MEPS 321:133-142 (2006)  -  doi:10.3354/meps321133

ABSTRACT: Timing of larval release in benthic marine invertebrates plays an important role in determining the reproductive success and extent of larval dispersal. Few studies have been conducted on diel variations in planula release by corals. Five brooding corals Seriatopora hystrix, Stylophora pistillata, Pocillopora damicornis, Euphyllia glabrescens, and Tubastraea aurea in Nanwan Bay, southern Taiwan, were selected to compare diel patterns of planula release. Corals were collected from the field and maintained in outdoor, flow-through systems to quantify the hourly release of planulae. Planulation by S. hystrix and S. pistillata was highly synchronized with 1 peak of planula release occurring close to sunrise. Planulae of P. damicornis and E. glabrescens were released throughout the day, and usually 2 peaks occurred in the early morning and at night. Planulation of the ahermatypic coral T. aurea occurred throughout the day without a consistent peak. The diel cycle of planulation for all 3 pocilloporids and E. glabrescens suggests that the light-dark cycle may be the cue that induces planula release. The majority of planulae of these 4 species being released in the dark might be beneficial for minimizing predation effects. The peak planulation occurring close to sunrise might be advantageous for exploiting light cues after sunrise by mature planulae in order to quickly settle, shortening the time they remain in the water column and promoting settlement within the natal reef. Variations in diel patterns of planula release show that variable strategies of reproductive timing exist for brooding species.

KEY WORDS: Diel periodicity · Planulation · Coral · Seriatopora hystrix · Stylophora pistillata · Pocillopora damicornis · Euphyllia glabrescens · Tubastraea aurea