Macrobenthic assemblage structure and organismal stoichiometry control faunal processing of particulate organic carbon and nitrogen in oxygen minimum zone sediments

W. R. Hunter*, L. A. Levin, H. Kitazato, U. Witte

*Corresponding author for this work

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Abstract

The Arabian Sea oxygen minimum zone (OMZ) impinges on the western Indian continental margin between 150 and 1500 m, causing gradients in oxygen availability and sediment geochemistry at the sea floor. Oxygen availability and sediment geochemistry are important factors structuring macrofaunal assemblages in marine sediments. However, relationships between macrofaunal assemblage structure and sea-floor carbon and nitrogen cycling are poorly understood. We conducted in situ C-13:N-15 tracer experiments in the OMZ core (540 m [O-2] = 0.35 mu mol l(-1)) and lower OMZ boundary (800-1100 m, [O-2] = 2.2-15.0 mu mol l(-1)) to investigate how macrofaunal assemblage structure, affected by different oxygen levels, and C:N coupling influence the fate of particulate organic matter. No macrofauna were present in the OMZ core. Within the OMZ boundary, relatively high abundance and biomass resulted in the highest macrofaunal assimilation of particulate organic carbon (POC) and nitrogen (PON) at the lower oxygen 800 m stations ([O-2] = 2.2-2.36 mu mol l(-1)). At these stations the numerically dominant cirratulid polychaetes exhibited greatest POC and PON uptake. By contrast, at the higher oxygen 1100 m station ([O-2] = 15.0 mu mol l(-1)) macrofaunal C and N assimilation was lower, with POC assimilation dominated by one large solitary ascidian. Macrofaunal POC and PON assimilation were influenced by changes in oxygen availability, and significantly correlated to differences in macrofaunal assemblage structure between stations. However, macrofaunal feeding responses were ultimately characterised by preferential organic nitrogen assimilation, relative to their internal C:N budgets.

Original languageEnglish
Pages (from-to)993-1006
Number of pages14
JournalBiogeosciences
Volume9
Issue number3
DOIs
Publication statusPublished - Mar 2012

Keywords

  • matter
  • C-N
  • rapid response
  • macrofaunal community
  • ecological stoichiometry
  • Arabian Sea
  • sea benthic community
  • Indian continental-margin
  • N-P ratios
  • in-situ experiments

Cite this

Macrobenthic assemblage structure and organismal stoichiometry control faunal processing of particulate organic carbon and nitrogen in oxygen minimum zone sediments. / Hunter, W. R.; Levin, L. A.; Kitazato, H.; Witte, U.

In: Biogeosciences, Vol. 9, No. 3, 03.2012, p. 993-1006.

Research output: Contribution to journalArticle

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N2 - The Arabian Sea oxygen minimum zone (OMZ) impinges on the western Indian continental margin between 150 and 1500 m, causing gradients in oxygen availability and sediment geochemistry at the sea floor. Oxygen availability and sediment geochemistry are important factors structuring macrofaunal assemblages in marine sediments. However, relationships between macrofaunal assemblage structure and sea-floor carbon and nitrogen cycling are poorly understood. We conducted in situ C-13:N-15 tracer experiments in the OMZ core (540 m [O-2] = 0.35 mu mol l(-1)) and lower OMZ boundary (800-1100 m, [O-2] = 2.2-15.0 mu mol l(-1)) to investigate how macrofaunal assemblage structure, affected by different oxygen levels, and C:N coupling influence the fate of particulate organic matter. No macrofauna were present in the OMZ core. Within the OMZ boundary, relatively high abundance and biomass resulted in the highest macrofaunal assimilation of particulate organic carbon (POC) and nitrogen (PON) at the lower oxygen 800 m stations ([O-2] = 2.2-2.36 mu mol l(-1)). At these stations the numerically dominant cirratulid polychaetes exhibited greatest POC and PON uptake. By contrast, at the higher oxygen 1100 m station ([O-2] = 15.0 mu mol l(-1)) macrofaunal C and N assimilation was lower, with POC assimilation dominated by one large solitary ascidian. Macrofaunal POC and PON assimilation were influenced by changes in oxygen availability, and significantly correlated to differences in macrofaunal assemblage structure between stations. However, macrofaunal feeding responses were ultimately characterised by preferential organic nitrogen assimilation, relative to their internal C:N budgets.

AB - The Arabian Sea oxygen minimum zone (OMZ) impinges on the western Indian continental margin between 150 and 1500 m, causing gradients in oxygen availability and sediment geochemistry at the sea floor. Oxygen availability and sediment geochemistry are important factors structuring macrofaunal assemblages in marine sediments. However, relationships between macrofaunal assemblage structure and sea-floor carbon and nitrogen cycling are poorly understood. We conducted in situ C-13:N-15 tracer experiments in the OMZ core (540 m [O-2] = 0.35 mu mol l(-1)) and lower OMZ boundary (800-1100 m, [O-2] = 2.2-15.0 mu mol l(-1)) to investigate how macrofaunal assemblage structure, affected by different oxygen levels, and C:N coupling influence the fate of particulate organic matter. No macrofauna were present in the OMZ core. Within the OMZ boundary, relatively high abundance and biomass resulted in the highest macrofaunal assimilation of particulate organic carbon (POC) and nitrogen (PON) at the lower oxygen 800 m stations ([O-2] = 2.2-2.36 mu mol l(-1)). At these stations the numerically dominant cirratulid polychaetes exhibited greatest POC and PON uptake. By contrast, at the higher oxygen 1100 m station ([O-2] = 15.0 mu mol l(-1)) macrofaunal C and N assimilation was lower, with POC assimilation dominated by one large solitary ascidian. Macrofaunal POC and PON assimilation were influenced by changes in oxygen availability, and significantly correlated to differences in macrofaunal assemblage structure between stations. However, macrofaunal feeding responses were ultimately characterised by preferential organic nitrogen assimilation, relative to their internal C:N budgets.

KW - matter

KW - C-N

KW - rapid response

KW - macrofaunal community

KW - ecological stoichiometry

KW - Arabian Sea

KW - sea benthic community

KW - Indian continental-margin

KW - N-P ratios

KW - in-situ experiments

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DO - 10.5194/bg-9-993-2012

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EP - 1006

JO - Biogeosciences

JF - Biogeosciences

SN - 1726-4170

IS - 3

ER -