Coral spawn timing is a direct response to solar light cycles and is not an entrained circadian response
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Broadcast spawning corals release gametes into the oceans with extraordinarily accurate timing. While the date of spawning is set by the lunar cycle, the hour/minute of spawning is set by the solar cycle. In this report, we describe experiments that test whether the time of spawning is regulated by an entrained biological clock or whether it is directly controlled by the solar cycle. Montastraea franksi samples were collected on the morning of the predicted spawning. Fragments from colonies were kept under three different lighting conditions and spawning monitored. The three conditions were sunset times of 0, 1 or 2 h earlier than normal. Fragments from the same colony spawned differently under these three conditions, with an early sunset causing a corresponding early shift in spawning. These results indicate that spawn timing is not controlled by a circadian rhythm and that it is directly controlled by local solar light cycle.
KeywordsBroadcast spawning Circadian rhythm Biological clock Mass spawning
This research was supported by NOAA and the Flower Garden Banks National Marine Sanctuary. Additional support was provided by Galatee Films by providing ship time and we would like to especially thank Antoine de Cozette for help in coordinating field work. Field work was aided by Sarah Davies, Kurt Carlson, Jay Reichman, Mike Nickell, Emma Hickerson and the crew of the M.V. Fling.
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