Establishment and persistence of seep vestimentiferan aggregations on the upper Louisiana slope of the Gulf of Mexico

This study investigated the population size structures, growth rates and ages of 2 coexisting vestimentiferan tubeworms (Lamellibrachiacf.luymesiandSeepiophila jonesi) at hydrocarbon seeps in the Gulf of Mexico in order to determine the factors contributing to their establishment and persistence. Population size structures of 12 complete aggregations indicated that both vestimentiferans recruit roughly simultaneously during the early stages of aggregation development, after which time recruitment largely ceases. By staining the vestimentiferan tubesin situand measuring subsequently deposited tube material between 1 and 3 yr later, we found thatL. cfluymesigrew faster thanS. jonesioverall and within individual aggregations. Using the relationship between growth rate and length for each species we also showed that the mean ages and age ranges of individuals of both species were very similar in younger aggregations. A long life span appears to be characteristic of vestimentiferans at these seep sites. Staining, redeployment and subsequent collection of 2 small clusters of vestimentiferans showed that above their point of attachment to the solid substrate, these species elongate their tubes only at the anterior-most end. These species also possess the ability to elongate their tubes in a posterior direction below their point of attachment to the solid substrate. In these seep vestimentiferans, a combination of spatial and temporal limitation of suitable settlement sites may have driven the evolution of a long life span over which reproduction may occur many times.