Variations in pallial organs and eulatero-frontal cirri in response to high particulate matter concentrations in the oyster Crassostrea gigas

Abstract

Variations in gill, palp, and adductor muscle areas and in the length and spacing of eulatero-frontal cirri (EFC) were investigated in specimens of the Japanese oyster (Crassostrea gigas) within the same bay in two nearby sites (15 km) differing in turbidity. Significant variations occurred on a small geographical scale. In particular, individuals from the higher turbidity zone had smaller gills and larger labial palps. For a standard oyster (1 g dry body weight), gill area was 25% larger in oysters from the low-turbidity zone, while palp area was 66% larger in oysters from the high-turbidity zone. No difference was observed for total adductor muscle area. Intersite differences in the mean length of EFC and in the distance between two adjacent cirri sampled on ordinary filaments in the midregion of the gill were studied by image analysis. Cirri tended to be longer and more evenly spaced in oysters from the higher turbidity zone, although differences were not significant at the 5% probability level. The geometric characteristics of the EFC were apparently not modified in response to high turbidity, although the wide individual variability observed may have prevented detection of ciliary adaptation.