Observations on the food of Antedon bifida (Echinodermata: Crinoidea)

The gut contents of specimens of the temperate crinoid Antedon bifida (Pennant) were collected from Dalkey, County Dublin, at monthly intervals for 1 yr, and occasionally from other areas around the Irish coast. Quantitative analysis showed the main components to be detritus (65%), plankton (18%) and inorganic particles (17%). This composition was remarkably constant throughout the year and at all locations, the main variation being in the plankton which was at a minimum in February (4%) and reached a maximum in August (36%). Food particle collection appeared to be nonselective within the appropriate size group, the essential feature of a particle being that it would fit into the ambulacral groove. Fragile planktonic diatoms and dinoflagellates, which occurred in blooms in summer and autumn, were digested by A. bifida, but more robust diatoms passed intact through the gut. Histochemical investigations indicate that the bulk of the detritus is refractory, and it is suggested that its associated micro-flora and micro-fauna may be a major source of nutriment for this crinoid.