Seasonal variations of growth and agar composition of Gracilaria multipartita harvested along the Atlantic coast of Morocco

The biology and agar composition and properties of Gracilaria multipartita, a common species along the coasts of Morocco, have been studied on samples collected monthly for one year. Growth of the alga was maximum in spring and autumn, and the seaweed partially decayed after its maximum fertility was reached in June and October. The agar content and composition showed seasonal variations. The agar content was maximal in winter (30% dw), and decreased during the growth periods to minima in June and October (25% dw) which also corresponded to the maxima of fertility. The agar composition was characterized by high 6-O-methyl galactose (38-59 mol%) and 3,6 anhydrogalactose (24-39%) contents together with galactose (12.6-25.7 mol%) and sulphate (24-5.0% dw). The gel strength varied between 246 and 511 g cm(-2) and increased after alkali treatment to reach a maximum of 880 g cm(-2). The gel strength decreased after the alga reached its maxima of fertility, indicating a possible relationship between growth, fertility and agar metabolism. The content and quality of agar from G. multipartita growing in Morocco are suitable for an industrial use of the seaweed for the production of food-grade agar.