摘要
Dreissenid mussels have become important components of the Great Lakes biological community since their introduction in the 1980s, but much remains to be understood regarding their effect on energy and nutrient flows in pelagic systems. Here, we report a new method that tracks incorporation of resources of molluskan origin into food webs used by aquatic birds. Biochemical tracers (fatty acids and stable carbon isotopes) are used to characterize species associated with pelagic and benthic food webs in Lake Ontario. Our focus is on the polymethylene-interrupted fatty acids (PMI-FAs) because previous research identified mollusks as their primary source. We found that PMI-FA mass fractions were greater in organisms associated with benthic (e.g. round goby) versus pelagic (e.g. alewife) food webs. Double-crested cormorants that had recently consumed benthic prey fish, i.e. goby, had greater proportions of PMI-FAs in their blood plasma than birds which showed no signs of recent goby ingestion. We did not detect an increase in mass fractions of PMI-FAs in cryogenically archived cormorant eggs following expansion of dreissenid mussels in Lake Ontario. However, following the introduction and expansion of round goby in the lake, PMI-FAs were detected at greater levels in cormorant eggs. These results illustrate how only after dreissenid mussel-facilitated establishment of round goby was the full extent of exotic species disruption of food webs manifested in fish-eating birds. These food web changes may be contributing to negative impacts on aquatic birds exemplified by the emergence of Botulism Type E as a significant mortality factor in this ecosystem.