Diversity of Meiofauna from the 9°50′N East Pacific Rise across a Gradient of Hydrothermal Fluid Emissions

Background: We studied the meiofauna community at deep-sea hydrothermal vents along a gradient of vent fluid emissions in the axial summit trought (AST) of the East Pacific Rise 9 degrees 50'N region. The gradient ranged from extreme high temperatures, high sulfide concentrations, and low pH at sulfide chimneys to ambient deep-sea water conditions on bare basalt. We explore meiofauna diversity and abundance, and discuss its possible underlying ecological and evolutionary processes. Methodology/Principal Findings: After sampling in five physico-chemically different habitats, the meiofauna was sorted, counted and classified. Abundances were low at all sites. A total of 52 species were identified at vent habitats. The vent community was dominated by hard substrate generalists that also lived on bare basalt at ambient deep-sea temperature in the axial summit trough (AST generalists). Some vent species were restricted to a specific vent habitat (vent specialists), but others occurred over a wide range of physico-chemical conditions (vent generalists). Additionally, 35 species were only found on cold bare basalt (basalt specialists). At vent sites, species richness and diversity clearly increased with decreasing influence of vent fluid emissions from extreme flow sulfide chimney (no fauna), high flow pompei worm (S: 4-7, H-loge': 0.11-0.45), vigorous flow tubeworm (S: 8-23; H-loge': 0.44-2.00) to low flow mussel habitats (S: 28-31; H-loge': 2.34-2.60). Conclusions/Significance: Our data suggest that with increasing temperature and toxic hydrogen sulfide concentrations and increasing amplitude of variation of these factors, fewer species are able to cope with these extreme conditions. This results in less diverse communities in more extreme habitats. The finding of many species being present at sites with and without vent fluid emissions points to a non endemic deep-sea hydrothermal vent meiofaunal community. This is in contrast to a mostly endemic macrofauna but similar to what is known for meiofauna from shallow-water vents

Food partitioning between the amphipods Echinogammarus ischnus, Gammarus fasciatus, and Hyalella azteca as revealed by stable isotopes

Colonies of introduced Dreissena mussels provide substrate and food resources for benthic invertebrates resulting in increases in population abundance of many species including the native amphipod Gammarus fasciatus. Conversely, abundance of Gammarus is inversely associated with that of an introduced amphipod species, Echinogammarus ischnus. In this study, we explored carbon and nitrogen isotopic composition of E. ischnus, G. fasciatus, and Hyalella azteca and of Dreissena faeces/pseudofaeces from western Lake Erie to investigate possible exploitative competition among amphipods. Carbon isotopic composition (δ 13C) of H. azteca and G. fasciatus were similar, indicating that they share food resources, whereas E. ischnus was significantly depleted indicating its use of different resources. Dreissena faeces/pseudofaeces may be a part of G. fasciatus diet as revealed by carbon isotopic signatures, explaining, in part, why its abundance is positively associated with Dreissena. Phytoplankton may be the primary food source for juvenile E. ischnus and G. fasciatus as they had lighter carbon isotopic signatures than adult amphipods, suggesting an ontogenetic diet shift by both species. Isotopic separation of G. fasciatus and E. ischnus suggests that the latter is replacing the former by a mechanism other than exploitative competition for food

Invertebrates associated with residual ballast water and sediments of cargo-carrying ships entering the Great Lakes

Most ships entering the Great Lakes carry cargo and declare no-ballast-on board (NOBOB) status. Approximately 250 of these vessels annually load Great Lakes\u27 ballast water when they offload inbound cargo and then discharge this water (which has now mixed with residual water previously present in the tanks) when they load out-bound cargo. This procedure potentially allows nonindigenous species present in ballast residuals to invade the Great Lakes. We collected residual sediment, water, and associated organisms from 38 NOBOB ships entering the Great Lakes. We recorded seven established Great Lakes\u27 nonindigenous species, including some discovered since ballast water exchange was implemented. Occurrences of species not yet invaded indicate that this vector provides further opportunity for invasion. Collectively, NOBOB vessels appear to constitute a greater risk than ballasted vessels, as they make up a greater proportion of the traffic entering the lakes (∼90%), and they do not undergo ballast exchange. Invertebrates in residual water appear to have a greater opportunity for discharge than those in sediments, although most in the water fraction have already invaded this system. Invertebrate numbers in residual freshwater ballast could be dramatically lowered if these vessels flushed with open-ocean water prior to entering the Great Lakes. © 2005 NRC