ECOLOGICAL PROSPECTING OF THE MANGROVE AND MARINE SEAGRASS AS NURSERY HABITATS FOR REEF FISH IN SAN ANDRÉS ISLAND, INSULAR COLOMBIAN CARIBBEAN

Abstract

The structure of the ichthyofauna associated to an area of mangrove swamp and two areas of seagrass beds was evaluated in San Andrés Island (Biosphere Reserve Seaflower) to determine the character of nursery of those ecosystems. The composition, abundance, and development state of fishes in each biotope was evaluated using visual censuses in band transects during the rainy season. A total abundance of 1908, mainly young (98%), specimens was counted. A richness of 27 species, 18 genus, and 13 families, a Shannon’s index of 2.0, a dominance of 0.22 and an equitability of 0.61 were found. Richness was higher at the seagrass (20 species) than at the mangrove (13 species); abundance was higher in the mangrove (1.86 ind/m2); and the largest diversity was found in a meadow associated to mangroves (H = 2.23). The nature of the mangrove and seagrasses as nursery habitats was determined as well as their combined functionality when they are close to each other. The high potential as connecting species between nursery habitats and coral reefs of Abudefduf saxatilis, Acanthurus chirurgus, Chaetodon capistratus, Gerres cinereus, Haemulon flavolineatum, Haemulon sciurus, Halichoeres bivittatus, H. poeyi, Lutjanus apodus, Scarus iseri, Sparisoma viride, Thalassoma bifasciatum, of the species of genera Eucinostomus and Stegastes, and of two morphotypes of Clupeidae was determined, given their relatively high densities of juvenile in the swamp and seagrass beds. Depth changed moderately among habitats (about one meter) showing positive correlation with oxygen (0.84). pH and temperature were correlated negatively (0.93). Density of mangrove roots is low compared to other Caribbean localities (11.7 ± 4.0 roots/m2). Length of Thalassia testudinum leaves varied significantly between seagrass beds and their covering was higher than other substrates in the seagrass beds. The remarkable diversity and density of economically important fish species, the particular configurations of the biotopes, and the status of interconnection or isolation between mangroves and seagrass beds, suggest the relevancy of the structural and functional protection of these habitats. The results agree with the literature and enrich it, and are input for the management of the resources in Seaflower.