Numerical Simulations of Pulsing Soft Corals and the Photosynthesis of their Symbiotic Algae*

Sessile octocorals in the family Xeniidae actively and almost constantly pulse their tentacles; this behavior is unusual as the movement is not for locomotion or to facilitate feeding. A prior experimental study suggested that the pulsing mixes the fluid and enhances the photosynthesis of their symbiotic algae by removing the photosynthesis byproduct, oxygen. It is hypothesized that the coral’s main energy source is from this symbiotic photosynthesis. To investigate this phenomenon, mathematical modeling and numerical methods are used. The immersed boundary method is used to simulate the fluid-structure interaction of the tentacle pulsing and resulting fluid motion. The fluid simulations are coupled to a photosynthesis model, which tracks the oxygen concentration in the fluid. In these simulations, physical parameters are varied to gain insight into the role of fluid inertia and diffusivity on mixing in the fluid and the resulting photosynthesis dynamics.