Interactive effects of irradiance, temperature and photoperiod on the growth and reproduction of a marine filamentous species of Bangiales (Rhodophyta) from the Strait of Messina (Italy)

The vegetative growth and reproductive phenology of filamentous members of the Bangiales from the Strait of Messina, employing both field and culture studies, were investigated with the aim to characterize these populations. The induction of reproductive structures on gametophytes was observed to be under the influence of environmental factors. The temperature and the light intensity strongly influenced the differentiation of carpogonia on female gametophytes, so that these did not develop at high temperatures neither in the field nor in culture and did not develop at high light intensity in culture. The development of spermatangia was not related to any of the culture conditions tested except for the high temperature condition which was lethal for most thalli. In the field, spermatangia were observed from December to July in conditions of both long and short day length and up to a maximum temperature of 18.8 degrees C. Optimal conditions for growth were observed at temperatures between 15 and 21 degrees C, while at higher temperatures (25 degrees C) thalli grew poorly or died. The light intensity did not affect the total growth or the growth rate of gametophytes, while in short day lengths growth rate decreased. Chromosome counts for the gametophytes, measured in vegetative cells, gave n=3.