Microcystin-LR concentration in aquatic food web compartments from lakes of varying trophic status

Microcystin-LR (MC-LR) concentrations were examined in water, phytoplankton, invertebrates, and two fishes for up to 3 years in four central Alberta lakes spanning a trophic gradient in total phosphorus from 15 to over 500 mu g . L(-1) in epilimnetic waters. MC-LR was not detected by HPLC in phytoplankton from an oligo-mesotrophic lake, was less than 150 ng cellular toxin-L(-1) of lake water in a eutrophic-hypereutrophic lake, and was up to 6000 and 11 000 ng . L(-1) in two hypereutrophic lakes. MC-LR in phytoplankton was strongly correlated with the abundance of the cyanobacterium Microcystis aeruginosa, and with aqueous microcystin concentration, determined by protein phosphatase bioassay (r = 0.83). MC-LR was also detected in zooplankton (up to 67 mu g . g(-1) of biomass) and MC-LR concentration in zooplankton and phytoplankton were correlated (r = 0.69). Although nine groups of macroinvertebrates were analyzed, MC-LR was only detected in gastropods (up to 120 mu g . g(-1)). MC-LR appears to be transferred to invertebrates through grazing activity. MC-LR was not detected in the livers of northern pike (Esox lucius) and white sucker (Catostomus commersoni) collected from one lake containing toxin-producing phytoplankton. Accumulation of MC-LR in aquatic food webs appears to occur in the primary consumer with probable transfer of the toxin to higher trophic levels.