Nutrient fluxes from an Arctic seabird colony to the adjacent coastal marine ecosystem

Eirik A. Finne,Øystein Varpe,Geir W. Gabrielsen,Amanda E. Poste,Joël M. Durant

doi:10.1007/s00300-022-03024-5

Abstract

AbstractSeabirds are important vectors for nutrient transfer across ecosystem boundaries. In this seasonal study, we evaluate the impact of an Arctic colony (Alkhornet, Svalbard) of Black-legged Kittiwakes (Rissa tridactyla) and Brünnich’s Guillemots (Uria lomvia) on stream nutrient concentrations and fluxes, as well as utilization by coastal biota. Water samples from seabird-impacted and control streams were collected regularly throughout the melt season (June–September) for nutrient and organic carbon analysis. Stable carbon and nitrogen isotope analysis (δ13C and δ15N) was used to assess whether seabird-derived nitrogen (N) could be traced into filamentous stream algae and marine algae as well as consumers (amphipods). Concentrations of nitrate (NO3−) and nitrite (NO2−) peaked in July at 9200 µg N L−1 in seabird-impacted streams, 70 times higher than for control streams. Mean concentrations of phosphate (PO43−) in seabird-impacted streams were 21.9 µg P L−1, tenfold higher than in controls. Areal fluxes from seabird-impacted study catchments of NO3− + NO2− and PO43− had estimated ranges of 400–2100 kg N km−2 and 15–70 kg P km−2, respectively. Higher δ15N was found in all biota collected from seabird-impacted sites, indicating utilization of seabird-derived nitrogen. Acrosiphonia sp. from seabird-impacted sites had higher δ15N values (20–23‰ vs. 3–6‰) and lower C:N ratios (10.9 vs. 14.3) than specimens collected from control sites, indicating reliance on seabird-derived nitrogen sources and potentially higher N-availability at seabird-impacted nearshore sites. Our study demonstrates how marine nutrients brought onshore by seabirds also can return to the ocean and be utilized by nearshore primary producers and consumers.

Highlights

Nutrient availability is a strong regulator of marine net primary production (Field 1998)
Seasonal changes were observed for TP concentrations, with highest values recorded in June and July. While both stream groups had TP concentrations up to 127 μg L −1, most of the P was dissolved as PO43− in seabird-impacted streams, as compared to control streams which never had PO43− values above 4 μg P L−1. SiO2 concentrations were similar between seabird-impacted streams and control, and all streams had low concentrations when the streamflow was high in July
Our first hypothesis proposes elevated nutrient concentrations in streams near the seabird colony. This is well supported by our results, where nutrient concentrations, and especially dissolved inorganic forms of nitrogen (DIN) and DIP, were higher in seabirdimpacted streams than control streams, and differences between study streams were best explained by the median Normalised difference vegetation index (NDVI) values in the catchments (Fig. 3)

Summary

Introduction

Nutrient availability is a strong regulator of marine net primary production (Field 1998). There are many examples of animals functioning as vectors for nutrient transport, where these fluxes can be of a similar or higher magnitude than passive transport (Varpe et al 2005; Subalusky and Post 2019). One such example is colonial seabirds, which are responsible for a large part of the animal-mediated nutrient fluxes across the land-sea ecotone (Otero et al 2018). Seabird-derived nutrients have even been shown to fuel multiple trophic interactions, spanning both marine and terrestrial ecosystems in the Baltic Sea (HentatiSundberg et al 2020) Many of these interactions can risk weakening, or even disappear, as multiple seabird populations around the world experience declining populations trends (Paleczny et al 2015; CAFF 2017). A recent estimate attributes > 44% of seabird deposited nitrogen (N) and phosphorus (P) to come from species with declining populations (Plazas-Jiménez and Cianciaruso 2020)

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