The macroalga Ulva ohnoi constitutes a considerable fraction of green tides in coastal areas of Japan, but little is known about the physiological characteristics of this species. To investigate the environmental factors that promote the formation of green tides, we tested the responses of U. ohnoi and another common Japanese species, Ulva pertusa, to various levels of irradiance at different water temperatures. Because the two species are morphologically similar, we identified them using the PCR‐restriction fragment length polymorphism method. Under laboratory conditions, we evaluated the photosynthetic, dark respiration, and relative growth rate at a range of water temperatures (5 to 35°C) and photosynthetically active radiation (0 to 1000 μmol photons m−2 s−1). The maximum gross photosynthetic rate of U. ohnoi was larger than that of U. pertusa. The dark respiration rates revealed no significant differences among the species and temperature conditions. At 500 μmol photons m−2 s−1, the relative growth rate of U. ohnoi was larger than that of U. pertusa in higher temperature and the difference was the largest at 20°C. The estimated compensation irradiance and estimated saturation irradiance of U. ohnoi and U. pertusa ranged from 0.709 to 5.510 and 40.530 to 58.674 μmol photons m−2 s−1, which were lower than those in other intertidal green macroalgae, from 6 to 11 and 50 to 82 μmol photons m−2 s−1, respectively. Thus, U. ohnoi which exists as free‐floating near the water surface and accumulating inside the green tide can survive extensively in the water column of the intertidal zone, furthermore, the species can maintain rapid growth in this situation. Therefore, as a result of this study, it is suggested that the ecological success of U. ohnoi in shallow waters such as the tidal flats, estuarine, and coasts of the inner bay in comparison with U. pertusa.

中文翻译：

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高光和高温条件下石菖蒲和石菖蒲（Ulvophyceae）的光合作用和生长，以及对日本绿潮的影响

巨藻石莼在日本沿海地区的绿潮中占有相当大的比例，但对该物种的生理特征知之甚少。为了研究促进绿潮形成的环境因素，我们测试了大野大洋杉和另一种常见的日本物种 Ulva pertusa 在不同水温下对不同水平的辐照度的反应。由于这两个物种在形态上相似，我们使用 PCR 限制性片段长度多态性方法对其进行了鉴定。在实验室条件下，我们评估了水温（5 至 35°C）和光合有效辐射（0 至 1000 μmol 光子 m-2 s-1）下的光合作用、暗呼吸和相对生长速率。U. ohnoi 的最大总光合速率大于 U. pertusa。暗呼吸速率显示物种和温度条件之间没有显着差异。在 500 μmol 光子 m−2 s−1 时，U. ohnoi 在较高温度下的相对生长速度大于 U. pertusa，差异在 20°C 时最大。U. ohnoi 和 U. pertusa 的估计补偿辐照度和估计饱和辐照度范围为 0.709 至 5.510 和 40.530 至 58.674 μmol 光子 m-2 s-1，低于其他潮间带绿藻的 6 至 11 和分别为 50 到 82 μmol 光子 m−2 s−1。因此，在水面附近自由漂浮并在绿潮中积累的大野鱼可以在潮间带的水体中广泛生存，并且在这种情况下可以保持快速生长。因此，作为本研究的结果，