Stoichiometric controls of mercury dilution by growth.
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.
Karimi
Roxanne
R
Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA. rkarimi@dartmouth.edu
Chen
Celia Y
CY
Pickhardt
Paul C
PC
Fisher
Nicholas S
NS
Folt
Carol L
CL
D000818:Animals; D000460:Chlorophyta / Q000187:drug effects / Q000254:growth & development; D003621:Daphnia / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D007201:Indicator Dilution Techniques; D008767:Methylmercury Compounds / Q000494:pharmacology*; D010839:Phytoplankton / Q000187:drug effects / Q000254:growth & development
D008767:Methylmercury Compounds