| Two species of vestimentiferan tubeworms harboring chemoautotrophic symbionts commonly co-occur at hydrocarbon seeps on the upper Louisiana slope of the Gulf of Mexico. I investigated the growth rates, longevities, population size structures, general chemical environment, biomass and associated community structure of these vestimentiferans to better understand their contribution to both the cold seep and the deep-sea ecosystems. Both vestimentiferans grow slowly, as compared to their hydrothermal vent relatives, and can live for centuries. Size structures of entirely collected aggregations show that both species settle simultaneously and in constant proportions to an exposed substrate but that the recruitment period is temporally constrained. Data collected here and in several other recent studies suggest that environmental modification resulting from competition for suitable settlement sites drives the evolution of a long life span over which reproduction can occur many times in seep vestimentiferans. Hydrogen sulfide, the energy source for these species, occurs patchily in and around vestimentiferan aggregations. Although sulfide occurs in very high concentrations (millimolar) in the sediments beneath the aggregations, it rarely occurs at concentrations greater than 0.1 micromolar in water bathing their primary gas exchange organs (plumes) above the sediment surface. Spatial variation in vestimentiferan growth rate and physiological condition suggest that multi-scale environmental variability plays a critical role in the ecology of seep vestimentiferans. The biomass of vestimentiferan aggregations greatly exceeds estimates available for the surrounding seafloor and rivals that in some of the most productive coastal marine systems. In addition, a diverse suite of seep endemic and non-endemic fauna inhabits these aggregations, and faunal composition varies dramatically between different aggregations. Present evidence suggests that vestimentiferan modification of the seep chemical environment creates a successional pattern of colonization dominated by endemic primary consumers early and non-endemic predators late in the lifespan of an aggregation. The long lifespan characteristic of vestimentiferans at these seep sites enables them to function as long-term sources of organic carbon and habitat in an environment otherwise limited in these resources. Thus, vestimentiferans are capable of shaping the community structure and composition of cold seep environments as well as the surrounding deep-sea. |
