Diet and feeding behaviour of the sea cucumber Cucumaria frondosa in the St Lawrence estuary, eastern Canada

Combined laboratory and field experiments showed that sea cucumbers (Cucuma ria frondosa) from. the St. Lawrence estuary in eastern Canada have well-de fined feeding cycles with marked seasonal and tidal variations. Typical fee ding behaviour involved extension of the tentacles, which were then success ively introduced into the oral cavity. Field observations and analysis of i ntestinal contents and indices demonstrated that C. frondosa fed mainly dur ing spring and summer. Their diet comprised an abundance of phytoplanktonic cells (Coscinodiscus centralis, Chaetoceros debilis, Skeletonema costatum, and Thalassiosira gravida), with occasional ingestion of small crustaceans and a variety of eggs and larvae. Food types found in the digestive tract were closely related to the periodic abundance of plankton species in the w ater. Fewer individuals were observed feeding during fall and winter; they mostly ingested nonliving particles and the intestinal indices were low. In field populations, feeding rates were highest during ebb and rising tides, whereas under laboratory conditions without tidal variation, individuals s howed no distinct feeding periods. However, individuals maintained under la boratory conditions and periodically provided with phytoplanktonic cells de monstrated a strong ability to detect the food in the water and react accor dingly by extending their tentacles and beginning to feed. The results of t he study suggest that food availability, rather than physical parameters su ch as temperature or current, best explains the cyclic feeding behaviour of C. frondosa at seasonal and tidal scales.