Abstract
Distribution, density an size structure of Oreaster reticulatus and Luidia senegalensis (Echinodermata: Asteroidea) in Cubagua Island, Venezuela. There is limited biological information about the starfish Oreaster reticulatus and the nine-armed starfish Luidia senegalensis in Venezuelan waters. These species are currently considered threatened in many localities of the Caribbean, Brazil and Colombia. Therefore, the aim of this study was to describe their population density, size distribution and population structure in Cubagua Island. During 2008, 52 stations located around the island were evaluated using band transects of 50m2. Each organism was counted and measured (maximum radius), and its size was compared to the maturity length reported in the literature. The results for O. reticulatus include: 167.3ind./ha; 33% juveniles and 67% adults; average size of 10.7±5cm (range: 2.2-21cm); a wide distribution around the island, with higher densities in the Eastern and Southwest areas. The 50% of the specimens were found in seagrass beds, 25% in sand, 16% in areas covered by decomposed seaweeds, 9% in oyster beds and 1% coralline patches. The densities of O. reticulatus were higher than those reported in the Caribbean, Panama and Puerto Rico, but lower than Venezuelan National Parks: Mochima and Morrocoy; as well as in the Virgin Islands and Belize. For L. senegalensis we found an average density of 40ind./ha; 95% exceeded the reported size at maturity, with mean length of 12cm±3.5cm (range: 3.5-22.3cm); they were found only in 15% of the stations of which 92.5% were sandy bottoms and the other 7.5% oyster beds. The degree of aggregation of L. senegalensis was greater than O. reticulatus, with an estimated k of 0.06. However, it was not possible to compare the densities of L. senegalensis with any other study. For both species is recommended to carry out reproductive studies and to monitor their population densities to infer temporal variations.
Highlights
Luidia senegalensis (Lamarck 1816), ha sido objeto de pocos estudios, a pesar de ser común en muchas áreas del Atlántico tropical occidental (Halpern 1970)
Tallas menores a la de madurez sexual), que en su mayoría fueron fondos de Thalassia (40%), ostrales (40%) y arenales (20%)
Los animales encontrados fuera del área de las transectas fueron medidos para reforzar el análisis de estructura de tallas, pero no fueron incluidos en los cálculos de densidad poblacional
Summary
Área de Estudio: El estado Nueva Esparta se encuentra ubicado sobre la plataforma continental de la región nororiental de Venezuela y está conformado por las islas de Margarita, Coche y Cubagua. Las zonas con elevadas proporciones de individuos inmaduros fueron identificadas cuando el porcentaje de individuos menores a la talla de madurez superó el 65% de los ejemplares encontrados por celda (en zonas con más de 2 individuos). Área de estudio: Las 52 celdas de muestreo, presentaron sustratos predominantes en el siguiente orden: arena (n=26), praderas de fanerógamas (n=10), bancos de moluscos (n=8), parches de coral y zonas cubiertas de algas en descomposición (n=3 cada uno), y parches de octocoral (n=2) (Fig. 1). El 50% de los individuos se ubicó en fondos de pastos marinos, un 25% en arenales, 16% en zonas cubiertas por algas en descomposición, 9% en ostrales, 1% en parches de coral, y no fueron encontrados en sustratos donde dominaban los octocorales. Fueron identificadas cinco zonas con proporciones elevadas de juveniles
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