Biological and geological dynamics over four years on a high-temperature sulfide structure at the Juan de Fuca Ridge hydrothermal observatory

An extensive videoscopic study of a high-temperature sulfide structure on the Juan de Fuca Ridge (northeast Pacific) examined temporal variation in vent community distribution and Links between faunal and environmental changes. Video imagery was acquired during a total of 5 manned submersible and ROV (remotely-operated vehicle) dive programs between 1991 and 1995. The structure was systematically mapped for each year of the study and a series of analytical tools was developed to quantify changes in biological and geological features and observable flow patterns. Results show: (1) heterogeneous faunal distribution characterized by decimeter-scale patchiness and general absence of vertical gradients; (2) apparent Links between community distribution, and environmental features such as fluid now patterns, substratum and temperature/chemical conditions; (3) a significant influence of perturbations on community dynamics; (4) absence of directional biological succession at the time scale examined (years). Overall, these observations strongly suggest that many hydrothermal community changes are initiated by gradual and abrupt flow modifications. Results are compiled in a dynamic succession model for sulfide edifices where community transitions are driven by flow variations, and by biological processes operating at sub-annual time scales. We conclude by stressing the need for extended monitoring of short-term dynamics in order to understand the relationship between hydrothermal communities and their environment.