The role of gorgonians as engineering species, in the structure and diversity of benthic communities

Trabajo final presentado por Guillem Corbera Pascual para un Máster en Oceanography de la University of Southampton, realizado bajo la dirección del Dr. Josep-Maria Gili del Institut de Ciències del Mar (ICM-CSIC) y de la Dra. Laura Grange (NOC).-- 36 pagesGorgonians are autogenic ecosystem engineers that create three-dimensional structures via their own tissues. Dense aggregations of these species are known to produce changes in the environment, modifying abiotic and biotic factors. A large number of species benefit from the positive effects caused by gorgonians, which can attract organisms from nearby habitats finally increasing the biological diversity of the habitat. Despite their ecological importance in the functioning of ecosystems, this is the first attempt to analyse the effects of gorgonian population traits, such as density and size, on the surrounding megafaunal organisms and epibionts, using video-transects as reference material. The images used for this project were recorded by means of ROVs in two very contrasting environments: the Mediterranean and the Weddell Sea. Images covered an area of 420 m2 where over 7000 organisms could be identified. Statistical analyses showed that increases in gorgonian density and size have a positive effect on megafaunal species richness and diversity, although the strength of such relationships was not equivalent. Density seems to play a more important role in determining megafaunal diversity than population structure does. In the case of epibionts, both gorgonian attributes were positively correlated to abundance and species richness. These results are probably explained by the changes that highly dense patches of gorgonians produce to the environmental surrounding, mainly to water currents and sediment transport, as well as the opportunity that these aggregations offer to the associated fauna to find places to settle and hide from predatorsPeer Reviewe