The Coral Sweepstakes


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coral sweeping
Vortical ciliary flows enhance the exchange of oxygen and nutrients between corals and their environment. Paths of tracer particles between two adjacent polyps of the reef coral Pocillopora damicornis, spaced about 3 mm apart, are color coded to reflect local flow velocity



Corals get their oxygen and nutrients from the water that flows around them. Research in the group of Dr. Assaf Vardi of the Weizmann Institute’s Plant and Environmental Sciences Department and Prof. Roman Stocker of the Massachusetts Institute of Technology (MIT) now reveals a surprise dimension of reef-bound coral life: The polyps (corals are actually a symbiotic combination of polyp and alga) use their cilia – tiny hairs covering their surface – to sweep the surrounding water. This sweeps in nutrients as well as sweeping away waste products.





The motion of tracer particles (1m diameter, imaged by dark field microscopy; 4x magnification) reveals the rapid vortical flows driven by cilia covering the surface of a reef-building coral. By actively mixing their boundary layer, corals enhance the exchange of oxygen and nutrients with the environment


By adding tracer particles to the corals’ environment and filming them with high speed videography and powerful microscopy techniques, Dr. Orr Shapiro of Vardi’s lab – at the time a guest of Stocker’s group – and Dr. Vicente Fernandez of Stocker’s lab captured, for the first time, the polyps’ cilia in action.

The findings, which appeared in the Proceedings of the National Academy of Sciences (PNAS), help explain the long evolutionary success of corals and give some hope for their future.




Coral Cilia. Cilia covering the surface of reef-building corals beat synchronously to drive rapid vortical flows (150x magnification)




Dr. Assaf Vardi’s research is supported by the Human Frontiers Science Program (HFSP); Roberto and Renata Ruhman, Brazil; Selmo Nussenbaum, Brazil; the Brazil-Israel Energy Fund; the Lord Sieff of Brimpton Memorial Fund; the European Research Council; and the estate of Samuel and Alwyn J. Weber. Dr. Vardi is the incumbent of the Edith and Nathan Goldenberg Career Development Chair.