Relationship between coral distributions and physical variables in Amitori Bay, Iriomote Island, Japan

Abstract

AbstractThe relationship between coral distributions and physical variables was investigated in Amitori Bay, Iriomote Island, Japan. Field observations were conducted to obtain data on coral distributions, sea temperature, sea salinity, wind speed, and river flow rate. The observed data were then used in ocean and wave model numerical simulations and soil particle tracking analysis to obtain the spatial and temporal distributions of wave height and the numbers of soil particles. The main results of this study indicate that wave height and the number of soil particles have a significant correlation with coral distribution. Higher wave heights result in greater coverage of tabular coral and lower coverage of branching coral. A greater number of soil particles relates to lesser coverage of tabular coral. On the contrary, the number of soil particles is not correlated with branching coral coverage. The potential habitats for tabular corals largely depend on the species. Acropora hyacinthus is distributed in conditions with low numbers of soil particles, A. digitifera is distributed in conditions with low numbers of soil particles and high wave heights, and A. millepora is distributed in conditions with high numbers of soil particles and low wave heights. Averages of diversity index of the coral types at the mouth and inner parts of the bay are lower than average of the whole region, but average of diversity index at the intermediate part of the bay with the intermediate physical disturbances is higher than it, which seems to support the intermediate disturbance hypothesis.