Temporal and spatial variation in the reproductive ecology of the vent-endemic amphipod Ventiella sulfuris in the eastern Pacific

Populations of the vent-endemic amphipod Ventiella sulfuris were compared from 6 East Pacific Rise (EPR) vent sites of different ages, 3 from the northern EPR and 3 from the southern EPR. Although vent age affected amphipod abundance, with no individuals at the oldest vent, other population/reproductive parameters were found to be site dependent rather than vent age dependent. There was little within-site variation in population structure and reproductive output, probably the result of high within-site motility. However, there were significant between-site and between-field differences, indicating a high degree of population and reproductive variability and a moderate degree of vent fidelity. Since population structure and reproductive output varied between sites, the possibility of their use as biomarkers of vent 'condition' is discussed. The reproductive ecology of V. sulfuris is described for the first time and compared to that of other vent amphipod species. Unlike other species studied, reproductive output is relatively high. Adults move to the periphery of vents to reproduce and brood; after brooding, they moult again, return to feed at vent habitats (e.g. mussel and tube worm beds), and undergo a new phase of gonad maturation and emigration.