The rhymically pulsing Heteroxenia fuscescens soft coral.Pulse corals (e.g., Xenia and Heteroxenia spp.) are among the more enigmatic sessile invertebrates. Many hobbyists and non-hobbyists alike find their rhythmic, hypnotic pulsing behavior fascinating and relaxing to observe, but precisely why they pulse the way they do has long been a source of befuddlement. We know the pulsing isn’t related to prey capture because pulse corals are sustained via the symbiotic zooxanthellae residing in their tissues as well as the direct absorption of dissolved nutrients from the water, not by the oral ingestion of planktonic organisms. So what’s the purpose of pulsing continuously? The intriguing results of a recent study conducted on Heteroxenia fuscescens by researchers at the Hebrew University of Jerusalem and the Technion-Israel Institute of Technology may finally shed light on the mystery. The study essentially found (and I’m grossly oversimplifying this, so I would advise reading more about the actual study in the April 2013 issue of PNAS) that the pulsing action creates an upward water flow that facilitates optimum gas exchange, thereby enhancing the rate of photosynthesis of the zooxanthellae, and more efficiently mixes the water and dissolved nutrients around the colony. Whatever the definitive explanation for why pulse corals pulse, equally mysterious is why these corals sometimes slow or cease their pulsing action for no readily apparent reason—an occurrence very commonly observed in captive colonies. More: Why Did My Pulse Corals Stop Pulsing?… More:
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