PERCEPTION AND SELECTION OF MACROPHYTE DETRITAL FALLS BY THE BATHYAL ECHINOID STYLOCIDARIS-LINEATA

Many deep-sea animals are known to exploit patchy food resources such as animal carcasses and sunken plant remains, but the mechanisms by which such foods are located remain generally unknown. The bathyal echinoid Stylocidaris lineata is an omnivorous deposit feeder that ingests sediment, dead animal remains, seagrass blades, and macroalgae such as Sargassum spp. Using a submersible, we investigated the ability of urchins to locate and exploit large falls of detritus. Individuals quickly arrived at packets of Thalassia testudinum and Sargassum spp. placed on the bottom, and they preferred these food items significantly over inert controls. However, the echinoids demonstrated no significant tendency to move toward the scent of upstream T. testudinum, either in situ or in laboratory flume experiments. Individuals moved at net speeds up to 30 m day-1. The existing evidence suggests that S. lineata locate food by chance encounter, not distant chemoreception.