Vital seagrass beds being ‘overwhelmed by invasive alien seaweed’ – Coastwatch warns

Seagrass is a vital habitat for many marine species and acts as a ‘blue carbon’ store

Some of Ireland's most important seagrass beds, which capture CO2 and provide a habitat for many marine species, are being damaged by the spread of an alien invasive seaweed, the environmental group Coastwatch has warned.

Seagrass beds in Kilmore Quay in Co Wexford, Bantry Bay in Co Cork and at Fenit beach in Tralee Bay, Co Kerry, have been damaged by the species known as sargassum muticum.

In the worst affected-area, a large zostera marina seagrass meadow, straddling St Patrick's Bridge near Kilmore Quay, is being progressively killed off, Coastwatch director Karin Dubsky confirmed.

“EU regulation and national law state that it is an offence to allow dispersal and spread of listed invasive alien species. Landowners who find a listed invasive species must act to prevent spread, but it is still unclear who is responsible at sea,” she added.

The damage in Co Wexford was at an important Natura 2000 site, which includes the Saltee Islands special area of conservation. "The invasive seaweed has had time to form a blanket over seagrass and displace it in patches, while both still coexist in other places, but seagrass is losing the battle," Ms Dubsky pointed out.


As as emergency measure, Coastwatch was removing the seaweed by hand using trained volunteers when it becomes accessible by wading or by snorkelling at low tide. “We don’t know if this is legal or not,” she said.

Fortunately, laboratory tests on sargassum samples from the site confirmed its suitability as soil conditioner and fertiliser. As a consequence, local farmers were taking it and applying it to their land, she said.

“Volunteer removal has been slow but with good results. More help is urgently needed, both for the sake of the seagrass and as sargassum is starting to break off and will spread further,” Ms Dubsky said. Its latest effort to remove sargassum was undertaken on Wednesday afternoon.

While seagrasses provide “high-value blue carbon habitats”, they were vulnerable and can be easily overrun, she said. The presence of sargassum at Fenit had only occurred very recently, so it could be removed quickly, she said.

Legal clarity

Ms Dubsky believed that as the damage was occurring along foreshores, it was the responsibility of the Department of Housing, Local Government and Heritage to curb this invasive species but she had been told there was a lack of legal clarity on this.

An obvious way to address the issue was for local authorities to have some role, as they do with land-based invasive species, Ms Dubsky said.

She hoped that the Maritime Area Planning Bill being published this week would provide a mechanism to provide protection for Ireland’s seagrass populations and submerged forests.