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Gooday, AJ, Levin LA, da Silva AA, Bett BJ, Cowie GL, Dissard D, Gage JD, Hughes DJ, Jeffreys R, Lamont PA, Larkin KE, Murty SJ, Schumacher S, Whitcraft C, Woulds C.  2009.  Faunal responses to oxygen gradients on the Pakistan margin: A comparison of foraminiferans, macrofauna and megafauna. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 56:488-502.   10.1016/j.dsr2.2008.10.003   AbstractWebsite

The Pakistan Margin is characterised by a strong mid-water oxygen minimum zone (OMZ) that intercepts the seabed at bathyal depths (150-1300 m). We investigated whether faunal abundance and diversity trends were similar among protists (foraminiferans and gromiids), metazoan macrofauna and megafauna along a transect (140-1850 m water depth) across the OMZ during the 2003 intermonsoon (March-May) and late/post-monsoon (August-October) seasons. All groups exhibited some drop in abundance in the OMZ core (250-500 m water depth; O(2): 0.10-0.13 mL L(-1) = 4.46-5.80 mu M) but to differing degrees. Densities of foraminiferans >63 mu m were slightly depressed at 300 m, peaked at 738 m, and were much lower at deeper stations. Foraminiferans >300 mu m were the overwhelmingly dominant macrofaunal organisms in the OMZ core. Macrofaunal metazoans reached maximum densities at 140 m depth, with additional peaks at 850, 940 and 1850 m where foraminiferans were less abundant. The polychaete Linopherus sp. was responsible for a macrofaunal biomass peak at 950 m. Apart from large swimming animals (fish and natant decapods), metazoan megafauna were absent between 300 and 900 m (O(2) <0.14-0.15 mLL(-1) = 6.25-6.69 mu M) but were represented by a huge, ophiuroid-dominated abundance peak at 1000 m (O(2) similar to 0.15-0.18 mLL(-1) = 6.69-8.03 mu M). Gromiid protists were confined largely to depths below 1150 m (O(2) > 0.2 mLL(-1) = 8.92 mu M). The progressively deeper abundance peaks for foraminiferans (> 63 mu m), Linopherus sp. and ophiuroids probably represent lower OMZ boundary edge effects and suggest a link between body size and tolerance of hypoxia. Macro- and megafaunal organisms collected between 800 and 1100 m were dominated by a succession of different taxa, indicating that the lower part of the OMZ is also a region of rapid faunal change. Species diversity was depressed in all groups in the OMZ core, but this was much more pronounced for macrofauna and megafauna than for foraminiferans. Oxygen levels strongly influenced the taxonomic composition of all faunal groups. Calcareous foraminiferans dominated the seasonally and permanently hypoxic sites (136-300 m); agglutinated foraminiferans were relatively more abundant at deeper stations where oxygen concentrations were >0.13 mLL(-1)( = 5.80 mu M). Polychaetes were the main macrofaunal taxon within the OMZ; calcareous macrofauna, and megafauna (molluscs and echinoderms) were rare or absent where oxygen levels were lowest. The rarity of larger animals between 300 and 700 m on the Pakistan Margin, compared with the abundant macrofauna in the OMZ core off Oman, is the most notable contrast between the two sides of the Arabian Sea. This difference probably reflects the slightly higher oxygen levels and better food quality on the western side. (C) 2008 Published by Elsevier Ltd.

Fodrie, FJ, Levin LA, Rathburn AE.  2009.  High densities and depth-associated changes of epibenthic megafauna along the Aleutian margin from 2000-4200 m. Journal of the Marine Biological Association of the United Kingdom. 89:1517-1527.   10.1017/s0025315409000903   AbstractWebsite

The Aleutian margin is a dynamic environment underlying a productive coastal ocean and subject to frequent tectonic disturbance. In July 2004, We used over 500 individual bottom images from towed camera transects to investigate patterns of epibenthic megafaunal density and community composition on the contiguous Aleutian margin (53 degrees N 163 degrees W) at depths of 2000 m, 3200 m and 4200 M. We also examined the influence of vertical isolation on the megafaunal assemblage across a topographic rise at 3200 m, located 30 km from the main margin and elevated 800 m above the surrounding seafloor. In comparison to previous reports from bathyal and abyssal depths, megafaunal densities along the Aleutian margin were remarkably high, averaging 5.38 +/- 0.43 (mean +/- 1 standard error), 0.32 +/- 0.02 to 0.43 +/- 0.03 and 0.27 +/- 0.01 individuals m(-2) at 2000 m, 3200 m and 4200 m, respectively. Diversity at 2000 M Was elevated by 15-30% over the deeper sites (3200-4200 m) depending on the metric, while evenness was depressed by similar to 10%. Levels of richness and evenness were similar among the three deeper sites. Echinoderms were the most abundant phylum at each depth; ophiuroids accounted for 89% of individuals in photographs at 2000 m, echinoids were dominant at 3200 M (39%), and holothurians dominated at 4200 m (47%). We observed a 26% reduction in megafaunal density across the summit of the topographic rise relative to that documented on the continental slope at the same depth. However, the two communities at 3200 m were very similar in composition. Together, these data support the modified 'archibenthal zone of transition' framework for slope community patterns with distinct communities along the middle and lower slope (the upper slope was not evaluated here). This study fills a geographical gap by providing baseline information for a relatively pristine, high-latitude, deep-sea benthic ecosystem. As pressures grow for drilling, fishing and mining on high-latitude margins, such data can serve as a reference point for much-needed studies on the ecology, long-term dynamics, and anthropogenically induced change of these habitats.

Woulds, C, Cowie GL, Levin LA, Andersson JH, Middelburg JJ, Vandewiele S, Lamont PA, Larkin KE, Gooday AJ, Schumacher S, Whitcraft C, Jeffreys RM, Schwartz M.  2007.  Oxygen as a control on seafloor biological communities and their roles in sedimentary carbon cycling. Limnology and Oceanography. 52:1698-1709.   10.4319/lo.2007.52.4.1698   AbstractWebsite

C-13 tracer experiments were conducted at sites spanning the steep oxygen, organic matter, and biological community gradients across the Arabian Sea oxygen minimum zone, in order to quantify the role that benthic fauna play in the short-term processing of organic matter (OM) and to determine how this varies among different environments. Metazoan macrofauna and macrofauna-sized foraminiferans took up as much as 56 +/- 13 mg of added C m(-2) (685 mg C m(-2) added) over 2-5 d, and at some sites this uptake was similar in magnitude to bacterial uptake and/or total respiration. Bottom-water dissolved oxygen concentrations exerted a strong control over metazoan macrofaunal OM processing. At oxygen concentrations > 7 mu mol L-1 (0.16 ml L-1), metazoan macrofauna were able to take advantage of abundant OM and to dominate OM uptake, while OM processing at O-2 concentrations of 5.0 mu mol L-1 (0.11 ml L-1) was dominated instead by (macrofaunal) foraminiferans. This led us to propose the hypothesis that oxygen controls the relative dominance of metazoan macrofauna and foraminifera in a threshold manner, with the threshold lying between 5 and 7 mu mol L-1 (0.11 to 0.16 ml L-1). Large metazoan macrofaunal biomass and high natural concentrations of OM were also associated with rapid processing of fresh OM by the benthic community. Where they were present, the polychaete Linopherus sp. and the calcareous foraminiferan Uvigerina ex gr. semiornata, dominated the uptake of OM above and below, respectively, the proposed threshold concentrations of bottom-water oxygen.