Quagga Mussel

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.

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.

Quagga mussels are prodigious water filterers, removing substantial amounts of phytoplankton and suspended particulates from the water. By removing the phytoplankton, quagga mussels, in turn, decrease the food source for zooplankton, therefore altering the food web. Impacts associated with the filtration of water include increases in water transparency, decreases in mean chlorophyll concentrations, and accumulation of pseudofaeces. Water clarity increases light penetration, causing a proliferation of aquatic plants that can change species dominance and alter the entire ecosystems. The pseudofaeces that are produced from filtering the water accumulate and impact the environment. As the waste particles decompose, oxygen is used up, water acidity increases (decreased pH), and toxic byproducts are produced.

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%.