Under the sea: Pulsing corals in ambient flow

TL;DR

This study uses 3D simulations to analyze how ambient flow influences the fluid dynamics generated by pulsing corals, revealing complex interactions that affect nutrient exchange and particle capture.

Contribution

It provides the first detailed analysis of how ambient flow interacts with pulsing coral dynamics using advanced 3D fluid-structure interaction simulations.

Findings

Ambient flow can enhance or diminish coral-generated jets.

Pulsing slows horizontal flow near polyps in strong background flows.

Flow interactions impact nutrient exchange and particle capture.

Abstract

While many organisms filter feed and exchange heat or nutrients in flow, few benthic organisms also actively pulse to enhance feeding and exchange. One example is the pulsing soft coral (Heteroxenia fuscescens). Pulsing corals live in colonies, where each polyp actively pulses through contraction and relaxation of their tentacles. The pulses are typically out of phase and without a clear pattern. These corals live in lagoons and bays found in the Red Sea and Indian Ocean where they at times experience strong ambient flows. In this paper, $3D$ fluid-structure interaction simulations are used to quantify the effects of ambient flow on the exchange currents produced by the active contraction of pulsing corals. We find a complex interaction between the flows produced by the coral and the background flow. The dynamics can either enhance or reduce the upward jet generated in a quiescent medium. The pulsing behavior also slows the average horizontal flow near the polyp when there is a strong background flow. The dynamics of these flows have implications for particle capture and nutrient exchange.