Alien species threatening ecology of Lough Derg

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.

Marine biologist, Dr Dan Minchin, claimed the lake is in a state known scientifically as “invasional meltdown” — meaning other alien species’ arrivals can more easily establish themselves.

Over the past few years, the threat from invasive animal species such as the zebra mussel and invasive plants such as curly waterweed and nuttall’s waterweed has increased in Lough Derg.

Mr Minchin, a member of the Lough Derg Science Group, recently discovered the presence of the asian clam at depths of more than 20 metres. He believes more sampling of rivers and lakes is needed to monitor the impact and spread of such species.

The zebra mussel arrived to Lough Derg in the early 1990s and has spread through many of the waterways and to isolated lakes, probably while attached to the bottom of boats.

While the mussels do not presently cause as much impact as about 10 years ago, they are still abundant and, competing with each other, have paved the way for further arrivals to take place.

The mussel has cleared the water by filtering out much of the free-living plankton and has enriched the lake bottom with its waste.

This has enabled aquatic plants to grow in deeper water where light can now reach resulting in extensive growths in shallow bays.

In the shallows, exotic aquatic garden plants are also present and can interfere with boat movement.

Mr Minchin warned the lake’s herring-like pollan is now faced with the possible loss of its normal food, a native shrimp that also lives in deeper water.

This is because an aggressive non-native look-alike, the bloody-red shrimp, has arrived and may feed on the young of the native shrimp.

“While some of these arrivals might have been foreseen, others are 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.”


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