Stonewort jungles in sheltered bays

The multi-species communities characterized by stoneworts (Charales) only form in very sheltered coastal habitats, on mud or clay bottoms. Suitable locations are typically lagoons or flads that are separated from the sea and the glo-lakes that develop from them. Layered stonewort habitats are considered to be manifestations of undisturbed flads and glos. The habitat can also occur, for example, in gaps in reed beds.

In particularly favorable locations, stoneworts fill the entire water column from bottom to surface. Such underwater jungles provide good shelter and feeding places for many fish, such as pike, perch and roach. In addition to fish, there are many snails, crustaceans and other invertebrates living among the vegetation. Especially in the least saline waters, many different insect larvae can be found.

Connection to the sea affects the species community

The most common stonewort species in multi-species Charales habitats are coral stonewort (Chara tomentosa), rough stonewort (C. aspera)and Baltic stonewort (C. baltica). In the least saline waters, fragile stonewort (C. globularis) and Nitella spp. grow as well. The species composition of the community reflects the connection of the site to the surrounding sea.

Several vascular plant species can also occur in the habitat type. The most common companion plants of stoneworts are spiny water nymph (Najas marina), fennel pondweed (Stuckenia pectinata) and Eurasian watermilfoil (Myriophyllum spicatum).

Populations are decreasing and species compositions are becoming poorer

Sheltered stonewort habitats occur throughout the Finnish coastal area, often in connection with flads. The habitat has been estimated to have declined by 30–50 percent over the past 50 years, and in some areas even more. Due to this decline, sheltered stonewort habitats are considered threatened with the status of vulnerable habitat.

The decline in the habitat is due to, among other things, dredging, boat traffic, coastal construction and eutrophication. In particular, the coral stonewort, the typical species of sheltered bays, is very sensitive to eutrophication and water movement.

The effects of eutrophication on the stonewort habitats are milder in the Gulf of Bothnia than in the Gulf of Finland and the Archipelago Sea. Even where the habitat has been preserved, its species composition has been depleted over a wide area.

Species of sheltered stonewort habitats

Coral stonewort (Chara tomentosa)

Rough stonewort (Chara aspera)

Baltic stonewort (Chara baltica).

Fragile stonewort (Chara globularis)

Nitella spp.

Spiny water nymph (Najas marina)

Sago or fennel pondweed (Stuc­kenia pectinata)

Eurasian watermilfoil (Myriophyllum spicatum)