Do non-estuarine mangroves harbour higher densities of juvenile fish than adjacent shallow-water and coral reef habitats in Curaçao (Netherlands Antilles)?

Abstract

Most mangroves occur in tropical estuaries and generally contain higher densities of fish than adjacent habitats such as seagrass beds and sand flats. The question of whether these fishes depend on estuaries per se has given rise to the concept of estuarine-dependence. On several Caribbean islands, mangroves are only found in non-estuarine bays and lagoons. To test whether fishes also depend on mangroves in non-estuarine conditions we determined juvenile and adult densities of a complete reef fish community in 4 bay habitats (mangrove, seagrass bed, channel, subtitdal mud flat) in the Spanish Water Bay and 4 depth zones (2, 5, 10 and 15 m depth) on the adjacent coral reef of the Caribbean island of Curacao (Netherlands Antilles), using a single visual census technique in all habitats. The results showed that non-estuarine mangroves did harbour a much higher total juvenile fish density, density of juvenile temporary bay residents (i.e. nursery species), and density of juvenile permanent bay residents (i.e. bay species) than adjacent seagrass beds, channel and mud flats, but a similar total juvenile fish density as the coral reef. The different patterns of abundance of juvenile fish are probably related to the degree of structural habitat complexity. For a number of nursery and bay species, juvenile fish were found almost exclusively in the mangroves and sometimes to a lesser extent in other bay habitats, but rarely on the coral reef, giving rise to the concept of 'bay habitat dependence'. Juvenile and adult habitats differed for at least 21 of the 50 most common reef species, suggesting partial or complete ontogenetic habitat shifts from the mangroves to the reef, from the channel to the reef, and from the shallow to the deeper coral reef. Different associations with habitat type were also found at the level of fish families.