Echinoderms in an anchialine cave in Mexico

Abstract

Five surveys in an anchialine cave from Cozumel Island, Mexico, were made in order to determine the diversity of invertebrates, especially of the phylum Echinodermata. Aerolito sinkhole (cenote), with an open coastal waters connection, was explored and the organisms were sampled by hand. The abiotic parameters (conductivity, salinity, oxygen, temperature, light and pH) were also measured. We identified three main classes of echinoderms from this cave. The first class is Asteroidea, located below the halocline in marine waters (37 ppt) at 256 m from the entrance and at 45 m from the entrance in marine waters. The second class is Ophiuroidea, located below the halocline in marine waters at 40 and 336 m from the entrance, and the third class, Echinoidea, is located in marine waters 60 m from the entrance. Only the asteroid species shows a depigmentated body; it is the unique species not found outside the cave. To date, only few species of Holothuridae have been reported from caves. We discuss the colonization and adaptations to cave life these animals show.