Acropora coral pore morphology and its internal hydrodynamics

Abstract

Pore networks are the pivotal channel for mass transport within Acropora corals, enabling coral’s reef-building capabilities in their marine ecosystems. The interactions of the coral with its surrounding water can be described as a complex hydrological system where the exchange of fluids transporting different agents is constantly occurring. Despite being of critical importance, there is a lack of modeling frameworks to represent coral’s pore structure and how it interacts with the outside. In this paper, combining micron-scale computed tomography (micro-CT), image processing, and lattice Boltzmann fluid simulations, we determine the preliminary pore scale hydraulic properties based on one single branch. Also, we quantify the anisotropy of the skeleton permeability tensor by using Darcy’s law at low Reynolds numbers. Consistently, the methods we used provide evidence for a tree-like structure, which governs the internal flow to spread across the coral, maximizing the residence time of solutes. We also compared the skeleton’s inner pore structure with the terrestrial trees’ growth region, aiming to identify the structural and functional similarities that could enhance the understanding of the coral branch’s morphology and functional roles. Our work gives a novel perspective to characterize the internal hydraulic properties of the skeleton, which enhances the understanding of nutrient transport during coral growth and facilitates further biomimetic applications in coastal defense designs.