The Role of Habitat-Specific Foraging in Determining Intra- and Inter-Population Variation in Mercury Concentrations in Threespine Stickleback Fish

Mercury concentrations vary among species utilizing different food webs (littoral versus limnetic) within a lake, and among lakes where a species utilizes different food webs.  Threespine stickleback fish occur as distinct littoral or limnetic specialists in thousands of populations, with some lakes containing both forms. This diversity provides an opportunity to examine the importance of foraging habitat on mercury dynamics both within and between populations of the same species. We assessed trophic ecology (littoral reliance and trophic position) and mercury concentrations in stickleback from Alaskan lakes with littoral specialists, limnetic specialists, or distinct populations of both types.  In the lake with both littoral and limnetic specialists, limnetic specialists had higher mercury concentrations, in part due to higher trophic positions, but mercury concentrations were elevated even when differences in trophic position were accounted for.  Across lakes concentrations were higher in littoral populations.  However, mercury concentrations in stickleback paralleled concentrations in primary consumers from both littoral and limnetic food webs, suggesting differences among lakes reflect the bioavailability of mercury rather than trophic processes.  These preliminary data suggest mercury concentrations reflect a combination of trophic and biogeochemical processes, underscoring the importance of examining both when assessing the factors controlling mercury concentrations in fishes.