Fisheries Technology Institute, Hyogo Prefectural Technology Center for Agriculture, Forestry and Fisheries, Akashi, Hyogo 674-0093, Japan
In order to elucidate the mechanism of bleaching of seaweed Phrphyra by Eucampia zodiacus blooming, we examined the effects of nitrogen, phosphorus and silicon on its growth in culture. The maximum specific growth rate ( μm) was 2.4-2.6 d−1 at 20°C and 1.0-1.3 d−1 at 9°C nutrient saturated conditions respectively. The half-saturation constant for growth (Ks) of nitrate, phosphate and silicate were 0.86 and 0.76 μM-N, 0.31 and 0.29 μM-P, 0.88 and 0.91 μM-Si at 20 and 9°C respectively. The minimum cell quota of N, P and Si were calculated 1.0, 1.6 pmol-N/cell, 0.16, 0.24 pmol-P/cell and 2.6, 3.8 pmol-Si/cell at 20 and 9°C respectively.
E. zodiacus was able to grow using nitrate, nitrite, ammonium and glutamine were found to be good nitrogen soures but uric acid, urea and other amino acids were not so well utilized or none. E. zodiacus was capable of using a wide variety of inorganic and organic phosphorus compounds of different molecular structure successfully as a sole P source.
These results suggest that E. zodiacus poses serious damage on “Nori” cultivaiton compared to other species which caused bleaching of seaweed.