Trophic position of Antarctic amphipods—enhanced analysis by a 2-dimensional biomarker assay

Abstract

The discrepancy between the ecological significance of amphipods in the Antarctic and our poor knowledge of their ecofunctional role calls for a more detailed investigation of their trophic status in this ecosystem. A total of 12 amphipod species from suspension feeder to scavenger have been considered in this study. Our objective was to investigate whether the combination of fatty-acid and stable-isotope signatures into a 2-dimensional trophic biomarker assay would increase accuracy in the identification of Antarctic benthic amphipod trophic position. Amphipod isotopic averages ranged from-29.3 ‰ (δ 13 C) and 4.1 ‰ (δ 15 N) for the suspension feeder Ampelisca richardsoni to-21.7 ‰ (δ 13 C) and 11.9 ‰ (δ 15 N) for the high predator Iphimediella sp. Cluster analysis of the fattyacid composition separated the amphipod species into 4 trophic groups: suspension feeders, macroherbivores, omnivores and scavengers. The suspension feeder was isolated due to an important proportion of 18:4(n-3), a fatty-acid biomarker of phytoplankton. Macro-herbivores were found to rely heavily on macroalgal carbon, containing a high percentage of arachidonic acid (20:4(n-6)). Scavenger amphipods revealed a unique fatty-acid composition dominated by 1 single fatty acid, 18:1(n-9), probably the result of a very intensive de novo biosynthesis to cope with starvation periods. Our data emphasise the need to combine different types of information to be able to draw the right conclusions regarding trophic ecology. Indeed, in some cases, the exclusive use of 1 type of tracing method, fatty acids or stable isotopes, would have resulted in misleading/false conclusions in the trophic classification of amphipods. Therefore, a 2-dimensional biomarker assay is a useful tool to elucidate the trophic positions of benthic amphipods.

Fishing for scavengers: an integrated study to amphipod (Crustacea: Lysianassoidea) diversity of Potter Cove (South Shetland Islands, Antarctica)

“…femoratus in the food web of Potter Cove needs more detailed study as omnivorous species in general do not necessarily have a flexible position in food webs (Johnston et al 2011). Studies addressing species-specific feeding and decomposition rates (Lastra et al 2014) as well as stable isotope and fatty acid analyses (Nyssen et al 2002(Nyssen et al , 2005 are needed to further elucidate the role and importance of lysianassoid amphipods in the coastal Antarctic ecosystem, which are exposed to a rapidly changing environment due to climate-induced glacier retreat.…”

Assemblages and habitat preferences of soft bottom Antarctic Amphipoda: Admiralty Bay case study

“…This kind of separation was observed between some other representatives of Ampeliscidae (Mills 1967) and might also be associated with different food preferences. Ampelisca richardsoni, living in shallower water, is known to feed on phytoplankton (Nyssen et al 2005) that could be less available in deeper parts of the shelf, so one can expect that Ampelisca anversensis uses also some other type of food. However, no stomach content studies are available yet.…”

“…The only information about the habitat type for the second species-K. setimana-comes from Signy Island, where it was reported from muddy bottoms of shallow waters (Thurston 1974). Also Ampelisca richardsoni is known as filter-feeder which consumes mainly phytoplankton (Nyssen et al 2005). This species leads rather sedentary life, which is a common feature of representatives of the family Ampeliscidae.…”

Trophic niche partitioning of littoral fish species from the rocky intertidal of Helgoland, Germany

“…Initially, these markers were reported as a measure for trophic relations among copepods (ElSabaawi et al 2009) as well as other crustaceans, e.g. amphipods and krill (Stevens et al 2004;Nyssen et al 2005;Schmidt et al 2006;Hagen et al 2007). It can be speculated that taxonomic differences and differences in fatty acid metabolism between benthic versus pelagic consumers as well as vertebrate versus invertebrates might be responsible for the contrasting results.…”