Effect of the Tidal Cycle on Lysosomal Membrane Stability in the Digestive Gland of Mya arenaria and Mytilus edulis L.

Abstract

For the correct use of a stress index in the assessment of disturbances due to pollution, it is indispensable to know whether the response investigated exhibits natural fluctuations which could subsequently bring biases to the interpretations. Stability of the lysosomal membrane was measured at short time intervals during two full tidal cycles in the digestive gland of Mytilus edulis L. and Mya arenaria. In both species, destabilisation of the lysosomal membrane was observed during emersion periods. There was no indication of membrane destabilisation in the soft-shelled clams when they were submerged. In mussels, the destabilisation of the lysosomal membrane was observed occasionally during the immersion period. Air exposure and the associated hypoxia appeared to be the factors explaining the lysosomal responses in these two species. The physiological importance of these findings seems closely linked to the role of lysosomes in the well known process of proteolysis via controlled autophagy and to phasic digestive rhythms, two strategies for a maximal utilisation of limited food resources during the tidal cycle. These results demonstrate for the first time to our knowledge, under natural conditions, the differences of lysosomal responses between two bivalve species inhabiting the intertidal zone. It appeared finally, that the infaunal bivalve M. arenaria is most suitable as a sentinel species when the lysosomal membrane destabilisation is chosen as a biomarker of stress in field conditions.