eider swimming

Project: Why are mussel-eating sea birds declining?

Several benthic feeding sea bird populations, including common eider (Somateria mollissima), have declined dramatically in recent decades. Likewise, one of their main prey items, i.e. the blue mussels (Mytilus spp.), have declined in size in recent decades. Hence, the overall goal of this project is to test if the decline in common eider could be due to changes in the quality of the food items.

Project information

Project manager
Samuel Hylander
Other project members
Maciej Ejsmond, Marc Hauber, Vittoria Todisco, Katerina Wagner, Anna Ejsmond, Linnaeus University
Participating organizations
Linnaeus University
Carl Trygger Foundation
1 Jan 2023–31 Dec 2025
Ecology (Department of Biology and Environmental Science, Faculty of Health and Life Sciences)

Blue mussels are main prey items for common eider.
Blue mussels are main prey items for common eider. Picture: Marc Hauber

More about the project

This project aims at understanding why several sea bird populations are declining in the Baltic Sea. For example, the well-known common eider is heavily impacted with great concern in the society. There is a need to understand the mechanisms leading to these population declines.

One of the main hypothesis is that it is caused by a diminished quality of food resources (e.g. thiamine content). Thiamine is a crucial vitamin for metabolism and deficiency of this food constituent has been demonstrated in several marine species.

We will therefore:

  1. Quantify the thiamine content of the main food item of common eider, i.e. the blue mussel in a large range of sites.

  2. Develop a model of how nutrients are affecting reproductive outcome and survival of these birds

  3. Synthesize and test hypotheses as to why mussel eating birds are declining and if thiamine deficiency is a likely mechanism causing this environmental disturbance.

This will be the first time a model is developed to understand the significance of thiamine in this part of the food web. Our approach will be a key tool in understanding the role of micronutrient availability for the population number of common eiders and other mussel eating seabirds.

The project is part of the research in the Food Web Ecology research group, Linnaeus University Centre for Ecology and Evolution in Microbial model Systems (EEMiS) and the Linnaeus Knowledge Environment Water.