The ecology of seep communities in the Gulf of Mexico biodiversity and role of Lamellibrachia luymesi /

by Cordes, Erik.

iii Cold seeps are common habitats along the continental margin in all the world’s oceans. In the Gulf of Mexico, they occur in the salt dome province of the upper Louisiana slope, and along the base of the continental rise from Florida to Texas. Some of the most common inhabitants of cold seeps are vestimentiferan tubeworms which are entirely reliant on internal sulfide-oxidizing chemoautotrophic symbionts for their nutrition. The most common vestimentiferan tubeworm of the upper Louisiana slope is Lamellibrachia luymesi. This, and other species of tubeworms, form aggregations of hundreds to thousands of individuals which harbor a diverse community. In this study, a total of 40 tubeworm aggregation and mussel bed samples containing at least 171 macrofaunal species were collected at seeps from 520 to 3300 m depth. The upper Louisiana slope communities progress through a predictable sequence of successional stages. The youngest aggregations contain high biomass communities dominated by endemic species, with biomass decreasing over time as the relative abundance of nonendemic fauna in upper trophic levels increases. This process is mainly driven by the abundance of hydrogen sulfide in the epibenthic layer. Models support the hypothesis that L. luymesi alters its environment by releasing the sulfate generated by its internal symbionts into deeper sediment layers. This alters the distribution of sulfide leading to declines in sulfide concentration among the tubeworm tubes. The combination of these lines of evidence support the assertion that L. luymesi is a significant ecosystem engineer at hydrocarbon seeps in the Gulf of Mexico.