Antipredatory chemical defenses of selected Antarctic benthic organisms J. Moles 1 L. Núñez-Pons 2, S. Taboada 1, J. Cristobo 3, C. Avila 1 Department of Animal Biology (Invertebrates) and Biodiversity Research Institute (IrBIO), University of Barcelona, Spain 2 Hawaii Institute of Marine Biology, University of Hawaii, PO Box 1346, Kaneohe, USA 3 Centro Oceanográfico de Gijón, Instituto Español de Oceanografía, Spain Two of species selected for deterrent bioassays. A – The solitary and unpalatable ascidian Molgula pedunculata. B – The chemically-defended sponge Cinachyra antarctica. INTRODUCTION Antarctic benthic communities are largely structured by predation, being echinoderms, and particularly sea stars, the main predators. Therefore, through evolution, sessile and sluggish organisms have developed an array of antipredatory mechanisms, being chemical defenses are quite extended, yet still poorly understood in Polar Regions. MATERIAL AND METHODS Samples were collected at shelf depths in the (1) Eastern Weddell Sea and (2) Bouvet Island, and at shallow-water depths at the (3) South Shetland Islands. RESULTS We assessed the incidence of feeding repellents in organisms from 11 phyla including algae, sessile invertebrates, and vagile fauna. Among the 65 species tested, 72% were studied here for the first time for antipredatory properties. Our results reflect a wide-ranging presence of chemical defenses in Antarctic benthic fauna in nearly all the taxa studied, with 45% of the species demonstrating significant activities, being the extracts of ascidians, cnidarians and sponges the more noxious. Results are in agreement with previous studies from similar localities, but significantly lower from shallow environments (Furrow et al. 2003, Taboada et al. 2013). SCUBA photographs taken at 15 m depth in Deception Island (South Shetland islands). A – piles of Odontaster validus devouring a completely buried bivalve, Laternula elliptica. B – Odontaster validus on the abundant and non-deterrent sponge Mycale (Oxymycale) acerata. DISCUSSION Repellent activities were more frequent in lipophilic extracts, thus suggesting a greater use of non-polar defensive natural products. Some species displayed intraspecific variation in chemical defense among conspecific samples of different localities. Whether this difference may be due to trade-offs between internal physiological processes or to external interactions within the ecosystem, requires further investigation. Some species seemed to accomplish the predicted superficial location of repellents according to the ODT towards Antarctic keystone predators (Rhoades & Gates 1976). Other internal distributions found of protective chemical agents might instead respond to the production of defended larval stages (Lindquist et al. 1992). Our study provides further evidence of the broad presence of defensive metabolites in Antarctic ecosystems, with many new organisms added to the list of chemically defended species. Number of active and inactive species tested for each phylum regarding to ether extracts. AB ABAcknowledgements The authors wish to thank C. Angulo, M. Ballesteros, M. Bas, A. Riesgo, and J. Vázquez for laboratory and field support. Thanks are due to Prof W. Arntz and the crew of the R/V of Polarstern for allowing our participation in the Antarctic cruises ANT XV/3 and XXI/2 (AWI, Bremerhaven, Germany). Funding was provided by the Spanish government through the ECOQUIM and ACTIQUIM Projects (REN , REN E ANT, CGL /ANT, CGL , and CTM /ANT). References Furrow F.B. et al. (2003) Mar. Biol. 143(3), 443–449; Lindquist N. et al. (1992) Ecol. Monograph. 62, 547–568; Rhoades D.F. & Gates R.G. (1976) Recent Adv. Phytochem. 10, 168–213; Taboada S., et al. (2013) Polar Biol. 36(1), 13–25. When possible, organisms were dissected to determine possible anatomical allocation of deterrent compounds to test the Optimal Defense Theory (ODT; Rhoades & Gates 1976). The common, eurybathic, and generalist sea star Odontaster validus was chosen to perform feeding repellence bioassays, using ether (lipophilic) and butanol (hydrophilic) extracts from our samples. 123