Box model analysis for the estimation of the water mass transport in coral reef region, Japan

Sekisei lagoon is the largest coral reef region, with a radius of 20 km, in Japan (between Ishigaki Island and Iriomote Island in Okinawa Prefecture), and suffered damage to only about 30% of its corals when the worldwide coral bleaching occurred in 1998. The water exchange of a coral reef region is an important environmental factor affecting the health, growth, distribution, and the transport of coral eggs and larvae. Box model was assembled for the Sekisei lagoon including large coral reefs, and applied to estimation of the water mass transport between the lagoon and adjacent areas. The model was based on the continuities of the heat flux, salinity, and water mass. We developed and applied the terms of water inlet and outlet to the traditional models, which consists of only river discharge for the initial, and the boundary condition of the advection term. The following input parameters were obtained by the in-situ observations: water temperature, salinity, flow direction and velocity. The climatic parameters such as solar radiation and precipitation were based on the publications of the data set of weather conditions. Comparison between the results of the simulation and the ground truth data showed reasonable agreement for the mass transport of the seawater. This model can be utilized to the improved analysis of the physical environment in the coral reef areas in the future.