Chemo–ecological interactions in Antarctic bryozoans

Abstract

The role of bioactive metabolites in ecological interactions involving Antarctic bryozoans has been scarcely studied. Bryozoans are one of the most abundant and diverse members of the Antarctic benthos and are preyed upon by diverse kinds of predators. They seem to be casual food items of the common Antarctic sea urchin Sterechinus neumayeri and the ubiquitous omnivorous amphipod Cheirimedon femoratus. In this study, the cytotoxic activity against embryos and sperm of the sea urchin S. neumayeri and the substrate preferences of the amphipod C. femoratus were assessed using organic extracts from Antarctic bryozoans, in order to determine the presence of chemical defenses. New adapted protocols were designed using a solidifying gel for simulating bryozoans’ surface. We analyzed 32 organic extracts from 16 samples that belonged to 13 different bryozoan species. No cytotoxicity was detected against embryos of S. neumayeri, while 12 of the 13 bryozoan species were cytotoxic to sperm at natural concentrations. In the substrate preference assays, the amphipod C. femoratus was repelled by ten species. The variable bioactivities found in both types of organic partitions of extracts indicated the presence of both lipophilic and hydrophilic defenses. Inter- and intraspecific variability of chemical defenses was detected also, suggesting environmental-induced responses, symbiotic production, and/or genetic variability. Possible alternative defensive mechanisms are also discussed for species with low or no chemical defense. Our results clearly support the fact that chemically mediated bioactivity in Antarctic bryozoans is common, and there is a likely ecological role of cytotoxic and repellent compounds for their protection.