Chironomid assemblage changes and chitin degradation in response to ~ 1700-years of seabird population fluctuations at the world’s largest colony of Leach’s Storm-Petrels (Atlantic Canada)

Abstract

Seabirds are prominent biovectors whose guano and other wastes are an important source of nutrients that can eutrophy terrestrial and aquatic environments surrounding their breeding and nesting habitats. When these ornithogenically derived nutrients are introduced to waterbodies, they alter aquatic conditions, resulting in shifts in benthic invertebrate communities. In this paleolimnological study, we examined subfossil Chironomidae (non-biting midge) assemblages to assess the impacts of changes in the colony size of the Leach’s Storm-Petrel in three ponds on Baccalieu Island (Newfoundland and Labrador, Canada) over the past ~ 1700 years. Our results indicate that chironomids tracked the growth of the storm-petrel colony (determined by five additional paleolimnological proxies) starting in the early-1800s, and the decline of the colony in the 1980s. Given the shallow nature of the study ponds, assemblage changes likely occurred due to a combination of fluctuations in pH, metal concentrations, and bottom-water oxygen. In the ponds influenced by storm-petrels, we observed a poorly described form of degradation in subfossil chironomids that we attribute to chitinolytic processes mediated by bacteria and/or fungi that thrive on organic matter in productive aquatic systems. This study provides complementary proxy data regarding bottom-water habitats for use alongside other established paleolimnological methods to determine the long-term population dynamics of seabirds.