MEPS 470:79-99 (2012)  -  DOI: https://doi.org/10.3354/meps10019

Living on the edge: single-species dominance at the Pakistan oxygen minimum zone boundary

Rachel M. Jeffreys1,*, Lisa A. Levin2, Peter A. Lamont3, Clare Woulds4,5, Christine R. Whitcraft2,6, Guillermo F. Mendoza2, George A. Wolff1, Gregory L. Cowie4

1School of Environmental Sciences, University of Liverpool, 4 Brownlow Street, Liverpool L69 3GP, UK
2Center for Marine Biodiversity and Conservation and Integrative Oceanography Division, Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, California 92093-0218, USA
3Scottish Association for Marine Science, Dunstaffnage Marine Laboratory, Oban, Argyll PA37 1QA, UK
4School of GeoSciences, University of Edinburgh, Edinburgh EH9 3JW, UK
5Present address: School of Geography, University of Leeds, University Road, Leeds, West Yorkshire LS2 9JT, UK
6Present address: Biological Sciences, California State University Long Beach, 1250 Beltflower Blvd, Long Beach, California 90840-3702, USA

ABSTRACT: Oxygen minimum zones (OMZs) are naturally occurring, low-oxygen water masses that create hypoxic conditions where they impinge on the seafloor. Their lower boundaries are characterised by elevated densities of hypoxia-tolerant fauna and an abundant food supply. The polychaete Linopherus sp. nov. (Amphinomidae) is the dominant taxon at the Pakistan margin (PM) lower OMZ, at near suboxic dissolved oxygen (DO) concentrations of 5 to 8 µM. We explored the response of Linopherus sp. nov. to gradients in oxygen and organic matter (OM) availability from depths of 700 to 1100 m during the inter- and late monsoon periods. Linopherus sp. nov. was present from 800 to 1000 m, and highest densities were found at 850 m. Population size structuring was evident and smaller individuals were present at depths of lowest DO concentrations. Linopherus sp. nov. showed morphological adaptation to low DO, and respiratory surface areas were significantly larger in worms at sites of lowest DO concentrations. Stable carbon isotopes (δ13C) revealed that Linopherus sp. nov. feeds mainly on sedimentary OM while enriched δ15N values suggest that Linopherus sp. nov. also utilises predation as a foraging strategy. Lipid biomarkers indicate an omnivorous lifestyle, in which Linopherus sp. nov. uses phytodetrital, bacterial and invertebrate/carrion food sources. Pulse-chase experiments demonstrated that Linopherus sp. nov. consumes phytodetritus and contributes significantly to OM processing, potentially altering OM quality and thus the availability of food resources to the benthic community. Severe oxygen stress leads to single-species dominance, which in turn simplifies macrofaunal ecosystems and thus reduces trophic complexity.


KEY WORDS: Oxygen minimum zone · Hypoxia · Single-species dominance · Organic matter processing · Linopherus · Stable isotopes · Lipid biomarkers


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Cite this article as: Jeffreys RM, Levin LA, Lamont PA, Woulds C and others (2012) Living on the edge: single-species dominance at the Pakistan oxygen minimum zone boundary. Mar Ecol Prog Ser 470:79-99. https://doi.org/10.3354/meps10019

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