TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 64 (No. 6), pp. 961-967, 2008

Short Contribution

Factors Controlling Dissolved Silica in Coral Reef Surface Water of Urasoko Bay, Ishigaki Island, Japan

Kazuo Abe*

Ishigaki Tropical Station, Seikai National Fisheries Research Institute, Fisheries Research Agency, Fukai-Ota, Ishigaki, Okinawa 907-0451, Japan

(Received 9 November 2007; in revised form 22 May 2008; accepted 23 May 2008)

Abstract: From August 2006 to August 2007, the concentrations of dissolved silica (Si(OH)4) were monitored in the surface water of Urasoko Bay and the mouth of the stream that runs into the bay. Urasoko Bay is located on the northern coast of Ishigaki Island, Okinawa, Japan, which is in a subtropical area of the North Pacific Ocean and is surrounded by a relatively poorly developed fringing reef. Added to these samples were freshwater from the upstream area and brackish water that exudes at the beach site, which were collected from April to June 2007. Rainwater samples were also collected during the study period. The concentration of Si(OH)4 generally decreased from upstream to the bay site, and, on clear days, Si(OH)4 data from all study sites (the bay, beach, stream mouth, and upstream) plotted against salinity fell on a single straight line. When the influence of rainwater was, the results were scattered below the straight line, which suggests dilution by rainwater with a much lower Si(OH)4 concentration. These findings show that offshore seawater, rainwater, and upstream freshwater regulate the concentration of Si(OH)4 in the surface water of Urasoko Bay.

*E-mail: abek@fra.affrc.go.jp

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