'Unbelievable infestation' in the Shannon is spreading rapidly

OFFALY'S Heritage Officer Amanda Pedlow told a recent Council meeting that an invasive species in the Shannon has become “a massive problem.”

The Heritage Officer told the councillors during the February meeting of Birr Municipal District that the Quagga Mussel was first noted in the Shannon during the early summer of 2021 and since then its spread has been rapid.

“These mussels are smaller than Zebra Mussels and they are advancing up the riverbed of the Shannon at an alarming rate,” she pointed out.

The silty riverbed of the Shannon is an ideal habitat for the species.

“The mussels probably invaded the system via boats,” Amanda said, “and now they are so widespread it doesn't seem possible to beat them back.” She said in an ideal world boatowners would clean the hulls of their boats more regularly to prevent this sort of infestation.

“This infestation is unbelievable in the rapidity of its spread,” she remarked. “It's looking likely it will affect the whole Shannon catchment region. It takes over everything. It takes over the whole habitat. Everything that was living on the river bed is wiped out. It's adversely affecting the Shannon and is a serious issue."

Back in the early summer of 2021 scientists reported the first finding of the Quagga mussel in the Shannon’s two great lakes the Ree and Derg, and that it was abundant in Lough Ree over a wide range of depths.

They are also present in the Shannon river between these lakes." The scientists said the Quagga has the potential to be “a high impact invasive species in Ireland." It was placed in the Top 10 2017 Horizon Scan list of species most likely to arrive, establish and have impact between 2017 and 2027.

Quagga mussel is listed on the Third Schedule Part 2 of the European Communities (Birds and Natural Habitats) Regulations 2011 in Ireland.

Quagga mussel is a filter feeder removing planktonic organisms from the water. It has a high filtration rate likely to result in further changes to the water quality and nutrient dynamics of lakes in particular.

The Quagga is competing with native mussel species and with the alien invasive zebra mussel.

The presence of the quagga mussel is likely to lead to a further surge in fouling, including of man-made structures in the water, of boats and water craft.

It may have additional impacts on water quality. It is having an impact on the ecological integrity of the Shannon's aquatic ecosystems. In invaded areas, it is significantly reducing native plant, invertebrate and fish populations.

Quagga has a wide ecological tolerance and is suited to Irish climatic conditions, therefore its alarming expansion is not surprising.

It appears to have a preference for cooler water and can settle on finer sediments than the zebra mussel explaining its greater abundance at depth in colonized lakes. It can produce up to 1 million eggs per year.