Propagação em massa e efeito da fertilização na produção de biomassa de Gracilaria birdiae em condições de laboratório e de campo

Abstract

Despite the rapid expansion in recent decades, seaweed cultivation still does not meet the demand of industries for algal materials. In this sense, it is necessary to develop protocols that enable the deployment of commercial cultivations and avoid overexploitation of natural beds. Vegetative propagation and cultivation under pulses are methods that minimize costs and produce a great amount of propagules in a sustainable way. This study aimed to evaluate the growth of Gracilaria birdiae propagules cultivated under nutrient pulses. The study was divided into three experiments: (1) indoor, (2) outdoor and (3) in the field. The indoor experiment, performed under controlled conditions, was conducted in 12 aquaria (10 L) with filtered seawater and 40 propagules of G. birdiae (~ 0.5 g / L). The propagules were submitted to three treatments, in triplicate, with fertilization pulses: (T1) shrimp-pond effluent; (T2) fertilizer for aquarium (Mbreda®); (T3) fertilizer extracted from Ascophyllum nodosum (Acadian®). A series of three aquaria (without fertilization pulses) was used as control. The outdoor experiment, where the propagules have been exposed to environmental variations, was conducted in 12 aquaria (30 L), with a density of about 1 g/L of biomass, and submitted to the same treatments described above. The field experiment consisted in the cultivation of the propagules from the previous experiments (indoor and outdoor) in the sea and in an organic shrimp farm. Propagules that were cultivated in treatments T2 and T3 showed the highest values of biomass and growth rate throughout the experiments as well as higher content of nitrogen. This indicates that both fertilizers have the necessary nutrients and in balanced proportions for growth of G. birdiae. The propagules that were cultivated in the organic shrimp farm obtained lower biomass values and growth rates than those cultivated in the sea because of the greater variation of temperature and salinity. Under these stressing conditions, propagules of T3 performed much better due to the bioactive compounds in the A. nodosum extract, which increase the resistance to abiotic stress. Positive values of biomass and growth rate in all experiments show the viability of producing G. birdiae biomass from in vitro propagation to cultivation on field. According to the obtained results, the propagules had better performance when cultivated under pulses of fertilizers and the developed protocol may be applied to the production of propagule stocks.