Abstract
The nutritional requirements of Skeletonema costatum, a red tide phytoplankter, and effects of the preparation of inoculum on algal growth potential (AGP) assay using this alga as a test organism were studied. In addition, the AGP of Osaka Bay waters was measured and the growth limiting nutrients were determined.
The nutrient concentrations necessary for the maximum growth of S. costatum were 1.6 mg·l-1 of nitrogen, 0.5 mg·l-1 of phosphorus, 5 10 mg·l-1 of silicon, and 5 10 ng·l-1 of vitamin B12. The AGP was found to be dependent on the preparation of the algal inoculum. The accurate AGP was obtained only when sufficient nutrient-starved algal cells were inoculated into the samples, but insufficient starvation of cells gave an overestimation. The satisfactory inoculum was obtained from twice starvation with vitamin B12-free medium but contained 1/100 of the other nutrients as much as the concentration necessary for maximum growth. Based from the results of the assay methods, the AGPs of Osaka Bay waters were about 105 cells·ml-1, and the growth limiting nutrients were determined to be nitrogen and phosphorus.
