What do juvenile mangrove fish want to do when they grow up?

Worldwide, juvenile fish are highly abundant in mangrove habitats and this is especially true for tropical marine ecosystems. Mangroves can act as nurseries to juvenile fish offering protection from predators and a ready supply of food. It has long been considered in conservation circles that such nursery habitats should be protected in order to increase the replenishment of adult fish populations in nearby coral reefs. However, this last idea has actually never been proven, and it could be argued that mangroves act as a sink rather than a source of potential recruits.

Taking a longitudinal approach of following cohorts over time, we evaluated evidence for mangrove-derived replenishment of 10 coral reef fishes by drawing on data from 2 concurrent fish monitoring efforts conducted in Biscayne National Park, Florida, USA, over the period 1999 to 2007. Annual indices of abundance were calculated for fish estimated to be age-0 to 4+ in both habitats, and correlation analyses, with appropriate temporal lags, were performed. Statistically significant (p < 0.05; r2 = 0.30 to 0.71) correlations between juvenile abundances in mangrove habitats and adult abundances on the reef tract 1 to 2 yr later emerged for 4 species: Abudefduf saxatilis, Lutjanus apodus, L. griseus, and Sphyraena barracuda.

This study is novel in that it uses a long term data set > 2 years. It is also one of the few longitudinal studies that matches juvenile abundance with adult abundance in mangrove habitats. The results clearly illustrate that some species spend time as juveniles in mangroves and later migrate to coral reefs. This mangrove-reef ontogenetic connectivity has potential for conservation issues such as nursery habitat assessment and marine reserve design.

Jones, D., Walter, J., Brooks, E., & Serafy, J. (2010). Connectivity through ontogeny: fish population linkages among mangrove and coral reef habitats Marine Ecology Progress Series, 401, 245-258 DOI: 10.3354/meps08404