Influences of geothermal sulfur bacteria on a tropical coastal food web

peer reviewedABSTRACT: The activity of the geothermal plant at Bouillante in Guadeloupe (French West Indies) releases thioautotrophic bacteria into the coastal environment. Fish counts reveal that fish abundance increases with higher availability of this bacterial resource. In order to evaluate the trophic role of these bacteria, isotopic compositions (C, N, S) of potential consumers were evaluated on transects at increasing distance from the source of bacteria. The 3 mobile fish species examined (Abudefduf saxatilis, Acanthurus bahianus, and Stegastes partitus) ingested and assimilated chemosynthetic bacteria. Similarly, the isotopic composition of the mobile sea urchin Diadema antillarum was different close to the discharge channel, suggesting a diet mainly composed of sulfur bacteria. In contrast, endofauna sampled from the nematode community did not show a diet influence by chemosynthetic bacteria. A broad variety of epifaunal organisms with passive and active suspension-feeding activities were also investigated, including sponges (Aplysina fistularis and Iotrochota birotulata), barnacles (Balanus sp.), bivalve molluscs (Spondylus tenuis) and cnidarians (Pseudopterogorgia sp.), but no strong evidence for sulfur bacteria contributions were determined in the diets of any of these organisms. This was also true for the omnivorous predator annelid Hermodice carunculata. In this coastal oligotrophic environment, only certain opportunistic species seem to benefit from the emergence of a new food item such as chemosynthetic bacteria