Coupling high-resolution coral bleaching modeling with management practices to identify areas for conservation in a warming climate: Keramashoto National Park (Okinawa Prefecture, Japan)

Abstract

Increases in sea-surface temperature due to global warming are a major threat to tropical and subtropical corals as exposure to high water temperatures is the primary cause of coral bleaching. To continue receiving high ecosystem services from coral reef ecosystems in the future, it is important to predict the growth conditions of corals and take appropriate countermeasures to protect them at both global and local scales. The Kerama Islands (part of the Nansei Islands, Japan) were selected as the study area. The islands have been designated as a national park and attract substantial tourism, which utilizes the coral reef ecosystem. The selected study site is significant as it is known to act as a source of coral larvae for the surrounding area. In this study, coral bleaching and mortality rates under present and +1.5 °C/+2.0 °C water temperature conditions were estimated using a 1) three-dimensional hydrodynamic model with a spatial resolution of 100 m and 2) statistical model describing the relationship between various environmental parameters and coral bleaching and mortality rates. Applying a local hydrodynamic model enabled us to obtain high-resolution spatial and temporal variations in water temperature and current speed, and these data were used to obtain statistical model data. Coral conservation sites were prioritized based on 1) projections of the spatial distribution of bleaching and mortality rates under global warming conditions and 2) locations of the main diving and conservation points, with the intention of continuing the present use and management locations. The results of this study are expected to contribute to the management of coral reef ecosystems through conservation and adaptation strategies at local scales.

Keywords: Coral reef; Global warming; Hydrodynamics; Management; Simulation.