Drag coefficients for single coral colonies and related spherical objects

Abstract

Lay AbstractWhile spheres and cylinders are sometimes used to model the flows over and through coral canopies or isolated coral colonies, these models may not adequately represent the effects of complex coral geometry. We report the results of a series of lab experiments measuring drag on branching coral colonies and spherical objects. Our results show that the drag on an individual branching coral can be much higher than on a sphere. This difference is highest at low velocities, when the flow interacts with the coral's inner branches. In contrast, the drag on a perforated plastic ball is much closer to what is observed for single coral colonies, suggesting that at high flows the inner branches of the coral do not contribute to the drag. Using our findings, we also show that drag is likely to dominate inertial forces for wavy conditions commonly found on coral reefs. These findings will help us understand how benthic (bottom‐dwelling) organisms live in environments with complex and sometimes challenging hydrodynamics.