A long-term temporal analysis of heavy metal concentrations in seabird feathers with implications for overgeneralized trophic dynamics

Anthropogenic deposition and natural cycling of heavy metal can impact ecosystem function: They can accumulate in marine sediment layers and remain there for long periods of time. As these metals accumulate and move through the ecosystem to higher trophic level organisms, these metals have known toxic effects including decreased reproductive success and compromised immune systems. Seabird feather levels may be representative of broader ecosystem signals and heavy metal cycling. This study combines heavy metal concentration data from seabird feathers and builds on the results of previous studies looking at trophic declines across time. The aim is to emphasize the importance of tracking trophic levels of top predators, looking at heavy metal concentrations from the 1880s to 2016, as well as carbon and nitrogen stable isotopes to determine if changing trophic levels will alter estimated trends and environmental heavy metal concentrations. We present temporal trends in seabird tissue concentration, and examine the complex field of trophic transfer, proposing a protocol for interpreting environmental concentrations. Our results show that trophic declines do not drastically impact directional trends, but that extrapolating to other trophic levels creates a large margin of uncertainty. We observe declines in heavy metals that correspond with relevant legislation, and suggest further studies into lesser known metals to strengthen environmental monitoring methods.