Golden kelp: how did the alien seaweed end up in Irish waters?

After the gales, the season’s shearing of kelp has left many beaches in western coves knee-deep in a dark and pungent harvest. Torn from their grip on seabed reefs, old plants have been rolled ashore in the surf, complete with knuckled holdfasts, stipes and blades, their slithery tangle sharp with the whiff of iodine.

Iodine, indeed, was once the value of the harvest, when the “sea rods” of Laminaria were piled into stone-ringed kilns on the shore and burned to ash for extraction, the clouds of smoke drifting up to the hills.

Today it’s the kelp in the sea that offers industrial profit from harvesting for alginates or biofuel. Against this must be weighed the seaweed’s great value to marine life, as a carbon store and as a coastal undersea brake on the landward surge of storms.

Some 90 Irish bays and coasts are already protected from kelp extraction as Special Areas of Conservation, and many will need to be left alone. But mechanical harvesting is already in prospect at sites such as Bantry Bay, with talk of a national potential of 10 million tonnes.

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A review by the Marine Institute in 2004 urged a precautionary, ecological approach. Out of this and other warnings has come KelpRes, shorthand for research into the diversity, productivity and resilience of kelp ecosystems. The project is vital to government licensing of future industrial harvesting and to kelp's future in a warming, acidifying sea.

At NUI Galway last month, a dozen students signed up for training as "scientific divers" in the KelpRes project, funded by the Environmental Protection Authority. Its leader is Dr Kathryn Schoenrock, whose past research on seaweed and climate took her down to seabeds off Antarctica and Greenland.

Kelps are the ecosystem engineers of undersea coastal life. There are five native species, varying as water deepens from the shore but only two form forests,

Dominant kelp

First to show above retreating spring tides is the ultra-flexible, dark brown Laminaria digitata. Then, going deeper, come fronds from the 2m stems of Laminaria hyperborea, sometimes called cuvie or tangle. This is the dominant kelp of coasts from the Arctic to Iberia, growing in Irish waters down to 30m in 5 per cent of surface light. It feeds, shelters or is colonised by an Amazon-rich diversity of other plants , fish and animals. Its food supply matters even to seabirds.

Off the shore of Sussex, my home county, bottom trawling and dredging have pounded the former kelp forest past regeneration, and a ban on trawling has been introduced the hope of rewilding some 300sq km of seabed.

At Bantry Bay, machine harvesting proposed by the Kerry company BioAtlantis Aquamarine has met with local and environmental resistance. This culminated in a judicial review of the foreshore licence awarded by the Minister of State for Housing.

The Marine Institute’s 2004 review of kelp’s potential was matched by studies for the National Parks and Wildlife Service of its ecological role in the sea. Its report in 2005 ruled out any harvesting in protected bays and called for more research into farming kelp – this, perhaps, in coastal waters already rich in nutrient run-off from farming.

Last year the new KelpRes project was given an unexpected new direction by discovery of an alien seaweed, found growing in 2018 in a cove on the coast of north Mayo.

This was the golden kelp, Laminaria ochroleuca, whose range is normally confined to the south coast of England, France and Spain. Its cluster of plants in Scots Port, near Belmullet, was more than 1,000km from its nearest population in the UK and even farther from France.

Spore release

The samples were identified by Kathryn Schoenrock and genetically confirmed last year as stemming from the southern species. This prompted speculation of a trawler from Spain or Portugal taking shelter from bad weather at Scots Port and, at some point, releasing the kelp’s spores in water from its tanks.

The plants could also simply have drifted north, joining the many alien species arriving now in Ireland. Golden kelp is notably bare of other sea life, so Schoenrock, concerned for its possible impact on native kelp forests, has appealed to citizen scientists among Ireland’s divers to report any more that they see.

She can already count on the trained volunteers of Seasearch, whose own field survey at Belmullet discovered the kelp and who now have joined the KelpRes team.

The founding of Seasearch Ireland in 2009, approved by by the Irish Underwater Council, completed the network of divers and snorkellers across these islands who have become citizen scientists, eager to study and record the underwater world.

Its Irish volunteers have so far collected 50,000 records of more than 1,000 species, all provided to the National Biodiversity Data Centre. This has been the best contribution to our coastal underwater knowledge since the State-funded BioMar survey of 25 years ago.