Physiological assessment of the mariculture potential of a Gracilaria caudata (Gracilariales, Rhodophyta) variant

On the Brazilian coast, the red alga Gracilaria caudata is exploited for agar production. Recently, among the common red wild type (RD), a greenish-brown variant (GB) was collected from a natural population. The aim of this work was to compare the growth (GR), photosynthesis, and pigment content of GB and RD tetrasporophytes cultivated under two irradiances, 70 and 150 μmol photons m −2 s −1 , for a period of 28 days. The GB variant is deficient in phycoerythrin, but it produced higher levels of allophycocyanin (APC) and phycocyanin (PC) at 150 μmol photons m −2 s −1 . At this irradiance, no difference of phycoerythrin content was observed between strains, suggesting that RD could be using this pigment as a nitrogen source. RD growth rates, irrespective of irradiance, were higher when compared to GB up to 14 days, although no differences were observed in photosynthesis. During the 14-day period, both color strains showed higher GR, maximum electron transport rate, and effective quantum yield at 150 μmol photons m −2 s −1 when compared to 70 μmol photons m −2 s −1 . After that, although no differences were observed in the photosynthetic properties, a decrease in GR was seen at both irradiances when RD and GB simultaneously differentiated tetrasporangia. The GB, although fertile, was better able to maintain its growth and even exceed the growth rates of RD in the last week (150 μmol photons m −2 s −1 ). This characteristic could be advantageous to the species, favoring GB in natural populations, since G. caudata is normally found in the fertile state along the Brazilian coast, and most individuals are tetrasporophytes. This feature could also be important to the selection of this GB strain for future mariculture in Brazil. In addition, their higher concentration of PC and APC could open prospects for a possible use as source of material for pharmaceuticals and fluorescent applications.