Bioaccumulation of Heavy Metals by Leach’s Storm-Petrels (Hydrobates leucorhous) in the North and South Atlantic Ocean during the Non-breeding Period

Abstract

Leach’s storm-petrels (Hydrobates leucorhous) have experienced a significant decline in Atlantic Canada and are currently listed as “Threatened” by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). Many factors may underlie this decline, including exposure to heavy metals. While mercury (Hg) levels have been measured in blood and eggs of breeding storm-petrels, these short-term indicators have not been associated with impacts on hatching or fledging success. However, longer-term Hg intake and the extent of exposure to other heavy metals during the non-breeding period remain unknown. In this study, secondary feathers were assayed to assess variation in heavy metals concentration among five overwintering regions in the Atlantic Ocean. Using geolocation data, centroid locations for each overwintering region were calculated for February, when feathers are grown. Overwintering region was a significant predictor of Hg concentrations, whereas other heavy metal varied without a clear regional effect. Foraging indicators were also strong predictors of Hg concentrations, whereas colony of origin had no influence, likely due to high individual plasticity in non-breeding migration behavior. Hg concentrations were negatively correlated with δ¹⁵N values, emphasizing the role of diazotrophic organisms in reducing baseline nitrogen levels in oligotrophic ecosystems such as the mid-Atlantic, while sulfate-reducing bacteria simultaneously enhance methylmercury bioavailability. In contrast, Hg concentrations were significantly lower in more productive upwelling regions like the Benguela system, where rapid export to deep sediments through decaying phytoplankton biomass and sinking particles drive Hg biodilution. Given their extensive migration across the Atlantic Ocean, Leach’s storm-petrels serve as valuable bioindicators of heavy metal pollution. This study provides the first insight into exposure and bioaccumulation of heavy metals during the non-breeding period of Leach’s storm-petrels. My results can serve as a baseline for assessing migration-to-breeding carry-over effects on adult survival and fledgling survival to maturity in the Atlantic population, as these factors remain unexamined. Furthermore, combining these findings with sulfate-isotope analysis could help future studies to better understand Hg biogeochemistry and contaminant dynamics within Leach’s storm-petrel preys during the overwintering period. Keywords: Mercury biodilution effect; upwelling; oligotrophic region; sulfate reducing bacteria; diazotrophs; detoxification