Seabirds of Newfoundland and Labrador: Using stable isotope techniques to investigate changing trophic position over ~120 years, and examining their influence on terrestrial coastal ecosystems

Morrissey, Molly M. (2023) Seabirds of Newfoundland and Labrador: Using stable isotope techniques to investigate changing trophic position over ~120 years, and examining their influence on terrestrial coastal ecosystems. Masters thesis, Memorial University of Newfoundland.

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Abstract

Seabirds breeding around Newfoundland and Labrador (NL) are facing multiple destabilizing trends in recent decades, including major fisheries collapses and increasingly erratic temperature cycling in the north-west Atlantic Ocean. Evidence suggests that these seabirds are foraging on poorer quality prey, which could have consequences for terrestrial ecosystems near seabird colonies, as seabirds are one of the major nutrient biovectors in the world. In this thesis I employ stable isotope analysis (SIA) to investigate temporal and spatial questions related to NL seabird ecology. In the first research chapter, I use stable isotopes of nitrogen (δ15N), as well as amino-acid specific stable isotopes of nitrogen (δ15NAA), as a proxy for seabird trophic level. I measured δ15N values in breast feathers of four common breeding NL seabirds (Atlantic puffin Fratercula arctica, Leach’s storm-petrel Hydrobates leucorhous, common murre Uria aalge, and razorbill Alca torda) over a period of 120+ years (1899-2021). The results indicate that Atlantic puffins, razorbills, and common murres are feeding at lower trophic levels than they were historically, while Leach’s storm-petrels’ trophic position has remained steady. In the second research chapter, I measured δ15N values in zooplankton, phytoplankton, and sediments in freshwater ponds near a large seabird community at Cape St. Mary’s Ecological Reserve (CSM), Newfoundland. Our results show that the pond nearest to the community had the highest δ15N values in zooplankton, sediment, and phytoplankton, decreasing as pond distance increased. Overall, this thesis demonstrates that 1) NL seabirds are foraging at lower trophic levels than they were historically, and 2) seabird derived nutrient inputs are incorporated into freshwater food webs near colonies. This study provides data for both researchers and managers working in seabird conservation and considers broader terrestrial implications of declines in seabird populations.

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