Carpospore release and sporeling development in Gracilaria gracilis (Gracilariales, Rhodophyta) from the southwestern Atlantic coast (Chubut, Argentina)

The agarophyte Gracilaria gracilis is an economically valuable species exploited in Argentina and the carpospore study is relevant since such spores are used as inoculum for commercial aquaculture. The aims of this work were to describe the carpospore release periodicity and carposporeling development and to evaluate the influence of temperature, irradiance, and day length on carpospore release under laboratory conditions. Desiccation, osmotic shock, and spontaneous discharge were compared as sporulation induction methods and the last one was the best method for improved carpospore release (ANOVA: F = 6.4018, P < 0.05; least significant difference (LSD) test: P < 0.05). The number of carpospores released per cystocarp per day at 13 A degrees C was significantly greater than at 18 A degrees C (Student's t test: t = 3.89, P < 0.01). Moreover, carpospore release at 12:12-h light/dark (L/D) photoperiod was higher than at 8:16-h L/D photoperiod (Student's t test: t = 2.54, P = 0.01). No evidence of differences in the number of carpospores per cystocarp per day between high, medium, and low irradiance was recognized (ANOVA: F = 0.82, P > 0.25). Sporulation time course analysis showed a peak during the first week with a total carpospore release at the end of the sixth week of about 2,000 carpospores cystocarp(-1) day(-1). Carpospore germination and sporeling development were in agreement with the description for other Gracilaria species. This is the first work on carpospore release and germination for an Argentinian strain of G. gracilis and the results could be of interest for further commercial spore culture.