Invasive seaweed look out

Scientists from NUI Galway and Seasearch Ireland are asking divers and marina users to keep an eye out for Undaria pinnatifida commonly known as Wakame or Japanese kelp. This species was first recorded in Ireland in 2014 but had been found in Carrickfergus Marina in Northern Ireland two years prior to that. Having subsequently been recorded at Dun Laoghaire and Greystones Harbours scientists believe it is likely to be far more widespread than currently recorded.

What can I do?

We are asking any marine users who see a kelp species matching the description below to send a photo to SeasearchIreland@gmail.com to confirm the identification and then our colleagues from the KelpRes team in NUIG intend to collect samples of the seaweed for genetic analysis.

Why is it important to know the location?

International experience with Wakame would indicate it is much more likely to occur in marinas and on other man-made structures. From here it can attach to boats and be carried to other parts of the country when boats are moved. Marinas and harbours with wakame need to alert users to the danger of spreading this species to allow people to take biosecurity measures such as cleaning or drying out their boat before moving it.

Current distribution in Ireland

Following the initial record from Belfast Lough, Northern Ireland in 2012, Wakame has subsequently been recorded at Carlingford Lough in 2014 and Kilmore Quay in Wexford in 2016. Since then it has been recorded by Seasearch diver Frances O’Sullivan of the Dalkey Sub Aqua club recorded it in Dun Laoghaire Harbour in 2017 and by Seasearch Ireland and KelpRes divers at Greystones Harbour in 2020. Given the widespread nature of the records on the east coast it is thought that the species is likely to occur in suitable habitats between these areas and may have spread to other areas of the coast.

Identification of Wakame

Wakame can be distinguished from other species of kelp found in Ireland by it’s large size, undulate margins and distinctive midrib. The distinctive midrib on this species makes it easy to distinguish from other kelp species in Irish waters while dabberlocks (Alaria esculenta), another species of seaweed with a distinctive midrib is typically much smaller. The image below can be downloaded for use as an identification tool in the field.

Why take genetic samples?

Studying the genetics of invasive species is important in terms of identifying vectors for introduction and vectors for spread. For example in Zebra mussels Dreissena polymorpha (a freshwater invasive species) a study combing genetic analysis with field work revealed leisure boats from the United Kingdom as the most likely source (vector) of introduction. If the Wakame populations in Ireland are extremely similar genetically that would likely indicate a single introduction event and subsequent spread, a close genetic clustering might indicate multiple introduction events from the same location, while a number of different genetic populations might indicate multiple introduction events from multiple locations.

Wakame in Greystones Harbour 2020

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