Historical seabird population dynamics and their effects on Arctic pond ecosystems: a multi-proxy paleolimnological study from Cape Vera, Devon Island, Arctic Canada

摘要

Rapid environmental changes occurring in polar regions may pose a signifi cant threat to the ~10 million seabirds currently inhabiting the Canadian Arctic. However, a paucity of long-term data on seabird population dynamics makes effective management diffi cult. As top predators in the oceanic pelagic foodweb, seabirds provide marine-derived nutrients to freshwater habitats via their guano, causing trophic cascades that may be tracked using paleolimnological techniques. Diatoms (Bacillariophyceae) are the most commonly used bioindicators in paleolimnological studies and, because they are known to respond sensitively to changes in trophic status, may be effective proxies for tracking changes in seabird population dynamics. Here, we present diatom data obtained from sediment cores in seabird-affected ponds near Cape Vera, Devon Island, High Arctic Canada. We also report on additional sedimentary proxies that can be used to track seabird infl uence, namely stable isotopes of nitrogen (δ~(15)N) and spectrally-inferred chlorophyll-a. Sedimentary δ~(15)N appears to track well the proximity of the ponds to the seabird colony, as seabird wastes are elevated in δ~(15)N relative to terrestrial and freshwater sources. Interpretations are less straightforward for sedimentary chlorophyll-a profi les and diatom-inferred changes, which show no consistent relationship to one another or to shifts in sediment δ~(15)N. Diatom proxies show changes consistent with δ~(15)N where there have been large shifts in δ~(15)N through time, but no clear pattern where δ~(15)N inputs have remained relatively stable. As such, diatom assemblage changes alone may be too blunt a tool to reconstruct bird populations at Cape Vera. Our results support previous research fi ndings that diatom assemblages do not respond in a simple manner to prolonged nutrient enrichment in high Arctic ponds, which is in part related to the overriding infl uence of climate on aquatic biota in these ice-dominated systems.