Salt Marsh Plants of the Polish Baltic Coast

The Baltic Sea, as a semi-enclosed body of water with restricted exchange with the North Sea, has a salinity substantially lower than oceanic conditions. At the surface in Pomeranian Bay and the Gulf of Gdańsk, salinity typically ranges between six and eight parts per thousand — roughly a quarter of open-ocean salinity. This has consequences for the composition of coastal plant communities: species that dominate Atlantic salt marshes in Britain or France are either absent or restricted to areas where local salinity is elevated by factors such as evaporation in shallow lagoons, reduced freshwater input or proximity to saline groundwater.

The Baltic Salt Marsh Environment

True salt marshes, in the strict sense of regularly flooded vegetated flats with a structured zonation of halophytes, are less extensive on the Polish coast than on Atlantic-facing coastlines. The limited tidal range and lower salinity restrict the extent of intertidal habitat. However, several habitat types function as analogues:

• The margins of coastal lagoons (particularly the Szczecin and Vistula lagoons) where water exchange with the sea is restricted
• The inner shores of the Puck Bay, which are sheltered from wave action and receive some saline influx
• Shallow depressions and swales behind fore-dunes where seawater spray raises surface salinity
• The mouths of small coastal rivers where salinity gradients develop near the sea

Sea Purslane — Atriplex portulacoides

Sea purslane is a semi-woody perennial shrub with silvery-grey, mealy leaves. On Atlantic coasts it is a defining species of mid-marsh zones, often forming a distinct band between glasswort stands below and common cord grass above. On the Polish Baltic coast, it occurs in scattered localities, primarily in sheltered positions in the Szczecin Lagoon area and around Puck Bay. Its silvery appearance results from a dense covering of salt-excreting glandular hairs — one of several mechanisms by which it manages ion load.

The salt glands on Atriplex portulacoides excrete sodium chloride directly onto the leaf surface. This differs from the vacuolar salt sequestration strategy of glasswort and represents a different physiological approach to the same ecological problem.

Sea Lavender — Limonium vulgare

Sea lavender, with its spray of small purple-blue flowers on wiry branched stems, flowers in late summer and is one of the more conspicuous of the salt marsh plants. Limonium vulgare is a perennial with a deep tap root that enables it to access subsurface water during summer dry periods when the upper salt marsh surface becomes intensely saline through evaporation.

In Poland, Limonium vulgare is at or near its eastern Baltic distribution limit. Botanical records document it from the Vistula Lagoon margin and from several points along the inner coast of Puck Bay. The species is included in monitoring programmes for rare and threatened coastal halophytes under the Polish Red Data Book of Plants.

Lesser-Known Halophytes

Several additional species contribute to the salt marsh flora of the Polish Baltic coast:

• Spergularia marina — lesser sea spurrey, an annual of open saline ground, frequently associated with glasswort stands
• Suaeda maritima — annual sea blite, a fleshy annual with cylindrical leaves occupying the lowest vegetated zone alongside glasswort
• Puccinellia maritima — common saltmarsh grass, a perennial grass that forms the turf component of mid-marsh zones where it occurs
• Aster tripolium — sea aster, a conspicuous composite with lilac ray florets, flowering August to October, and one of the most visible plants of the Polish salt marsh flora
• Triglochin maritima — sea arrowgrass, a slender perennial of wet saline grassland margins

Conservation and Threats

Coastal salt marsh habitats in Poland fall under EU Habitats Directive protection as habitat types 1330 (Atlantic salt meadows) and related types. National monitoring data collected under the Natura 2000 reporting framework documents the condition of these habitats at designated sites.

The primary pressures on Baltic salt marsh vegetation in Poland include ongoing eutrophication of lagoon waters, which promotes vigorous growth of common reed (Phragmites australis) that can displace lower-growing halophytes; modification of water exchange between lagoons and the open sea; and in some locations, direct reclamation or infrastructure development in the coastal zone.

References: IUCN Red List; Encyclopedia of Life; GBIF occurrence data.