Interações competitivas entre Epizoanthus gabrieli Carlgreen, 1951 (Ordem Zoanthidea) e corais na Baía de Todos os Santos e suas implicações para a comunidade recifal.

Abstract

Some coral reefs of Todos os Santos Bay have undergone a drastic change in the benthic community. In 2003, they began to be dominated by the zoanthid Epizoanthus gabrieli. This phenomenon is a consequence of coral reef degradation that now reaches approximately 20% of coral reefs worldwide and and threatens another 35%. The most dramatic consequences of this degradation are the phase shift phenomena which are characterized by reduction of coral abundance and increase of organisms that do not build reefs. Despite their importance, only a phase shift to the domain of macroalgae has been sufficiently studied. Given this situation, it is urgent to create functional models that demonstrate the ecological processes that occur in the installation of alternative states that persist over time. These models provide important information that can help in decision making on management measures both for prevention and recovery of these ecosystems. The aims of this work are (i) to verify if this phenomenon is a phase shift, (i.e. the reduction of the abundance of coral and persistence of high coverage E. gabrieli for more than five years of monitoring), (ii) evaluate the effects of competition between this zoanthid and recruits and adult coral with manipulative experiments and (iii) study the effects of dominance on the fish assemblage. The result confirmed the existence of a phase shift, suggesting that the abundance of E. gabrieli increased in 2003 or before and in 2007 there was a reduction in coral cover, and that this condition remained until at least 2013. The three coral species tested show great sensitivity to contact with E. gabrieli, with necrosis in 78% of the colonies and with overgrow in 35% of cases in a period of 118 days. In addition, a model made from the data of a proportion of coral colonies in contact with this zoanthid and coverage of E. gabrieli suggests that when the zoanthid reaches 6% coverage, 50% of coral colonies come in contact with it. These data are strong evidence that the reduction of coral cover observed between 2003 and 2007 was caused by competition between these organisms. There was no negative effect on the recruitment of coral on artificial substrate free in reefs dominated by E. gabrieli or near their colonies. This suggests that a presumed reduction of coverage of this zoanthid should be accompanied by an increase in coral recruitment rates and the competition by inhibition of recruitment does not support an effect of hysteresis. It was found that this phase shift reduces species richness of reef fishes, by ten species unless reefs normal, and that favor mobile invertivores to the detriment of carnivores and sessile invertivores. However there was no difference in the abundance of fish.