Composición y estructura de la macrofauna asociada con agregaciones de dos especies de bivalvos en Isla de Cubagua, Venezuela / Composition and structure of the macrofauna associated with beds of two bivalve species in Cubagua Island, Venezuela

ABSTRACT

Bivalve aggregations constitute a microhabitat for a wide variety of organisms in intertidal, subtidal and deep-water marine benthic habitats. Increase in density of bivalve beds could offer more crevices and substratum for the associated fauna, affecting community composition. Beds of the Atlantic Pearl Oyster (Pinctada imbricata) and the Turkey Wing (Arca zebra) of contrasting population densities were evaluated to determine the composition and structure of the associated macrofauna of three taxa (Crustacea Decapoda, Mollusca and Echinodermata). We evaluated plots of three levels of bed density in both species, the associated fauna were identified and counted. Other species were collected by qualitative samples. Univariate and multivariate descriptors were tested comparing the associated fauna between the beds of two species at three levels of density. In these beds a total of 104 species belonging to 58 families were recorded. Mithraculus forceps (Majidae), Crucibulum auricula (Calyptraeidae) and Ophiotrix angulata (Ophiothrichidae) were the most common species found in these assemblages. The medium and high-density bivalve beds exhibited greater species number, abundance, Shannon diversity, evenness, taxonomic diversity, and taxonomic distinctness of associated fauna, than low-density bivalve beds. Moreover, multivariate analysis detected different assemblages of associated fauna between beds with different densities. Additionally, similarities were found in the communities of macrofauna in both beds of P. imbricata and Arca zebra. Our results suggest that bivalve aggregations at Cubagua Island provide additional habitat for macrofauna living in other shallow habitats such as Thalassia beds, corals and rocky environments. Bed density, associated with topographic complexity, represents an important factor for the composition and complexity of the associated fauna.

RESUMEN

Las agregaciones de bivalvos constituyen un microhábitat para una gran variedad de organismos en el ambiente intermareal, submareal y en aguas profundas. Agregaciones de la ostra perla (Pinctada imbricata) y pepitona (Arca zebra) a diferentes densidades poblacionales se evaluaron para determinar la composición y estructura comunitaria de la macrofauna asociada en tres taxa (Crustacea Decapoda, Mollusca y Echinodermata). La hipótesis nula de no diferencias en descriptores univariados y multivariados fue probada comparando la fauna asociada entre las agregaciones de las dos especies a tres niveles de densidad. En estas agregaciones se identificaron 102 especies de 55 familias. Mithraculus forceps (Majidae), Crucibulum auricula (Calyptraeidae) y Ophiotrix angulata (Ophiothrichidae) fueron las especies más comunes encontradas en estas asociaciones. Las densidades medias y altas de las agregaciones de bivalvos presentaron mayor número de especies, abundancia, diversidad de Shannon, equidad, diversidad taxonómica y distinción taxonómica de la fauna asociada que las agregaciones de baja densidad poblacional. Análisis multivariados detectaron diferentes estructuras de los ensambles de la fauna asociada en agregaciones de bivalvos con densidad baja en comparación con los de densidad media y alta. Adicionalmente no se detectaron diferencias en la fauna asociada entre las especies. La densidad de las agregaciones de bivalvos, asociada a la complejidad topográfica, es un factor importante para la composición de la fauna asociada.