Abstract
Estuaries and bays harbouring mangroves and seagrass beds provide important food sources for millions of people, but are in decline world-wide as a result of anthropogenic disturbances. They are considered important nurseries for juvenile coral reef fish, but this has only been based on their high densities of juvenile fish. However, a true nursery is a habitat that contributes more per unit area to the production of individuals that recruit to the adult reef population than other coastal habitats in which juveniles occur. If the higher densities of juveniles in mangroves/seagrass beds never reach the reef fish population, then these habitats do not function as productive nurseries, but only as sinks for juveniles. This proposal aims to quantify whether density, growth and survival of juvenile fish is higher in mangroves/seagrass nurseries than on the reef, and whether movement of fish takes place from these nurseries to the coral reef. Only in such way can it be established whether or not these habitats serve as true nurseries for reef fishes. Movement to the reef provides the strongest proof for this, and will therefore be studied using advanced techniques such as analysis of otolith microchemistry and stable isotopes, and long-term fish tagging. Quantitative mathematical models will be made to calculate how reef fish population viability depends on input of juveniles from mangrove/seagrass nurseries versus coral reef, and on the size of nursery habitats. This increases our understanding of the ecological interactions between tropical ecosystems, and of the population dynamics of tropical reef fish with spatially separated life-stage habitats. These data are of high importance for a sustainable management of these coastal habitats and commercial fish stocks on the reef. This is needed since Caribbean reefs are over-fished and many people depend on reef fish as a source of protein or income.
Netherlands