Effects of Irradiance and Temperature on the Release and Growth of Carpospores from Gracilaria cornea J. Agardh (Gracilariales, Rhodophyta)

Abstract

Carpospore liberation, germination and carposporeling growth were investigated in Gracilaria cornea J. Agardh at different combinations of temperature and irradiance in laboratory cultures. Maximum number of carpospores released per cystocarp approached 2500 at 25 °C and 10 μmol m −2 s −1 . Student Newman Keuls multiple comparisons showed that the number of carpospores released were significantly different (P < 0.05) between low (10, 25, 50 μmol m −2 s −1 ) and high (75 and 100 μmol m −2 s −1 ) irradiances at 25 °C. The highest carposporeling specific growth rates ranged from 4.6 to 5.2% d −1 , corresponding to a doubling time of 19.2 to 21.7 days and occurred at 25 and 28 °C at the lowest irradiance levels tested (10 and 25 μmol m −2 s −1 ). At 31 °C spore release and sporeling growth were significantly depressed regardless of irradiance. Favourable conditions for carpospore release were found at 25 °C and low irradiances (10, 25 and 50 μmol m −2 s −1 ). The best conditions for sporeling growth in G. cornea were at 25–28 °C and low irradiance. These temperatures corresponded to the environmental conditions during spring on the G. cornea beds from the Yucatan coast.