The quagga mussel (Dreissena rostriformis, also known as Dreissena bugensis or Dreissena rostriformis bugensis) is a species (or subspecies) of freshwater mussel, an aquatic bivalve mollusk in the family Dreissenidae. It has an average lifespan of 3 to 5 years.
The species is indigenous to the Dnipro River drainage of Ukraine, and is named after the quagga, an extinct subspecies of African zebra, possibly because, like the quagga, its stripes fade out towards the ventral side.
The invasive quagga mussel is currently of major concern as it spreads in the rivers and lakes of Europe and also in the Great Lakes of North America where it was brought by overseas shippers that use the Saint Lawrence Seaway.
Appearance
The quagga mussel shell is generally black, yellow, and/or zig-zagged. However, a large range of shell morphologies 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 also slightly larger than the zebra mussel, about wide, roughly about the size of an adult human's thumbnail.
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 one liter or more of water each day, where they remove phytoplankton, zooplankton, algae, and even their own veligers. Any undesirable particulate matter is bound with mucus, known as pseudofeces, and ejected out the incurrent siphon. The particle-free water is then discharged out the excurrent siphon.
Reproduction
The quagga mussel is a prolific breeder, possibly contributing to its spread and abundance. Dreissena spp. are dioecious (either male or female) with external fertilization. A fully mature female mussel is capable of producing up to one million eggs per year. After fertilization, 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 3 to 4 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.
North America
Zebra mussels, the first dreissenid mussel introduced in North America, rapidly spread throughout many major river systems and the Great Lakes, causing substantial ecological and environmental impacts. The quagga mussel was first observed in North America in September 1989, when it was discovered in Lake Erie near Port Colborne, Ontario. It was not identified as a distinct species until 1991. By 2021 the biomass of quaggas in the lower 4 Great Lakes was estimated to be so great as to become the primary regulator of phosphorus, remetabolizing and recirculating it instead of allowing it to sedimentize as normal.