Background: The diverse feeding habits of sea anemones have led them to be classified as opportunistic polyphagous predators. However, most studies have focused on the diet of temperate sea anemones, and little is known about the trophic ecology of tropical species and their role in tropical ecosystems. We studied the diet of the intertidal sea anemone Anthopleura nigrescens by examining the gut contents of specimens collected at two sites on Costa Rica’s Pacific coast, testing for differences in prey items captured between daytime and nighttime high tides.

Results: We found 25 prey items including: mollusks, crustaceans, annelids, insects and eggs. Juvenile bivalves, barnacle cyprids, and copepods were the main prey items. The anemones at Playa Dominical captured significantly more juvenile bivalves during nighttime high tides, and those at Mata de Limón captured more cyprids during daytime high tides.

Conclusions: This study shows that A. nigrescens is an opportunistic polyphagous predator, like most of its temperate counterparts.