Symbiosis between methane-oxidizing bacteria and a deep-sea carnivorous cladorhizid sponge

Abstract

Dense bush-like clumps of several hundred individuals of a new species of Cladorhiza (Demospongiae, Poecilosclerida) were observed near methane sources in mud vokanoes, 4718 to 4943 m deep in the Barbados Trench. The sponge tissue contains 2 main morphological types of extracellular symbiotic bacteria: small rod-shaped cells and larger coccoid cells with stacked membranes. Stable carbon isotope values, the presence of methanol dehydrogenase and ultrastructural observations all indicate that at least some of the symbionts are methanotrophic. Ultrastructural evidence of intracellular digestion of the symbionts and the stable C and N values suggest that the sponge obtains a significant portion of its nutrition from the symbionts. Ultrastructure of the sponge embryo suggests direct transmission through generations in brooded embryos. The sponge also maintains a carnivorous feeding habit on tiny swimming prey, as do other cladorhizids.