Bathypelagic Fish Association with the Mid-Atlantic Ridge

The bathypelagic zone, Earth’s largest living space, is essentially boundless in three dimensions for most of its extent, structured only by fluid features (e.g., salinity, temperature) of the seawater itself. However, near certain topographic features this zone intersects the seafloor. The mid-ocean ridge system is by far the largest of these features. Unlike the ecosystems of the continental margins, the mid-ocean ridge systems do not receive terrigenous nutrient inputs. Thus, the deep-water fauna associated with mid-ocean ridges ultimately depend on the generally limited local surface production. Despite this limited surface production, there is evidence that near-ridge demersal fish biomass is increased above the mid-Atlantic Ridge (MAR). Two processes by which organic matter can be transferred to the benthic boundary layer include: 1) sinking of aggregates and the carcasses of larger animals, and 2) vertical migration of living animals. To understand the dynamics of the latter process, deep-pelagic and demersal fishes were studied during the 2004 G.O. Sars Expedition, a field campaign of MAR-ECO. MAR-ECO, a Census of Marine Life project, is an international study of the animals inhabiting the northern Mid-Atlantic. Utilizing multiple technologies the water column (to 3500 m) and benthic realms were sampled. Taxonomic analysis to date has revealed over 300 fish species, with ongoing analysis expected to reveal more species, some new to science. Pelagic sampling collected 207 species, with typical orders dominating. Bottom trawling collected ca. 175 species, with typical demersal families, but also pelagic families occurring in numbers higher than would be expected by contamination alone. Discrete, near-bottom pelagic trawls confirmed this observation. In all, 84 species were caught in both pelagic and bottom trawls, with some species showing enhanced abundances in the near-bottom boundary layer, suggesting that overlap of deep-pelagic and demersal faunas is likely a key process regulating mid-ocean ridge community structure

Eggs in the Freezer: Energetic Consequences of Nest Site and Nest Design in Arctic Breeding Shorebirds

Birds construct nests for several reasons. For species that breed in the Arctic, the insulative properties of nests are very important. Incubation is costly there and due to an increasing surface to volume ratio, more so in smaller species. Small species are therefore more likely to place their nests in thermally favourable microhabitats and/or to invest more in nest insulation than large species. To test this hypothesis, we examined characteristics of nests of six Arctic breeding shorebird species. All species chose thermally favourable nesting sites in a higher proportion than expected on the basis of habitat availability. Site choice did not differ between species. Depth to frozen ground, measured near the nests, decreased in the course of the season at similar non-species-specific speeds, but this depth increased with species size. Nest cup depth and nest scrape depth (nest cup without the lining) were unrelated to body mass (we applied an exponent of 0.73, to account for metabolic activity of the differently sized species). Cup depth divided by diameter2 was used as a measure of nest cup shape. Small species had narrow and deep nests, while large species had wide shallow nests. The thickness of nest lining varied between 0.1 cm and 7.6 cm, and decreased significantly with body mass. We reconstruct the combined effect of different nest properties on the egg cooling coefficient using previously published quantitative relationships. The predicted effect of nest cup depth and lining depth on heat loss to the frozen ground did not correlate with body mass, but the sheltering effect of nest cup diameter against wind and the effects of lining material on the cooling coefficient increased with body mass. Our results suggest that small arctic shorebirds invest more in the insulation of their nests than large species

Overlap Between Pelagic and Demersal Fishes at the Mid-Atlantic Ridge

The deep-pelagic zone (\u3e 200 m) is essentially boundless in 3 dimensions for most of its extent, structured only by fluid features of the seawater itself. However, near certain topographic features the deep-pelagic zone intersects the seafloor. The mid-ocean ridge system is by far the largest of these features. Unlike the ecosystems of the continental margins, the mid-ocean ridge systems do not receive terrigenous nutrient inputs. Thus, the deep-water fauna associated with mid-ocean ridges ultimately depend on the generally very limited local surface production. Despite this limited surface production, there is evidence that near-ridge demersal fish biomass is increased above the mid-Atlantic Ridge (MAR). To understand the dynamics of the MAR an international study, MAR-ECO, of the animals inhabiting the northern Mid-Atlantic was undertaken. Utilizing multiple technologies the meso-, bathy- and benthopelagic realms were sampled using pelagic and bottom trawls, ROV video and bottom long-lines. Taxonomic analysis to date has revealed at least 294 species (74 families, 22 orders), with ongoing analysis expected to reveal more species, some new to science. Pelagic sampling collected ca. 206 species, with typical orders dominating (e.g., Myctophiformes, Stomiiformes, Osmeriformes). Bottom trawling collected ca. 175 species, with typical demersal families (Alepocephalidae, Macrouridae, Ophidiidae, Moridae), but also pelagic families occurring in numbers higher than would be expected by contamination during deployment and retrieval alone. Discrete, near-bottom pelagic trawls confirmed this observation. In all, 84 species were caught in both pelagic and bottom trawls, with some species showing enhanced abundances in the near-bottom boundary layer, suggesting that overlap of deep-pelagic and demersal faunas is likely a key process regulating mid-ocean ridge community structure

Fishes of the Northern Mid-Atlantic Ridge Collected During the MAR-ECO Cruise in June/July 2004

Deep-sea oceanic fishes were studied during the MAR-ECO 2004 cruise in mid-Atlantic Ridge (MAR). The pelagic and benthic biotopes were prospected with pelagic and bottom trawls to about 3500 m. The survey produced ca. 60000 specimens that were identified to at least 294 species. Several specimens of the families Bathylagidae, Oneirodidae, Cetomimidae, Syngnathidae, Ophidiidae, Psychrolutidae, Zoarcidae, may be new. The high incidence of rare species (e.g. Mirognathus normani; Ataxolepis sp., Gyrinomimus sp.)may be a good indication of the sampling extent. The pelagic layers are dominated by specialized small-body fishes. The samples (n=127) accounted for more than 50000 specimens of ca. 206 species, 57 families and 17 orders. Myctophiformes, Stomiiformes, Osmeriformes, Perciformes and Aulopiformes represented 74% of the species. The most speciose families were Myctophidae, Stomiidae, Alepocephalidae and Melamphaidae. In numbers the Gonostomatidae (i.e. Cyclothone spp.), Sternoptychidae and Bathylagidae dominated. In terms of biomass, important families included the Serrivomeridae and Platytroctidae. Benthosema glaciale, Cyclothone microdon, Bathylagus euryops, Lampanyctus macdonaldi, Serrivomer beanii,Maurolicus muelleri, dominated the collections, especially at the northern stations. The 22 bottom trawl samples collected ca. 175 species, in 52 families and 21 orders. Considering the typical demersal fishes, the Osmeriformes and Gadiformes dominated the samples (25 and 23 species). Alepocephalidae and Macrouridae were among the most diverse families (16 species), followed by Ophidiidae (7 species). Coryphaenoides rupestris, C. brevibarbis, and Haulosauropsis macrochir dominated the catches (50% of the individuals). The taxonomic composition of pelagic and demersal assemblages varies along the region studied. The pattern shows an increase of richness and a decrease in evenness and dominance toward lower latitudes. The sub-Polar Front is the major biogeographic boundary in the studied area