Extraction and identification of toxic organic substances from decaying green alga Ulva prolifera

In this study, the extraction, identification, and antialgal activity of toxic organic substances from decaying green alga Ulva prolifera, a disaster-causing alga on green tides in the Yellow Sea, were investigated. The toxic organic substances of U. prolifera were isolated by a sequence of procedures, namely, liquid-liquid extraction (LLE), silica gel chromatography column separation (SGCC), C18 solid phase extraction (C18 SPE), and acid-alkali separation (AAS) and their antialgal activities were tested against diatom Skeletonema costatum. The results showed that the 96h-EC₅₀ value in each procedure was 57.00 mg•L^-1, 12.14 mg•L^-1, 11.70 mg•L^-1, and 6.31 mg•L^-1 in turn. Additionally, the initial (ethyl acetate extract in LLE) and final (Organic phase A in AAS) yield of toxic organics were 318 mg•kg^-1 and 9 mg•kg^-1 (the wet weight of U. prolifera). The final active fractions were preliminary identified as five 16- and 18-carbon fatty acids and four enols using GC-MS. The study may further evaluate the effect of bioactive substances on marine life after U. prolifera green tides bloom.