SHORT-TERM ADAPTATION OF DIGESTIVE PROCESSES IN THE COCKLE CERASTODERMA-EDULE EXPOSED TO DIFFERENT FOOD QUANTITY AND QUALITY

Feeding and digestive parameters were analysed in cockles Cerastoderma edule fed for 3 days on two foods of different qualities, both foods given in two different concentrations. With low quality food, gut cont ent was found to increase with ingestion rate. Such increased capacity of the gut to allocate food precludes negative effects upon throughpu t time, and so absorption efficiency remained nearly constant at the t wo food concentrations. With high quality food, gut content remained a t high constant values and consequently enhancement of food ingestion rate with a high food ration leads to a significant reduction in throu ghput time, resulting in lower absorption efficiencies. Significantly higher levels of amylases and cellulases have been found within the di gestive gland of cockles fed high quality diets. Coincidentally, absor ption of carbohydrates is increased and absorption of lipids decreased in such diets as compared to low quality diets. Implications of the p ositive correlation between digestive enzyme activity and food quality are discussed in relation to the role that both digestive investments and endogenous faecal losses play in digestive processes. Results obt ained in this study indicate that investments in the form of digestive enzymes are a key factor in the functional response of cockles to sho rt-term variations in the food regime.