DOI: 10.5061/dryad.sqv9s4n0s
title: Data from: Coral tentacle elasticity promotes an out-of-phase motion that improves mass transfer

description: 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.
description: Table
 S2. Flow conditions and the measured phase difference in the field
 experiments on individuals of <i>A. diaphana </i>(A) and
 colonies of <i>D. favus</i> (B). <i>u</i><sup><i>c</i></sup> is the horizontal current velocity, <i>A</i> is the average amplitude of the horizontal wave-induced velocity <i>u</i><sup><i>w</i></sup><i>,</i> SD is its standard deviation, <i>f</i> is wave frequency calculated as the inverse of the period, and Δ<i>φ</i> is the phase difference between the water and tentacle velocities.   Table S3. Conditions of the <i>D. favus</i> laboratory experiments. <i>D</i><sub><i>T</i></sub> and <i>L</i><sub><i>T</i></sub> are the tentacle's diameter and length, <i>u</i><sup><i>c</i></sup> the horizontal current velocity, <i>A</i> the amplitude of the wave-induced horizontal velocity <i>u</i><sup><i>w</i></sup>, <i>f</i> the wave frequency calculated as the inverse of the period <i>f=1/T</i>, and Δ<i>φ</i> the phase difference calculated as the difference between the phase in the sine-fitted horizontal water and the tentacle velocities. The Reynolds number, <i>Re=</i><i>U</i><sub><i>m</i></sub><i>D</i><sub><i>T</i></sub><i>/ν</i>, and the Keulegan–Carpenter number, <i>KC=</i><i>U</i><sub><i>m</i></sub><i>T/</i><i>D</i><sub><i>T</i></sub> where calculated using the maximal velocity of the horizontal phase-averaged period, <i>U</i><sub><i>m</i></sub><i>=</i>max⁡<i>(</i><i>u</i><i>)</i>, and the kinematic viscosity of sea-water <i>ν</i>.   Table  S4. Flow conditions during the <i>G. fascicularis</i> laboratory experiments. <i>u</i><sup><i>c</i></sup> is the current velocity, <i>A</i> is the wave amplitude of the wave-induced horizontal velocity <i>u</i><sup><i>w</i></sup>, <i>f</i> is the wave frequency calculated as the inverse of the period <i>f=1/T</i>, and Δ<i>φ</i> is the phase difference between the water and tentacle velocities.