Carbon flow and trophic structure of an Antarctic coastal benthic community as determined by δ13C and δ15N

Stable isotopes of carbon and nitrogen were used to determine the different carbon pathways and trophic assemblages amongst coastal benthic fauna of the Windmill Islands, East Antarctica. Macroalgae, pelagic POM, sediment POM and sea ice POM had well-separated δ13C signatures, which ranged from −36.75‰ for the red alga Phyllophora antarctica, to −10.35‰ for sea ice POM. Consumers were also well separated by δ13C, ranging from −21.42‰ for the holothurian Staurocucumis sp. up to −7.47‰ for the urchin Sterechinus neumayeri. Analysis of δ13C and δ15N revealed distinct groups for suspension feeders, grazer/herbivores and deposit feeders, whilst predators and predator/scavengers showed less grouping. Consumers spanned a δ15N range of 8.71‰, equivalent to four trophic levels, although δ15N ratios amongst consumers were continuous, rather than grouped into discrete trophic levels. The study has built a trophic model for the Windmill Islands and summarises three main carbon pathways utilised by the benthos: (1) pelagic POM; (2) macroalgae/epiphytic/benthic diatoms and (3) sediment POM/benthic diatoms. The movement of carbon within the coastal benthic community of the Windmill Islands is considered complex, and stable isotopes of carbon and nitrogen were valuable tools in determining specific feeding guilds and in tracing carbon flow, particularly amongst lower-order consumers.

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► δ13C and δ15N were used to identify carbon flow and trophic structure in an Antarctic coastal benthic system.
► Carbon sources were well separated by δ13C and feeding guilds separated into defined isotopic groups.
► Trophic levels were less defined, suggesting a trophic continuum.
► Based on our model, carbon flow to consumers can be summarised into three main pathways.
► δ13C and δ15N were useful tools for determining trophic assemblages in this complex benthic food web.