Morphological and biological traits of antarctic peninsular macroalgae influencing distribution and abundance of associated amphipods

Coastal macroalgal communities provide a rich source of nutrients and a variety of habitats for associated mesograzers. Benthic macroalgae dominate biomass in near-shore Antarctic Peninsular communities. We examined the distribution and abundance of gammarid amphipods associated with 8 common species of Antarctic macroalgae. Divers collected ten individuals of each targeted algal species in a mesh bag (< 1 mm) and the associated epifauna later washed on to a sieve mesh (1.4 mm) and sorted. Algal morphometrics considered included canopy and thallus volume, and the order and number of branches. A total of 28 species of amphipods were identified with mean abundances ranging from 0.02 2.3 individuals/g algal wet wt. Cluster analysis revealed that the three algal species that were most highly branched harbored the greatest abundance and diversity of amphipods. Palatability assays using the common omnivorous amphipod (Gondogeneia antarctica) presented fresh thalli and finely ground dried algal tissues embedded in alginate food pellets revealed no correlation between palatability and amphipod-algal associations. In a parallel study, we found that those algal species harboring the greatest abundance and diversity of amphipods were chemically defended against amphipod herbivory. Thus our findings suggest that both algal morphology and chemical defenses influence the distribution and abundance of macroalgal-associated amphipods in Antarctic Peninsular marine communities. Supported by the Office of Polar Programs, NSF.