecting oyster population dynamics in the Mullica River through interannual variations in spatfall.