Behaviour and feeding of the nassariid gastropod Cyclope neritea, abundant at hydrothermal brine seeps off Milos (Aegean Sea)

Field observations and laboratory experiments were made on Cyclope neritea, a small (similar to 10 mm diameter) burrowing stenoglossan gastropod with a flattened shell found in very high densities (>200 m(2)) in Paleohori Bay on the south coast of Miles (Aegean Sea). Cyclope neritea forms a high proportion of the biomass at seeps in this bay, where the medium to fine sand overlies hot, sulphidic brines. About half the animals were found on the surface in the daytime, an exception to the normal habit of this species which usually emerges from the sediment only at night. The C. neritea were aggregated on the thinner bacterial mats over the seeps. In the laboratory, C. neritea remained active for 3 h at sulphide concentrations up to 1 mM, the highest concentration in the interstitial water in the upper 25 mm of sediment at the seeps. Although the species can tolerate elevated salinity and temperature, it shows little adaptation for sulphide detoxification by oxidative pathways. It may survive at the seeps by its behaviour pattern, especially the use of the extensible siphon to access oxic water above the sediment boundary layer, and perhaps by exclusion of sulphide from the tissues. Cyclope neritea ingests large quantities of sand together with adhering bacteria and diatoms, but also scavenges on other animals killed by the extreme conditions of the seeps.