Connectivity Between Coastal Habitats of Two Oceanic Caribbean Islands as Inferred from Ontogenetic Shifts by Coral Reef Fishes

Abstract

Mangroves and seagrass beds are considered important nursery habitats for juveniles of coral reef fishes. Studies have mostly focused on the fish community of just one habitat, so the connectivity between different coastal habitats is often unclear. In this study, density and size of reef fish were determined using a single sampling technique in four non-estuarine bay habitats and four reef zones in Curacao and Bonaire (Netherlands Antilles). The data indicate that of the complete reef fish community at least 21 species show ontogenetic cross- shelf shifts in habitat utilization. The 21 species mainly utilized shallow-water habitats (mangroves, seagrass beds, channel and shallow reef) as nursery habitats and the deeper coral reef zones (> 5 m depth) as adult life- stage habitats. Fish species utilized 1-3 different nursery habitats simultaneously, but habitat utilization clearly differed between species. Previous studies showed that the dependence on these nursery habitats is very high, based on reduced density or absence of adults on coral reefs where these habitats were absent. The strong connectivity between several coastal habitats during the ontogeny of various commercially important reef fish species is evidence for the inclusion of bay habitats within boundaries of fishery reserves or marine protected areas. bay species were defined as species which are abundant in bays as juveniles and adults, and are not present or occur in low abundances on the coral reef. Studies showed that juveniles of 17 nursery species are highly associated with mangrove/seagrass dominated bays (Nagelkerken et al. 2000b, Nagelkerken and van der Velde 2002), but are largely absent in bays lacking these nursery habitats (Nagelkerken et al. 2001a). Further- more, these species are rarely found as juveniles on the coral reef (Nagelkerken et al. 2000b). In addition, Nagelkerken et al. (2002) demonstrated that 10 out of the 17 nursery species show absence or highly reduced densities of adults on reefs of islands completely lack- ing mangroves and seagrass beds. This suggests a high dependence of these nursery species on mangroves and seagrass beds, and implies that their density on the reef is a function of the presence of these habitats. Previous studies have shown that in mangrove/