The quagga mussel (Dreissena bugensis) is a species of freshwater mussel, an aquatic bivalve mollusc in the family Dreissenidae. It has a lifespan of 3 to 5 years. It has sometimes been treated as a subspecies of the otherwise fossil species Dreissena rostriformis, as Dreissena rostriformis bugensis, but is currently accepted as a distinct species. The species is indigenous to the Dnipro River drainage of Ukraine, and is named by analogy with the closely related zebra mussel after the quagga, an extinct subspecies of African zebra, possibly because, like the quagga, its 'zebra stripes' fade out towards the ventral side. The quagga mussel is currently of major concern as an invasive species where it has spread in the rivers and lakes of Europe and also in the Great Lakes of North America, where it was brought by overseas shipping that uses the Saint Lawrence Seaway.
Appearance The quagga mussel shell is generally black, yellow and/or zig-zagged. However a large range of shell morphology is seen, including a distinct morph in Lake Erie that is pale or completely white. The shell has a rounded carina and a convex ventral side. The quagga mussel resembles the zebra mussel, just as its namesake (quagga) resembles the zebra. The quagga mussel shell can be distinguished from the zebra mussel shell because it is paler toward the end of the hinge. It is similar in size to the zebra mussel, growing to about 4 cm (1.6 in) wide.
Diet
The quagga mussel is a filter feeder: it uses its cilia to pull water into its shell cavity through an incurrent siphon, where the desirable particulate matter is removed. Each adult mussel is capable of filtering a litre or more of water each day, removing phytoplankton, zooplankton, algae and even their own veligers. Any undesirable particulate matter is bound with mucus, known as pseudofaeces, and ejected out of the incurrent siphon before having a chance to move through the digestive system. Post-digestion, particle-free water is then discharged out of the excurrent siphon.
Reproduction The quagga mussel is a prolific breeder, possibly contributing to its spread and abundance. Like all Dreissena species, it is dioecious (either male or female) with external fertilisation. A fully mature female mussel is capable of producing up to one million eggs per year. After fertilisation, pelagic microscopic larvae, or veligers, develop within a few days and these veligers soon acquire minute bivalve shells. Free-swimming veligers drift with the currents for three to four weeks feeding by their hair-like cilia while trying to locate suitable substrata to settle and secure byssal threads. Mortality in this transitional stage from planktonic veliger to settled juvenile may exceed 99%. In 2019, the genome of a quagga mussel from the Danube River in Austria was sequenced, revealing how larvae use a system of intercellular 'cleavage cavities' and an expanded set of aquaporin transmembrane water channels for osmoregulation in low-salinity freshwater environments during the early stages of their development.
Invasive species
Europe Quagga mussels are presumed to have originated in the Ukrainian section of the Black Sea and probably began to spread further into eastern Europe in the 1940s. Today, they are an invasive species found throughout western Europe. In Romania, quagga mussels were first found in 2004 in the Danube River. In Germany, quagga mussels were first identified in 2005, and now populate many inland waters, such as the Rhine–Main–Danube Canal, the Main, and the Rhine. They were first identified in Switzerland in 2015, and in Lake Constance in 2016, where they have since spread massively and caused considerable problems, in particular to the machinery in waterworks. In 2014, the species was reported at Wraysbury Reservoir, not far from London's Heathrow Airport in the valley of the River Thames. In Ireland, the mussels were first discovered in 2021 in two lakes on the River Shannon: Lough Derg and Lough Ree. The mussel is expected to compete with existing zebra mussels and native species, becoming widespread due to its ecological tolerance and suitability to Irish climatic conditions. By 2025, they had spread into Northern Ireland.
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