ECOLOGICAL DRIVERS OF MERCURY ACCUMULATION IN THREESPINE
STICKLEBACK FISH
James Willacker
Mercury is a widespread environmental contaminant known for the neurotoxicity of the
methylated forms, which bioaccumulate and biomagnifiy in aquatic food webs. The
bioaccumulation of mercury in fishes is a complex process influenced by numerous chemical,
physical, ecological, and physiological factors at multiple hierarchical levels. We utilized the
ecological diversity of threespine stickleback fish (Gasterosteus aculeatus) to examine the
relative importance of various biological factors in governing mercury accumulation within and
between populations. In Benka Lake, Alaska, a lake with both benthic and limnetic ecotypes of
stickleback, we found that male stickleback and stickleback foraging in limnetic habitats had
higher total mercury concentrations than females or benthic foraging individuals. Further, we
found that the relationships between mercury concentration, trophic position, and habitat-specific
foraging differed between the sexes such that trophic position and reliance on benthic prey were
of approximately equal importance in female fish but trophic position was more important than
reliance on benthic prey in male fish. When these same factors were examined in six lakes
spanning a range of trophic ecologies we found that sex and trophic position were more
important determinants of mercury concentrations than reliance on benthic prey; however, there
was substantial variation in the relative importance of these parameters in individual lakes. Our
results suggest that the primary factors regulating variable mercury accumulation across lakes
relate to mercury bioavailability rather than ecological differences. Finally, we examined
temporal trends in the mercury concentrations of stickleback from Benka Lake. Our findings
indicate that the temporal patterns observed in stickleback likely result from numerous
physiological and ecological processes. Further, we found that the importance and magnitude of
these factors acting upon mercury concentrations varied between sexes, ecotypes, or both.
Collectively, our results demonstrate that the ecological factors driving mercury concentrations
in stickleback are complex, likely integrate multiple confounding interactions, and often vary by
sex, ecotype, and population.