Growth, nitrogen and phosphorous uptake rates and O2 production rate of seaweeds cultured on coastal fish farms

To improve the water quality in coastal fish farms throughout year, we cultured Undaria pinnatifida at 12-19 deg C, Laminaria japonica at 13-26 deg C, and Ulva pertusa at 17-28 deg C in the Yatsushiro Sea. The growth, N and P uptake rates and O2 production rate of seaweeds were estimated. The growth of the seaweeds cultured were identified and measured. Each of the seaweeds cultured was collected monthly and analyzed for N and P contents. The observed N and P uptake rates per the blade and thallus area (Psub(N,P), mg N,P/square msub(s)/day) of each seaweed were calculated by the following formula: Psub(N,P) = (Csub(N,Pt)-Csub(N,P0)) x alpha / t, where Csub(N,P0) is the N and P contents at the start of the experiment (mg N,P/g dry), Csub(N,Pt) is the N and P contents day t (mg N,P/g dry), alpha is the dry weight per the blade and thallus area, and t is the cultivation days. The calculated N and P uptake rates of the seaweeds cultured were estimated from the dissolved inorganic nutrients concentrations, irradiance, and water temperature characteristics found at the fish farms. The O2 production rates of the seaweeds were measured by the Winkler's method used light and dark oxygen bottles on fine day in the fish farm. The allowable volumes of seaweeds cultured for N uptake to N load in fish farming area, and for O2 production to O2 consumption by a fish cultured in cage were estimated by using the maximum N uptake rate and the maximum O2 production values, respectively.