AK BRIN: Lara Dehn, Graduate Fellow

Lara Dehn was first funded by our sister program, Alaska EPSCoR. She has done work with their Outreach Program and now, she is one of our Internal Awards Graduate Fellowship Recipients.

Feeding ecology of Arctic marine biota as determined by heavy metal dynamics

Project description
The objectives of this study are to develop a better understanding of biomagnification of selected heavy metals in the Arctic marine food web, to determine trophic level effects of these metals to aid in delineation of contaminant pathways and to establish baseline values for subsistence harvested marine mammals in Alaska. It is hypothesized, that heavy metals can be discriminators for prey as well as ecological relationships in the Arctic.

It is widely recognized that trophic position is tightly linked to contaminant accumulation. However, the accumulation of certain metals seems to be associated with the prey consumed or the feeding habitat rather than trophic level. It has been shown, that cadmium (Cd) concentrations in the kidney of bowhead whales (Balaena mysticetus) are higher than in some top level consumers even though this species feeds on pelagic krill (Woshner et al., 2001a; Bratton et al., 1997). It is likely that whales and other marine mammals are therefore exposed to elevated concentrations of heavy metals in their diet and that diet selection of these animals will influence metal distribution in tissues.

For this study, liver, kidney and muscle (and epidermis in the case of whales) have been collected from a variety of Arctic marine mammals in northern Alaska and Canada as well as potential prey items. All tissues will be analyzed for total mercury (THg) and methyl mercury (MeHg), as well as selenium (Se), cadmium (Cd), silver (Ag), copper (Cu) and zinc (Zn). Stable isotopes d13C and d15N and stomach contents analysis are used as trophic level discriminators to evaluate bioaccumulation, trophic transfer and pathways of these heavy metals in the Arctic marine food web.

Poster session - materials presented at the AAAS (September 19-20,2002)
Click on graphs below to see a larger version in another window.

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Fig. 1 a & b show age versus stable nitrogen and carbon isotopes in ringed seals (Holman and Barrow) and bearded seals. d15N displays a wide range with no significant difference between ringed (Holman and Barrow) and bearded seals, indicating a similar trophic position. The observed variation likely displays diverse feeding habits in bearded seals and dependence on either krill or Arctic cod in ringed seals. d13C is significantly more enriched in benthic feeding bearded seals than ringed seals. Seals harvested in Canada are significantly more depleted in stable carbon isotopes than Alaskan seals.
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Fig 2 a & b show significant differences in total mercury (THg) and methyl mercury to THg ratio (%MeHg) in ringed, bearded and spotted seal liver. Piscivorous spotted seals have the lowest THg concentrations, but the highest MeHg to THg ratio, suggesting that %MeHg is a better indicator for piscivory than THg alone.
Fig 3: Butchering a subsistence harvested bearded seal (Erignathus barbatus) in the community of Barrow, Alaska.
Fig 4: Processing seal tissues for a science fair project with students from the Barrow Highschool.

Reference list
Bratton, G. R.; Flory, W.; Spainhour, C. B., and Haubold, E. M. Assessment of selected heavy metals in liver, kidney, muscle, blubber, and visceral fat of Eskimo harvested bowhead whales Baleana mysticetus from Alaska's North Coast. Barrow, Alaska: Department of Wildlife Management, North Slope Borough; 1997.

Woshner, V. M.; O'Hara, T. M.; Bratton, G. R.; Suydam, R. S., and Beasley, V. R. Concentrations and interactions of selected essential and non-essential elements in bowhead and beluga whales of Arctic Alaska. Journal of Wildlife Diseases. 2001; 37(4):693-710.

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