Seasonal Variation of Turbidity in a Fringing Reef Water in Urasoko Bay, Ishigaki Island: Re-suspension due to Northerly Winds

Abstract

Degradation of coral reef ecosystems are recognized in many areas around the world. Increase of seawater turbidity due to terrigenous sediments is regarded as one of the major cause of the degradation. We investigated levels and temporal variability of the turbidity during a two-year period at Urasoko Bay, a fringing coral reef of Ishigaki Island, Japan. At the near shore station, the median value of the turbidity was 2.26 NTU with the maximum of 92.9 NTU. At the two stations, 150m and 370m offshore, the median values of the turbidity were 0.58 NTU and 0.36 NTU, respectively. Correlation of the turbidity with the precipitation was weak, but wind showed significant correlation with the turbidity. Especially, the wind of the northwestern direction tended to increase the turbidity. These observations suggested that re-suspension of the bottom sediments by the wind driven turbulence and the wind-current with high turbidity and low salinity affected the variability of the turbidity in the Urasoko Bay.