Current S-022 Research at Palmer Station

This project provides an evaluation of the importance of mesograzers in western Antarctic Peninsula marine communities by examining the role of mesoherbivores in structuring macroalgal communities and by elucidating the ecological interactions of mesograzers with a dominant group of benthic macroinvertebrates, the marine sponges. Moreover, chemical studies are being conducted to gain a more thorough understanding of the chemical defenses that Antarctic Peninsula sponges direct towards crustacean mesograzers. The goals are a direct outcome of the our past studies of the chemical ecology of shallow-water marine macroalgae and invertebrates on the Antarctic Peninsula, as well as our earlier studies in McMurdo Sound, Antarctica. The near shore environments of the western Antarctic Peninsula are uniquely suited to their proposed research objectives as they harbor extremely high densities of benthic amphipods, as well as rich assemblages of both macroalgae and sponges. We are focusing on three sets of questions concerning the importance of mesograzers, and amphipods in particular, in nearshore habitats of the western Antarctic Peninsula.

First, building on our previous studies that have established that mesoherbivores, and specifically amphipods, are a conspicuous and dominant component of the macroalgal community, we are testing the hypothesis that mesoherbivory is particularly heavy in western Antarctic Peninsula marine communities and has an important influence on algal community structure. Initial studies are documenting which species of amphipods feed in whole or part on microalgae and macroalgae, the incidence and distribution of filamentous endophytes in dominant macroalgae, and comparative night time patterns of amphipod abundances on macrophytes. Specific hypotheses being tested include whether predation pressure by mesoherbivores is responsible for the relative lack of filamentous epiphytes but not filamentous endophytes in these communities and whether macroalgal-mesograzer and macrophyte-endophyte relationships are chemically mediated.

Second, building on quantitative studies that documented associations between Antarctic sponges and amphipods, we are examining the broad hypothesis that mesograzers in general, and amphipods in particular, interact with and prey upon sponges to a greater extent than heretofore recognized in Antarctic communities. Specific questions include whether amphipods commonly associate with sponges and whether such associations are host-specific. The functional basis of these associations are being considered by examining whether the sponges are used as prey, and if so, whether there is evidence that some sponges produce secondary metabolites that show efficacy against mesograzers such as amphipods. If amphipods are not consuming sponges then sponges might be providing structural or chemical refuge from predators such as fish.

Third, building on our previous findings that many Antarctic macroalgae and sponges are chemically defended and that some Antarctic sponges may produce secondary metabolites that inhibit molting and thus cause mortality in crustacean mesograzers, we are testing the hypotheses that: 1) Antarctic algae and invertebrates biosynthesize secondary metabolites that deter feeding by amphipod predators; and 2) pigments found in three Antarctic sponges are tryptophan catabolites produced as defenses against crustacean predators that impact molting. They are basing their evaluation of these hypothesis on isolation and characterization of the specific anti-feeding metabolites, on biosynthetic studies to establish the metabolic origin of the pigments, and on bioassays to establish the chemical defense roles of both groups of compounds.

Go to summary of most recent work at McMurdo Station