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What Is Dwarf eelgrass - (Zostera japonica)?

Habitat: Grows on mud or sand in sheltered bays and estuaries 

Distribution in Ireland: Coastal Areas

Status: Established 

Family name: Zosteracea

Reproduction: Dwarf eelgrass (aka Japanese eelgrass) reproduces by means of pollen grains. A male flower produces the pollen grains, which, via water, have to reach a female flower, where the seeds are subsequently formed.  

Dwarf Eelgrass - Zostera japonica

Dwarf eelgrass

Dwarf Eelgrass - (Zostera japonica)

This alien invasive species is believed to have been introduced with a shipment of Japanese oysters some time in the first half of the twentieth century. 


Dwarf eelgrass is mainly found in sheltered bays where the seabed is sand, mud or silt. It occurs in the inter-tidal zone and at depths down to about 3 m

Dwarf eelgrass (with flowers) on mud-flats

How To Identify Dwarf eelgrass?

Leaves: Dark green flat & thin

Size:  Blade width 1.5 mm

Stems: un-branched stems, and the

Flowers: enclosed on separate shoots. 

Dwarf eelgrass root

Dwarf eelgrass root structure

Dwarf Eelgrass - Zostera japonica - ID Guide ID Guide V5.png

Dwarf eelgrass - Zostera japonica ID guide

Dwarf Eelgrass - (Zostera japonica)

Dwarf Eelgrass is a grass-like aquatic plant that forms lush meadows in shallow, sheltered bays and estuaries. These meadows cushion the shoreline from wave energy, delaying the break down of pollutants. 

Dwarf eelgrass meadows

Why Is Dwarf eelgrass A Problem?

The intertidal seagrass Dwarf eelgrass (Zostera japonica), which is distributed in intertidal and shallow subtidal zones, is exposed to nutrients from over-enriched land-based discharge and storm water runoff before they can be washed out to sea.

Dwarf eelgrass colonizes open tidal mud flats, prime foraging grounds for birds.

It slows water currents and traps new sediments.


The dense root system binds soil particles, transforming soft mud into a firm bottom layer.


These changes destroy essential habitat for shrimp and other small mud-dwelling and burrowing animals, many of which are staple prey items for shorebirds.


However, recent studies show some areas of seagrasses can have a beneficial contribution to biodiversity. 

European Communities (Birds and Natural Habitats) Regulations 2011 non-native invasive plant species A-Z (Updated 2017)

There are currently 35 invasive plant species listed in the European Communities (Birds and Natural Habitats) Regulations (annex 2, Part 1)...


Click on a species from the following list to find out more regarding non-native species subject to restrictions under Regulations 49 and 50.

  1. American Skunk-CabbageLysichiton americanus

  2. Brazilian Giant-RhubarbGunnera manicata

  3. Broad-Leaved RushJuncus planifolius

  4. Cape PondweedAponogeton distachyos

  5. Cord-GrassesSpartina (all species and hybrids)

  6. Curly Waterweed - Lagarosiphon major

  7. Dwarf Eel-GrassZostera japonica

  8. FanwortCabomba caroliniana

  9. Floating PennywortHydrocotyle ranunculoides

  10. Fringed Water-LilyNymphoides peltata

  11. Giant HogweedHeracleum mantegazzianum

  12. Giant KnotweedFallopia sachalinensis

  13. Giant-RhubarbGunnera tinctoria

  14. Giant SalviniaSalvinia molesta

  15. Himalayan BalsamImpatiens glandulifera

  16. Himalayan KnotweedPersicaria wallichii

  17. Hottentot-FigCarpobrotus edulis

  18. Japanese KnotweedFallopia japonica

  19. Large-Flowered WaterweedEgeria densa

  20. Mile-a-Minute WeedPersicaria perfoliata

  21. New Zealand PigmyweedCrassula helmsii

  22. Parrots FeatherMyriophyllum aquaticum

  23. Red AlgaGrateloupia doryphora

  24. RhododendronRhododendron ponticum

  25. SalmonberryRubus spectabilis

  26. Sea-Buckthorn Hippophae rhamnoides

  27. Spanish Bluebell Hyacinthoides hispanica

  28. Three-Cornered LeekAllium triquetrum

  29. WakameUndaria pinnatifida

  30. Water ChestnutTrapa natans

  31. Water FernAzolla filiculoides

  32. Water LettucePistia stratiotes

  33. Water-PrimroseLudwigia (all species)

  34. WaterweedsElodea (all species)

  35. WireweedSargassum muticum

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