EGG DISPERSAL IN A CARIBBEAN CORAL-REEF FISH, THALASSOMA-BIFASCIATUM .1. DISPERSAL OVER THE REEF PLATFORM

Pelagically-spawning coral reef fishes are hypothesized to select site s for spawning that result in eggs being rapidly transported away from reef areas. Experiments at an inshore reef platform off the southwest coast of Puerto Rico were conducted to test this hypothesis, with the bluehead wrasse as the model species. Fluorescent dye was released to simulate spawning events during spawning times at eight spawning and eight nonspawning sites. The leading edge of each dye plume was marked at 10-min intervals until it moved off the reef platform. Differences in movement and pathways of water parcels originating from spawning a nd nonspawning sites were compared in terms of the total time water pa rcels spent over the reef platform, the distance they traveled over th e reef platform, the depths and substrates over which they passed, and their initial current speeds. Comparisons were made on different scal es: all spawning sites were compared with all nonspawning sites on the scale of the entire reef platform and on each of the three individual reefs making up the platform. Dye from spawning sites and dye from no nspawning sites moved over large, overlapping portions of the reef pla tform. Differences between spawning and nonspawning sites were general ly in harmony with the hypothesis, but significant differences primari ly were restricted to the scale of the platform and the largest indivi dual reef (total distance traveled, depth after 10 min, current speed) . Only depth after 10 minutes showed significant differences at all sc ales studied. In addition, the distributions of all spawning sites and nonspawning sites over the entire reef platform were not equal; in pa rticular no spawning occurred over the forereef. In general, the resul ts of this study provide evidence that supports the hypothesis that fi shes choose specific spawning sites offering certain advantages relati ve to off-reef transport of eggs; however, these advantages may only b e manifested over the short term.