Spatio-temporal variation of macroalgal assemblages in southwestern Madagascar

The spatial and temporal distribution of macroalgal assemblages at 10 sites in the Baie de Ranobe and Baie de Toliara in southwestern Madagascar were investigated during warm (February to March) and cool (July to August) seasons. Algal species were identified and coverage estimated at six habitats between the shore and 15 m depth, based on surveys with 0.5 m x 0.5 m quadrats along transects of 30 m long by 5 m broad. Ninety eight taxa (53 red, 24 green, 21 brown) were identified of which 42 were edible. Species dominance varied by bay and season, with Sargassum latifolium dominating during the warm season, and Hypnea musciformis and Ulva lactuca prevalent during the cool season. Algal cover did not differ significantly between bays, but cover differed significantly between habitats. S. latifolium, U. lactuca, and H. musciformis were prominent on the algal shelf, Ulva reticulata on the inner shelf, and Amansia rhodantha on the outer shelf. Edible seaweed proportions increased during the cool season, particularly at algal and inner-shelf habitats. Generalized Linear Model analysis confirmed significant differences in edible algal cover across habitats and seasons. The potential of sustainably using macroalgae for aquaculture and human consumption in southwestern Madagascar is highlighted.