Biodiversity and Chemical ecology in Antarctic bryozoans = Biodiversitat i ecologia química de briozous antàrtics

Resumen

The current thesis covers two important and poorly known aspects of Antarctic bryozoans: biodiversity and chemical ecology. The comparative analyses of diversity carried out here (Chapters 1 and 2) between Antarctica and the last separated fragments of Gondwana support the hypothesis of the sequential separation of Gondwana. We discuss that the high number of species from the Argentine Patagonian (AP) region shared with Antarctica found in our study question the real extent of Antarctic isolation for cheilostome bryozoans. The presence of shared common bryozoan species between these two regions may also be explained by the free migration of marine organisms in and out of the Polar Front, via the deep abyssal plains and the potential passive northwards transport of larvae (or perhaps even adults) to considerable distances, via the branch of the Antarctic Circumpolar Current (ACC) flowing northward along the continental shelf of Argentina, the Falkland/Malvinas Current. The role of the Scotia Arc and other dispersal pathways, like eddies of ACC, and human dispersal mechanisms, may increase the bryozoan connection found between the Antarctica and the AP region. Also, our studies (Chapters 1 and 2) are among the first characterizations of the bryozoan communities, mainly at the slope, from the AP region, and from the Southern Ocean (SO), specially the Weddell Sea. The bathymetric distribution from the AP region and the SO found in our studies fits well with the limits of the continental shelf, the slope and the deep sea. Interestingly, our research also shows an expansion in the known distribution of diverse bryozoan species from the AP region and the SO. Our results stress the importance of taxonomical studies in these scarcely explored regions, reporting a high number of new genera and species, and new records too. Among the new species found in our study, a bryozoan of the genus of Reteporella characterized by rare giant spherical avicularia is described in Chapter 3, leading us to discuss which are the potential roles of the avicularia. Since the studied bryozoan communities, below areas affected by local disturbances (iceberg scours and anchor ice), are mainly subject to biotic factors such as competence and predation, the evolution has favoured the development of chemical mechanisms in benthic organisms, which have also been investigated here (Chapters 4 and 5). Our studies are among the first reports on chemical ecology of Antarctic bryozoans. In order to study these chemical interactions, new adapted protocols were designed using sympatric and abundant predators. Our findings demonstrate the importance of diverse chemical ecology mechanisms against competence and predation in Antarctic bryozoans. Most bryozoan species tested here display cytotoxicity and/or repellent activity against the sea urchin Sterechinus neumayeri and the amphipod Cheirimedon femoratus, respectively (Chapter 4). In Chapter 5, our results demonstrate that bryozoans seem to be readily defended against at least one of the two abundant predators, Odontaster validus and C. femoratus. The intra- and interspecific variability in bioactivity suggest an adaptive response to diverse abiotic and biotic factors, presence of microorganisms and/or genetic variability. The general trend in our study indicates the presence of a combination of both chemical and physical defensive mechanisms in most bryozoan species, suggesting complementary traits. In general, these results lead to the conclusion that this phylum is very active with extended repellent activities.