Survival and growth performance of Crassostrea virginica along an estuarine gradient

Abstract

In Eastern Canada, an increasing number of pests, predators and pathogens in downriver areas (close to the ocean) have led the aquaculture industry to consider growing oysters in upriver areas (close to the river source). In this study, oyster growth performance was compared between downriver and upriver environments by means of stock transfer experiments within the Richibucto estuary. In May 2009, seed oysters (~26 mm shell height) originating from two downriver sites (salinity ~20–30 ‰) were transferred upriver (salinity ~5–20 ‰). Follow-up measurements in October 2009 revealed that the seed transferred upriver grew and survived as well as seed that remained downriver, while the mortality rates of adult oysters (shell height ~66 mm) were lower at the upriver site. Meat content was unaffected in adult oysters transferred upriver. However, there were indications that the upriver environment promoted shell growth (mm) in adult oysters. Oysters transferred upriver had a gain in shell height (LSM ± SE) over the oysters that remained downriver (2.7 ± 0.5 vs. 1.8 ± 0.5 mm) and in shell width [Median (95 % CI); 2.8 mm (1.9, 3.6) vs. 1.0 mm (0.3, 1.2)]. Therefore, the holding of adult oysters upriver during the spring–summer period confers productivity advantages on top of protection from diseases and predation. By contrast, productivity losses were recorded when relocating adult oysters originating from the upriver environment. More specifically, final organic meat content were approximately 35 % less in adult oysters transferred downriver compared to those that remained upriver (0.48 ± 0.04 vs. 0.74 ± 0.04 g). Results suggest that transfers along the river impact physiological processes such as gametogenesis and shell formation in adult oysters.