Effect of temperature on light-limited growth of the harmful diatom Eucampia zodiacus Ehrenberg, a causative organism in the discoloration of Porphyra thalli

The diatom Eucampia zodiacus Ehrenberg is one of the harmful diatoms which indirectly cause, through nutrient depletion, discoloration of Pophyra thalli. The effect of temperature on light-limited growth of E. zodiocus was examined at 13 irradiance levels (5-350 mu mol m(-2) s(-1)) in combination with five temperatures (8.0-25.0 degrees C). The results showed that all the parameters of growth-irradiance curves, such as the maximum growth rate half saturation constant (Ks) threshold value of irradiance (I-o) and saturation irradiance for growth (S), increased with increasing temperature. On the basis of the relationship between temperature and growth-irradiance curves and seasonal fluctuation of the light environment in Harinia-Nada, the effect of irradiance on the population dynamics of E. zodiacits during the period from October to March was evaluated using two indices, depth of the threshold irradiance for growth (D-t) and depth where a half of its maximum growth rate is attained (D-k). D-1 and Dk remained almost stable from October to December, but gradually increased in early March. This indicates that the rang of depth at which E. zodiactis wasable to grow increased markedly in early spring when E. zodiacus blooms in Harinia-Nada. As the vegetative cells of E. zodiacus tend to distribute in relatively deeper water layers, where growth is limited by irradiance, the increase in the depth range over which E. zodiacits is able to grow is concluded to be an important factor allowing development of its blooms. (c) 2005 Elsevier B.V. All rights reserved.