EFFECTS OF ALTERED SALINITY, DARKNESS AND ALGAL NUTRIENT STATUS ON FLORIDOSIDE AND STARCH CONTENT, ALPHA-GALACTOSIDASE ACTIVITY AND AGAR YIELD OF CULTIVATED GRACILARIA-SORDIDA

The red alga, Gracilaria sordida, was cultivated under growth conditions giving nutrient- starved and nutrient-enriched algal cultures. These cultures were then subjected to darkness and altered salinity. Water fluxes in or out of the alga, following the osmotic gradient, resulted in changed algal water content with changed external salinity. Furthermore, the nutrient content of the seaweed influenced its process of osmotic acclimation, starch content and agar yield. The inorganic ion content of enriched algae was lower, and their floridoside pool increased significantly under conditions of darkness and high salinity. A decrease in salinity-enhanced a- galactosidase activity, especially in enriched tissue, indicating increased floridoside degradation under these conditions. Starch degradation occurred during darkness, predominantly in enriched tissue. In addition, starch degradation increased in enriched tissue on exposure of algae to hypersaline followed by hyposaline conditions. In general, lower agar yields were obtained from enriched algae, being almost restored to control values after conditions of altered salinity. Nutrient-starved algae showed increased agar yield when subjected to altered salinity. Unchanged salinity and darkness resulted in decreased agar yield. The observed changes in agar yield, a-galactosidase activity, contents of floridoside, ash, and starch of Gracilaria sordida are discussed in relation to changes in cultivation conditions. © 1991 British Phycological Society.