Lunar cyclic population replenishment of a coral reef fish: shifting patterns following oceanic events

We examined the relationship between the pelagic environment and the lunar timing of reproduction and recruitment of a coral reef fish by comparing patterns exhibited by fish under normal oceanographic conditions with patterns exhibited by fish that experienced significantly different pelagic conditions (i.e. encounter with meso-scale, low-salinity North Brazil Current [NBC] rings passing by the island of Barbados). We used a 20 mo time series of bluehead wrasse Thalassoma bifasciatum recruitment, and compared larval growth and the timing of settlement and (successful) spawning recorded in the otoliths of individual recruits that encountered an NBC ring (RING fish) with those that did not (NO RING fish). Spawning occurred during all times of the lunar cycle, but during NO RING conditions, only those larvae spawned during the first-quarter moon were retained nearshore. Successful NO RING recruits were spawned during the first-quarter moon, grew rapidly as larvae, and settled during the third-quarter moon and neap tides. In contrast, during RING events, larvae spawned during all lunar phases were retained nearshore. Successful RING recruits were spawned over the entire lunar cycle, grew more slowly as larvae, and settled during both quarter moons. Fish settling during the first-quarter moon were of higher condition than third-quarter-moon settlers, which is consistent with the concept of higher predation losses and selective mortality of settlers during less-than-optimum periods. Synchronized settlement patterns can be decoupled from spawning patterns by pelagic processes and flexible larval growth schedules. Variable pelagic conditions may contribute to the maintenance of daily reproduction and flexible growth histories in marine species.