Jones, Holly P.
Ph.D. (Doctor of Philosophy)
Department of Biological Sciences
Seabirds are crucial components of many marine and island ecosystems, and yet they are the world’s most threatened group of birds. They spend most of their lives at sea, where they face numerous threats including climate change, pollution, and fisheries. When they return to land to breed, they are threatened by human disturbance and invasive species. This research examines seabird response to threats on land and at sea using stable isotope analysis. Seabirds provide multiple ecosystem services, such as depositing rich marine-derived nutrients into the islands where they nest. Invasive predators disrupt this bottom-up control by decimating seabird populations. Successful island management via eradications of invasive mammalian predators has led to terrestrial recovery on multiple seabird islands. However, there is little information on the impact of these eradications to the nearshore environment, an ecologically and economically significant habitat. This project uses macroalgae, an important primary producer in the coastal environment, to investigate how nearshore communities and seabird-derived nitrogen concentrations are impacted by predator eradications. Study islands were selected in the Hauraki Gulf of northern New Zealand, representing different eradication histories: never invaded by mammalian predators and those eradicated at various times in the last 30+ years. Distinct algal communities were identified by invasion history with species overlap at islands from similar eradication years. We found seabird-derived nitrogen (δ15N) in algae was higher during the rainy season, decreased with sampling depth, and decreased with wave action. Macroalgae nutrient response to recovery time was unique to individual species and often opposite to what was expected, justifying further research into algae growth and chemical processes in changing nutrient environments. Documenting differences in nearshore habitats with varying invasion histories is crucial in understanding the extent to which seabirds act as a conduit of the land-sea interface and the impacts of island management strategies. At sea, the largest danger to seabirds is fisheries. Seabird response to this threat varies widely with most studies focusing on larger fish-eating species. There is no information on small seabird species’ responses as they are assumed to be less impacted. Using stable isotope analysis of museum feather samples spanning 145 years, we examined historical changes in storm petrel diet between pre- and post-fishing expansion periods. Prior to fishing expansion (around 1950), there were significant trends toward lower δ15N and δ13C over time. Decreasing δ15N prior to 1950 suggests a possible shift to lower trophic level prey (e.g. plankton). Decreasing δ13C values prior to 1950 suggests a possible shift in proportion of pelagic and demersal prey. Prey location in the ocean column results in differing δ13C but not δ15N values due to varying contributions of 13C enriched or depleted particulate organic matter to prey diet. After 1950, there were no significant carbon and nitrogen trends over time. Increased δ15N variance after fishing expansion suggests a less specialized diet, as storm petrels were likely feeding on a variety of prey sources from different trophic levels. Seabirds exhibit large foraging plasticity and this study was the first to show a potential response to fisheries in one of the smallest seabird species. Examining seabird response to threats at sea and habitat response to management on land are important in contributing to seabird conservation in a changing environment.
Rankin, Lyndsay L., "Seabird threats on land and at sea: Measuring nearshore response to invasive predator eradications and storm petrel diet response to fishing expansion" (2019). Graduate Research Theses & Dissertations. 7581.
Northern Illinois University
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