The numerous habitats in the Baltic Sea are teeming with life

Take a peek under the surface! The sand dancing in the swirling water looks deserted. By a big rock, the flash of a fish’s fin may be glimpsed, but deeper it is already so dark that the large isopod crustacean creeping along the bottom cannot be seen with the naked eye. There are a huge number of different habitats in the Baltic Sea that are buzzing with life.


Nature as an entity is easier to research and understand when it is divided into smaller parts. The different habitats on land are rather well-known by now, for example, the forests that can be subdivided into boreal, temperate broadleaf and mixed forest based on the types of trees that grow in the area. The same applies to fields, meadows and even rocky areas covered with lichen.

Correspondingly, there are many types of habitats and landscapes underwater as well. On the coast of Finland, the variations in depth, salinity, seafloor geography and types of substrate create a multitude of different habitats, where biotopes with different species alternate.

A biotope is a habitat with uniform environmental conditions and specific species

The biotopes in the Baltic Sea are classified according to HELCOM’s HUB classification system (Helcom Underwater Biotope and Habitat Classification System), which first classifies habitats according to availability of light, and then according to substrate type and whether there is any vegetation present, and finally, according to the dominant species of the biotope.

Using the HUB system, researchers can estimate the amount and quality of bladder wrack communities living on hard rocky areas on the seafloor with a lot of light, for example. In the fragmented world underwater, environmental conditions can change quickly, so a bladder wrack community can co-exist with another bladder wrack community, or even on the same area as a community of filamentous alga or red alga, or a community of blue mussels.

 Rakkohaurua ja putkilokasveja kirkkaassa vedessä
A canopy of bladderwrack, i.e. Fucus vesiculosus, is important for many other organisms

All biotopes have a specific assemblage of species, and interaction between the species creates the habitat in combination with the environmental conditions. The bladder wrack attaches to rocky surfaces and uses nutrients in the water to grow. The organic matter on the surface of each individual bladder wrack is consumed by the benthos sheltered by the bladder wrack. The benthos is then eaten by larger predators, such as fish. The top of the food chain is occupied by humans and sea mammals, who use the fish for nutrition.

Each biotope has a unique food web that plays a part in maintaining the Baltic Sea and its biodiversity.