CONDITION INDEX OF THE EASTERN OYSTER, CRASSOSTREA VIRGINICA (GMELIN, 1791) IN SAPELO ISLAND GEORGIA-EFFECTS OF SITE, POSITION ON BED AND PEA CRAB PARASITISM

Abstract

The condition index (CI) is a tool that has been used to estimate the effect that different environmental factors have on oyster meat quality. The CI of oysters in five beds in Sapelo Island and the Doboy Sound (Georgia, United States) were calculated using three different methodologies. Values from each site were used to: (1) compare two sites located in relatively large systems (river/sound) and three sites in a small creek to test for differences due to system size and related nutrient availability; (2) determine the effect of a parasite, the pea crab (Pinnotheres spp.), on oyster CI; and (3) determine the effect of differential position of oysters on a bed, with respect to CI (oysters were collected from areas of the bed that are permanently submerged and areas with the longest dry periods between tidal cycles). With respect to the three analyses mentioned earlier, it was found that oyster CIs for sites in larger systems (river and sound sites) were significantly higher than those in sites with lower flux and width (creek sites) and that the presence of pea crabs as parasites can reduce CI by ~50%. In addition, no difference in CI was found between oysters collected from different positions in the oyster bed, indicating that the CI was not altered within a site from effects of exposure. This relatively unusual finding is discussed but suggests the robustness of CI as an intersite analysis tool. Not all differences found in the comparisons were significant for all CIs used, but qualitative results among them were consistent. These variations in significance and the adequacy of each method for analysis are briefly discussed.