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

Abstract

Combined laboratory and field experiments showed that sea cucumbers (Cucumaria frondosa) from the St. Lawrence estuary in eastern Canada have well-defined feeding cycles with marked seasonal and tidal variations. Typical feeding behaviour involved extension of the tentacles, which were then successively introduced into the oral cavity. Field observations and analysis of intestinal contents and indices demonstrated that C. frondosa fed mainly during 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 water. 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 showed no distinct feeding periods. However, individuals maintained under laboratory conditions and periodically provided with phytoplanktonic cells demonstrated a strong ability to detect the food in the water and react accordingly by extending their tentacles and beginning to feed. The results of the study suggest that food availability, rather than physical parameters such as temperature or current, best explains the cyclic feeding behaviour of C.frondosa at seasonal and tidal scales.