Shell powder as source of calcium in the development of Gelidium floridanum (Rhodophyta, Gelidiales) tetraspores and explants

This work aimed to improve the techniques for cultivating the species Gelidium floridanum, testing different sources of calcium. Tetraspores and explants were grown in the laboratory for 20 days with seawater enriched with 50% von Stosch solution and oyster or mussel shell powder (252 mg L-1 and 336 mg L-1), or calcium chloride (147 mg L-1 and 295 mg L-1). Tetraspores or explants cultivated with no calcium salts or shell powder were used as control. Tetraspore germination rate and morphology, and germling morphology, average length, and growth rate were evaluated. Besides, the morphology, upright axes formation and growth rate of explants were also evaluated. There was no difference in tetraspore germination among treatments and control. Treatments with shell powder impaired tetraspore viability, indicated by a greenish color, cellular disorganization, and delay in germ tube development. Germlings cultivated with CaCl2 show better initial development but with no improvement compared to control. Concerning explants, those cultivated with mussel shell powder showed the highest growth rate (3.92 and 4.28% day(-1), according to concentration) in relation to other treatments. In particular, those cultivated with 252 mg L-1 mussel shell powder had a significant formation of upright axes (10.15 +/- 0.85 upright axes) compared to the control (5.18 +/- 0.42 upright axes). Based on these results, we recommend using mussel shell powder at a concentration of 252 mg L-1 to optimize explant cultivation.