A planimetric study of the mean epithelial thickness (MET) of the molluscan digestive gland over the tidal cycle and under environmental stress conditions

Abstract

Thinning of the digestive epithelium of marine molluscs may provide an index of environmental stress. Variability in epithelial thickness, as a consequence of the large variety of environmental and populational variables which could affect MET (Mean Epithelial Thickness), may counter the value of the index. Variation in MET of the intertidal gastropod Littorina littorea (L.) has been studied under experimental tidal conditions and, based on published data, under natural tidal conditions in the bivalves Mercenaria mercenaria (L.) and Mytilus edulis L. using a planimetric method. We found no significant variation in MET in all cases. The present results are discussed in relation to those obtained with L. littorea experimentally exposed to Cd and which show a significant reduction in MET after long sublethal exposure periods. © 1990 Biologische Anstalt Helgoland.