Effect of the structural complexity of a coral reef on wave propagation: a case study from Komaka Island, Japan

Abstract

The structural complexity of coral reefs has an essential impact on coastal wave propagation. Nevertheless, bathymetry data, from which complex structures of several meters in size can be ascertained, have yet to be used for numerical modelling. To investigate the effects of coral reef structural complexity on coastal wave propagation, we first obtained 1-m resolution bathymetry data from a multibeam echosounder on Komaka Island, Japan. Then we conducted numerical simulations of storm waves over the obtained bathymetry. The simulation results using fine topographic resolution demonstrate that vorticity over the reef slope is significant due to the structural complexity of coral reefs, including spurs and grooves. This implies that complex features of several meters over the reef slope induce wave-driven currents, which is often a pathway for nutrient transport. However, the calculated wave energy densities over the reef flat are mostly the same, even when coarse bathymetry resolution is used. Thus, the overall reef slope, edge, and flat account for most of the dissipation process of storm waves, whereas complex structures of several meters in size have little impact. In contrast, the coral structures several meters in size contribute to the ecosystem by facilitating seawater rather than dissipating extreme waves.