Pacific invader sets down roots in Strangford Lough


A fast-growing seaweed from the Pacific has taken root in the northern end of Strangford Lough and looks set to crowd out habitats and native species. Efforts so far to displace the invader, sargassum muticum or japweed, have met with failure, but the fight goes on, Ms Caroline Nolan, officer for the Strangford Lough Management Committee, said.

"It is a truly remarkable plant," she declared. It is a perennial, can reset itself from broken scraps of plants and can grow at up to five metres a season. "You can almost see it growing."

The lough is an important European marine habitat and is on the UK's list for designation as a Special Area of Conservation. The management committee, an advisory body appointed by the British government to advise on the lough's overall management, is not best pleased about the japweed's arrival because of its potential to block mariculture and disturb recreational use of the lough.

It was thought to have arrived here in 1995 on the back of a Pacific oyster, Ms Nolan explained. It rapidly established itself in the northern lough and then spread southeastward along the shoreline, carried on the tides.

It made an earlier arrival in France and then the south of England and it could now easily spread from Strangford around the Irish coastline. "It could and is likely to. It tends to travel mainly on the basis of tides and wind conditions," Ms Nolan said.

"Most attempts at eradicating japweed have failed," she said. The plant produces prodigious numbers of "germlings" which set near the parent, and tearing up plants only leaves behind plant scraps and germlings that in turn can drift along and reset themselves nearby.

It also has the disconcerting ability to "hop from place to place along the seabed". It fixes to shells and stones when small but then develops tiny air bladders which make it buoyant. It can then float away, dragging its stone anchor behind to colonise another new location.

It populates the seabed from low tide locations and has been found as deep as 25 metres. While it can obstruct boats and is a mooring nuisance, on the positive side sargassum can provide a good habitat for a range of species from sea anemones to small fish.

The hope is that populations of this new invader will stabilise after an initial population explosion. Even so the committee is now asking people living around the lough to help monitor its spread by reporting sightings of japweed to the Strangford Lough Management Committee office in Portaferry (012477 28886). People are advised not to try to remove the weed themselves because of the risk of spreading germlings.