Lough Derg in ‘invasional meltdown’ from alien species

THE arrival of almost 20 alien species in Lough Derg has increased the risk of further unwanted invaders, which could change the entire ecology of the lake, a local marine biologist has warned.

In fact, Dr Dan Minchin of the Lough Derg Science Group claimed the lake is in a state known scientifically as an “invasional meltdown”, meaning other alien species can more easily establish themselves.
Over the past few years, the threat from invasive animal species, such as the zebra mussel, curly waterweed and nuttall’s waterweed has increased in Lough Derg.
Dr Minchin, who discovered the presence of the Asian clam in the lake, believes more sampling of rivers and lakes is urgently needed to monitor the impact and spread of such species.
The zebra mussel arrived in Lough Derg in the early 1990s and has spread through many of the waterways and to isolated lakes, most probably by attaching to the bottom of boats. While zebra mussels are not impacting as as much as 10 years ago, they are still abundant and have paved the way for further arrivals.
The mussel has cleared the water by filtering out much of the free-living plankton and has enriched the lake bottom with its wastes. This water clearance has enabled aquatic plants to grow in deeper water where light can now reach, which results in extensive growths in shallow bays, upsetting spawning and boating areas.
Zebra mussels now provide a place for a small crustacean, an amphipod, which originates from the Black Sea region, to build its muddy tube in which it hides on the mussel shell surfaces and is now abundant.
Dr Minchin said it is not known how it arrived. Amongst the dead zebra mussel shells strewn on the lake bottom are other crustaceans from Europe and North America. The large native lake mussels have not been seen for 10 years and the native amphipod crustaceans are in decline.
He warned the lake’s only vertebrate, the herring-like pollan not found anywhere outside of Ireland, is now faced with the loss of its normal food, a native shrimp. This is because an aggressive non-native, the bloody-red shrimp, has arrived and may feed on the young of the native shrimp.
“While some of these arrivals might have been forseen there are others on the way and by knowing their spread in Europe we should try to prevent them from arriving.
“Lough Derg may be one of the most impacted lakes in Ireland. Similar impacts are known to have taken place in Europe, for example in Lake Balton, Hungary and in the Great Lakes of North America.
“It should be possible with good management to at least slow down their spread. The Asian clam has arrived and more changes can now be expected. How can Lough Derg and other sections of the Shannon International River Basin achieve good water quality statu? Alien species are long-term arrivals and have not been fully quantified in relation to the Water Framework Directive.
“However a recent method, the biopollution assessment method has been developed, with scientists who have used it in the Baltic Sea area, that now independently quantifies the impact of alien species. This is a useful method managers can use to report the status of a waterbody, such as Lough Derg,” he noted.