Estudo da ação alelopática de extratos de coral-sol (Scleractinia, Tubastraea) sobre o comportamento e a sobrevida de larvas congêneres

Abstract

Secondary metabolites are organic compounds, which are not very abundant, but provide very important characteristics to living beings, acting in competition and enhancing the survival of plants and animals. Marine invertebrates are considered organisms with great chemical potential for the production of organic molecules derived from secondary metabolites. Dendrophilliid corals known as 'sun corals' were introduced on the southeastern coast of Brazil (22-23oS), and are now found dispersed in natural and artificial environments along the northeastern coast, being recognized by aspects of colonial morphology as 'dendroid' (more elongated polyps) and 'plocoid (smaller polyps, flush with the surface of the colonies). The literature has supported the identification of two species, Tubastraea tagusensis (dendroid morph) and T. coccinea (plocoid morph) for the sector of Todos-osSantos Bay (BA), but, taxonomically, there are divergences about the occurrence of the congener dendroid – parallel studies are addressing the issue and indicate the existence of other species. In fact, sun coral has been characterized by its chemical composition with a strong allelopathic effect, which apparently seems to support its competitive success and rapid occupation of new spaces. Additionally, biological aspects, such as continuous reproductive cycles and probable production of embryos/larvae by parthenogenesis, guarantee differentiated reproductive rates – indeed, hundreds of larvae can be released by a single colony in a planulation event. Thus, based on in situ observations, during a biofouling monitoring protocol with the occurrence of sun coral, a hypothesis was outlined about the chemical action potential varying between the morphotypes of the colonies - which would influence the dynamics of intrageneric competition and prevalence of dendroid and plocoid morphs in populations. Therefore, a sample design was formulated to investigate the influence of secondary compounds (obtained from methanolic extracts) on congener larvae. As a proposal, two tests were carried out, in addition to the control, one with an extract of the dendroid morphotype on plocoid larvae, and another with an extract of plocoid on morphotype dendroid. As a result, it was found that larval survival was significantly affected in all experiments performed. However, extracts obtained from dendroid colonies revealed a greater effect of toxicity when compared to biological tests using extracts of the plocoid morphotype. Observations made at 24-hour intervals showed that larvae in the highest concentrations (500 µg/ml and 1000 µg/ml) were affected more quickly when compared to larvae in lower concentrations (10 µg/ml and 100 µg/ml) and to the control group (medium without extract/0 µg/ml). It was proven that the action of extracts can differ between4 morphotypes, affecting intrageneric relationships. Future studies, involving other representatives of benthic communities, may clarify whether the allelopathic effects are uniformly perceived and whether there is any expectation that native organisms are adapting to the new chemical repertoire.