In the Baltic Sea, the depth distribution of bladderwrack, Fucus vesiculosus, is used as a measure of water quality in both regional and national environmental monitoring. It is included as part of the assessment criteria in the EU water framework directive in most of the nations around the Baltic Sea. Large depth distribution is used to indicate good water quality. Since bladderwrack have a key function in the Baltic Sea coastal ecosystems, large areas covered by the species are considered to contribute to high conservation values and multiple ecosystem services.

Despite the indicative role given to the species and its important ecological function in the ecosystem, very few studies have examined the development of the species on a Baltic Sea scale. The aim of this project is to perform a uniform analysis of how the depth distribution of Fucus vesiculosus has changed over the past decade in the whole Baltic Sea, and to investigate mechanisms for the possible changes. The project will follow up on results from the only previous analysis conducted on a whole Baltic Sea scale. The former project analyzed data from the measurement's start until 2001. The project is conducted in collaboration with research colleagues in several countries around the Baltic Sea, primarily Estonia, Finland, Germany, Latvia and Sweden.

The project intends to examine the following questions:

• Have the depth distribution of Fucus vesiculosus changed in the Baltic Sea over the past decade?
• Are the development of F. vesiculosus depth distribution coherence between the different basins of the Baltic Sea?
• Which variables are most important for F. vesiculosus depth distribution in the Baltic Sea?
• Is there a difference in the importance of these variables relevant for the depth distribution in the different basins of the Baltic Sea?