Plankton availability and retention efficiencies of cold-seep symbiotic mussels

Mussels from deep-sea methane/sulfide seeps in the Gulf of Mexico supplement their symbiotically acquired nitrogen by feeding selectively on nitrogen-rich bacterioplankton. The previously unknown natural diet of the mussels consists of bacteria, Synechococcus-type cyanobacteria, and protozoans. Overall retention increased with increasing mussel size, though the largest mussels did not retain bacteria; Mussels can obtain as much as 0.12 mu mol N g(-1) h(-1) by filter feeding on natural water-column communities. Previous calculations indicate that nitrogen acquired through the symbionts is inadequate for maximal growth, but our conservative estimates suggest that nitrogen obtained by filter feeding is similar to that acquired by symbionts and may be an important component in the nutritional requirements of seep mussels. Additionally, we conducted a series of in situ measurements of flow and food availability over an extensive mussel bed located at the Brine Pool. Our measurements indicate that biogenic flow due to mussel pumping generates near-bottom turbulence that prevents the development of a food-depleted layer over the mussel bed.