Ecology of Antarctic Marine Sponges: An Overview

Abstract

Sponges are important components of marine benthic communities of Antarctica. Numbers of species are high, within the lower range for tropical latitudes, similar to those in the Arctic, and comparable or higher than those of temperate marine environments. Many have circumpolar distributions and in some habitats hexactinellids dominate benthic biomass. Antarctic sponge assemblages contribute considerable structural heterogeneity for colonizing epibionts. They also represent a significant source of nutrients to prospective predators, including a suite of spongivorous sea stars whose selective foraging behaviors have important ramifications upon community structure. The highly seasonal plankton blooms that typify the Antarctic continental shelf are paradoxical when considering the planktivorous diets of sponges. Throughout much of the year Antarctic sponges must either exploit alternate sources of nutrition such as dissolved organic carbon or be physiologically adapted to withstand resource constraints. In contrast to predictions that global patterns of predation should select for an inverse correlation between latitude and chemical defenses in marine sponges, such defenses are not uncommon in Antarctic sponges. Some species sequester their defensive metabolites in the outermost layers where they are optimally effective against sea star predation. Secondary metabolites have also been shown to short-circuit molting in sponge-feeding amphipods and prevent fouling by diatoms. Coloration in Antarctic sponges may be the result of relict pigments originally selected for aposematism or UV screens yet conserved because of their defensive properties. This hypothesis is supported by the bioactive properties of pigments examined to date in a suite of common Antarctic sponges.

Palatability and chemical anti-predatory defenses in common ascidians from the Antarctic Peninsula

“…m -2 benthos, based on calculations using estimates from Huang et al 2007 andAmsler et al 2008) along the central western Antarctic Peninsula. This amphipod has been used as a model mesograzer in studies of the chemical feeding deterrent properties of Antarctic macroalgae (Amsler et al 2005) and sponges (Amsler et al in press). The preference of this amphipod for pellets containing organic extracts of marine algae or sessile invertebrates is a phenomenon commonly observed in this species (Amsler et al 2005, in press) and attributed to extracts being phagostimulatory.…”

“…For fresh tissue pieces, the controls used in statistical comparisons were the non-solvent food pellets. For pellets containing ascidian extracts, the controls were the corresponding solvent-treated control pellets that were offered to a different set of sea stars (Amsler et al 2005).…”

“…Amphipod feeding assays using alginate pellets were conducted using a 2-choice feeding assay model (Peterson & Renaud 1989, Amsler et al 2005). In each assay, an alginate pellet (disc-shaped, 1 cm diameter, 2 mm thick) prepared with 2% alginate and containing a 2% dried krill powder and either a hydrophilic or lipophilic ascidian extract was paired with a control alginate pellet containing solvent-only treated krill powder.…”

Long-distance island hopping without dispersal stages: transportation across major zoogeographic barriers in a Southern Ocean isopod

“…S. septemcarinata is an exception in this respect: It has enlarged pereiopods 5-7 which it uses to climb on substrata such as large Antarctic rossellid sponges (personal observation of CH and FL during the ICEFISH 2004 expedition). While the possibility of passive rafting on sponge fragments or even entire sponges with detached anchor ice (Dayton et al 1969) may provide a means for dispersal for the heavily glaciated Antarctic region, this is unlikely to be of importance for long-distance dispersal (McClintock et al 2005) in the subAntarctic islands today. During the last glacial periods, ice sheets extended far to the north (see also discussion in Fraser et al 2009) rendering the possibility of transport by anchor ice at the end of glacial periods not unlikely.…”

Effects of sponge and barnacle encrustation on survival of the scallop Chlamys hastata

“…This has been demonstrated in sessile bivalves such as mussels, clams, and oysters which can be less susceptible to predation if they are encrusted by epibionts that are unpalatable to the predator or that make the bivalve less conspicuous (Vance, 1978;Feifarek, 1987;Wahl et al, 1997;Laudien & Wahl, 1999). Sponges also possess chemical defenses to deter their own predators, including sea stars (Waddell & Pawlik, 2000;McClintock et al, 2005), and by encrusting a scallop they may make the scallop less palatable to a sea star predator.…”