Esker Islands

Compiled by Jan Ekebom, Finland

 

1. European Unions Natural Marine Habitat types definitions:

    1610 Baltic esker islands with sandy, rocky and shingle beach

     vegetation and sublittoral vegetation

PAL.CLASS.: 11.22, 11.23, 11.27, 11.28, 11.29, 16.122, 16.13, 16.132, 16.133, 17.21, 17.31, 19, 42C51 (1997 version)

1.1 Description of the habitat

Glaciofluvial islands (see footnote) consisting mainly of relatively well sorted sand, gravel or less commonly of till. May also have scattered stones and boulders. The vegetation of esker islands is influenced by the brackish water environment and often by the ongoing land upheaval, which causes a succession of different vegetation types. Several rare vegetation types (heaths, sands and gravel shores) and threatened species occur.

1.2 Characteristic species

Plants: Vascular plants: Artemisia campestris, Cakile maritima, Calluna vulgaris, Empetrum nigrum, Honkenya peploides, Juniperus communis, Lathyrus japonicus subsp. maritimus, Leymus arenarius, Pinus sylvestris, Potamogeton filiformis, Potamogeton pectinatus, Potamogeton perfoliatus, Myriophyllum sibiricum, Salsola kali. Algae: Ceramium tenuicorne, Chorda filum, Chara aspera, Cladophora glomerata, Fucus vesiculosus, Pilayella littoralis

Animals: Insects: Athetis lepigone, Simyra albovenosa, Actebia praecox; Molluscs: Cerastoderma glaucum, Mya arenaria.

1.3 Associated habitats

The esker islands can be found in association with the following habitat types: Sandbanks which are slightly covered by sea water all the time (1110), Annual vegetation of drift lines (1210), Perennial vegetation of stony banks (1220), Vegetated sea cliffs of the Atlantic and Baltic coasts (1230) and Boreal Baltic sandy beaches with perennial vegetation (1640).

1.4 References

Eklund, O. (1921). Vegetationen på Vidskär och Jurmo (Ab Korpo). Meddelanden af Societas pro Fauna et Flora Fennica, 47:178-215.

Syrjänen, K. (1995). Meriotakilokki Korppoon Jurmossa. Metsähallituksen luonnonsuojelujulkaisuja. Sarja A, 51: 1-49.

 

2. Additional HELCOM information

2.1 Description of the habitat

Esker islands are often elongated ridges (stretched), consisting mainly of relatively well sorted sand, gravel, stones, boulders, or of till. The sorted material of the esker islands may sometimes form a “tail/tails” behind a “head/heads” of bedrock.

The saline environment has an effect on the vegetation on land, favouring halophytic species, e.g. at high water levels or by seawater spray. Drift-walls may occur. Also, the ongoing land upheaval cause a succession of different vegetation types that, especially on larger islands, form a complex of biotopes/habitats covering the terrestrial part of the island as well as its underwater areas (base up until the shoreline). Several rare vegetation types e.g. heaths, sand and gravel shores with threatened and or declining species occur.

2.2     Distribution (past and present)

Esker islands occur mainly in the northern parts of the Baltic Sea but are most abundant on archipelago coasts. The largest esker islands in Finland and Sweden, e.g. Hailuoto and Gotska Sandön, may include dune areas, sandy plains, sandy banks or pine forests also common in other areas with sand or gravel.

2.3      Importance (sub-regional, Baltic-wide, global)

Esker islands provide a suitable habitat for many plant species favouring sand or gravel. In addition to above-mentioned species, the underwater vegetation feature species such as Tolypella nidifica, Zostera marina, and Ranunculus baudotii and fish species Coregonus lavaretus (Powan) and Stizostedion lucioperca (Pikeperch) which all may spawn or feed in the underwater areas of esker islands (they favour sand and/or gravel).

Esker islands occur in limited amount and new esker islands do not form (until glacial period). Pristine esker islands (in natural state) do not exist anymore and the abundance of esker islands in near natural state are decreasing. Therefore they are a unique Baltic-wide feature, which is also globally siginificant.

2.4     Status of threat/decline

Pristine esker islands (in natural state) do not exist anymore and the abundance of esker islands in near natural state are decreasing. Human activities cause pressures that may result in severe or irreparable damage.

2.5     Threat/decline factors

Eutrophication of the sea area surrounding an esker island is a serious threat since it increases the amount of dead plant material washed ashore which in turn increases the nutrient level of the shores which gradually changes the shore plant species diversity.

Building activities cause habitat loss or fragmentation The underwater areas surrounding esker islands were previously also threatened by sand uptake but present legislation and improved understanding of the esker islands values prevent this from taking place. However, dredging of shallow shores of esker islands is still a threat in some areas. Also, frequent recreational activities may cause abrasion/wear as well as visual, acoustic or physical disturbance to wildlife.

2.6      Options for improvement

As for many other biotopes/biotope complexes would a Baltic wide biotope inventory and a threat assessment make it possible to assess the status of esker islands. A decrease of the eutrophication also would result in a favourable development of esker islands.

2.7      References

Anon. (1999). EUR 15/2 – Interpretation Manual of European Union Habitats ver. 2.  European Commission DG Environment, Nature protection, coastal zones and tourism.

HELCOM (1998). Red List of Marine and Coastal Biotopes and Biotope Complexes of the Baltic Sea, Belt Sea and Kattegat - Including a comprehensive description and classification system for all Baltic Marine and Coastal Biotopes. HELCOM-Baltic Sea Environment Proceedings 75, Helsinki Commission. 115 pp.

 

Glaciofluvial = created during a glacial period by the running meltwater from the ice and the moving ice itself.