SPONGES AND OTHER OPHIUROID MICROHABITATS (OPHIUROIDEA: ECHINODERMATA) AT REEF ENVIRONMENTS OF SAN BERNARDO ARCHIPELAGO (COLOMBIAN CARIBBEAN)

Abstract

Ophiuroids are conspicuous dwellers of exposed and cryptic microhabitats available in coral reefs. This investigation pretended to discern ophiuroid community composition at microhabitats available in sponges and other reef components of different character (biotic v s. abiotic) or position over the substrate (elevated v s. non-elevated), at shallow reefs within the Montastraea spp. zone at San Bernardo Archipelago (Colombian Caribbean). Evaluating the abundance of organisms related to availability of different microhabitats, schemes of exclusive or preferential occupation of a particular elevated component were determined. These schemes, are discussed as initial cues that suggest the existence of benefic ecological relations. Samplings were performed at three stations. Four 20 meter transects were surveyed on each station, three during daytime and one during night. Presence and abundance of ophiuroids and microhabitat availability (area or volume) were quantified v i s u a l l y. Eleven types of microhabitats were identified. Vertical microhabitats and specially sponges and octocorals, were the most common substrate components at the study area. The ophiuroid community was composed by 22 morphotypes. Only Ophiopsila sp. 1 (with excavating habits) was restricted to one particular kind of substrate. Many other species did not use restrictedly any particular type of microhabitat, but used exclusively structures of particular characteristics (elevation, character or cripticity). T h e occupation of inferior surfaces of non-elevated components was determined by ophiuroid’s necessity of reaching cryptic conditions, and this necessity was linked to photosensitive species, or those especially vulnerable to predators, and to its consequent seek of protection. Elevated components and particularly 13 sponge species were characteristically occupied by Ophiothrix angulata - O. orstedii complex and by O . s u e n s o n i i. Sponges with different morphologies are discussed to bring differential advantages to dwelling ophiuroid species. It is suggested that a probable benefic ecologic relationship (not obligated) exists between these brittle-star species and some of the most frequently occupied sponge species. Nevertheless this must be appropriately tested by experimental work.