A comparison of growth and survival of subtidal Crassostrea virginica (Gmelin) in South Carolina salt marsh impoundments

Abstract

Four South Carolina salt marsh impoundments and their associated tidal creeks were assessed for the culture of subtidal Crassostrea virginica. The impoundments were chosen primarily for their diversity and ranged from old large impoundments with appreciable tidal exchange and surrounded by extensive low marsh, to new small impoundments with little tidal exchange and surrounded by maritime forest. Floating and bottom hardware cloth trays (1.22 × 0.61 × 0.14 m) each holding 200 seed oysters (initial length, y = 43.8 mm ) were placed at each location and sampled monthly for growth and survival. Coincidental monthly estimates of primary production ( 14C), phytoplankton concentrations and total organic carbon were performed. Ancillary data collected biweekly at all locations included standard hydrographic information (temperature, salinity, pH and turbidity) and nutrient determinations (nitrates, nitrites, orthophosphates and silicates). Results indicated that over a 6-month period (October–April) growth at all locations was significantly (α = 0.001) greater in ponds than in adjacent creeks and greater in floating than bottom trays. Growth means ranged from as little as 1.00 mm/month in the Wando River, to median values of approximately 2.25 mm/month in tidal creeks, to a relatively high growth rate of 3.11 mm/month in Blue Heron Pond (Kiawah Island). Survival was high in all areas ranging from 85.0% at Blue Heron Pond to 94.5% at Kiawah Creek. There was no significant difference in survival in comparisons among locations. A direct correlation of growth in oysters, primary production and phytoplankton biomass was established. This relationship was reiterated by indications of an inverse correlation between nutrient concentrations and growth.