Biochemical composition of the brown tide causative species Aureococcus anophagefferens cultivated in different nitrogen sources

A large-scale algal bloom, caused by Aureococcus anophagefferens, has plagued the coastal embayment of Qinhuangdao, China since 2009. The bay scallop agriculture industry in this area has been adversely affected. Researchers claimed that the poor nutritional value of brown tide cells might be responsible for the detrimental effects on bivalve mollusks. To verify whether brown tide cells are nutritionally inadequate food sources, the biochemical composition (total extractable lipids, amino acids, fatty acids, and monomelic carbohydrates) of the Chinese strain A. anophagefferens was determined during the late logarithmic growth phase when culturing in different nitrogen sources (nitrate, urea and nitrate-urea mixture). Cells cultured in nitrate contained 39.12% protein, 21.99% total extractable lipid, 10.25% total carbohydrates, and a relatively high amount of polyunsaturated fatty acid (PUFA) (51.98%, percentage of total fatty acids), including eicosapentaenoic acid (EPA) (4.81%) and docosahexaenoic acid (DHA) (14.56%). The gross biochemical composition and PUFA content in A. anophagefferens in nitrate cultivation are comparable with values found in the literature of frequently used species in bivalve feeding. Nine monomelic carbohydrates were significantly reduced when cultivated in urea and nitrate-urea mixture (P<0.05). The DHA, EPA, and PUFA contents significantly decreased when cultivated in urea (P<0.05). Although the nutritional value of A. anophagefferens dropped when cultured in urea, it is still comparable with certain favorably used algal species in bivalve feeding (i.e., Skeletonema costatum), indicating that A. anophagefferens is not a nutritionally inadequate food source.