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

[摘要] The Arabian Sea oxygen minimum zone (OMZ) impinges on the western Indiancontinental margin between 150 and 1500 m, causing gradients in oxygenavailability and sediment geochemistry at the sea floor. Oxygen availabilityand sediment geochemistry are important factors structuring macrofaunalassemblages in marine sediments. However, relationships between macrofaunalassemblage structure and sea-floor carbon and nitrogen cycling are poorlyunderstood. We conducted in situ ¹³C:¹⁵N tracer experiments in the OMZcore (540 m [O₂] = 0.35 μmol l^–1) and lower OMZ boundary (800–1100 m,[O₂] = 2.2–15.0 μmol l^–1) to investigate howmacrofaunal assemblage structure, affected by different oxygen levels, andC:N coupling influence the fate of particulate organic matter. No macrofaunawere present in the OMZ core. Within the OMZ boundary, relatively highabundance and biomass resulted in the highest macrofaunal assimilation ofparticulate organic carbon (POC) and nitrogen (PON) at the lower oxygen 800 m stations([O₂] = 2.2–2.36 μmol l^–1). At these stationsthe numerically dominant cirratulid polychaetes exhibited greatest POC andPON uptake. By contrast, at the higher oxygen 1100 m station ([O₂] = 15.0 μmol l^–1) macrofaunal C and N assimilation was lower, with POC assimilation dominated by one large solitary ascidian. Macrofaunal POCand PON assimilation were influenced by changes in oxygen availability, andsignificantly correlated to differences in macrofaunal assemblage structurebetween stations. However, macrofaunal feeding responses were ultimatelycharacterised by preferential organic nitrogen assimilation, relative totheir internal C:N budgets.

[学科分类] 地球化学与岩石