Why corals do calisthenics

Pulsating motion appears to flush water for better photosynthesis

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Like hyperactive flowers, xeniid corals open and then clench their little branched tops every few seconds much of the day and night. What makes these coral calisthenics worthwhile, experiments now suggest, could be the way they mix and freshen water to improve coral nutrition.

All that flexing roils the water near the corals and sweeps it upward and away, says marine ecologist Maya Kremien of Hebrew University of Jerusalem.