Gulf of Mexico chemosynthetic communities at oil seeps: estimating total density

Chemosynthetic communities occur on the continental slope of the Gulf of Mexico at sites where liquid oil and methane gas can be observed escaping from the substrate. Video and still photographs taken from submersibles suggest that seep mussels (Bathymodiolus-like: Mytilidae) are, together with the vestimentiferan, Lamellibrachia sp., biomass­ dominants in these communities. The mussel forms irregularly shaped beds that range in area from 1 to >20 m². Length frequency distributions of three collections of mussels show distinct size cohorts. Published length-weight relationship curves for mytilids are used to estimate the mean weight of the collected mussels. Large-area-imaging techniques are used to estimate the total area and mean density of mussel beds at one of the seep sites. These estimates will be combined to give a first order estimate of the mussels' standing-stock biomass.