MICROORGANISMS AS FOOD RESOURCES AT DEEP-SEA HYDROTHERMAL VENTS

We used stable isotopes of carbon and nitrogen to examine the diversity of microbial populations consumed as foods at deep-sea hydrothermal vents. Invertebrate consumers at Gorda and Juan de Fuca Ridge vent sites had variable carbon isotope compositions, implying the use of more than one microbial food resource. deltaC-13 values for consumer invertebrates at Gorda ranged between -13.2 parts per thousand (polynoid polychaete) and -43.7 parts per thousand (limpet); within Gorda microhabitats, deltaC-13 compositions of invertebrate species were also not uniform, differing by as much as 8-19 parts per thousand. At the Juan de Fuca site, deltaC-13 values showed a wide range (-14.6 to -33.9 parts per thousand) for nine invertebrate species collected from a dense community colonizing the surface of a sulfide flange. Carbon isotope differences between tubeworm symbioses and consumer invertebrates within microhabitats suggest that these symbioses may play a minor role as nutritional resources in vent food webs. Nitrogen isotope compositions of consumer species from vents were consistently depleted in N-15 relative to animals collected away from vents. deltaN-15 compositions of some vent individuals are among the lowest measured in any organism (< -10 parts per thousand) and likely reflect relatively abundant supplies of inorganic nitrogen compounds used by microbial populations at vents.