Seabird-driven shifts in Arctic pond ecosystems

Abstract

Migratory animals such as seabirds, salmon and whales can transport large quantities of nutrients across ecosystem boundaries, greatly enriching recipient food webs. As many of these animals biomagnify contaminants, they can also focus pollutants at toxic levels. Seabirds arguably represent the most significant biovectors of nutrients and contaminants from the ocean to the land, given their sheer numbers and global distribution. However, long-term census data on seabirds are rare. Using palaeolimnological proxies, we show that a colony of Arctic seabirds has experienced climate-induced population increases in recent decades. We then document increasing concentrations of contaminants, including polychlorinated biphenyls and cadmium, in pond sediments that are linked to biotransport by seabirds. Our findings suggest that climate-related shifts in global seabird populations will have the unexpected consequence of restructuring coastal ecosystems.

Figure 1

Maps showing the location of (a) Cape Vera on Devon Island and (b) the study ponds near Cape Vera. Photographs of (c) CV-9 and (d) CV-22.

Figure 2

Profiles of (i) δ¹⁵N (‰), (ii) inferred chlorophyll a (mg g⁻¹ dry mass), (iii) chironomid head capsule abundance (per g dry mass), (iv) Cd (μg g⁻¹ dry mass) and (v) $\sum \text{PCBs}$ (ng g⁻¹ dry mass) for the (a) CV-9 and (b) CV-22 sediment cores. Note the scale changes between study ponds for inferred chlorophyll a, chironomid head capsule abundance and Cd concentrations. The years 1963 and 1950 based on ¹³⁷Cs dating are reported on the right-hand side (Michelutti et al. 2008). Grey shading denotes the period of inferred seabird activity at the study sites.

Figure 3

Relationships between sedimentary δ¹⁵N and (a) inferred chlorophyll a concentrations (r=0.84), PCA axis 1 sample scores of (b) diatom (r=0.97) and (c) chironomid assemblages (r=0.89), (d) $\sum \text{PCBs}$ (r=0.85) and (e) Cd concentrations (r=0.94) in the CV-9 core.