Stoichiometric controls of mercury dilution by growth.

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Proceedings of the National Academy of Sciences of the United States of America, ISSN: 0027-8424, Vol: 104, Issue: 18, Page: 7477-82

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Karimi, Roxanne; Chen, Celia Y; Pickhardt, Paul C; Fisher, Nicholas S; Folt, Carol L
Proceedings of the National Academy of Sciences
Multidisciplinary; animals; chlorophyta; drug effects; growth & development; daphnia; metabolism; indicator dilution techniques; methylmercury compounds; pharmacology; phytoplankton; Biochemistry; Biology; Developmental Biology; Life Sciences; Marine Biology
article description
Rapid growth could significantly reduce methylmercury (MeHg) concentrations in aquatic organisms by causing a greater than proportional gain in biomass relative to MeHg (somatic growth dilution). We hypothesized that rapid growth from the consumption of high-quality algae, defined by algal nutrient stoichiometry, reduces MeHg concentrations in zooplankton, a major source of MeHg for lake fish. Using a MeHg radiotracer, we measured changes in MeHg concentrations, growth and ingestion rates in juvenile Daphnia pulex fed either high (C:P = 139) or low-quality (C:P = 1317) algae (Ankistrodesmus falcatus) for 5 d. We estimated Daphnia steady-state MeHg concentrations, using a biokinetic model parameterized with experimental rates. Daphnia MeHg assimilation efficiencies (approximately 95%) and release rates (0.04 d(-1)) were unaffected by algal nutrient quality. However, Daphnia growth rate was 3.5 times greater when fed high-quality algae, resulting in pronounced somatic growth dilution. Steady-state MeHg concentrations in Daphnia that consumed high-quality algae were one-third those of Daphnia that consumed low-quality algae due to higher growth and slightly lower ingestion rates. Our findings show that rapid growth from high-quality food consumption can significantly reduce the accumulation and trophic transfer of MeHg in freshwater food webs.