HYDROTHERMAL-VENT ALVINELLID POLYCHAETE DISPERSAL IN THE EASTERN PACIFIC .1. INFLUENCE OF VENT SITE DISTRIBUTION, BOTTOM CURRENTS, AND BIOLOGICAL PATTERNS

Deep-sea hydrothermal-vent habitats are typically linear, discontinuou s, and short-lived. Some of the vent fauna such as the endemic polycha ete family Alvinellidae are thought to lack a planktotrophic larval st age and therefore not to broadcast-release their offspring. The geneti c evidence points to exchanges on a scale that seems to contradict thi s type of reproductive pattern. However, the rift valley may topograph ically rectify the bottom currents, thereby facilitating the dispersal of propagules between active vent sites separated in some cases by 10 s of kilometers or more along the ridge axis. A propagule flux model b ased on a matrix of intersite distances, long-term current-meter data, and information on the biology and ecology of Alvinellidae was develo ped to test this hypothesis. Calculations of the number of migrants ex changed between two populations per generation (N-m) allowed compariso ns with estimates obtained from genetic studies. N, displays a logarit hmic decrease with increasing dispersal duration and reaches the criti cal value of 1 after 8 d when the propagule Aux model was run in stand ard conditions. At most, propagule traveling time cannot reasonably ex ceed 15-30 d, according to the model, whereas reported distances betwe en sites would require longer lasting dispersal abilities. Two nonexcl usive explanations are proposed. First, some aspects of the biology of Alvinellidae have been overlooked and long-distance dispersal does oc cur. Second, such dispersal never occurs in Alvinellidae, but the spat ial-temporal dynamics of vent sites over geological timescales allows short-range dispersal processes to maintain gene flow.