Trophic relationships in the nearshore zone of Martel Inlet (King George Island, Antarctica): ?13C stable-isotope analysis

Abstract

Carbon isotopic composition was used to assess the linkage between three different potential sources of energy and the community in the shallow coastal zone of Martel Inlet. Stable δ13C ratios ranged from −28.7‰ for the zooplankton plus phytoplankton to −14.4‰ for the grazer Nacella concinna. Microphytobenthos (−16.7‰) was considerably more enriched in 13C than were suspended particulate matter (SPM) (−25.6‰) and macroalgal fragments (−23.6‰ and −21.1‰), indicating that stable carbon isotope analysis might be used to discern the relative contribution of these sources of primary production. There is a benthic-pelagic coupling between plankton, benthic suspensivores, the ophiuroid Ophionotus victoriae and the icefish Chaenocephalus aceratus. Benthic grazers such as N. concinna, deposit feeders such as Yoldia eightsi and the nematodes showed a tight coupling with the microphytobenthos and the sediment. Some omnivorous/depositivorous polychaetes, echinoids, amphipods and the fish Notothenia coriiceps showed values close to the ratios of the macroalgal fragments. Benthic carnivores and/or scavengers were generally enriched over suspensivores and depleted in relation to microphytobenthos grazers, showing a considerable overlap in δ13C values throughout the food web, without any clear coupling with the primary sources of organic matter. The trophic web in the shallow zone of high benthic production and under seasonal ice cover in the Antarctic is more complex than it is in shelf areas, where SPM is the main food source. The soft-bottom community in the shallow zone of Martel Inlet is enriched in 13C due to the significant input of carbon from the microphytobenthos and macroalgal fragments.