Organisms of the planktonic food web convey essential nutrients as well as contaminants to animals at higher trophic levels. We measured concentrations of methyl mercury (MeHg) and essential fatty acids (EFAs, key nutrients for aquatic food webs) in four size categories of planktonic organisms - seston (10-64 microm), micro-(100-200 microm), meso-(200-500 microm), and macrozooplankton (>500 mic...