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Gooday, AJ, Bett BJ, Escobar E, Ingole B, Levin LA, Neira C, Raman AV, Sellanes J.  2010.  Habitat heterogeneity and its influence on benthic biodiversity in oxygen minimum zones. Marine Ecology-an Evolutionary Perspective. 31:125-147.   10.1111/j.1439-0485.2009.00348.x   AbstractWebsite

Oxygen minimum zones (OMZs; midwater regions with O(2) concentrations <0.5 ml l(-1)) are mid-water features that intercept continental margins at bathyal depths (100-1000 m). They are particularly well developed in the Eastern Pacific Ocean, the Arabian Sea and the Bay of Bengal. Based on analyses of data from these regions, we consider (i) how benthic habitat heterogeneity is manifested within OMZs, (ii) which aspects of this heterogeneity exert the greatest influence on alpha and beta diversity within particular OMZs and (iii) how heterogeneity associated with OMZs influences regional (gamma) diversity on continental margins. Sources of sea-floor habitat heterogeneity within OMZs include bottom-water oxygen and sulphide gradients, substratum characteristics, bacterial mats, and variations in the organic matter content of the sediment and pH. On some margins, hard grounds, formed of phosphorites, carbonates or biotic substrata, represent distinct subhabitats colonized by encrusting faunas. Most of the heterogeneity associated with OMZs, however, is created by strong sea-floor oxygen gradients, reinforced by changes in sediment characteristics and organic matter content. For the Pakistan margin, combining these parameters revealed clear environmental and faunal differences between the OMZ core and the upper and lower boundary regions. In all Pacific and Arabian Sea OMZs examined, oxygen appears to be the master driver of alpha and beta diversity in all benthic faunal groups for which data exist, as well as macrofaunal assemblage composition, particularly in the OMZ core. However, other factors, notably organic matter quantity and quality and sediment characteristics, come into play as oxygen concentrations begin to rise. The influence of OMZs on meiofaunal, macrofaunal and megafaunal regional (gamma) diversity is difficult to assess. Hypoxia is associated with a reduction in species richness in all benthic faunal groups, but there is also evidence for endemism in OMZ settings. We conclude that, on balance, OMZs probably enhance regional diversity, particularly in taxa such as Foraminifera, which are more tolerant of hypoxia than others. Over evolutionary timescales, they may promote speciation by creating strong gradients in selective pressures and barriers to gene flow.

Hughes, DJ, Lamont PA, Levin LA, Packer M, Feeley K, Gage JD.  2009.  Macrofaunal communities and sediment structure across the Pakistan margin Oxygen Minimum Zone, North-East Arabian Sea. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 56:434-448.   10.1016/j.dsr2.2008.05.030   AbstractWebsite

Benthic macrofauna and sediment column features were sampled at five stations along a bathymetric transect (depths 140, 300, 940, 1200, 1850 m) through the Pakistan margin Oxygen Minimum Zone (OMZ) during the 2003 intermonsoon (March-May) and late-post-monsoon (August-October) periods. Objectives were to compare patterns with those described from other OMZs, particularly the Oman margin of the Arabian Sea, in order to assess the relative influence of bottom-water oxygenation and sediment organic content on macrofaunal standing stock and community structure. Macrofaunal density was highest at the 140-m station subject to monsoon-driven shoaling of the OMZ, but there was no elevation of density at the lower OMZ boundary (1200 m). Numbers was extremely low in the OMZ core (300 m) and were not readily explicable from the environmental data. There was no consistent depth-related trend in macrofaunal biomass. Macrofaunal densities were consistently lower than found off Oman but there was less contrast in biomass. A significant post-monsoon decline in macrofaunal density at 140 m was driven by selective loss of polychaete taxa. Polychaeta was the most abundant major taxon at all stations but did not dominate the macrofaunal community to the extent reported from Oman. Cirratulidae and Spionidae were major components of the polychaete fauna at most stations but Acrocirridae, Ampharetidae, Amphinomidae and Cossuridae were more important at 940 m. Polychaete assemblages at each station were almost completely distinct at the species level. Polychaete species richness was positively correlated with bottom-water dissolved oxygen and negatively correlated with sediment TOC, C:N ratio and total phytopigments. Community dominance showed the opposite pattern. The strongly inverse correlation between oxygen and measures of sediment organic content made it difficult to distinguish their relative effects. The strongly laminated sediments in the OMZ core contrasted with the homogeneous, heavily bioturbated sediments above and below this zone but were associated with minimal macrofaunal biomass rather than distinctive functional group composition. In general, data from the Oman margin were weak predictors of patterns seen off Pakistan, and results suggest the importance of local factors superimposed on the broader trends of macrofaunal community composition in OMZs. (C) 2008 Elsevier Ltd. All rights reserved.