Dietary lipid constraints of Arthrospira platensis for survival and growth of Daphnia magna

Abstract

Arthrospira (‘Spirulina’) is a filamentous cyanobacterium that is used as a dietary supplement for humans and animals due to its high protein content and the production of various bioactive compounds. However, this “superfood” is unsuitable as a sole resource for Daphnia magna, possibly due to a lack of essential biochemicals. Here, we explored possible lipid limitation of D. magna feeding on A. platensis by supplementing with cholesterol and/or the long-chain PUFA, eicosapentaenoic acid (EPA). Daphnids were reared on long-filament (untreated), or short-filament (fragmented) A. platensis supplemented with cholesterol- and/or EPA-containing liposomes. For comparison, daphnids was fed Chlamydomonas reinhardtii (standard algal food). D. magna reared on cholesterol-supplemented A. platensis survived throughout the study period, grew well, and produced eggs, even better than those grown on Chlamydomonas reinhardtii. Whereas D. magna raised on A. platensis supplemented with EPA did not survive longer. This demonstrates that sterol limitation is the primary factor explaining the inadequate quality of A. platensis as food for D. magna. The sterol analysis also showed that, no sterol was detected in A. platensis, while ergosterol and fungisterol were found in C. reinhardtii. Supplementing A. platensis with both cholesterol and EPA enhanced growth and reproduction, implying that A. platensis also has dietary PUFA limitations, and this is important once sterol requirements are met. As sterol limitation causes huge consequences on zooplankton life history performance, incorporating dietary lipid limitation as a potential barrier for energy and carbon flow is crucial to enhance our understanding of food web dynamics and ecosystem functioning.