The Fluid Dynamics of Collective Pulsing Behavior in Xeniid Corals Public Deposited

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  • March 19, 2019
  • Samson, Julia
    • Affiliation: College of Arts and Sciences, Department of Biology
  • Collective pulsing to generate fluid flow is an important phenomenon across different biological scales and systems and is essential for many vital functions. Examples of collective behavior in fluids occur at all levels: from swimming bacteria to fish schools. Often in these systems, the collective behavior (whether it be pulsing, swimming, or something else) is not predetermined but emerges from individual responses to changes in the local environment. Their responses, in turn, alter the environment, creating a feedback loop. In my dissertation, I focus on the collective pulsing behavior and fluid dynamics of xeniid corals (Cnidaria: Alcyonaceae: Xeniidae). First, I isolate the fluid dynamic aspects and describe the characteristic flow patterns generated by the pulsing of an individual coral polyp. Based on these findings, I develop a 3D computational model that I use to investigate the importance of scaling, as determined by the Reynolds number, on the fluid dynamics of coral pulsing. Then, I isolate the behavioral aspect and quantify the patterns of collective behavior. Comparing empirical date to several models, including a random walk model, a Markov chain model, and a coupled phase oscillators model, I show that the behavioral patterns observed in pulsing corals can be reproduced by a weakly coupled phase oscillator model or an uncoupled phase oscillator model with varying intrinsic frequencies. Although polyps within a colony are physically connected and share a diffuse nerve net, I find no evidence of information transfer controlling the pulsing behavior between polyps. Finally, I make the first step toward merging collective behavior and fluid dynamics into one model. Using the method of Immersed Boundary with Finite Elements (IBFE), I simulate both single polyps and polyp pairs and compare their flow fields. Additionally, I investigate the effect of phase difference and distance between polyps on the flows generated by polyp pairs. I find no interactions between components of the flow field and conclude that the phase differences and distances between polyps used in my simulations do not result in any significant flow benefit to the polyps. This finding is consistent with the behavioral observations of collective pulsing; from the results in this dissertation, it does not seem that the polyps pulse in a coordinated manner. The contributions of my thesis include the description and quantification of a novel mechanism of mixing displayed by xeniid corals, which could serve as inspiration in the design of small-scale fluid mixers, and the development of a 3D model of collective pulsing behavior, which could be used as a framework to investigate different aspects of coral fluid dynamics and inform decision-making regarding the protection and conservation of corals and coral reefs.
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Rights statement
  • In Copyright
  • Patek, Sheila
  • Miller, Laura
  • Bruno, John
  • Hedrick, Tyson
  • Kier, William
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2018

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