A Biophysical Retention Mechanism for Self-Recruitment : Direct Evidence from Tracking Coral Reef Fish Larval Patches

The hypothesis that reef fish larvae have some influence on their dispersal is examined by direct observations of pelagic processes. For this purpose, we utilized highresolution and quasi-synoptic measurements of current and ichthyoplankton fields in the vicinity of the island of Barbados, West Indies. The study was conducted during May of 1996 and 1997, in an area extending approximately 15 km from shore, running 20 km parallel to the western shore of Barbados, and of 0-100 m depth. Sampling was designed to track bicolor damselfish (Stegastes partitus) cohorts from when they hatch on the reef, throughout their 29-d pelagic larval duration. Time series of the in situ 3-D flow field was used to predict larval trajectories and estimate larval fluxes out of the study area. Formation, maintenance, and advection of larval patches were described by comparing predicted and observed distributions of stage-specific larval S. partitus. Discrete stage-specific larval patches with a mean size of 29.4 to 13.2 km (for pre-flexion and post-flexion stages respectively) extended to ca.30 m depth, indicating that coral reef fish larvae initially dispersing as patches tend to remain coherent throughout their pelagic duration. Larval behavior was critical to predict accurately larval transport. Particularly, ontogenetic vertical migration combined with vertical stratification of the currents represented a retention mechanism for locally spawned larvae. Currents experienced by early larval stages prior to the onset of vertical migration played a large role in retention variability and subsequent recruitment. Retention rates in the vicinity of Barbados were consistent with observed interannual variability in the recruitment strength of S. partitus, further supporting the retention hypothesis. Finally, this study verifies that tracking larval trajectories within in situ flow conditions is a useful tool in answering ecological questions. ∗ Corresponding author. Rosenstiel School of Marine and Atmospheric Science, Division of Marine Biology and Fisheries, 4600 Rickenbacker Causeway, Miami, Florida 33149-1098, Fax: 305-361-4600, Phone: 305-361-4025 – E-mail: [email protected]