Modeling Coral Breakage at Kure Atoll

Abstract

Given the current state of climate change, coral reefs throughout the world are under increasing pressure to survive. One factor influencing the development of coral reef ecosystems is the energy of the surface waves passing above them. The waves cause the water particles beneath them to flow in elliptical orbits, and the bottom of these orbits can create strong flows which can cause coral fingers to break off. This study follows the work of Storlazzi et al. [2005] in an attempt to model the likelihood of coral breakage at Kure Atoll. To accomplish this, the wave field is modeled using the third generation wave model Simulating Waves Nearshore (SWAN) [Booij et al. 1999], with boundary conditions and wind forcing provided by WaveWatch III [Tolman 2002]. The SWAN results for the velocity of the wave orbitals are fed into the hydrodynamic ‘Force Balance Model’ of Storlazzi et al. [2005], which estimates the applied stress of the water on the coral, and compares this with measured mechanical strengths. The results, which differ from Storlazzi et al. [2005], indicate that the corals of Kure Atoll are well suited to their environment, and are hardy enough to withstand typical wave conditions year round. Additionally, the extreme event results indicate that corals can withstand open ocean wave heights of up to nine meters, due in part to the fact that high resolution modeling indicates that some of the wave energy is lost as the waves approach the shallow coral reef zones. Finally, this study highlights the need for extensive documentation in the presentation of mathematical models: because the documentation of Storlazzi et al. [2005] did not explicitly define all equations utilized, it is impossible to completely compare the results of this study and the previous one, leaving questions as to why the results differ so greatly.