Coral tentacle elasticity promotes an out-of-phase motion that improves mass transfer

Dror Malul, Roi Holzman*, Uri Shavit

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Corals rely almost exclusively on the ambient flow of water to support their respiration, photosynthesis, prey capture, heat exchange and reproduction. Coral tentacles extend to the flow, interact with it and oscillate under the influence of waves. Such oscillating motions of flexible appendages are considered adaptive for reducing the drag force on flexible animals in wave-swept environments, but their significance under slower flows is unclear. Using in situ and laboratory measurements of the motion of coral tentacles under wave-induced flow, we investigated the dynamics of the tentacle motion and its impact on mass transfer. We found that tentacle velocity preceded the water velocity by approximately one-quarter of a period. This out-of-phase behaviour enhanced mass transfer at the tentacle tip by up to 25% as compared with an in-phase motion. The enhancement was most pronounced under flows slower than 3.2 cm s -1, which are prevalent in many coral-reef environments. We found that the out-of-phase motion results from the tentacles' elasticity, which can presumably be modified by the animal. Our results suggest that the mechanical properties of coral tentacles may represent an adaptive advantage that improves mass transfer under the limiting conditions of slow ambient flows. Because the mechanism we describe operates by enhancing convective processes, it is expected to enhance other fitness-determining transport phenomena such as heat exchange and particle capture.

Original languageEnglish
Article number20200180
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1929
StatePublished - 24 Jun 2020


  • mass transfer
  • oscillating flows
  • waves


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