CONTROL OF ALGAL GROWTH BY MACROPHYTES AND MACROPHYTE-EXTRACTED BIOACTIVE COMPOUNDS

Algae (Selenastrum capricornutum and Microcystis aeruginosa) were resp ectively assayed in a mixed-culture system using various concentration s of macrophytes obtained from Egeria densa, Cabomba caroliniana, and Myriophyllum spicatum in order to evaluate their inhibitory effects on algal growth due to possible secretion of anti-algal bioactive compou nds under coexistence conditions. Based on this methodology, we also e valuated the methanol extract from macrophyte tissues, their extract f ractions from a polarity-based fractionation process, and the biodegra ded filtrate from the most inhibitory fraction df each macrophyte al a n initial concentration which was quantitatively confirmed to produce strong inhibition of algal growth, although in this case, heterotrophi c bacteria was also added to the assays. Algal assays investigating co existence showed clear inhibitory effects which confirm the secretion theory, and also indicated the occurrence of a species-specific reacti on. In these assays, and in those using the methanol extract fractions , M. spicatum demonstrated the strongest inhibitory effects on both al gae. The extract fraction assays showed that in all cases the fraction containing the highest polarized compounds was the most inhibitory on e, while the examined filtrates showed rapid biodegradation of all the ir anti-algal bioactive compounds in parallel with a substantial incre ase in biomass of heterotrophic bacteria. Copyright (C) 1996 IAWQ.