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Hard bottom communities along the western Antarctic Peninsula region are dominated by thick macroalgal forests, which support high densities of mesograzers, particularly amphipods, and also numerous gastropods. The macroalgae are chemically defended from consumption by the mesograzers and other herbivores and they provide the mesograzers a chemically defended refuge from predation by omnivorous fish. The macroalgae benefit in return because the mesograzers remove epiphytic algae from them. Since these two assemblages are major components of the community, this can be viewed as a community-wide mutualism. Most subcomponents of these interactions have also been documented in lower latitude communities and the similarities and differences between the communities in Antarctica and in other regions are discussed. [ABSTRACT FROM AUTHOR]

Chemical defenses against herbivores are common in macroalgae from Antarctica, particularly in those species that typically dominate benthic communities. Conversely, although little studied, chemical defenses do not appear to be as important in the ecological relationships of Arctic macroalgae. Mesoherbivory may be particularly heavy in Antarctic macroalgal communities, but Antarctic macroalgae produce chemical defenses against both mesoherbivores and macroherbivores. Antarctic macroalgae have been useful in testing and extending chemical defense theories. While physical defenses may also be important in some Antarctic macroalgal-herbivore relationships, particularly with respect to mesoherbivores, physical defenses do not appear to have wide-spread importance against macroherbivores. In Arctic macroalgae, physical defenses may be of more overall importance in reducing mesoherbivory. Antarctic macroalgae also produce compounds with the potential to control biofouling by sympatric microalgae. [ABSTRACT FROM AUTHOR]

Nearshore marine benthic algal communities along the western Antarctic Peninsula harbour extremely high densities of amphipods that probably play important roles in nutrient and energy flow. This study extends our evaluation of the importance of amphipods in the nearshore Antarctic Peninsular benthic communities and focuses on sponge associations. We found a mean density of 542 amphipods per litre (L) sponge for twelve species of ecologically dominant sponges. The highest mean density (1295 amphipods per L sponge) occurred with Dendrilla membranosa Pallas. The amphipod community associated with the 12 sponges was diverse (38 species), with mean species richness values ranging from two to eight species. Mean Shannon diversity indices (H') ranged from 0.52 to 1.49. Amphipods did not appear to have obligate host relationships. Qualitative gut content analyses indicated that 12 of the 38 amphipod species were found with sponge spicules in their guts. However, only one of the amphipods, Echiniphimedia hodgsoni Walker, had considerable amounts of spicules in the gut. Organic lipophilic and hydrophilic extracts of the twelve sponges were presented in alginate food disks to a sympatric omnivorous amphipod in feeding bioassays and extracts of only two sponges deterred feeding. [ABSTRACT FROM AUTHOR]

Investigates the chemical ecology of antarctic sponges from McMurdo Sound, Antarctica. Evaluation of extracts from sponges for the presence of defensive substance; Preparation of the extracts from the freeze-dried sponges to achieve separation of potential interfering agents; Bioactivity of antarctic sponge extracts.