Title : Biomass assessment and cultivation trial of the edible red macroalgae Gracilaria corticata in southwest of Madagascar
Abstract:
Seaweed is still not widely used as a food source in Madagascar, despite the fact that these plants represent potentially exploitable resources. This study focuses on the macroalgae Gracilaria corticata, with the aim of using this species in human food to solve the problem of malnutrition. The biomass of G. corticata in the bays of Ranobe and Toliara on the south-west coast of Madagascar was estimated in July-August 2023 from ten sites (BR1, BR2, BR3, BR4, BR5, BT1, BT2, BT3, BT4 and BT5). Each sample consisted of 4 transects and 24 quadrats, giving a total of 40 transects and 240 quadrats for all the sites. The collected samples were then taken, weighed and dried, with the dry weights expressed in g.m-2. G. corticata was grown using two different methods, the off-bottom method and the long-line method, over a period of 45 days at Sarodrano. Growth performance was recorded every 15 days. The results showed that the average biomass in Ranobe bay was 23.14 g.m-2 and that in Toliara bay was 17.17 g.m-2. In Ranobe Bay, biomass is correlated with the recovery rate, with a positive correlation of 0.98. Given the quantity of G.corticata available in its natural state in these bays, phycoculture could be envisaged to exploit this specie.
However, during the trial period, the rate of cuttings lost increased significantly, from 9.09% to 85.45% for the off-bottom method and from 7.78% to 77.78% for the long-line method. Furthermore, the highest average weight of G. corticata at the end of culture was 164±61.7 g. This was observed in the off-bottom method, while 145±6.1 g was observed in the long-line method. In addition, the specific growth rates (TCS) obtained showed a high value of 3.26±0.28 %. d-1 for the long-line method and 2.43±2.73 %. d-1 for the off-bottom method. These results demonstrate the feasibility of cultivating these algae on the Sarodrano reefs, opening up promising prospects for seaweed farming in Madagascar and regional food security.
Keywords: South-west of Madagascar, Gracilaria corticata, biomass, phycoculture, long-line, off-bottom.
