Successional mechanism varies along a gradient in hydrothermal fluid flux at deep-sea vents

Invertebrate communities inhabiting deep-sea hydrothermal vents undergo substantial succession on time scales of months. Manipulative field experiments assessed the relative roles of environmental state and biotic interactions in determining temporal succession along a spatial gradient in vent fluid flux at three vent sites near 9degrees50' N on the East Pacific Rise (2500 in water depth). Species colonization patterns on cubic basalt blocks (10 cm on a side) deployed by the submersible Alvin revealed both positive (facilitation) and negative (inhibition) biological interactions, in the context of established succession theory. Over a series of four cruises from 1994 to 1998, blocks were exposed to colonists for consecutive and continuous intervals in short-term (5 + 8 = 13 mo) and longer-term (8 + 29 = 37 mo) experiments. Colonists grouped into a mobile functional group were less abundant in the continuous interval (13 mo) than in the synchronous pooled-consecutive intervals (5 + 8 mo) of the short-term experiment, indicating that early colonists inhibited subsequent recruitment. Colonists grouped into a sessile functional group exhibited the opposite pattern, indicating facilitation. Similar trends, though not statistically significant, were observed in the longer-term experiment. The character of species interactions varied along a gradient in hydrothermal fluid flux (and inferred productivity), with inhibitory interactions more prominent in zones with high temperatures, productivity, and faunal densities, and facilitative interactions appearing where temperatures, productivity, and densities were low; Analyses of primary succession on introduced basalt blocks suggest that biological interactions during early vent. community development strongly modify initial patterns of settlement, even in the absence of sustained temporal change in the vent fluid flux.