PARENT SESSION
Oral Session #56: Aquatic Ecology: Plankton. Presiding: N. Hairston.
Wednesday, August 8, 2001. 1:00 PM to 5:00 PM. Hall of Ideas I.
Algal cell density effects in the accumulation of mercury and zinc by diaptomid copepods.
PICKHARDT, PAUL1, FOLT, CAROL1, CHEN, CELIA 1, KLAUE, BJORN2, 1 2
ABSTRACT- The build-up of methylmercury (MeHg) in fish to levels of concern has been well documented. However, lake-to-lake variation in fish burden is great and not predicted by aqueous metal concentrations. Much of this variation could be due to differences in the amount of MeHg that enters the planktonic food web. We investigated the role of phytoplankton density in the uptake of metals (MeHg, inorganic Hg, Zn) into zooplankton. We hypothesized that an increase in phytoplankton density results in lower mass-specific mercury concentrations in both algae and zooplankton. In contrast, we hypothesized that Zn burdens in zooplankton would be independent of phytoplankton densities because Zn uptake is regulated. To test these hypotheses, we conducted 48-hour laboratory trials, wherein adult copepods were fed metal-labeled algae at three algal densities. Algae were labeled by exposure to stable isotopes of MeHg, Hg, and Zn at environmentally realistic concentrations (<20 ng Hg⋅l-1, <2.5 ug Zn⋅l-1). Metals in water, phytoplankton and zooplankton were analyzed via HR-ICP-MS. As predicted, we found that copepod MeHg burdens were significantly lower at high algal densities and Zn burdens did not vary across treatments. However, burdens of inorganic Hg were constant with algal densities counter to our prediction. Our results confirm the importance of phytoplankton density in the accumulation of the biomagnifying MeHg to copepod grazers and emphasize the diverse pathways of uptake that characterize different metals.
KEY WORDS: methylmercury, zooplankton, Cryptomonas erosa, copepod