Invasive seaweeds Identification

In order to record invasive seaweeds you need to be able to identify them. Luckily Dr. Marianela Zanolla of NUI Galway has produced some wonderful identification sheets for 8 species of interest. All 8 sheets can be downloaded here.

A bright red/pink seaweed typically found in the lower intertidal or subtidal this species can be particularly abundant in autumn and winter.

Harpoon Weed (Asparagopsis armata)

A large kelp up to 2 m long it is yellow to dark brown in colour with a distinctive midrib. Typically found on man made surfaces or in rocky habitats.

Wakame (Undaria pinnatifida)

A large kelp species up to 2m long. Golden in colour it typically has a smooth holdfast and stipe.

Laminaria ochroleuca

Up to 10 cm in diameter, light brown colour, sinuous shape, rough when touched. Low intertidal to high subtidal, growing on rocks or on other seaweed. Abundant in Spring.

OysterThief (Colpomenia peregrina)

Usually up to 2 m. Light brown colour. Attached by a disc-shaped holdfast. Highly branched, bushy. It has leaf-like proliferations and small gas vesicles along the thallus. Slimy to the touch.

Wireweed (Sargassum muticum)

Dark green in colour. Erect finger-like fronds, growing up to 40 cm long, branching repeatedly into two equal parts. Found in sheltered areas (also rock pools), low intertidal to high subtidal.

Codium fragile

Up to 33 cm long and 36 wide. Brown/green colour, not iridiscent. The edges of the fronds are thickened. Attaches by stolons and rizhoids.

Has not been recorded in Ireland to date

Several morphologies. Green colour. Fronds are rounded or filiform, in groups and connected to each other by stolons, which in turn are attached to substrata by thin rhizoids.

Has not been recorded in Ireland to date

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