First survey of sessile communities on subtidal rocks in an area with hydrothermal vents: Miles Island, Aegean Sea

The major epibenthic communities on subtidal rocks of Palaeochori Bay and t he marine tract on the southern coast of Milos island (Greece) were describ ed down to 44 m depth. Six sites were investigated by snorkelling and SCUBA diving. Samples, photographs and video images were also taken to integrate information. Three out of the six sites were close to hydrothermal vents, a common feature in the area. In total, nine major epibenthic communities w ere found, most of which were characterised by a diverse algal growth down to the maximum depth explored. Macrobenthic cover was severely reduced only in the close proximity of vents, a white flocculent bacterial mat covering the rock at the point from which fluid escaped. Large-scale effects of ven ts on the epibenthic communities were not detected. However, the abundance of species with warm-water affinity was recognisable in both algal and anim al dominated communities, which may be related to higher winter temperature in the vent area. Epifaunal communities under overhangs were composed of d istinct groups of suspension feeders at vent as compared to non-vent sites: this might indicate differences in trophic conditions. Mounds of the bioco nstructional coralline al,oa Mesophyllum lichenoides were conspicuous only at vent sites, thus suggesting enhanced biodeposition of carbonates due to Vent activity.