Equinodermos asociados a formaciones arrecifales en Zihuatanejo y Acapulco, Guerrero, México

Abstract

El conocimiento de los equinodermos de la región de Zihuatanejo y Acapulco, Guerrero, es escaso, y el existente refiere principalmente a listados taxonómicos. Con esos antecedentes, en este trabajo, se describión y caracterizó la comunidad de equinodermos asociada a arrecifes coralinos a partir de transectos de banda de 50 m de largo por 1 m d ancho. Durante 2004 se realizaron dos muestreos prospectivos (uno en época de lluvias y otro en época de secas). En total se registraron diez especies, tres asteroideos, seis echinoideos y un holoturoideo. La diversidad promedio obtenida en los 13 sitios estudiados (1.036 bits ind-1) se considera baja al compararla con la diversidad mácima posible (3.322 bits ind-1) debido a la dominancia del erizo negro Diadema mexicanum y la estrella de mar Phataria unifascialis, con densidades promedio de 1.45±0.60 ind m-2 y 0.12±0.02 in m-2, respectivamente. Durante la época de estiaje se presentó la mayor diversidad, misma que se mantiene sin diferencias entre localidades. El arreglo espacial de la composición de especies de equinodermos obtenido por el análisis de escalamiento multidimensional denota la formación de cinco conglomerados de localidades, donde posiblemente el tipo de fondo y la cobertura arrecifal son las variables determinantes.

Knowledge of echinoderms from Zihuatanejo and Acapulco, Guerrero is currently limited to taxonomic listings. This work attempts to characteriza better the community of these organisms associated to coral reefs in this region using band transects of 50m length by 1 m width. Two samplings were carried out in 2004, one in the rainy season and other in the dry season. Ten species, three Asteroidea, six Echinoidea and one Holothuroidea, were found. The mean values obtained for diversity in the 13 study sites (1.036 bits ind-1) are considered low when compared with the maximum possible diversity (3.322 bits ind-1), and this is likely due to the dominance of the black sea urchin Diadema mexicanum and the starfish Phataria unifascialis, with densities reported of 1.45±0.60 ind m-2 and 0.12±0.02 in m-2, respectively. The highest diversity was associated with low tide, which is not differente between localities. The spatial arrangement of the echinoderm species composition obtaine by the multidimensional scaling analysis denotes the formation of five conglomerates according to similarity, where the substratum and reef cover are the possible determinant variables. The four predominant species (D. mexicanum, P. unifasciales, Toxopneustes roseus and Hesperocidaris asteriscus), whose densities wre compared with those of other sites of the Oriental Tropical Pacific, show, in general, inferior values for Echinoidea and intermediate values for the Asteroidea. For the specific case of D. mexicanum, there are differences in the densities between localities, dephts, and time of year, and the mean value obtained of 1.45±0.60 ind m-2 was low compared to densities recorded in other zones. Also, it was observed that in some localities, such as Playa Coral, Caleta de Chon, Punta del Cerro Colorado, and Zacatoso, the sea urchin densities increased considerably during the rainy season, and these high densities maintain a positive correlations with coral cover, which is indicative of a balanced ecosystem. It was also detected that in localities close to Acapulco, which undergo more tourist actividy, suc as Isla Roquet, Ensenada de Llantos, and Pichilingue, the diversity of echinoderms is lower (0.6 bits ind-2) and the abundance of D. mexicanum is higher. These results, plus those of other sutdies at Acapulco Bay, suggest that pertinent actions should be taken to avoid simiilar phase shifts on reefs of Ixtapa-Zihuatanejo, which are currently considered to be the best developed in the Mexican Tropical Pacific.