Stonewort meadows in exposed shores

Stoneworts (Charophyta) are a unique group of green algae. Externally, stoneworts look like vascular plants, but based on their structural features, they are classified as algae. Evolutionarily, stoneworts are intermediate between algae and vascular plants.

Stonewort-dominated habitats occur in a wide variety of habitats, from sheltered bays to fairly open sandy beaches. The species composition of the community varies depending on the substrate and the exposure of the habitat.

Rough stonewort dominates exposed habitats

The most common stonewort species in Finland is the rough stonewort (Chara aspera). It tolerates a wide range of environmental conditions, but dominates in open, exposed sandy and gravelly bottoms, where it forms shallow, stubble-like growths.

On exposed shores dominated by rough stonewort, other stonewort species can also grow in small numbers: C. baltica, C. canescens, C. globularis and bird’s nest stonewort (Tolypella nidifica). In addition, some vascular plants can occur there, such as Ruppia maritima and fennel pondweed (Stuckenia pectinata). The material of the bottom substrate and the salinity of the water affect the species that rough stonewort can find as its companions in different places.

Stonewort meadows occur along the entire coast

Exposed stonewort-dominated areas are found along the entire coast of Finland, and no significant geographical variation is known. The habitat occurs in patches. The patches are quite small, but they may form long chains along the coast.

The most common nearby habitats are seagrass beds and horned pondweed Zannichellia and widgeonweed Ruppia habitats.

Eutrophication and water traffic destroy vegetation

Exposed stonewort meadows suffer from eutrophication-induced turbidity, filamentous algal growth and siltation of the bottom. Water traffic and dredging can also destroy habitats.

The habitat is estimated to have declined by 20–30 percent over the past 50 years, which is why it is classified as near threatened. However, exposed stonewort meadows have been better preserved than sheltered stonewort communities on mud and clay bottoms, which are assessed as an endangered habitat type.

Species of exposed stonewort habitats

Rough stonewort (Chara aspe­ra)

Baltic stonewort (Chara baltica)

Bearded stonewort (Chara canescens)

Fragile stonewort (Chara globularis)

Bird’s nest stonewort (Tolypella nidifica)

Beaked tasselweed or widgeon grass (Ruppia maritima)

Sago or fennel pondweed (Stuckenia pectinata)