Pyropia haitanensis is one of the main cultivated macroalgae in China. In recent years, the cultivation of P. haitanensis conchospores in seawater is conducted in advance to obtain earlier harvest. However, the high seawater temperature may exert negative impacts on the algae. Seven temperature conditions (25, 26, 27, 28, 29, 30 and 31 degrees C) were set in the culture of P. haitanensis to investigate the effects of temperature on the conchospore germination and early seedling development of P. haitanensis. The results showed that conchospore germination rate decreased with the increase in temperature. The temperatures of 25 and 26 degrees C were suitable for P. haitanensis conchospore germination. Higher temperature (27 degrees C) promoted conchospore germination on the 1st and 2nd days but decreased the germination considerably on the 3rd day. The conchospore mortality rate reached 89 after culture at high temperature (31 degrees C) for 4 days. Additionally, the development of conchospore seedlings was normal, the total number of cells increased, and the survival rate was high (53-90) in the range of 25-29 degrees C. At 25 degrees C, the absolute growth rate of seedlings was as high as 302. However, the development slowed down and the absolute growth rate decreased with the increase in temperature. At 30 and 31 degrees C, seedling development was abnormal or even ceased, the survival rate was as low as 20 (30 degrees C) and 11 (31 degrees C), and the absolute growth rates were negative under the two conditions. The mortality of seedling was remarkably higher at 31 degrees C than at other temperatures and gradually increased with the increase in temperature (25-31 degrees C). And, the potential mechanisms underlying high temperature damages were analysed. Therefore, the temperature range suitable for the seedling collection and cultivation of P. haitanensis conchospore is 25-29 degrees C.
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