Variation in the hydrothermal vent clam, Calyptogen magnifica, at the Rose Garden vent on the Galapagos spreading center

Abstract

Abstract Calyptogena magnifica occupy a relatively restricted habitat at the Rose Garden hydrothermal vent site on the Galapagos Rift. These clams are found in areas with very low flow of vent water and gain exposure to hydrogen sulfide by inserting their well-vascularized foot into cracks that contain this flow. Vent water is undetectable around the siphons of many of the individuals, and they therefore probably take up sulfide through their foot, and oxygen and inorganic carbon through their gills. Age estimates indicate that the bulk of the recruitment of C. magnifica occured between 1971 and 1976. Isotopic evidence indicates that symbionts are the main source of both nutritional carbon and nitrogen for the clams, and that the symbionts assimilate both of these substrates from inorganic sources. Carbohydrate and protein in the clam soft tissues, as well as the elemental sulfur content of their gills, decrease with increasing clam size. There is only slight variation in most of the parameters measured, and none of the parameters show nearly the variation seen in the other hydrothermal vent bivalve, Bathymodiolus thermophilus . However, several parameters, such as δ 13 C, condition index, and some bacterial enzyme activities, vary significantly with habitat.