It is unfortunate that the invasive alien plant species Lagarosiphon Major (commonly known as African pond weed), has been identified and found growing in upper Lough Corrib. It appears to be well established in some parts of the lake and it is know to colonise waters up to a depth of 20 feet. We have written to all of the relevant regulatory bodies and have requested them to mount a public awareness campaign to help prevent the further spread of the weed. The weed can be spread from one water body to another from particles of weed becoming attached to boats, engines, fishing gear or trailers. It beholds all boat users to ensure this does not happen. A working group being spearheaded by the Central Fisheries Board and involving the other regulatory bodies has been established and they are currently assessing the situation with a view to implementing strategies to control and contain the spread of the weed.
For more info see www.cfb.ie/pr/lmb.htm
Until recently, physical obstacles such as mountains, oceans and deserts limited the spread of plant and animal species. However, with increases in the frequency of global travel certain species are introduced inadvertently or deliberately into new areas. Such species are termed ‘non-native’ or ‘alien’ species. Although some of these species do not cause undue harm in their new habitat, others become problematic and are termed ‘invasive’. Invasive alien species such as the zebra mussel threaten the native species, the environment and the economy.
Zebra Mussels – an unwanted invader
Zebra Mussels are freshwater shellfish that are approximately thumbnail size at the adult stage. They usually have shells with striped colouration of alternate light and dark bands. Although small in size, zebra mussels irreversibly destroy freshwater ecology and cause major problems by blocking water abstraction pipes of water treatment plants and boat engines. The Zebra Mussel was first described by the Russian zoologist Pallas in the 1700’s. It is native to the Aral and Caspian seas in Russia and it has successfully spread to Europe, America and Canada via ballast water in ships and attached to boat hulls.
At the adult stage, zebra mussels can each filter up to 1 litre of freshwater per day. Since 10,000 of these shellfish can cover a surface area of 1 metre-squared, they remove vast quantities of phytoplankton and small zooplankton from the water. Consequently, the entire food web is affected leading to changes in fish populations. Usually there is a shift from pelagic to benthic-feeding fish. It is feared that species that require clean gravel to spawn could be affected by layers of zebra mussels attaching onto hard surfaces (Maguire et al., 2004). In addition, they cause phytoplankton blooms of toxic cyanobacteria since Zebra Mussels ‘spit out’ nasty plankton and prefer to feed on other types of plankton. Cyanobacteria (sometimes termed ‘blue-green’ algae) may pose a serious health risk for humans, since they produce hepatotoxic microcystins that may not be fully removed by water treatment plants and may be introduced to the drinking water supply.
How they spread
Zebra Mussels were first detected in Lough Derg on the Lower Shannon in 1997 although it is believed that they arrived there around 1994 on second-hand boats that were imported from Great Britain. Since then, these nuisance bivalves have colonised much of the Shannon-Erne waterway. Zebra Mussels use byssal threads to attach onto a variety of hard and soft surfaces and are readily transported upstream by boat traffic or overland on boat hulls, on nets and on equipment. They spread naturally downstream with water currents thereby allowing them to colonise lakes and slow-flowing waterways.
Many Irish lakes are at high risk
of becoming infested with zebra mussels. They have been introduced into
lakes in Counties Sligo, Clare, Leitrim, Roscommon and Westmeath. The
Western Region Zebra Mussel Control Initiative aims to prevent the further
spread of zebra mussels into other Irish waterways including the Great
Once the water temperature rises above 12°C, eggs are released by the female adult mussels and the males release sperm (see Zebra Mussel Lifecycle diagram). This usually occurs between May and September although this may vary. Veligers emerge several hours after fertilization. They remain suspended in the water and feed heavily on plankton. Usually in the Summer/Autumn they reach the post-veliger stage when they are too heavy to remain afloat and therefore settle on the bottom using byssal threads to attach to objects. Once they settle they detach their byssal threads and move about. One year later they have reached the adult stage and after a second year they may measure 3.9cm in length.
Clearer Water Does Not Mean Cleaner Water
Mussels increase water clarity through their strong filtering action. As a result, sunlight can penetrate to greater depths resulting in prolific weed growth and boat movement may be impeded. However, clearer water does not mean cleaner water. In the short term, the fish catchability might seem to improve. This is because the fish can see the fly easily but this simply leads to stock depletion. Already, research conducted on Lough Erne demonstrated a shift in the ratio between the numbers of roach and of perch from 2:1 to 1:1. (Maguire et al., 2004). Native freshwater mussels such as the swan and duck mussel (Anodonta Sp.) are seriously threatened since zebra mussels attach onto their outer shells, preventing them from feeding, thereby starving them to death. Lough Derg on the Lower Shannon has experienced a similar reduction in the presence of native mussels.
Recommendations for best practice
In order to prevent the cross-transfer of aquatic invasive species please consider the following advice.
If a boat, diving equipment, machinery or nets have been in zebra mussel infested waterways, please heed the following:
1. Visually inspect all boats, nets
and equipment for the presence of adult zebra mussels and vegetation.
Western Region Zebra Mussel Control Initiative
The Western Region Zebra Mussel
Control Initiative is actively educating boat-owners, anglers and wildfowlers
in particular about the threats posed by the Zebra Mussel to our inland
waterways. The initiative was formed as a result of an action in the
Galway County Heritage Plan 2004 – 2008. Seed funding was granted
from The Heritage Council and from Galway County Council. The Initiative
includes representatives from local authorities in the West and Clare
County Council, Regional Fisheries Boards, State bodies, scientists,
angling and boating organizations and interested individuals.