Seabird-mediated changes in sedimentary sterols and stanols

Effective conservation strategies for at-risk animal species greatly benefit from long-term trend data. Yet, most populations lack continuous monitoring beyond 30 years, with many often lacking monitoring altogether. Paleolimnology provides a retrospective method for reconstructing animal populations over thousands of years. Here we critically evaluated the efficacy of sterols and stanols as a supporting proxy to reconstruct seabird colony dynamics of a well-studied colony with distinct peaks in population size over ∼1700 years on Baccalieu Island, Newfoundland and Labrador (Canada). We analyzed sediment from a waterbody adjacent to the world's largest colony of Leach's Storm-Petrel ( Hydrobates leucorhous ), a nearby reference pond with no colonial seabird influences, and storm-petrel feces to determine the pathway of introduction of sterols and stanols to sediment to better understand their preservation and potential transformation over time. Cholesterol represented over 95 % of sterols/stanols in storm-petrel feces, reflecting the piscivorous and planktivorous invertebrate diet of the bird. In sediment, cholesterol increased over the last ∼200 years, coinciding with the increase in seabird colony size, but did not track the population decline ca. 1980 CE. The diagenetic products of cholesterol, such as cholestanol, 5α-cholestanone, and epi-coprostanol, however, closely tracked both increases and decreases in two known peaks in seabird population size (ca. 500 CE and ca. 1980 CE). Other sterols, such as campesterol, desmosterol, fucosterol, β-sitosterol, and 5α-stigmastanol, may track the indirect environmental impacts of the seabird colony, such as nest formation and fecal-derived nutrient enrichment of the terrestrial environment. Our findings support the use of sterols and stanols as effective and informative proxies for reconstructing long-term animal populations, especially when considered in a multi-proxy framework. • Sterols and stanols from sediment track 1700 years of seabird population dynamics. • Diagenetic products of cholesterol efficiently track recent population declines. • Plant-derived sterols reflect indirect colony effects on the terrestrial environment. • Sterols and stanols enhance multi-proxy sediment reconstructions of animal populations.