Methylmercury enters an aquatic food web through acidophilic microbial mats in Yellowstone National Park, Wyoming.

SummaryMicrobial mats are a visible and abundant life forminhabiting the extreme environments in YellowstoneNational Park (YNP), WY, USA. Little is known of theirrole in food webs that exist in the Park’s geothermalhabitats. Eukaryotic green algae associated with aphototrophic green/purple Zygogonium microbial matcommunity that inhabits low-temperature regions ofacidic (pH ~ 3.0) thermal springs were found to serveas a food source for stratiomyid (Diptera: Stratiomy-idae) larvae. Mercury in spring source water wastaken up and concentrated by the mat biomass.Monomethylmercury compounds (MeHg + ), whileundetectable or near the detection limit (0.025 ng l - 1 )in the source water of the springs, was present atconcentrations of 4–7 ng g - 1 dry weight of matbiomass. Detection of MeHg + in tracheal tissue oflarvae grazing the mat suggests that MeHg + entersthis geothermal food web through the phototrophicmicrobial mat community. The concentration ofMeHg + was two to five times higher in larval tissuethan mat biomass indicating MeHg