MEPS 462:163-174 (2012)  -  DOI: https://doi.org/10.3354/meps09840

ABSTRACT: The main predators of Antarctic benthic organisms are vagile invertebrates, including dense amphipod populations. Marked seasonalities of food availability drive consumers to develop opportunistic behaviors, which favors the evolution of defensive chemistry in potential prey. We used the circumpolar omnivorous amphipod Cheirimedon femoratus and a new feeding preference assay using alginate caviar-textured food pearls to examine the incidence of lipophilic deterrents in Antarctic benthic organisms. The method showed remarkable discriminatory potential for unpalatable metabolites. We obtained a total of 52 fractions from 40 samples that represented 31 species (including sponges, cnidarians, ascidians, a bryozoan, an echinoderm, a hemichordate and algae) from the Weddell Sea and the South Shetland Islands. Unpalatability was found in 42 extracts from 26 species. The remaining 10 extracts from 7 samples did not exhibit unpalatability, indicating either that deterrents are contained in fractions not tested here, or that alternative defensive traits might protect these organisms. Within the 4 major taxonomical groups, the ascidians showed the highest repellencies, followed by sponges, cnidarians, and algae. These organisms from distant Antarctic locations may represent both host biosubstrata and potential prey for C. femoratus. Thus, this amphipod could be a significant inducer of chemical protection in its hosts due to the localized and constant contact created by inhabiting and feeding on the same organism. Defense sequestration in specific body-structures, as predicted by the Optimal Defense Theory, was detected in an octocoral sample. We suggest that some of the tested organisms could combine several defensive strategies to prevent predation. Altogether, our results indicate that chemical defenses are broadly used among Antarctic benthic organisms to avoid predation by the opportunistic amphipod C. femoratus, and thus, chemical ecology is a key aspect in the functioning of Antarctic ecosystems.

KEY WORDS: Cheirimedon femoratus · Antarctic invertebrates · Antarctic algae · Chemical ecology · Omnivorous amphipod · Unpalatability · Feeding preference assays