WA3 Metals and Bioaccumulation
254 Portland Ballroom
8:00 AM - 12:00 PM, Wednesday
() Stable isotopes unravel the mystery of intraspecific contaminant variability in top predators in San Francisco Bay.
Stewart, A1, Luoma, S1, Hieb, K2, 1 U.S. Geological Survey, Menlo Park, CA, USA2 California Fish and Game, Stockton, CA, USA
ABSTRACT- Selenium (Se) is a potent reproductive toxin for which a link has been shown between bioaccumulation and effects. Differences in selenium accumulation among coexisting species have been explained by food web preferences. That is, top predators that feed within a clam-based food web have higher Se concentrations than those in a crustacean-based food web. Within a given species, however, Se concentrations can be highly variable and cannot be explained by allometric factors (e.g. size). Here we used stable isotopes (
13C and 34S) to identify food web structures and foraging locations of top predators (fish and diving ducks) within the San Francisco Bay estuary. Understanding food web pathways and feeding locations can explain why some individuals had accumulated more Se than others of the same species. Our results showed that primary consumers 13C and 34S values were progressively enriched with increasing salinity. Similarly, predator isotopic signatures were found to match those of primary consumers at the base of their food web. For example, a white sturgeon tissue 13C value of -23 ‰ corresponded to isotopic values determined for the estuarine clam, Potamocorbula amurensis collected in the upper regions of the estuary, suggesting that this sturgeon foraged predominantly in this location. Foraging location explained from 30 to 70% of the intraspecific variability in predator Se concentrations. Moreover, Se concentrations in top predators from both food webs were strongly related to stable isotope signatures. This means that fish foraging in the upper estuary (and thus possessing depleted 13C and 34S values) are more likely to accumulate high levels of Se. Discriminating feeding ranges in top predators may play an important role in highlighting primary locations of contaminant exposure and identifying through feeding behavior, those individuals and populations most at risk.
Key words: selenium, bioaccumulation, variability, stable isotopes