Chemotactic tube-foot responses of the spongivorous sea star Perknaster fuscus to organic extracts of sponges from McMurdo Sound, Antarctica

Studies were continued to investigate the ability of secondary metabolites sequestered in Antarctic sponges to cause feeding deterrent responses (tube foot retractions) in a common predator of Antarctic sponges, the sea star Perknaster fuscus. Lipophilic (dichloromethane/methanol) and hydrophilic (m ethanol/water) extracts of 15 new species of Antarctic marine sponges were tested for their ability to induce sustained tube-foot retraction. One addi tional species, Cinchyra antarctica, was re-tested from a previous study be cause we discovered a colour morph that was of comparative interest. Employ ing established protocols, sponge extracts were imbedded in silicone and pr esented to an extended tube-foot on the tip of a glass rod. Extracts often of the 15 new species of sponges (67%) caused significantly longer tube-foo t retractions than controls. Among all sponges tested, significant tube-foo t retraction activity was primarily associated with dichloromethane/ methan ol extracts (eleven sponge species or colour morphs), while significant tub e-foot retraction activity was less common in response to methanol/water ex tracts (three sponges species or colour morphs). Both lipophilic and hydrop hilic extracts from the sponges C. antarctica (yellow morph) and Scolymasti a joubini elicited significant tube-foot retraction activity, suggesting th at more than one compound from these species might elicit tube-foot retract ions in P. fuscus. Overall these findings lend considerable support to the hypothesis that there has been significant evolutionary selection for chemi cal defences among Antarctic marine sponges in McMurdo Sound, in contrast t o earlier biogeographic selection models that predicted low levels of chemi cal defences in polar marine invertebrates.