River Marströmmen

Biodiversity – crustaceans and fish
River Marströmmen has a unique aquatic environment with high natural values. Four species of glacial relict crustaceans occur in the system: Mysis relicta, Pallaseopsis quadrispinosa, Limnocalanus macrurus and the very rare Gammaracanthus lacustris.

The water system is also home to around 15 species of fish and is particularly important as a spawning and nursery area for trout, whitefish and lamprey.

The project will improve the ecological status of the river by removing two migration barriers and restoring habitats along a stretch of about three kilometers. A shallow lake and wetlands will be restored. In the estuary, reeds will be cleared and three artificial reefs will be built.

Recruitment of important predatory fish such as pike and perch is favored, as well as species such as lamprey and trout.

Impacts and ecological status

According to the EU Water Framework Directive, the ecological status of River Marströmmen varies from unsatisfactory to high in different parts of the system. The main negative factors are:

• lack of connectivity – migration barriers such as dams make fish migration difficult,
• morphological changes – removal of boulders and larger substrates, straightening and draining of wetlands and shallow lakes negatively affect bottom structures, habitat diversity and hydrology; and
• eutrophication – the coastal ecosystems of Kalmarsund and the Marströmmen estuary suffer from excess nutrients and reduced recruitment of predatory fish such as pike and perch.

Restoration measures
According to the Natura 2000 management plan for “Stora Ramm and River Marströmmen”, ensuring free migration, natural hydrology and water level variations as well as preserving viable habitats and populations is a priority.

The Improve Aquatic LIFE project will implement the following actions:

• Two migration barriers will be removed, opening up 3 kilometers of the river for free migration of fish and other species.
• Habitat restoration on 600 meters of the river, focusing on important habitats for migrating fish.
• Restoration of a 50-hectare shallow lake and 10 hectares of wetlands, to recreate a more natural hydrology downstream.
• In the estuary, 0.4 hectares of reeds will be cleared and three reed beds will be built.

The measures are expected to improve connectivity, hydrology, water quality, biodiversity, fish production and habitats. Recruitment of important predatory fish such as pike and perch will benefit, as well as species such as lamprey and trout.