2.2.4 Feeding

Bivalves are filter feeders and feed primarily on phytoplankton – microscopic plant life. In juveniles and adults, the ctenidia, or gills, are well developed and serve the dual purpose of feeding and respiration. The ctenidia are covered with cilia – tiny vibrating hairs – whose concerted and co-ordinated beat induces a current of water.

When resting on or in a substrate, water is drawn into the animal through the inhalant opening or the inhalant siphon, through the gills and then is returned to the surrounding water through the exhalant opening or siphon. The gills collect plankton and bind it to mucous. Strands of food-laden mucous are passed anteriorly by means of ciliary action along special grooves on the gills to the labial palps whose role is to assist in directing food into the mouth. Bivalves can exercise some selection of their food and periodically the palps reject small masses of food, pseudofaeces, that are expelled from the mantle cavity, often by the vigorous “clapping” together of the shell valves.
What constitutes optimum foods for bivalves remains largely unknown however phytoplankton undoubtedly forms the major portion of the diet. Other sources of food may be important such as fine particles of non-living organic material (detritus) along with associated bacteria and also dissolved organic material.