MCCLINTOCK, James B.; AMSLER, Charles D.; BAKER, Bill J.; VAN SOEST, Robert; Univ. of Alabama at Birmingham; Univ. of Alabama at Birmingham; Univ. of South Florida; University of the Netherlands: The Ecology of Antarctic Marine Sponges
Sponges are dominant components of marine communities surrounding the continental shelf of Antarctica. High in terms of species diversity (400-450 species) and in biomass, these assemblages contribute considerable structural heterogeneity and extensive surface areas for epibiotic organisms. They also represent a significant source of nutrients to a variety of prospective predators, including a unique suite of spongivorous sea stars, whose selective feeding has important ramification upon community structure. The highly seasonal and short lived macroplankton blooms that typify antarctic seas are paradoxical when considering the planktivorous habit of sponges. Despite their generally slow growth, antarctic sponges must either efficiently exploit alternate sources of nutrition such as DOM and microplankton or be under resource constraints. In contrast to predictions that patterns of fish spongivory should select for an inverse correlation between latitude and chemical defenses in marine sponges, chemical defenses are not uncommon in antarctic sponges. A variety of secondary metabolites deter predation by sympatric sea stars and, in at least one sponge species, are sequestered in the outermost body layers, an optimal allocation pattern for an organism preyed upon by sea stars. Metabolites have also been found to short circuit molting in sponge-feeding amphipods and prevent fouling by benthic diatoms. Coloration in a select group of antarctic sponges may be the result of relict pigments originally selected for in temperate or tropical conditions as aposomatics or UV screens, that have been evolutionarily conserved because they themselves have bioactive defensive properties. This hypothesis is supported by an examination of the ecological bioactive properties of pigments from four common antarctic sponges.
