The Aquatic Nuisance Species (ANS) Task Force has called them “devastating”, this was in reference to a tiny shell fish that may be smaller than a quarter or a penny but has caused billions of dollars in damages around the United States. Although the name ‘zebra mussels’ might sound exotic and adorable because zebras remind us of Africa and mussels remind us of seafood, the actual creatures are anything but adorable. Zebra and quagga mussels are small shell fish with stripes reminiscent of zebra patterns – although not all of the shells will have stripes on them.They are native to Eastern Europe in the Black and Caspian seas; however, they are now found being a nuisance all over the United States. These little shell fish are considered an invasive species, mostly due to their ability to reproduce quickly and their lack of natural predators. Mature females typically produce 30,000 to 40,000 per year, and up to 1 million eggs as they get older; the males release anywhere up to 200 million sperm into the water. “Zebra mussels will clog up everything,” said Marion Clarke, a professor at University of Florida’s Institute of Food and Agricultural Sciences referring to how these tiny shell fish can get into drainage and drinking water pipes, as well as water intakes for hydro-electric power plant, and leave lots of shells when they die. And when they are not clogging up things, they cause various problems from making beaches uncomfortable and unsafe, damaging boat motors and, invading lawns and golf courses. The more serious issues are their ability to contaminate drinking water reservoirs with toxins, their disruption of ecosystems and their threat to drive other species to near-extinction levels.
But how did they get here?
Zebra mussels are fresh-water bivalves, ocean water is actually toxic to them. Yet they inch-long shell-dwellers left their native have invaded thousands of square miles in the United Kingdom, the Czech Republic, the Netherlands, the United States; oh, and in Italy and Sweden. In North America, they are found in hundreds of water bodies across thirty north-eastern and central states. It is believed that the first zebra and quagga mussels to arrive in Continental America around 1986 as stowaways in the fresh water ballasts of vessels that traveled between Europe and the United States. When these vessels released the fresh water into navigable rivers, the mussels found their way into the Great Lakes and there, they wrecked havoc on the local ecosystem. Zebra and quagga mussels are filter feeders, which means they feed on suspended organisms and organic matter suspended in water like plankton. As such, the mussels tend to make bodies of water clearer, which may initially sound like a great idea, and ideal for owners of aquariums, but actually isn’t. Clear water means plants which are rooted to lake floors, particularly weeds, get more light than they would normally have if there was particulate suspended in the water. This can lead to overgrown weeds in water bodies, which can then become difficult to navigate. While they eat all other forms of algae, they ironically stay away from the blue-green algae – the toxic kind which contaminates water and kills both wild and domestic animals. When these mussels wipe out all other forms of algae and leave the blue-green variant without natural competitors, this may lead to the dreaded algae blooms and the foul smells that comes with them. As for the aquarium owners, indeed tank water will remain clearer; however, when that water is eventually recycled, it is likely to end up in public water works with larvae of the mussels still in it. Additionally, their rapid reproduction techniques result in other native fish which feed on algae cannot compete. Because these critters cling on to everything they can, submerged wood, plastics, trees, metals and even other fish and native mussels, and can survive several days outside of water, they are able to travel hundreds of miles clinging on to the undercarriages of recreational boats and other vessels that have on invaded lakes. This is how they have been spread from the great lakes to other places inland.
No place seems out of bounds
As discussed, Zebra mussels are small enough to find their way into pipes, particularly ones from the Great Lakes which feed into the processing plants for drinking water. But these critters may also find their way further up the network and into drinking water pipes. This was the case with water sourced from Lake Michigan. Residents complained that their tap water had an unusual smell and an unpleasant taste. This was effectively due to zebra mussels and their excretions; specifically: “… infestation of water treatment plants results in potable water tainted by mussel feces, pseudofeces and decaying bodies”. The substance may not be toxic enough to humans however, the thought of these mussels is enough to put one off tap water for a while. In addition to water pipes, they also can clog up irrigation systems and, according to Maj-Britt Angarano, iron and steel substrates, like water pipes, which have mussel attachment have their corrosion exacerbated and this leads to increasing costs of repair, maintenance and replacement. The mussels also seem to thrive in irrigation systems, as some golf courses have found out. The Irrigation water tends to supply the mussels with nutrients and oxygen while the pipes themselves offer protection from potential predators and harshly cold weather. Additionally, ponds in and around golf courses often have rich nutrients and allow the mussels to thrive. The mussels also found their way onto recreational areas where they litter the beaches and foul the air, discouraging tourism. Lake Pelican, for example, a popular tourist and recreational spot, became unpleasant when the zebra mussel population exploded seemingly out of nowhere. “I’m not talking just little cuts but razor-blade cuts, like drops of blood up the dock,” said an owner of a cabin close by referring to the sharp shells of these shellfish.
How to be rid of zebra and quagga mussels
Because of the high economic costs and their undesirable impact on ecosystems, research has been poured into methods of controlling zebra and quagga mussels through depopulation and prevention. For starters, those with recreational water vessels should always ensure that no stowaways are clinging on to their vehicles prior to driving off with them. If one travels to a lake with zebra or quagga mussels, diligence is required because once this invasive species it transported to a new location with viable conditions, the problem won’t stop. Those responsible for managing water pipes and irrigation systems could install filtration systems or meshed barriers, although these are only effective for adult mussels. There are several chemical methods which can be utilized to kill mussels. Chlorine is a known to kill adult mussels and prevent veliger (larvae) from developing. It is appropriate in certain areas however, it may impact other species. Ozonation, potassium permanganate and bromination (the addition of bromine) of water is more costlier and can be less effective for large water networks but can be good enough for smaller scale operations when there are concerns of harming other animals. Molluscicides (like pesticide for molluscs) which are effective are available on the market, and they can be just as effective as another method which utilizes a nitrogen-based acid to which prevent veligers from developing.
When pipes are already clogged up by these critters, there are methods to effectively clear them. Dewatering & Desiccation refers to the use of warm air from compressors. It is blown into winterized (de-watered) pipes and that tends to kill mussels, which then detach. In certain cases of severe infestation, after chemical methods are used, flushing the pipes is required. Sometimes mechanical removal is the only option if the pipes are too clogged. Finally, if it is the case that pipes are corroded to the point that they require replacement, the use of materials coated with chemicals that prevent the attachment of zebra and quagga mussels should be considered. This effectively prevents these pipes from getting clogged up in build-up of these rapidly multiplying nuisances.