Feeding and Digestion in Suspension-Feeding Bivalve Molluscs: The Relevance of Physiological Compensations

Abstract

SYNOPSIS. Intertidal suspension-feeding bivalves face reductions in the time available for feeding proportional to the duration of aerial exposure. Such individuals do not compensate by increasing their rates of feeding during immersion. Simulations of feeding behaviour, in terms of the energetic balance between the costs and the gains of changes in feeding rate, suggest that variation from the rates characteristic of the sublittoral condition would not enhance net energy gain for intertidal individuals. These findings are consistent with evidence of potential food limitation in the natural sublittoral habitat. Nevertheless, hydrodynamic factors may enhance the supply of food on the shore, so ameliorating the disadvantages of reduced feeding time. In addition, potential physiological compensations for reduced dietary quality include changes in gut residence time, the volume of gut occupied for digestion and (possibly) also in the provision of appropriate digestive enzymes. However, these compensations require days or weeks and are inappropriate on tidal time scales.