Food sources, behaviour, and distribution of hydrothermal vent shrimps at the Mid-Atlantic Ridge

Five species of bresilioid shrimp were investigated at seven hydrothermal s ites on the Mid-Atlantic Ridge: Menez Gwen, Lucky Strike, Rainbow, Broken S pur, TAG, Snake Pit and Logatchev. Samples were prepared for analysis of st able isotopes, elemental composition and lipids. Shrimp behaviour was obser ved from the submersible 'Alvin' and in the laboratory aboard RV 'Atlantis' . The distribution and zonation of the shrimp species was recorded. Juvenil e shrimp of all species arrive at the vents carrying reserves of photosynth etic origin, built-up in the pelagic larval stages. These reserves are used while the shrimp metamorphose to the adult form and, in Rimicaris exoculat a and Chorocaris chacei, while they develop epibiotic bacteria supporting s tructures, the modified mouthparts and the inside of the carapace. The main food of adult R. exoculata is filamentous bacteria that grow on these stru ctures. The intermediate sizes of C. chacei also feed on such bacteria, but the final stage gets some food by scavenging or predation. Mirocaris speci es scavenge diverse sources; they are not trophically dependent on either R . exoculata or mussels. Adults of Alvinocaris markensis are predators of ot her vent animals, including R. exoculata. The dense swarms of R. exoculata, with their exosymbionts, can be compared to endosymbiont-containing animal s such as Bathymodiolus and the vestimentiferan tube-worms of the Pacific v ents. Such associations, whether endo- or ectosymbiotic, may be necessary f or the development of flourishing communities at hydrothermal vents.