Corals are usually classified as being hard (stony) or soft. Within the soft corals, the Xeniidae or xeniid corals form a special family with some of their members displaying a typical pulsing behavior. This behavior is thought to increase nutrient and gas exchange between the animal and its environment, helping it increase its photosynthetic rate. Two aspects of this pulsing phenomenon really caught my interest: the fluid dynamics or physical aspect, and the behavioral aspect. Ultimately, I'm most interested in the interactions between the two: are fluid dynamics and pulsing behavior related in xeniid corals, and if so, how do they influence each other?
The flow pattern generated by a single pulsing polyp consists of two main components: an upward jet away from the polyp, and a set of vortices at the tip of the tentacles (a starting vortex during the opening phase of the pulse and a stopping vortex during the closing phase). These jet and vortices help increase local water mixing and avoid reusing water containing waste products.
Constant pulsing, however, is, an energetically expensive behavior to maintain, and it is possible that collective pulsing allows for better cost-to-benefit ratios in corals. This idea leads to some interesting questions: how can the corals' collective pulsing behavior be optimized to yield better cost-to-benefit ratios? Is collective pulsing coordinated within a colony? If so, given that corals do not dispose of a centralized nervous system (a.k.a. brain), how does this coordination take place? What are the effects of collective pulsing (coordinated or not) on the fluid dynamics around the colony? And vice versa, what are the effects of local fluid dynamics around the colony on the collective pulsing behavior?
Such a set of questions requires a varied array of tools to try to answer them. Using a combination of fieldwork, experimental data, and computational modeling, and drawing on the expertise and tools from mathematicians, engineers, and biologists, I am slowly unraveling the mechanisms behind this fascinating pulsing behavior of xeniid corals.
About this project
In August 2013, I started my Ph.D. at the University of North Carolina at Chapel Hill and joined the Miller Lab. At the heart of the group's research are fluid-structure interactions involving biological soft tissues, from pumping hearts to flying insects and swimming jellyfish.
I quickly decided I wanted to work on marine invertebrates and started poking the lab's upside-down jellyfish. After studying their flow patterns for a few months, I got interested in their group behavior and how it affects individual pulsing behavior and water flow around the colony. I shifted my focus to pulsing corals and started collaborating with Dr. Uri Shavit at the Technion in Haifa, Israel, Dr. Roi Holzman at the Inter-University Institute for Marine Sciences in Eilat, Israel, and Dr. Shilpa Khatri at the University of California at Merced.
Through this project, I have gone to many unexpected places, from coral reefs and shark-filled wrecks to network theory, with stops at Shinto shrines, fancy ski resorts, and math conferences. The ideas and experiments stemming from these travels will constitute the body of my thesis (ETA: summer 2018).
Publications from this project
Samson, J. E., Ray, D. D., Holzman, R., Shavit, U., Miller, L. A., Khatri, S. (submitted) A novel mechanism of mixing by pulsing corals.
Battista, N. A., Samson, J. E., Khatri, S., Miller, L. A. (2018) Under the sea: pulsing corals in ambient flow. In Mathematical Methods and Models in Biosciences (eds. R. Anguelov, M. Lachowicz), Biomath Forum: 22-34.
>> Find this chapter here.
Samson, J. E., Battista, N. A., Khatri, S., Miller, L. A. (2017) Pulsing corals: a story of scale and mixing, Biomath, 6: 1712169.
>> Find this paper here.