Current pattern and coral larval dispersion in a tropical coral reef system

Acoustic Doppler current profiler data from a towing ADCP were obtained from a tropical coral reef system during a diurnal tidal cycle. Nine transect repetitions were performed during the coral spawning period of August 2008 to elucidate the possible larvae trajectories within the study area. The principal current velocity component was parallel to the coast (northward direction). The currents were mainly induced by surface friction (winds) and advection. A divergent area was observed near the northern coral reef area, which decreased the probabilities for coral larvae fixation. However, the divergence was only observed during the flood period. During the ebb tide period, the sea level decreased and constrained the denser sea water to a depth of approximately 5 m from the bottom; as a result, the coral larvae had a greater probability of fixating to the hard sea floor. The coral larvae trajectories were determined from the vertical water velocity, which was calculated using the continuity equation, the surface temperature, and the biovolumes of zooplankton, which were calculated from the backscatter intensity of the ADCP. In addition, the residence time of the system (2.41 days) suggests that some of the larvae likely fixate in less than 3 days, although other larvae may be able to drift off the area for up to 40 days. Three coral reefs were identified as the providers of coral larvae within the northern Veracruz Reef System. The dominant northward current velocity was always less than 30 cm s−1.