Chemical Mediation of Antarctic Macroalga-Grazer Interactions

Abstract

Macroalgal forests along the western Antarctic Peninsula (WAP) support dense assemblages of small macroalgal-associated invertebrates, particularly amphipods but also others including gastropods. Most of the macroalgal species, including all the larger, ecologically dominant brown macroalgae, elaborate chemical defenses against herbivory to amphipods as well as fish and sea stars. Consequently, the vast majority of the macroalgal biomass in these forests is unpalatable to potential consumers. A great deal of progress has been made on understanding these relationships during the past decade. Although the macroalgae are seldom consumed by the associated invertebrates and fish, many of the invertebrates, particularly the amphipods, benefit from associating with the chemically defended macroalgae because omnivorous fish avoid feeding on them. The amphipods benefit their macroalgal hosts by greatly reducing biofouling by diatoms and other epiphytic algae. This chapter reviews progress in understanding the chemical defenses of Antarctic macroalgae. It also reviews the community-wide mutualistic interaction between macroalgae and its associated amphipods as well as recent studies examining the extent to which this mutualistic interaction also occurs with macroalgal-associated gastropods.