Feeding and digestion in two intertidal gammarids: Marinogammarus obtusatus and M. pirloti

The diet of two intertidal species of gammarid, Marinogammarus obtusatus Dahl and M. pirloti Sexton and Spooner is described. Both species feed largely, but not exclusively, on decaying algae, but may eat some living algae and, more rarely, carrion. Their feeding activities are influenced by the rhythmic pattern of tidal ebb and flow, feeding only when covered by water. When immersed by the incoming tide they ingest food rapidly for a while and then feed more intermittently, ingesting small amounts at a time until they are uncovered once more by the receding tide. They probably eat sufficient food to fill the gut twice in 24 hours. The optimum rate for the digestion of food is approximately five hours, although food remains in the gut for about 12 hours. The pH of the contents of the proventriculus, digestive gland and intestine of M. obtusatus is distinctly acid. Digestive enzymes are secreted only by the digestive gland. Carbohydrases are present which will hydrolyse soluble starch, glycogen, sucrose, maltose, arbutin, salicin, raffinose and melibiose. Inulin, lactose and cellulose are not hydrolysed. Non‐specific esterase and true lipase were detected by histochemical methods. It is concluded that the food supply available to these animals is plentiful and it is unnecessary to utilize the food supply to the maximum.