From seabirds to sediments: the ecological footprint of seabirds at a prominent North Atlantic breeding colony assessed using a multi-proxy paleolimnological approach

Abstract

Seabirds, by assimilating marine prey and subsequently redistributing nutrients through their feces and decaying remains, actively participate in the transfer of marine-derived nutrients from the sea to the land in their role as ecological intermediaries. Through analysis of lake/pond sediments influenced by these nutrients, paleolimnology has shed light on the ecological processes that shape seabird nesting habitats. However, there is a current need to develop species-specific proxies that can be used to identify the source of nutrient transfer in multispecies colonies. This thesis examines the historical shifts of the northern gannet (Morus bassanus) colony in Cape St. Mary's (CSM) Ecological Reserve using a paleolimnological approach, and also examines the use of sedimentary DNA (sedDNA) as a tool to identify relationships between the fecal bacterial communities of various seabird species breeding in Newfoundland and the bacterial communities of the sediments that they interact with. I inferred past colony sizes using a dated core collected from a pond 240 m upwind of the main breeding site (Bird Rock) and observed a significant increase across the proxy data associated with seabird presence (δ15N, P, Zn, Cd, and chlorophyll a), accompanied by shifts in dominant diatom assemblages. The records (dating back to the 1700s) indicate no evidence of gannets nesting on Bird Rock before this period. I then characterized the fecal bacterial communities of several species of pelagic seabirds and found that gannets exhibited a significantly different bacterial community structure compared to other seabirds nesting in Newfoundland. Finally, I examined the bacterial communities from the two ponds impacted by seabird nutrient transfer, as well as a reference pond, and found that the bacterial diversity in sediments of seabird influenced ponds has significantly lower diversity. Overall, this research (1) extends the current data available for seabirds nesting in CSM, namely gannets, beyond the current scope of knowledge provided by monitoring reports, and (2) provides insights into the affect ornithogenic nutrient transfer can have on the diversity and structure of bacterial communities in sediments of coastal systems.