Vascular plants compete for the light

The communities formed by different types of aquatic vascular plants are a common habitat type throughout the Finnish coast. They are found in almost all shallow waters, especially in sheltered areas. This habitat is most common at depths of less than four metres, where there is plenty of light.

In addition to light, vascular plants need a soft substrate to take root, most commonly in soft clay or mud, in which varying amounts of sand, gravel, small rocks or silt can also occur. Also, vascular plants can even grow large in surprisingly small pockets of sediment on otherwise rocky or stony shores, sometimes masking the smaller algae growing on the rocks beneath them.

A shoal of minnows swim among the reeds. Above the waterline, the reedbeds and the horizon can be seen in the distance.
A shoal of minnows, i.e. Phoxinus phoxinus, seek shelter among aquatic vascular plants.

Vascular plants are a diverse group

The species composition of vascular plant communities varies greatly along different parts of the coast. Plants are affected by salinity and the proximity to the coast is reflected by the strong representation of freshwater species. Some vascular plants thrive in turbid waters while others prefer the clearer waters of more open sites. Also, in terms of water-based nutrients, there are also some species in the diverse range of vascular plants which will benefit from every occasion.

Since aquatic environments are rarely constant, the vascular plant communities which are dominated by differing plant species often overlap and the species may vary greatly from year to year. The most common aquatic vascular plants occurring along the Finnish coast are the pondweeds, i.e. the fennel- (Stuckenia pectinata) and perfoliate pondweed (Potamogeton perfoliatus).

Vascular plants have various methods of survival and conquering new areas

In turbid waters, species commonly rely on strong rhizome roots and rapid growth towards the surface to survive. Although the water is often clearer in open areas, a plant’s attachment to the bottom and the elasticity of its stem and leaves are more important than rapid height growth. In sheltered areas, however, the destructive effects of waves on plant structures is reduced and large leaves floating on the surface effectively increase the surface area of the plant for photosynthesis.

Zostera and pondweed meadows

Vascular plant communities offer habitats for many other species

Vascular plant communities are usually diverse and, under favourable locations, form lush foliage that fill the entire water column, providing shelter and food for many invertebrates, as well as both adult and juvenile fish species.

Therefore, when viewed on the scale of the entire Baltic Sea, vascular plant communities exhibit very high species diversity and form one of its key underwater habitats.

Species of vascular plant communities

  • Fennel pondweed (Stuckenia pectinata
  • Perfoliate pondweed (Potamogeton perfoliatus)
  • Spiked water-milfoil (Myriophyllum spicatum)
  • Siberian water-milfoil (Myriophyllum sibiricum)
  • Brackish water-crowfoot (Ranunculus baudotii)
  • Tassel pondweed (Ruppia maritima)
  • Horned pondweed (Zannichellia palustris)