LOMVIA

Description

The importance of seabirds in the Arctic

Seabirds play a significant role in the functioning of Arctic food-webs: they consume a large biomass of marine prey and transport significant quantities of nutrients and pollutants from marine to terrestrial ecosystems, and between Arctic and temperate regions. They are also quarry for hunting in Canada, Greenland, the Faeroes and Iceland and their enormous colonies provide natural spectacles for ecotourism and the popular media. Seabirds therefore have considerable economic and cultural value and deliver important ecosystem services to the Arctic region.

The impacts of climate change

The rate of climate warming in the Arctic is among the most rapid on the planet, with dramatic effects upon the ice, atmosphere and oceanography of the region. Many seabird populations in the Arctic and North Atlantic Ocean are declining in response to warming due to loss of sea ice foraging habitat and inflow of warm Atlantic water, which causes unfavourable changes in plankton and fish communities. In some places, increased outflows from melting glaciers create new habitats, but these too will ultimately be lost as glaciers stagnate. These physical impacts may be exacerbated by competition from related temperate species moving northwards and outcompeting Arctic species as their habitats warm up. Ecologists are increasingly realising that inter-specific competition can have substantial effects on the magnitude and form of a species’ response to climate change.

Why guillemots?

Brünnich’s Uria lomvia (of which the project is eponymous) and common guillemots U. aalge are among the seabirds with the highest abundance, biomass and food consumption in seas above of 60^oN. They are sister species and have broadly similar lifestyles, being cliff-nesting pursuit divers that feed on small shoaling fish and krill at depths of up to 150 m within a 150 km range of their colonies. They are broadly segregated by their thermal preferences; Brünnich’s guillemots are a truly Arctic species and are found in sea temperatures between -2 and 8^oC while common guillemots are a temperate species found in warmer waters of between 2 and 16^o. They breed side-by-side at colonies in the subarctic and they have become a classic case study for how closely related species compete and coexist. None of these studies has examined how competition varies in relation to climate, but we predict that Brünnich’s guillemots are dominant in cold Arctic conditions but will lose out to common guillemots as temperatures warm.

Why Iceland?

Iceland is right on the edge of the Arctic Circle and experiences huge variability in the oceanography owing to complex interactions of ocean currents. Cold, ice-covered waters from East Greenland current flow to the north-west, warm saline Atlantic waters from the North Atlantic flow in from the south-west and sub-Arctic waters circulate to the north-east. This makes Iceland an “Arctic in miniature” as the degree of variability in oceanography and habitats that is usually only found across ocean basins is represented around a single small country. The variability in oceanography is reflected in the distribution of fish species and seabird diets; capelin and krill dominate diets in Arctic waters and sandeel in Atlantic waters.

How are Iceland’s seas changing?

A warming event associated with increased inflow of Atlantic water over the past decade is altering food-webs, including appearance of new fish species from southern waters, declines in abundance of sandeels and krill and retreat of capelin northwards. Both guillemot species bred in colonies around the entire coast but their numbers have declined between 1983-85 and 2006-08 at spatially variable rates. In the past decade, Brünnich’s guillemots have almost completely disappeared from the south coast. However, data to relate these observations to changes in marine habitats and prey stocks are lacking.

Objectives

Our proposal’s over-arching objective is to fill a notable gap in the CAO programme by “characterising the variability in food-webs that support two species of piscivorous seabird across the extreme spatial and temporal habitat gradients found around Iceland and quantify seabird population responses to this variability.” We will address this via five sub-objectives:

1. Examine spatial and seasonal habitat preference of Brünnich’s and common guillemots at colonies around the coast of Iceland in relation to the availability of the sea ice margin, meltwater plumes and different water masses
2. Quantify the response of guillemot colony size to variation in habitat availability across space and through time
3. Characterise the structure of the food-webs that support guillemots and how these vary seasonally and spatially in relation to habitat
4. Compare contemporary samples of guillemot diets and isotope ratios to those published from the 1990s to examine temporal shifts in food-webs structure and the environmental changes underpinning these
5. Quantify the degree of coexistence between the two guillemot species across environmental gradients and determine whether inter-specific competition may limit range and abundance

Approaches

We will study both guillemots at three sites around the coast of Iceland: Latrabjarg in the NW of Iceland (65.49,-24.53) which is within foraging range of the warm Iminger and the cold East Greenland current with its associated ice margins and glacier plumes. Grimsey is a small island 45 km to the north of Iceland (66.54, -18.00) close to the subarctic water of the East Icelandic current and warmer water of the Iminger current. Skrudor is an island in the E of Iceland (64.90, -13.62) where the East Icelandic current and North Atlantic Drift meet.

At each colony we will track birds with miniature GPS tags to obtain accurate information on at-sea distribution relative to key habitat features that will be derived from satellite remote sensing data. We will also equip birds with depth recorders so we can see where they dive and how deep. We will also collect blood and prey samples samples from guillemots and use stable isotope ratios in essential amino acids to describe diets and the sources of primary production. These have the potential to infer habitat use (e.g. sea ice algae from ice margins, diatoms from open-ocean and cryophytes from glacier plumes). We will analyse these data with cutting-edge modelling methods. These will allow us to quantify how habitat preference and diets differ among the two species and how this relates to environmental conditions. We will extend these models to understand how changes in habitats, competition and diets are related to large-scale distribution and long-term trends of the two species.