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Abstract

The relationship between juvenile oysters (spat) and larvae are important in understanding the overall sustainability of oyster populations. In this project, spatial and temporal variability of eastern oyster (Crassostrea virginica) spat were assessed from 2017-2019 in the Mullica River and correlated to oyster larval samples. Oyster spat samples covered four sites in the Mullica River upstream from its mouth at the Great Bay estuary. Oyster spat were sampled biweekly in July and August from 2017-2019. Site and sampling date differences each year were analyzed using a two-factor ANOVA. Significance was determined by the Tukey pairwise comparisons with a 95% confidence. The sampling dates for each year showed significant variation, most years showing the highest spatfall in mid-July. Spatial variation showed the Akimbo site having significantly higher spatfall  for 2017 and 2018. In 2019, Swan Point (furthest upriver) and Fitney Bit (furthest downriver) showed significant differences in spatfall from central river sites French's Point and Akimbo. Plankton samples were obtained on similar spatial and temporal scales, and bivalve larvae from these samples were imaged under a polarized microscope. Bivalves were extracted from images using MATLAB software and sorted into groups representing small oyster larvae (D-stage), larger oysters (veligers) and non-oysters. We compared oyster larval abundance to the total spat settlement index each year for the most downstream site, Fitney Bit and saw strong correlations. Correlating oyster larvae with spatfall allows us to understand the interannual variability between life stages in oyster populations, which is important for managing this commercially important resource in the Mullica River. 

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