Benthic fauna of a shallow-water gaseohydrothermal vent area in the Aegean Sea (Milos, Greece) |
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Authors: | F Thiermann I Akoumianaki J A Hughes O Giere |
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Institution: | Zoologisches Institut und Zoologisches Museum, Universit?t Hamburg, Martin-Luther-King-Platz 3, D-20146 Hamburg, Germany, DE Institute of Marine Biology of Crete, P.O. Box 2214, 21003 Iraklio, Crete, Greece, GR
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Abstract: | The benthic community of shallow-water hydrothermal vents (10 m water depth) in a sandy bay on the south coast of Milos,
Greece was studied. The macro- and meiofauna, as well as environmental factors such as temperature, salinity, sulfide concentration,
grain size composition, ATP concentration, organic carbon, chlorophyll a and phaeopigments were evaluated. Samples were taken along transects from a seagrass meadow into a hydrothermally active
area. Hydrothermally active spots were distinguished from the surrounding sediment by their black sediment coloration and
an overlying white bacterial mat. For comparison, a control transect from a seagrass meadow into bare sand in a non-vent area
in the same bay was studied. Overall, we found decreasing faunal diversity from the seagrass bed towards the hydrothermally
active area. Along this gradient, four different zones could be distinguished. (a) The seagrass area had a relatively low
diversity compared to the control stations, but much higher diversity than in the areas directly influenced by hydrothermal
activity. (b) The border zone between the seagrass and the hydrothermal area, with moderate sulfide concentrations, pH values,
seawater salinity and temperatures, was inhabited by an impoverished community dominated by the polychaete Capitella capitata, the nematodes Oncholaimus campylocercoides and Sabatieria sp., and an as yet undescribed chromadorid nematode (Chromadorina sp.). (c) The transition zone at the border of the hydrothermal area proper, with temperatures and sulfide concentrations
higher than in the border zone, was characterized by high salinity (60‰) and low pH values. Along with the gastropod Cyclope neritea, single specimens of C. capitata and O. campylocercoides occurred. (d) The hydrothermal area proper, characterized by high sulfide concentrations, had high sediment temperatures
and high salinities. The pH was as low as 6. Here, the gastropod Cyclope neritea was the only species occurring in considerable numbers. The gaseohydrothermal activity seems to largely exclude the surrounding
fauna in a graded zonal pattern. The increasing hydrothermal stress entrains a change of the ambient biota towards a depauperate
consortium of tolerant, opportunistic species, e.g. Capitella capitata (Polychaeta) and Oncholaimus campylocercoides (Nematoda). Although the hydrothermal area proper was characterized by a thick bacterial mat, the benthic community was characterized
not by bacteria feeders but by scavenging species.
Received: 13 September 1996 / Accepted: 24 October 1996 |
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