Above-Cliff Tundra Reveals Hidden Seabird Footprint: Evidence from Bjørnøya (Svalbard)

anglais. peer reviewed

anglais. Abstract Bjørnøya (Bear Island) hosts one of the largest seabird colonies in the Barents Sea, with high breeding densities on steep cliffs. While most guano-derived nutrients return to the ocean, a fraction is transported inland by wind, fertilizing tundra above the colonies. We investigated how these seabird nutrient subsidies influence tundra by analysing soil properties, δ15N in soil and plant tissues, vegetation composition, and plant cover along six transects spanning SEABIRD (above-colony) and REFERENCE tundra. PERMANOVA confirmed strong effects of seabird presence on soil chemistry, vegetation composition, and δ15N. SEABIRD soils were more acidic and had elevated NH4 +, NO3 −, PO4 3−, K+, total nitrogen (TN), phosphorus (P), organic carbon (TOC), Na, and moisture. Soil δ15N was markedly elevated in SEABIRD plots and closely tracked vegetation change. LINKTREE identified a NO3 − threshold of 354 mg kg−1, showing that higher NO3 − in SEABIRD plots sharply separated them from REFERENCE plots and defined the main differences in plant composition between the two groups. A distance-based linear model identified TN, P, and Na as strongest predictors of vegetation composition. SEABIRD plots had significantly higher median plant cover (87.5%) than REFERENCE plots (15%), characterized by vegetation dominated by mosses, lichens, and nutrient-responsive vascular species. A structural equation model revealed an indirect nutrient cascade: seabird-derived nitrogen, indicated by δ15N, increased soil fertility (TN and P), which in turn enhanced vegetation composition and cover. These findings show that seabird nutrients shape inland tundra above the colonies, revealing a redistribution mechanism with limited attention in Arctic research.

15. Life on land