SPATIAL DISTRIBUTION, ABUNDANCE AND RELATIONSHIP TO HABITAT FEATURES OF THE QUEEN CONCH EUSTROMBUS GIGAS (LINNAEUS) (MOLLUSCA: STROMBIDAE) IN NUESTRA SEÑORA DEL ROSARIO ARCHIPELAGO, CARIBBEAN COAST OF COLOMBIA

Abstract

Population density and spatial distribution of the Caribbean conch, Eustrombus gigas (Linnaeus), as well as its association to different habitats were evaluated at 184 stations sampled systematically in two seasons (wet and dry) in Nuestra Señora del Rosario archipelago. Each individual was counted and measured in a circular area of 1256.6 m2 (sampling unit) by SCUBA diving and in situ observations on the types of habitats were made. The average density (± SD) of the species was low compared with other regions in the Caribbean, 4.0 ind/ha ± 10.8 and 3.7 ind/ha ± 9.3, for the wet and dry seasons, respectively. Adults represented 89 and 64 % of the population surveyed for each season, and were specifically located at Bajo Tortugas and Isla Tesoro. Although reproductive activity was observed during the wet season, population density was below critical levels to guarantee the population´s reproductive success. The spatial distribution analysis showed that the abundance of adults was spatially structured in both seasons, with important aggregations at Bajo Tortugas and Isla Tesoro. Juveniles did not show spatial structure for neither season due to the low observed abundance. Multiple regression models explained 48 and 14 % of the total variance in the abundance of adults during the wet and dry seasons, respectively; with depth, mean grain size, and percentage of mixed coral as predictor variables. It is recommended to establish Bajo Tortugas and Isla Tesoro as special protected areas in order to maintain the adult spawning stock, while the same conservation measure should be implemented at Isla Arena in order to protect juveniles on seagrass beds.