Direct tracking of coral larvae: Implications for dispersal studies of planktonic larvae in topographically complex environments

Abstract

The larvae of broadcast spawning corals form visible surface aggregations following the annual spring mass spawning on the Great Barrier Reef. Aerial surveys revealed that these aggregations had patchy distributions which were related to local hydrodynamic features. Aggregations were observed along fronts associated with buoyancy differences between water masses, with boundary mixing at reef surfaces, and with island wakes. Secondary currents associated with these fronts accumulated the buoyant larvae into linear slicks. Fronts may be found in proximity to islands, reefs and coastal headlands. Hence, local topography may determine where larval aggregations occur as well as the fine-scale structure of these patches. Once aggregated into coral spawn slicks, larvae were advected away from reefs in complex, inter-reefal currents. Wind patterns determined the general direction of larval transport and overall degree of larval patchiness. These findings have important implications for modelling studies of larval dispersal and highlight the importance of topographically controlled fronts in structuring larval distributions.