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SCUBA News - #315 - October 2026
SCUBA News~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Welcome back lovely divers. Today, the world's 10 best wreck dives as voted for by our readers; dramatic encounters in South Africa; our creature of the month is the fascinating pulsating Xenia coral; hand-picked liveaboard deals to get you in the water for less and, as always, our run down of all the diving and marine conservation news.
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Mystery of the Pulsating Soft CoralIf you've dived in the Red Sea or Indo-Pacific you will have seen a type of soft coral repetitively "grabbing" at the water. They are so common that we take them for granted. But only one family of coral does this - the Xeniidae. Even within this family, only a few members pulsate .
Scientists have long assumed that these Xenids rhythmically pulsate to create a current to assist feeding and respiration. This is a very costly strategy, though, in terms of energy used. Until now it wasn't known exactly how much, and exactly what, benefit the coral gets from working this hard. Mystery solved after 200 yearsThe elegant motion of Xenids has been fascinating the scientific society for over 200 years. The first Xeniidae colonies were collected during Napoleon's invasion of Egypt during the years 1798-1799 when specimens of Xenia umbellata were brought back to Europe.
Researchers have now found that, surprisingly, these soft corals are the most efficient of any so far measured. After watching several coral colonies with an underwater infrared-sensitive camera night and day, the researchers made a surprising discovery: Heteroxenia corals cease to pulsate and take a half-hour break every single day in the afternoon. As yet, they can't explain the afternoon siestas. Volunteer divers helped with the investigation. They found that if a diver lightly touched the coral, the polyps "close" and remain motionless for a few minutes, after which the coral returns to its normal pulsation activity. The researchers used this behaviour in order to repeatedly measure the flow field around the Heteroxenia during pulsation and rest. Increased PhotosynthesisCorals host photosynthetic algae in their tissues. The symbiotic algae provides the coral with essential nutrients and lives off the waste of the coral. The researcher's found that the pulsation motions enhance the coral's photosynthesis rate.
The photosynthesis measurements led to the scientists next discovery. Analysis of the direction of water flow indicated that the motion of the polyps effectively sweeps water up and away from the coral tissues into the ambient water. Corals need carbon-dioxide during daytime and oxygen during nighttime, as well as nutrients like phosphate and nitrogen during day and night. One of the challenges for coral colonies is to render their surrounding waters rich in their essentials by efficiently mixing the water around them.
Even though the polyps' motions are uncoordinated - each polyp staring its grabbing at a different time - the accumulated effect of the polyps' activity is a significant enhancement of the water flow around the colony, particularly sweeping water away from the coral and reducing the probability of re-filtration of the same water. Without water motion, the oxygen concentration in the coral tissues would rise and the photosynthesis rate would drop. Corals, Currents and Resilience in AdversityMost hard corals feed more in faster flowing water. But not this soft coral. Water flow has no effect. However, if there is less food in the surrounding water then they pulse more slowly. Xenia are resistant to bleaching and able to cope with higher sea temperature. They are also invulnerable to excess nutrients and organic matter caused by run-off. Will we be seeing more Xenia at the expense of other corals in the future? Sources and ReferencesNadir, Elinor et al. (2025). Diffuse pacemaker mechanism with distinctive organization drives pulsation in the octocoral Xenia umbellata. Proceedings of the National Academy of Sciences. 122. 10.1073/pnas.2500611122. Cnidaria > Anthozoa > Octocorallia > Malacalcyonacea > Xeniidae > Xeniua > Xenia umbellata Diving news from around the World
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