Green sea fingers (Codium fragile subsp. fragile)

Distribution data supplied by the Ocean Biodiversity Information System (OBIS). To interrogate UK data visit the NBN Atlas.Map Help



Codium fragile subspecies tomentosoides is a dark green seaweed composed of erect, dichotomously branched fronds. These may be up to 1 m in length. The branches are round in cross section but may be flattened beneath dichotomies of branches. The branches are soft with a velvety texture. The fronds usually arise from a spongy disc-shaped holdfast. The subspecies of Codium fragile found in Britain are only distinguishable microscopically.

Recorded distribution in Britain and Ireland

Recorded from the Orkneys, south east Scotland, south and south west England, the west coast of Wales, Ireland and the west coast of Scotland.

Global distribution

Recorded in the Netherlands, western Mediterranean Sea and Atlantic Spain to Norway.


Codium fragile fragile grows in high densities and can dominate canopy species in infralittoral rocky reef communities.

Depth range


Identifying features

  • Large green algae with spongy texture.
  • Dichotomously branching.
  • Utricles have a pronounced median or submedian constriction.
  • Utricles are sharply mucronate.

Additional information

This alien species originated in the Pacific Ocean around Japan. It was introduced from mainland Europe to the River Yealm in Devon in 1939. It has been found to displace native species of Codium tomentosum.

There is extreme difficulty in distinguishing subspecies from each other. When viewed in section under a microscope, the utricles are shorter and stouter in the tomentosoides subspecies than in the Codium fragile subspecies atlanticum. Work by Provan et al. (2005) identified the species initially by the presence of numerous pointed spines on the surface of the alga, and by subsequent DNA sequencing.

This non-native species is known to occur in a number of marine Special Areas of Conservation (mSACs), in the UK e.g. Pembrokeshire. The impacts or rate of dispersal are not known due to earlier morphological confusion with native species.

Listed by

- none -


  1. Eno, N.C., Clark, R.A. & Sanderson, W.G. (ed.) 1997. Non-native marine species in British waters: a review and directory. Peterborough: Joint Nature Conservation Committee.

  2. Gibson, R., Hextall, B. & Rogers, A., 2001. Photographic guide to the sea and seashore life of Britain and north-west Europe. Oxford: Oxford University Press.

  3. Guiry, M.D. & Nic Dhonncha, E., 2002. AlgaeBase. World Wide Web electronic publication,

  4. JNCC (Joint Nature Conservation Committee), 1999. Marine Environment Resource Mapping And Information Database (MERMAID): Marine Nature Conservation Review Survey Database. [on-line]

  5. Maggs, C.A., 2005b. Green sea fingers Codium fragile subsp. tomentosoides. Marine Aliens project. [On-line],

  6. Provan, J., Murphy, S. & Maggs, C.A., 2005. Tracking the invasive history of the green alga Codium fragile ssp. tomentosoides. Molecular Ecology, 14, 189-194.

  7. Silva, P.C., 1955. The dichotomous species of Codium in Britain. Journal of the Marine Biological Association of the United Kingdom, 34, 565-577.


  1. NBN (National Biodiversity Network) Atlas. Available from:

  2. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. Accessed: 2024-05-27


This review can be cited as:

Oakley, J.A. 2007. Codium fragile subsp. fragile Green sea fingers. In Tyler-Walters H. and Hiscock K. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 27-05-2024]. Available from:

Last Updated: 13/08/2007