Effect of temperature and irradiance on the release, attachment and survival of spores of Gracilaria pacifica Abbott (Rhodophyta)

The maintenance of isomorphic life histories in algae has been difficult to explain when there is no difference between the ecological niche of the tw o adult phases. However, at the level of spores, physiological differences could exist in the reproduction and development between tetraspores and car pospores that could influence the composition of both phases in the field a nd interspecific competition. The release, attachment (winter vs. beginning of autumn) and survival (seasonal), of tetraspores and carpospores of Grac ilaria pacifica Abbott from Estero de Punta Banda, Baja California, Mexico, were studied in a gradient of temperature and irradiance. The release of t etraspores was directly affected by irradiance, while that of carpospores w as affected by irradiance and temperature. The attachment of tetraspores wa s directly affected by temperature and season while the attachment of carpo spores showed a response to changes in irradiance. Survival was influenced mainly by seasons. In spring, summer, and autumn (May, August-September, an d November/December respectively) both types of spores responded similarly, with the lowest survival rate in summer and the highest in other seasons. However in winter (January/February), the rate of survival of tetraspores w as an order of magnitude greater than in carpospores. The highest survival rate occurred at 21 degrees C and 24 degrees C, whereas the survival rate a t 15 degrees C was close to zero for both types of spores. These different responses between tetraspores and carpospores, suggest a different ecophysi ological response with regard to survival and interspecific competition in nature of the gametophyte vs sporophyte.