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Abstract:The concentrations of phycobiliproteins (phycoerythrin and phycocyanin), chlorophyll-a and total soluble proteins were determined monthly in three strains (red, green and brown) of Gracilaria domingensis (Kützing) Sonder ex Dickie, collected from natural populations on the coast of Rio Grande do Norte, Brazil. In all the strains, pigment and protein concentrations were higher in the months of less sunlight and greater nitrogen availability and decreased gradually with increased sunlight and decreased nutrient concentration. The red strain showed higher concentrations of phycoerythrin and total soluble proteins. The difference in the concentration of biochemical components over the course of the year indicates species acclimation to different environmental conditions.

Species of the genus Gracilaria are widely distributed around the world, and many are wild harvested and cultivated for phycocolloid production (agar) and human food. This study investigated the growth performance of three color strains of Gracilaria domingensis in an integrated organic system. The three chromatic variants (red, green, and brown) were cultured in a shrimp farm at two depths (surface and 20 cm). The highest relative growth rates were obtained in the first week of cultivation for all three strains studied. Although the growth rates and biomass were slightly higher at a depth of 20 cm, significant differences were not observed at different depths (p \ 0.05). The growth of the three strains varied significantly over time (p \ 0.001). The maximal growth values obtained were 11.25 ± 1.50% day -1 (red), 12.76 ± 3.96% day -1 (green), and 7.86 ± 1.75% day -1 (brown). The mean growth rates for the whole period were 4.63 ± 6.97, 3.38 ± 9.09, and 2.16 ± 6.61% day -1 for the red, green, and brown strains, respectively. The pigment content (chlorophyll a, phycocyanin, and phycoerythrin) of the three strains studied was higher at a depth of 20 cm, while the maximum electron transport rate (ETR max ) and photosynthetic efficiency were higher at the surface. The high growth rates obtained in this study demonstrate the great potential of this species for integrated organic farming. Moreover, the ecological success shown by the red strain suggests that this strain is the most suitable for integrated cultivation.