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The present study was carried out in Palaeochori Bay, south eastern coast of Milos, where outflow of hot gas bubbles and hydrothermal water seepage was observed. The study tests hypotheses about relationships between seawater temperature and species with warm-water affinities in areas close to shallow-water vents. We predicted that if temperature plays a major role in influencing abundance of species with warm-water affinities, then there should be more thermophilous species in areas with higher seawater temperature. Time series of seawater temperature were recorded in Palaeochori Bay and Pollonia Bay where hot emission was not observed. Temperature, water pressure and conductivity were measured every 30 min from 19 June 1996 to 16 June 1997. Fourteen qualitative samples of benthic flora were collected by SCUBA diving in six rocky sites. Photosamples of benthic assemblages were collected using an UW camera equipped with a wide-angle lens (15 mm) and an electronic flash unit. A constant area of 0.7 m(2) was sampled. Quantitative estimates of abundance of algal species were performed as percent cover. This paper shows that patterns of fluctuation in seawater temperature in Palaeochori were different from the control where no venting was found. In Palaeochori, algal assemblages were dominated by species with warm-water affinities that were not found elsewhere. These results are consistent with the hypothesis that temperature plays a major role in influencing abundance of species with warm-water affinities. According to our results, hydrothermal vents are potential oases that experience biological-physical coupling not yet clearly understood. They are important in affecting migration of alloctonous thermophilous species suggesting a possible role of vent areas as stepping stones for species migration.