''Codium fragile'', known commonly as green sea fingers, dead man's fingers, felty fingers,
Intertidal Organisms EZ ID Guides. Island County Beachwatchers. Washington State University Extension. 2006. forked felt-alga, stag seaweed, sponge seaweed,Guiry, M. D
''Codium fragile'' (Suringar) Hariot, 1889.
In: Guiry, M.D. & G. M. Guiry. (2013). AlgaeBase. National University of Ireland, Galway. Accessed through: World Register of Marine Species (WoRMS). green sponge, green fleece, and oyster thief,
Aquatic Invasive Species. Fisheries and Oceans Canada. is a species of

seaweed Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...

in the family Codiaceae. It originates in the Pacific Ocean near Japan and has become an

invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...

on the coasts of the Northern Atlantic Ocean.

Description

This siphonous

green alga The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/Streptophyta. The land plants (Embryophytes) have emerged deep in the Charophyte alga as ...

is of two subspecies in Great Britain and Ireland. They are similar, both are dark green in color. It forms long erect finger-like fronds. These grow to 40 cm or more long branching dichotomously. The cortex of the branches is formed by closely packed utricles, these are small cylindrical club-shaped structures formed from a single cell up to 1200 µm (micrometre) long.Burrows,E.M. 1991. ''Seaweeds of the British Isles''. Natural History Museum, London The rounded tips of these closely packed utricles give the frond a velvety texture. The fronds hang down from rocks during low tide, hence the nickname "dead man's fingers". The "fingers" are branches up to a centimeter wide and sometimes over 30 centimeters long. ''Codium fragile'' occurs in the low

intertidal zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...

, and subtidal on high-energy beaches. It has no gametophyte stage, and male and female gametes are both produced on separate plants.

Subspecies

Subspecies of ''C. fragile'' can only be distinguished microscopically.

''Codium fragile'' subsp. ''atlanticum''

This subspecies can be distinguished by the mucron or tip of the utricles. In this subspecies the mucron is short, no more than 20 µm long. ''Codium fragile'' subsp. ''atlanticum'' is known to have arrived in the southwest of Ireland around 1808. From there it may have spread by rafting or floating in the sea. Approximately 30 years later, it was found in Scotland. It is thought to have originally come from the Pacific Ocean near

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

. Since 1840, when it was first discovered in Scotland, it has spread the entire length of Britain, including

Shetland Shetland, also called the Shetland Islands and formerly Zetland, is a subarctic archipelago in Scotland lying between Orkney, the Faroe Islands and Norway. It is the northernmost region of the United Kingdom. The islands lie about to the no ...

. Between 1949 and 1955 it is known to have spread between Berwick-upon-Tweed and

St. Andrews St Andrews ( la, S. Andrea(s); sco, Saunt Aundraes; gd, Cill Rìmhinn) is a town on the east coast of Fife in Scotland, southeast of Dundee and northeast of Edinburgh. St Andrews had a recorded population of 16,800 , making it Fife's fourt ...

Fife Fife (, ; gd, Fìobha, ; sco, Fife) is a council area, historic county, registration county and lieutenancy area of Scotland. It is situated between the Firth of Tay and the Firth of Forth, with inland boundaries with Perth and Kinross (i ...

, a distance of 80 km. Populations of this algae occur mostly in northern Britain. Elsewhere in Europe it is found in several places, including Norway, Netherlands, France, Spain and the Azores. This species displaces the native ''

Codium tomentosum ''Codium tomentosum'' is a species of green seaweed in the family Codiaceae. Its common names include velvet horn and spongeweed. Description The holdfast of ''C. tomentosum'' is saucer-shaped and has closely woven strands giving it a unif ...

''. ''Codium fragile'' subsp. ''atlanticum'' is used as food in the Far East.''Codium fragile'' ssp. ''atlanticum''.
Joint Nature Conservation Committee, UK. Codium fragile (Suringar) Hariot, 1889

''Codium fragile'' subsp. ''tomentosoides''

This subspecies is distinguished from ''C.fragile'' subsp. ''atlanticum'' by its very pointed mucron (the tip of the utricle) – up to µm 68 long. The subspecies ''Codium fragile'' subsp. ''tomentosoides'' (syn. ''Codium mucronatum'' var. ''tomentosoides''), occurs along nearly the whole coastline of the eastern United States, from the

Gulf of St. Lawrence The Gulf of St. Lawrence () is the outlet of the North American Great Lakes via the St. Lawrence River into the Atlantic Ocean. The gulf is a semi-enclosed sea, covering an area of about and containing about of water, at an average depth of . ...

in Canada to North Carolina. It is a rapidly spreading invasive species. It originated in the Pacific Ocean around Japan, and was introduced into

New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...

from Europe in 1957. Its presence was first recorded in 1964 in the Gulf of Maine at Boothbay. It is now recorded around Ireland.Morton, O. 2003. The marine macroalgae of County Donegal, Ireland. ''Bulletin of Ireland biogeography Society'' No 27: 3 – 164 It has also been recorded from the Scilly Isles, the Channel Islands, and the south and west coasts of England and Scotland. This is a dominant subspecies in the subtidal zone, attaching to almost any hard surface. This results in increased maintenance labor for aquaculturists and reduces the productivity of cultured marine life. In established

shellfish Shellfish is a colloquial and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater envir ...

beds, this species can become a nuisance; it may attach to shellfish and then float away, carrying the animals with it. This was the inspiration for the common name "oyster thief".

''Codium fragile'' subsp. ''scandinavicum''

This subspecies was introduced from Asiatic coasts of the Pacific to Norway, and to Denmark in 1919.

''Codium fragile'' subsp. ''novae-zelandiae''

This subspecies is found in the low intertidal to subtidal zones around New Zealand at the North Island, South Island, Chatham Islands, Stewart Island, Auckland Island, Campbell Island as well as around the Falkland Islands.

References

{{Taxonbar, from=Q2712208 fragile Edible seaweeds