Cytotoxic Activity of Antarctic Benthic Organisms Against the Common Sea Urchin Sterechinus neumayeri

Abstract

Antarctic benthic communities below anchor ice and ice scour are subjected to intense biotic interactions, and this has propitiated the development of chemicals to avoid predation, competition, and/or fouling avoidance. In particular, Sterechinus neumayeri, a common eurybathic sympatric sea urchin species, can have a negative effect on early recruitment of benthic organisms through grazing. An adaptive response of these co-existing benthic animals may consist in displaying cytotoxic activities, poorly investigated so far in Antarctic ecosystems, in order to prevent the settlement of embryos and larvae of this sea urchin on them or near and, consequently, to decrease its grazing pressure. Cytotoxic activities of Antarctic benthic organisms, mainly from the deep waters of the poorly surveyed area of the eastern Weddell Sea, were assessed against embryos and sperm of the sea urchin S. neumayeri. A new methodology based in a standardized protocol was adopted for this species. Bioassays were performed at Deception Island (South Shetland Islands) during the Austral Summers of 2008-2009 and 2009-2010, using ether extracts at different concentrations from different benthic organisms collected in previous Antarctic expeditions. A high percentage (80%) of the species tested (29) from eight different phyla (Porifera, Echinodermata, Cnidaria, Chordata, Bryozoa, Annelida, Nemertea and Hemichordata) were toxic in one or both experiments. In the bioassay of cytotoxicity against embryos, seven of the 14 species (50%) tested did not reach the blastula stage at the highest extract concentration. In the case of the cytotoxicity against sperm, a total of 20 species were tested and all the extracts except one were toxic to the sperm at the maximum concentration. In addition, 6 species were dissected into parts to investigate the possible allocation of defensive compounds. Our results highlight the important role of cytotoxic activity of some Antarctic benthic organisms as a possible chemical defense and/or mechanism of competition for space or food against this common sea urchin.