Trophic ecology of massive shrimp aggregations at a Mid-Atlantic Ridge hydrothermal vent site

The source of nutrition of shrimp that form giant aggregations at Mid-Atlantic Ridge hydrothermal vents was explored by a combination of different molecular techniques. These animals have been hypothesized either to graze on the free-living, surface microbial community or to feed off epibiotic bacteria growing on their exoskeleton. Stable isotope compositions of potential food sources, consumer tissues, and gut contents suggest that the shrimp derive most of their carbon and nitrogen from the epibionts. However, probing of nucleic acids extracted from shrimp guts points to the existence of a gut microflora that is isotopically similar but genetically distinct from the epibionts. Carbon dioxide fixation experiments were carried out to compare the magnitude of potential primary productivity of the different nutritional sources of the shrimp. Relatively low and comparable rates were observed for both the free-living community and the epibionts but activity associated with gut preparations was surprisingly high. These high CO2 fixation rates in the gut may be indicative of a nutritional relationship between the shrimp and their gut microflora. Overall, the data indicate a nutritional symbiosis of the shrimp with their epibionts and possibly also with a separate gut microflora.