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

Corals rely almost exclusively on the ambient flow of water to support
their respiration, photosynthesis, 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 ~1/4 of a period. This
out-of-phase behavior enhanced mass transfer at the tentacle tip by up to
25% as compared with an in-phase motion where drag is minimal. 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, and, 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.