Because of their filter feeding habit, it has been estimated that these mussels can bioaccumlate organic pollutants in their tissues by as much as 300,000 times when compared to concentrations in the water in which they are living. These mussels have been associated with avian botulism outbreaks in the Great Lakes which have caused the mortality of tens of thousands of birds. In the Great Lakes this had lead to the collapse of amphipod populations that fish rely on for food and the health of fish populations has been severely affected. The encrusting of lake and river bottoms can displace native aquatic arthropods that need soft sediments for burrowing. This problem has been particularly acute in some areas of the USA that have a very rich diversity of native freshwater mussel species. Zebra and quagga mussels can kill native freshwater mussels in two ways: (1) attachment to the shells of native species can kill them, and (2) these invasive species can outcompete native mussels and other filter feeding invertebrates for food. Ecological problems also result from mussel invasions. Mussels adhering to boat hulls can increase drag, affect boat steering, and clog engines, all of which can lead to overheating and engine malfunctions. The shells of both mussel species are sharp and can cut people, which forces the wearing of shoes when walking along infested beaches or over rocks. Recreational activities on lakes and rivers are adversely affected as mussels accumulate on docks, buoys, boat hulls, anchors, and beaches can become heavily encrusted. These organisms clog water intake structures (e.g., pipes and screens), which greatly increases maintenance costs for water treatment and power plants. The Problem: Quagga and zebra mussel invasions have had catastrophic impacts in the ecosystems in which they have established. Quagga mussels have been found at depths of up to 540 feet in Lake Michigan where they filter feed year round.Consequently, quagga mussels may end up being the more problematic of these two mussel species in California. Zebra mussels were found at densities of around 899 per square meter, but quagga mussels now dominate at 7,790 mussels per square meter. For example, in Lake Michigan, zebra mussels made up 98.3% of mussels in 2000, by 2005 quagga mussels represented 97.7% of collected mussels. Where quagga and zebra mussels co-exist, quagga mussels appear to outcompete zebra mussels, and quagga mussels can colonize to depths greater than those achieved by zebra mussels and are more tolerant of colder water temperatures. These mussels can survive for 3-5 days out of water without suffering lethal desiccation. This occurs when boats are not cleaned and dried adequately and contaminated watercraft are then moved from infested waterways to pristine water bodies where mussels are accidentally introduced. Short distance spread between fresh waterways within countries most likely occurs via the movement of recreational boats. Ballast water discharge from transoceanic ships is thought to be responsible for the long distance spread of zebra and quagga mussels from their original home ranges in eastern Europe. Quagga mussels were first found in the USA in the Great Lakes in 1989, Nevada in 2007, and California in 2008. Zebra mussels have a long history of invasion and have successfully established in Great Britain (1824), The Netherlands (1827), The Czech Republic (1893), Sweden (1920), Italy (1973), the Great Lakes in the USA (1988), and California (2008).
0 Comments
Leave a Reply. |