Influence of lake trophic status on the occurrence of microcystin‐LR in the tissue of pulmonate snails

To assess the influence of lake trophic status on the occurrence of microcystin‐LR (MCLR) in the tissue of resident pulmonate snails, we sampled seven lakes of varying primary productivity in Alberta, Canada. Parameters associated with productivity were measured every 2 weeks from mid‐May through mid‐September 1995. Phytoplankton and resident pulmonate snails were collected and analysed for MCLR concentration via high‐performance liquid chromatography. 2. For all species of gastropod (i.e. Lymnaea stagnalis , Helisoma trivolvis and Physa gyrina ), the concentration of MCLR in the tissue was correlated ( P ≤ 0.03) with toxin in the phytoplankton, but not with extracellular aqueous microcystin ( P > 0.28). The concentrations of toxin in the tissues of L. stagnalis and P. gyrina were also correlated with the relative abundance of Microcystis spp. ( P < 0.01). 3. Given that Microcystis spp. abundance and MCLR concentration within phytoplankton are correlated with indicators of productivity, we conclude that trophic status is important in influencing the occurrence and concentration of MCLR in pulmonate snails.