Mostly Biomathematics Lunchtime Seminar

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Pulsing Soft Corals are Novel Mesoscale Mixers

Speaker: Laura Miller, Program in Bioinformatics and Computational Biology, The University of North Carolina at Chapel Hill

Location: Warren Weaver Hall 1314

Date: Tuesday, May 1, 2018, 12:30 p.m.

Synopsis:

We quantify for the first time the flow near the tentacles of soft corals whose active pulsations are thought to enhance their symbionts' photosynthetic rates by up to an order of magnitude. Flow measurements using particle image velocimetry reveal that the individual polyps generate a jet of water with positive vertical velocities that do not go below 1 mm/s and with average volumetric flow rates of about 0.7 cm^2/s. Our results also show that there is nearly continual flow in the radial direction towards the polyp with only about 3.3% back flow. 3D numerical simulations uncover a region of slow mixing between the tentacles during expansion. The combination of nearly continual flow towards the polyp, slow mixing between the tentacles, and the subsequent ejection of this fluid volume into an upward jet ensures the polyp continually samples new water with sufficient time for exchange to occur. We also consider the transport of fluid at scales above and below those for which the corals are found in nature. The results show that net transport is negligible at smaller scales, and continuous upward flow is produced at larger scales. Sustained net transport is necessary to bring in new fluid for sampling and to remove waste. As the Re is increased well above the biologically relevant range, the slow region of mixing necessary for gas exchange between the tentacles is reduced.