| Microcystins (MCYSTs) are potent liver toxins produced by cyanobacteria in fertile waters and have been implicated in poisonings of livestock, pets, wildlife and humans. Information concerning the fate of MCYSTs within food webs is scarce. This thesis explores aspects regarding the occurrence and effects of MCYSTs in pulmonate snails to ascertain whether gastropods figure in the uptake, accumulation and fate of cyanobacterial toxins in aquatic food webs.; A survey of lakes of varying primary productivity determined the concentration of MCYST in the tissue of Lymnaea slagnalis, Helisoma trivolvis and Physa gyrina was correlated with toxin in the phytoplankton (P ≤ 0.03). Additionally, toxin concentrations in L. stagnalis and P. gyrina were also correlated with the relative abundance of Microcystis spp. (P < 0.01). Considering Microcystis spp. abundance and phytoplankton toxicity are correlated with indicators of productivity, it is apparent that trophic status influences the seasonal occurrence and concentration of MCYST in snails. Subsequently, I showed that mean toxin concentrations in L. stagnalis collected from ten sites within Hastings Lake, Alberta, differs spatially, as 60% of the variation was attributed to sampling site differences and body mass.; I also demonstrated the majority of toxin detected in L. stagnalis originates from indigestible cyanobacteria, which is eliminated in ≈8 h. Nevertheless, lower concentrations (49 ng g−1) detected in snails beyond 24 h, confirms Microcystis digestion. In support, I determined that 83% of the total MCYST concentration was contained within the alimentary tract, while 17% was contained within the digestive gland, providing evidence for toxin uptake.; Depuration of MCYST from L. stagnalis was bi-phasic. Microcystin declined 80 and 95% (10 and 22°C, respectively) over the first 6 d (fast-phase), followed by reduced rates beyond 6 d (slow-phase). Temperature influenced depuration as fast-phase rates differed.; Orally administered MCYST caused histopathological changes in digestive glands of L. stagnalis. Severities were dose dependent and reminiscent of observed pathologies in liver of mammals and fish. Yet, aqueous MCYST did not affect developing L. stagnalis embryo, as the mean proportion of living snails in control and treatment groups were equal.; This thesis affords necessary insight on the importance of gastropods in accumulation and transfer of MCYSTs within the food webs of bloom-prone waters. |
