S1-2 Saturday, Jan. 4 08:00 - 08:30 Allies, Cheaters and Thieves: Macroalgal-Mesograzer Interactions on the Western Antarctic Peninsula HEISER, S*; SHILLING, AJ; AMSLER, CD; MCCLINTOCK, JB; BAKER, BJ; University of Alabama at Birmingham; University of South Florida ; University of Alabama at Birmingham; University of Alabama at Birmingham; University of South Florida email@example.com
Macroalgae dominate the hard benthos along the Western Antarctic Peninsula to depths of up to 40 m or more. Most of the macroalgae are chemically defended from a variety of macro- and mesograzers but harbor very high densities of amphipods. The amphipods benefit from living on the large, chemically-defended macroalgae because they gain refuge from fish which are their primary predators. A majority amphipod species do not consume most of the macroalgal species, but are of benefit to the macroalgae by keeping them relatively clean of epiphytic microalgae and filamentous macroalgae. One amphipod species, however, does consume some of the chemically defended red algal species and is able to sequester algal metabolites for its own use as defenses against fish. A combined genetic and chemical analysis of the alga from different collection sites revealed that it divides into two closely related haplotypes (‘phylogroups’), not distinct enough to be considered separate species, each of which is further divided into one of 14 groups (‘chemogroups’) with distinct mixtures of defensive, halogenated secondary metabolites. The amphipods feed on some of the chemogroups at significantly slower rates than others. Different sites are dominated by different chemogroups but experiments indicate that most individual algae retain their chemogroup for at least a year after transplantation between sites. Patterns of gene flow are being investigated as a potential source of the spatial variation in chemogroups.