FREE-LIVING MARINE NEMATODES FROM HYDROTHERMAL SEDIMENTS - SIMILARITIES WITH COMMUNITIES FROM DIVERSE REDUCED HABITATS

The meiofauna of hydrothermal deep-sea sediments in the North Fiji Bas in (NE Pacific) was investigated. Nematodes were the dominant taxon. T he structure of the hydrothermal nematode communities from the Fiji Ba sin is compared with (1) the communities from adjacent oxic deep-sea s ediments, (2) other hydrothermal vent areas and (3) shallow reduced en vironments such as cold seeps and subsurface anoxic sediments of eutro phic bottoms. Although the genus composition of the hydrothermal area and the biodiversity on a generic or functional morphological level di d not deviate greatly from the control areas, we found differences at the species level and in the size spectra and the species diversity. N one of the species found in the hydrothermal sediments occurred in the surrounding areas. The size spectra of the vent communities was shift ed towards larger nematodes, and species diversity was much lower in t he hydrothermal area. The similarity in nematode genus composition bet ween hydrothermal sites and control areas stands in contrast with the presence of a specialized endemic hydrothermal macrofauna. The absence of a planktonic life stage, in combination with small size, makes it more difficult for nematode species to migrate between isolated hydrot hermal patches.