In this study, the relationship between FAs and QN (and QP) was tested only under the extremely N (P)-deficient conditions, because we focus on the potential limitation of elemental and biochemical composition of phytoplankton as the determinant of food quality under nutrient deficiency. click here Our results revealed strong correlations between FAs and QN under N deficiency

in all three species, while only EPA in Rhodomonas sp. correlated significantly with QP under P deficiency. As mentioned above, phospholipids are one of major biochemical reservoirs of P in marine plankton (Van Mooy et al. 2009). Thus, the complex regulation of membrane lipid biosynthesis, e.g., phospholipids versus phospholipid substitutions, may explain the lack of common correlation between FAs and QP in the three species under P deficiency in this study. This PDE inhibitor hypothesis remains to be tested in further research. For all species in this study, TFAs (as well as SFAs and MUFAs) showed significant negative correlation with QN under N deficiency. This further indicates

the increase in the protein synthesis and the decrease in the synthesis of storage lipids when QN increases in all three species. In contrast, the correlation between PUFAs and QN revealed species-specific patterns under N deficiency, that is, negative in Rhodomonas sp., positive in P. tricornutum, and the lack of significant correlation in I. galbana. The significant correlation between PUFAs and QN in Rhodomonas sp. and P. tricornutum suggests the possible use of algal N content as the predictor of food quality. However, this correlation is species-specific, which indicates that algal N content as the predictor of food quality can check details be only used within each algal species but not in a mixed-species assemblage under N deficiency. This indication is in principle consistent with Müller-Navarra’s suggestion (1995) of algal P content as a good predictor of food quality within one algal species. More recently, Hartwich et al. (2012)

suggested that EPA concentrations can be estimated from phytoplankton biomass, while a separation of phytoplankton groups should be considered in the community with a high diversity of phytoplankton. While algal P content was suggested as a predictor of food quality by Müller-Navarra (1995), algal N content is suggested in this study. Müller-Navarra (1995) conducted experiments with freshwater algae Scenedesmus acutus and Cyclotella meneghiniana, while three species of marine phytoplankton were tested in this study. Thus, different aquatic systems, with distinct prevailing patterns of nutrient availability and ratios, may explain the differing roles of respective nutrients for food quality shown by Müller-Navarra (1995) and in our present study.