Community Development and Structure at Hydrothermal Vents

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The community ecology of hydrothermal vents has only begun to be investigated by examinations of the physiological ecology of adaptations in component vent biota and descriptive analyses of species occupation patterns. In Dec 1994, these scientists initiated a project at 9Ý50' N on the East Pacific Rise to take true advantage of the power of the deep submersible ALVIN to conduct experimental interventions in this deep sea environment, testing hypotheses to explain observed patterns of community development in space (zonation) and time (succession). During 3 cruises over 13 mo, 352 basalt settlement blocks were deployed in each of 4 zones (Tubeworm, Bivalve, Suspension feeder, and Periphery) at 3 vents to test experimentally how recruitment patterns are influenced by larval supply, physiological adaptations, and species interactions. This renewal award involves transplantation and recovery of the 123 blocks still remaining on the seafloor, on which sufficient colonization and growth will have occurred to enable the test of how biological interactions modify development of zonation and succession patterns after the early colonization phase. The focus will be specifically on the role of ( I ) competition for space among tubeworms (Riftia vs. Tevnia and Oasisia; and mussels vs. Riftia), (2) suppression of larval colonization by adult mussels, (3) predation by crabs and fishes in mediating interactions between competing guilds (grazing gastropods vs. sessile space occupiers), and (4) historical faunal occupation in repressing community change as venting fluxes wax or wane. Analysis of how different biological interactions influence community development along the environmental stress gradient with distance from venting source has fundamental ecological significance because the spatial gradients in physiological stress and environmental productivity in vents are confounded in the opposite way from the rocky intertidal and virtually all other communities from which comes our present understanding of how biological interactions vary along environmental stress gradients. The project will also address whether larval settlement is altered by the species composition and cover of pre existing biota, a theme specific to objectives of the RIDGE LARVE (Larvae At Ridge VEnts) Project and fundamental to the Temporal Variability component of RIDGE.