A highly unsaturated fatty acid predicts carbon transfer between primary producers and consumers

The factors that regulate energy transfer between primary producers and con sumers in aquatic ecosystems have been investigated for more than 50 years (refs 1-3). Among all levels of the food web (plants, herbivores, carnivore s), the plant-animal interface is the most variable and least predictable l ink(4-6). In hypereutrophic lakes, for example, biomass and energy transfer is often inhibited at the phytoplankton-zooplankton link(4), resulting in an accumulation of phytoplankton biomass instead of sustaining production a t higher trophic levels, such as fish. Accumulation of phytoplankton (espec ially cyanobacteria) results in severe deterioration of water quality, with detrimental effects on the health of humans and domestic animals, and dimi nished recreational value of water bodies(7,8). We show here that low trans fer efficiencies between primary producers and consumers during cyanobacter ia bloom conditions are related to low relative eicosapentaenoic acid (20:5 omega 3) content of the primary producer community. Zooplankton growth and egg production were strongly related to the primary producer 20:5 omega 3 to carbon ratio. This indicates that limitation of zooplankton production b y this essential fatty acid is of central importance at the pelagic produce r-consumer interface.