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Neira, C, Ingels J, Mendoza G, Hernandez-Lopez E, Levin LA.  2018.  Distribution of meiofauna in bathyal sediments influenced by the oxygen minimum zone off Costa Rica. Frontiers in Marine Science. 5   10.3389/fmars.2018.00448   AbstractWebsite

Ocean deoxygenation has become a topic of increasing concern because of its potential impacts on marine ecosystems, including oxygen minimum zone (OMZ) expansion and subsequent benthic effects. We investigated the influence of oxygen concentration and organic matter (OM) availability on metazoan meiofauna within and below an OMZ in bathyal sediments off Costa Rica, testing the hypothesis that oxygen and OM levels are reflected in meiofaunal community structures and distribution. Mean total densities in our sampling cores (400-1800 m water depth) were highest with 3688 ind. 10 cm(-2) at the OMZ core at 400 m water depth, decreasing rapidly downslope. Nematodes were overall dominant, with a maximum of 99.9% in the OMZ core, followed by copepods (13%), nauplii (4.8%), and polychaetes (3%). Relative copepod and nauplii abundance increased consistently with depth and increasing bottom-water O-2. Meiofaunal composition was significantly different among sites, with lower taxonomic diversity at OMZ sites relative to deeper, oxygenated sites. Vertical distribution patterns within sediments showed that in strongly oxygen-depleted sites less meiofauna was concentrated in the surface sediment than at deeper slope sites. Highest meiofaunal abundance and lowest diversity occurred under lowest oxygen and highest pigment levels, whereas highest diversity occurred under highest oxygen-concentrations and low pigments, as well as high quality of sedimentary pigment (chl a/phaeo) and organic carbon (C/N). The lower meiofaunal diversity, and lower structural and trophic complexity, at oxygen-depleted sites raises concerns about changes in the structure and function of benthic marine ecosystems in the face of OMZ expansions.

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.

Gooday, AJ, Bernhard JM, Levin LA, Suhr SB.  2000.  Foraminifera in the Arabian Sea oxygen minimum zone and other oxygen-deficient settings: taxonomic composition, diversity, and relation to metazoan faunas. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 47:25-54.   10.1016/s0967-0645(99)00099-5   AbstractWebsite

Previous work has shown that some foraminiferal species thrive in organically enriched, oxygen-depleted environments. Here, we compare 'live' (stained) faunas in multicorer samples (0-1 cm layer) obtained at two sites on the Oman margin, one located at 412m within the oxygen minimum zone (OMZ) (O(2) = 0.13 ml l(-1)), the other located at 3350 m, well below the main OMZ (O(2) similar to 3.00 ml l(-1)). While earlier studies have focused on the hard-shelled (predominantly calcareous) foraminifera, we consider complete stained assemblages, including poorly known, soft-shelled, monothalamous forms. Densities at the 412-m site were much higher (16,107 individuals.10 cm(-2) in the > 63-mu m fraction) than at the 3350-m site (625 indiv.10 cm(-2)). Species richness (E(S(100))), diversity (H', Fishers Alpha index) and evenness (J') were much lower, and dominance (R1D) was higher, at 412 m compared with 3350 m. At 412 m, small calcareous foraminifera predominated and soft-shelled allogromiids and sacamminids were a minor faunal element. At 3350 m, calcareous individuals were much less common and allogromiids and saccamminids formed a substantial component of the fauna. There were also strong contrasts between the foraminiferal macrofauna( > 300-mu m fraction) at these two sites; relatively small species of Bathysiphon, Globobulimina and Lagenammina dominated at 412 m, very large, tubular, agglutinated species of Bathysiphon, Hyperammina, Rhabdammina and Saccorhiza were important at 3350 m. Our observations suggest that, because they contain fewer soft-shelled and agglutinated foraminifera, a smaller proportion of bathyal, low-oxygen faunas is lost during fossilization compared to faunas from well-oxygenated environments. Trends among foraminifera (> 63 mu m fraction) in the Santa Barbara Basin (590 and 610m depth; O(2) = 0.05 and 0.15 ml(-1) respectively), and macrofaunal foraminifera(> 300 mu m) on the Peru margin (300-1250 m depth: O(2) = 0.02-1.60 mi l(-1)), matched those observed on the Oman margin. Tn particular, soft-shelled monothalamous taxa were rare and large agglutinated taxa were absent in the most oxygen-depleted ( < 0.20 mi l(-1)) stations. Foraminifera often outnumber metazoans (both meiofaunal and macrofaunal) in bathyal oxygen-depleted settings. However, although phylogenetically distant, foraminifera and metazoans exhibit similar population responses to oxygen depletion; species diversity decreases, dominance increases, and the relative abundance of the major taxa changes. The foraminiferal macrofauna ( > 300 mu m) were 5 times more abundant than the metazoan macrofauna at 412 m on the Oman margin but 16 times more abundant at the 3350 m site. Among the meiofauna (63-300 mu m), the trend was reversed, foraminifera were 17 times more abundant than metazoan taxa at 412 m but only 1.4 times more abundant at 3350 In. An abundance of food combined with oxygen levels which are not depressed sufficiently to eliminate the more tolerant taxa, probably explains why foraminifera and macrofaunal metazoans flourished at the 412-m site, perhaps to the detriment of the metazoan meiofauna. (C) 1999 Elsevier Science Ltd. All rights reserved.