CHEMICAL DEFENSE AGAINST HERBIVORY IN THE ANTARCTIC MARINE MACROALGAEIRIDAEA-CORDATA AND PHYLLOPHORA-ANTARCTICA (RHODOPHYCEAE)

Iridaea cordata (Turner) Bory and Phyllophora antarctica A. et E. S. G epp (Gigartinales, Rhodophyceae) are common in many high-latitude, sha llow benthic marine communities in Antarctica, but previous observatio ns have indicated little or no exploitation by potential herbivores. W e have measure retention of test disks over the mouths of the common A ntarctic sea urchin Sterechinus neumayeri Meissner, and we have used t his assay to examine potential chemical defenses in I. cordata and P. antarctica. Thallus disks of both macroalgal species were retained by the urchins for significantly shorter times than inert filter paper di sks and much shorter times than paper disks with a feeding stimulant. Both nonpolar and polar extracts of each macroalgal species added to d isks with a feeding stimulant significantly decreased retention times relative to controls. These results support the hypothesis that chemic al defenses in I. cordata and P. antarctica play a role in deterring p otential herbivores.