Abstract
This study evaluated the growth and biochemical composition of farming Gracilaria gracilis (Stackhouse) M. Steentoft, L. M. Irvine & W. F. Farnham in the Bizerte Lagoon (BL) and Bizerte Bay (BB) in the North Coast of Tunisia, using lantern nets. Effects of site and depth on alga daily growth rate (DGR) and biochemical composition were investigated. The DGR was affected by culture site (1.42 ± 0.65% day−1 and 1.19 ± 0.34% day−1 for the BL and the BB respectively). Agar yield, was higher (p < 0.05) in the BB than the BL (23.31 ± 2.64% vs. 19.19 ± 2.32%) with a higher (p < 0.05) 3,6-anhydrogalactose (3,6-AG) contents (41.37 ± 3.68% vs 23.30 ± 5.40%) and a lower (p < 0.05) sulphate degree (6 ± 2.00% vs 8.80 ± 0.86%). The proteins contents were independent of the site and depth of culture (20.74 ± 7.22% and 22.02 ± 6.34% for the BL and the BB respectively). R-phycoerythrin (R-PE) contents were significantly higher (p < 0.05) in the BB (0.86 ± 0.31 mg g−1) than those obtained in the BL (0.33 ± 0.12 mg g−1). The salinity, transparency, nitrate and ammonium were monitored in both sites, and their influences were discussed. Our results suggest that G. gracilis cultured in Bizerte Bay can be used in a cascading biorefinery approach.
Highlights
The red alga Gracilaria gracilis, which grow in Asian coasts, was introduced into the Mediterranean Sea[3], and established in the lagoons[4,5,6,7]
The Bizerte Lagoon (BL) water was less transparent compared to the BB (2.37 ± 0.25 m vs 4.50 ± 0.50 m)
If the physicochemical parameters of the BL and the BB generate a low DGR, which limit the alga quantities, we propose to improve the total economic value of the biomass by the extraction of others interested molecules such as proteins and R-PE
Summary
The red alga Gracilaria gracilis, which grow in Asian coasts, was introduced into the Mediterranean Sea[3], and established in the lagoons[4,5,6,7]. A low biomass supply was obtained due to the interaction with environmental factors (Grazing, epiphitism, hydrodynamism, etc...) and limited surface suitable for the benthic culture methods. As a consequence, these culture methods were applied only in a depth less than 2 m, which represent a 10% of the BL surface[8]. The purpose of this study was to provide new insights on G. gracilis growth capacities and biochemical composition (agar, proteins and R-PE) in the BL and the BB It may provide knowledge on algal biomass uses
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