Environmental influences on the diet timing of spawning in coral reef fishes

Multiple hypotheses have been proposed regarding the adaptive nature of dif ferent diel reproductive cycles observed in coral reef fishes. This study q uantified the spawning patterns of 11 different reef fish species at Johnst on Atoll (Central Pacific), while making simultaneous measurements of the e nvironmental factors likely to affect their spawning behaviors. The environ mental variables measured (time of day, tides, current velocity, current sp eed and abundance of piscivores) were correlated with observed spawning out puts through multifactorial analyses. High interspecific variability in spa wning patterns was found among the 11 monitored species. The majority of sp ecies spawned at a specific time of the day, in agreement with the timing o f spawning described at other locations, indicative of a fixed general resp onse by fishes across distribution areas. Spawning of most fishes with dayt ime spawning peaks was correlated with local changes in current direction a nd predatory risks, suggesting responses designed,to reduce the mortality o f propagules and adults. Dusk-spawning species generally did not respond to changes in flow direction and predator abundance, most likely due to their short spawning periods and the reduced predatory pressures that occurred a t dusk. Tides did not seem to be used exclusively as synchronizing cues by adult fishes for spawning. The influence of current speed in determining di el timing of spawning varied among species; some avoided spawning during lo w current speeds while the majority showed no clear response.