The sponge community of a subtidal area with hydrothermal vents: Miles Island, Aegean Sea

Sponges were sampled by SCUBA diving at six subtidal rocky sites, three of which were close to hydrothermal vents, a common feature on the sea-floor o ff the south-east coast of Miles. Twenty-five species (2 Calcarea and 23 De mospongiae) were found, few compared with the 589 recorded for the Mediterr anean, but an important addition to the scant information on the sponge fau na of the Aegean Sea. The number of species found at vent sites was consist ently higher than that found at non-vent sites, but no vent-obligate specie s could be identified. However, Geodia cydonium and three species of Cliona (C. copiosa, C. nigricans and C. rhodensis) showed a tendency to colonize vent areas. The former might take advantage of increased silica availabilit y, the latter of the enhanced deposition of carbonates near vents. Substrat um cover by sponges (estimated from wire-framed photographs of 0.7 m(2)), v aried greatly both among and within sites, mostly according to slope. Most sponge species preferred vertical to overhanging, shaded substrata. Proximi ty to vents seemed to have little or no influence on sponge cover, notwiths tanding a primary effect on species diversity. (C) 2000 Academic Press.