Healthy Rivers Need Strong Mussels

Aquatic creatures act like mini water filters

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Rosario Castanon, left, and Maude Tremblay.

Mention mussels in Ontario, and many people might think either of their dinner plate or of the invasive zebra mussel whose nasty habits – clogging water pipes, encrusting boat hulls, elbowing out native molluscs – have generated numerous headlines around the Great Lakes. But a U of G project aims to help rescue and restore threatened kinds of freshwater mussels that help to sustain other aquatic creatures and to clean rivers and streams in southern Ontario.

Out of 55 species of freshwater mussels in Canada, 41 species live in Ontario waterways, says integrative biology professor Joe Ackerman. Those include most of the 18 kinds listed as endangered, threatened or of “special concern” by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC).

An aquatic biologist, Ackerman hopes to learn enough about these imperiled bivalves – including what they eat, which species live together and what they need to complete a complicated life cycle – to help them regain their footing.

His university lab is the only one in Canada identifying fish hosts and raising juveniles of these often-overlooked invertebrates.

Burrowed away in the bottom of rivers and streams, mussels lack the profile and attention paid to endangered types of birds, mammals or fish in Ontario. But Ackerman says it’s important to learn about these anonymous creatures and protect them from extinction to avoid ripple effects on larger ecosystems and food chains.

Besides making up part of the natural biodiversity of the province’s aquatic ecosystems, these suspension and deposit feeders help to filter and clean water. Because they are sensitive to pollution – including silt and farm runoff as well as toxins from road salt to copper – they’re an important marker species for ecologists looking to gauge the health of rivers.

Says Maude Tremblay, a master’s student working with Ackerman: “They essentially clean the water. They’re important environmental indicators. If the water is very polluted, there will likely not be many mussels.”

Along with Rosario Castanon, a research technician and two-time Guelph grad, they are culturing various species in the Hagen Aqualab on campus. In a room whose floor-to-ceiling shelving units contain rows of plastic buckets and aquariums, the researchers raise juvenile mussels after infesting the fish that the molluscs rely on to help spawn new generations.

Among those fish are round gobies, an invader in Ontario waters that Tremblay is now studying as a possible host to help threatened mussels complete their life cycle.

Her co-adviser is Todd Morris, a research scientist at the federal Department of Fisheries and Oceans in Burlington, Ont., and chair of the Ontario Freshwater Mussel Recovery Team. Formed in 2003, that group includes U of G.

“The University has been a partner with us from the start,” says Morris. “The University of Guelph is a singular research facility for these species because of the Aqualab and the ability to rear and house them.”

The Guelph researchers are studying unionids, a large freshwater family whose members are also called river mussels or naiads. They’re found worldwide, says Ackerman, including here in southern Ontario where ample limestone provides lots of calcium needed to make shells.

Among native species here are the spike mussel, the mucket, the snuffbox mussel and the wavy-rayed lampmussel, says Tremblay, leafing through a copy of The Photo Field Guide to the Freshwater Mussels of Ontario.

Many of these indigenous types are on the COSEWIC roster as well as being listed under the federal Species at Risk Act. There are bright spots, says Morris. For instance, last year the status of the wavy-rayed lampmussel improved from endangered to special concern.

In the 19th and early 20th centuries, mussels were collected to use their shells for making buttons. That practice occurred in the Grand River, for instance, and ended only when button makers turned to plastic.

More recent threats include habitat degradation, declines in fish stocks needed for mussel reproduction and competition from invasive zebra mussels.

“Their presence is a positive indicator about the health of the ecosystem. That has positive implications for sport fishing,” says Morris, adding that mussels provide food for other animals, help to anchor the river bottom and act as a habitat for other organisms.

These benthic dwellers tuck themselves into the bottom mud, exposing their rear ends and pumping water to filter out food.

Mussels rely on fish to help spread their young. Adults release their larvae, called glochidia, to develop on the gills of fish. Juvenile mussels then detach themselves to find a new home on the bottom.

Some mussel larvae hitchhike on several kinds of fish. Others are specialists, relying on a particular fish species to complete the life cycle – another problem for molluscs whose host fish species might also be threatened, endangered or locally extinct.

Mussels have developed sometimes weird and wonderful ways to lure fish, says Ackerman.

The snuffbox mussel, an endangered species, relies on the log perch. The fish roots for food on the bottom by nudging aside rocks and pebbles with its snout. The bivalve closes its shell on the snout, not harming the fish but using “teeth” on the shell rim to keep its grip while pumping its larvae into the host’s mouth and gills.

A rainbow mussel has crayfish-like tentacles that attract bass. A phony “eyespot” on the fat mucket’s body attracts predators mistaking it for a prey fish. The orange nacre mucket resembles a dead fish lying on the bottom. “This is incredible, the kinds of mimicry used for luring fish,” says the Guelph biologist.

Learning more about the relations between mussels and fish is a large part of his project. They’re screening fish species as potential hosts for different molluscs. They’re also studying conditions needed by mussels, including anything from sediment types to water sources to food.

In Ackerman’s Science Complex lab, Castanon grows different kinds of algae to see which ones the mussels prefer to eat. Over in the Aqualab, they’re comparing growth rates of lab-raised juveniles with those of mussels in the wild. For the latter, they visit spots on the Grand River in Kitchener, Ont., to pluck out mussels and to angle for fish.

Ultimately, Ackerman hopes to give agencies information needed to support action plans for restoring mussel species and habitats. “Our ultimate goal is to develop tools to culture mussels so government agencies can return them to the wild.”

Morris says it’s also important to look at land uses to improve water quality. For instance, encouraging farmers to plant buffer zones of trees and shrubs along streams, for instance, can help to remove wastes from field runoff before they reach the water.

Ackerman’s research has involved many students and has been supported by organizations including the Canadian Wildlife Federation and the World Wildlife Fund.