Zebra mussels on fish11/18/2023 ![]() ![]() The Shannon system would be an obvious example.Ĭlearer water means many changes at a basic ecological level. No doubt many of you out there will have seen your local waters turn much clearer in recent years thanks to zebra mussel invasions. Mistakenly, many people assume clear water is clean water, but, as outlined above, selective feeding often means that the only significant biomass of algal species left are the potentially harmful blue-green’s. One Irish study ( Lucy, 2005 ) calculated that as of 1999, the total zebra mussel population of Lough Key in Roscommon (2000 acres in size) was capable of filtering the entire contents of the lake in just 10 days! Cleverly, zebra mussels are also able to selectively feed on algae, ejecting the potentially toxic blue-green algae (cyanobacteria) which can cause harmful algal blooms in our stillwaters.īut clearer water is cleaner water, right?įiltering this amount of algae from the water is the reason why water with zebra mussels turns clear after a relatively short period of time. One single adult mussel is easily capable of filtering up to 1 litre of water per day, which is quite astounding for such a small organism and the very reason why they are such an ecological problem. This is exactly what it sounds like, where mussels filter water through specially designed gills and remove all the desired microscopic plants (algae) and animals (zooplankton) to get their nutrients. Not only are they capable of rapid spread in new waterbodies, zebra mussels are highly efficient at what they do – filter feeding. This ability to survive is yet another reason why they are so invasive If kept moist, this can be several weeks. Did you know? Zebra mussels can survive out of water for well over a week by sealing their shell shut. Given the sharp edges to the shell (as many anglers will testify), zebra mussels can also cause health issues with recreational swimmers and bathers. As such, zebra mussels often cause problems with water intake pipes and canal locks, and are of serious concern to the much larger native swan and duck mussels, which can become smothered and killed by this invasive species. Silty lake and riverbeds do not suit the species, although zebra mussels can attach to old, dead mussel shells in the lack of other surfaces. Zebra mussels need structure, like rocks, stones, reeds, weed stems, submerged branches, anything really that gives them a secure hold. ![]() Like most mussels, they attach to substrates via short, strong byssal threads (known in culinary terms as “beards”). They can very quickly carpet the bottom of lakes and rivers, in incredible densities (called “druses”) of up to 50,000 individuals per square meter – sometimes more! Zebra mussels will attach to any hard substrate and can completely cover the river or lake bed Larvae drift around in the water column for anything up to a few weeks before settling on a suitable substrate. ![]() Zebra mussels are no different although they live for just 2-3 years on average, they can reproduce after 12 months and quickly multiply by releasing anything up to 1,000,000 larvae per year. They are more adaptable than “normal” species and often reproduce at very high rates. Rapid spread is one of the inherent characteristics of invasive species. Very few, if any, of these would have been checked on biosecurity grounds back then. Irish colonisation is thought to have occurred as a direct result of the lifting of VAT (value added tax) on second-hand crafts imported from the UK for personal use from 1993 onwards, and the subsequent rise in the number of boats. It spread rapidly throughout North America and colonised almost all of Europe too. The huge increase in global shipping trade throughout the 19 th and 20 th centuries allowed many species such as the zebra mussel to literally hitch a ride on board ships, in this case contained in ballast water, which even in many cases today is still filled and emptied at the start and end of a journey. The species originates in the Caspian and Black Sea areas and for millennia was confined to such areas until humans intervened, that is. This small, unassuming and quite attractive freshwater mollusc (with its zebra-like, striped shell) was first recorded in Irish waters in the early 1990s and in the UK far, far earlier, in the early 1800s. Take zebra mussels ( Dreissena polymorpha) as a prime example. I’d wager that whilst most of you reading this will have heard about various introduced species that are bad or damaging, few will understand exactly why. However, one of the biggest shortcomings of science, and scientists in general, is the lack of ability in communicating scientific terminology to the general public, anglers included. One of the most frequently heard phrases in recent years in relation to freshwater in “invasive species”.
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