Ecotypes of Gracilaria caudata (Gracilariales,Rhodophyta): physiological and morphological approaches considering life history phases

On the Brazilian coast, the red alga Gracilaria caudata J. Agardh is exploited for agar production. In view of its economic importance for potential mariculture, this work aimed to elucidate and characterize ecotypes along an extended Brazilian coastline by evaluating the effects of irradiance (70 and 150 μmol photons m^?2 s^?1) on the number of differentiated branches, growth rates (GRs), photosynthesis parameters, and pigment content of female gametophytes and tetrasporophytes from three distinct geographical areas: Ceará State (CE), Bahia State (BA), and São Paulo State (SP). Compared to low irradiance, high irradiance promoted higher GRs and a greater number of differentiated branches, as well as maximum electron transport rate (ETR_max) and maximum photosynthesis (P _max) in both phases. However, irrespective of population or irradiance, tetrasporophytes had higher ETR_max (3.30 μmol e^? m^?2 s^?1) than gametophytes (2.54 μmol e^? m^?2 s^?1), corroborating the hypothesis that tetrasporophytes have better physiological performance than gametophytes, implicating correspondingly better adaptive abilities. Under high irradiance, regardless of the period of cultivation (14 or 28 days), strains from CE presented the highest GR (15% day^?1) when compared to strains from SP (14% day^?1) and BA (13% day^?1). CE strains also had the highest number of differentiated branches and P _max. Based on these results, we suggest that CE strains are the best candidates for future experimental mariculture tests. Importantly, overall differences in physiological performance among the strains from different populations give evidence of intraspecific diversity, thus supporting the hypothesis of ecotypic differentiation and allowing this study to define different G. caudata ecotypes.