How can something so small upset the balance of the ecology of Georgian Bay?

By Donna Tucker

The Quagga Mussel was introduced to the Great Lakes via ballast water released from commercial shipping vessels before spreading into the St. Lawrence River and most Northeastern U.S. waterways in the late 1980s. It is now found throughout Ontario’s southern Great Lakes and Lake Simcoe.

The Quagga Mussel is native to the Caspian and Black Sea regions. It lives in freshwater or low-saline environments. It is observed on rocky and sandy bottoms or covered with aquatic vegetation. It is found in deeper waters than the Zebra Mussel (as deep as 100 metres), where temperatures are cooler and the waters are still or calm. Three years after Quagga Mussels were discovered in Lake Michigan, Zebra Mussels still comprised more than 98 per cent of the lake’s invasive mussel population. By 2005, that relationship had flipped, with Quaggas making up 97.7 per cent of the invasive mussel population.

The Quagga Mussel is a freshwater bivalve that resembles the Zebra Mussel. The Quagga Mussel is larger, rounder and wider. And broader than the Zebra Mussel. Both invasive species live in the same habitat as native freshwater mussels. Native mussels can be easily differentiated from invasive mussels because they are three to four times the size of the invaders. Native mussel shells are more oval, usually greenish or dark brown, with visible growth rings. Quagga Mussels harm native mussels, many of which are species at risk. They outcompete these species for food and will attach themselves to native mussels, suffocating them.

Both Zebra and Quagga Mussels attach to hard surfaces. They can easily attach themselves to boat hulls, trailers, motors, equipment, vegetation and other organisms. This allows them to be carried by boats and equipment between water bodies. Mussels are very small when they first attach to surfaces, making them very difficult to detect, as they are only a few millimetres in size. They reproduce quickly and are extremely difficult to eradicate once established in an area.  Females can release up to one million eggs each season. In larger water bodies and complex ecosystems, they may be impossible to eradicate unless they are detected and dealt with early on. They have an astounding ability to resist chemical and other methods of removal.  

Zebra and Quagga Mussels can survive for several weeks outside the water if left in a cool and moist environment. This means that mussels attached to boats or equipment can survive a trip between different bodies of water. Their microscopic free-swimming larvae can also survive for several weeks in small pools of water inside vessels or other equipment. These invasive mussels spread accidentally and are unintentionally carried on recreational boats or trailers. It is important to decontaminate vessels and equipment moving between bodies of water.

They can clog pipes, water intake systems (hydro facilities, agriculture irrigation systems), municipal water supplies and boat engines. Removal of mussels is both time-consuming and costly. These mussels are also a problem for recreation and tourism, as mussel shells can injure swimmers near the shore or docks, damage boat propellers and potentially dirty our drinking water. 

Quagga Mussels Covering a Boat Propellor

Like Zebra Mussels, Quagga Mussels have significant negative impacts on freshwater habitats by out-competing native species for food and forcing a necessary diet change for those trying to exist in the system.  They can alter food chains by removing the native species’ food sources, such as plankton. By completely covering rocks, Quagga Mussels can affect fish spawning areas, impacting fish eggs’ survival. The spread of Quagga Mussels is currently affecting whitefish stocks in the Great Lakes.

Have you noticed the increasing clarity of the water in Georgian Bay?  Quagga Mussels clear water of nutrients. Not only does this alter the food chain, it allows sunlight to penetrate deeper into the water, increasing the growth of some aquatic vegetation and exposing fish to damaging UV rays. Fish can get sunburned, too! Quagga Mussels are selective feeders, so they often choose not to feed on toxic algae, sometimes causing or worsening toxic algal blooms.

What can I do to stop the spread?

To learn more about Quagga Mussels, their effect on the Great Lakes and potential solutions, mark your calendar to see the documentary All Too Clear at the Stockey Centre on August 10.