See 6-minute video of mussels with fascinating action shots and commentary on their status. Linked with permission from the Missouri Department of Conservation.

For further information about Iowa's Mussels take a look at the sidebars
Sidebar: "Musseling" In!	Sidebar: Restoring Iowa's mussels	Sidebar: Keep zebras out of Iowa!

Mussels may seem like simple creatures, but their lives and their interactions with other species are surprisingly complex. Healthy native mussel populations are an indicator of healthy waterways—and the indications aren’t all good.

Mussels’ roles in nature

Approximately 300 species of freshwater mussels exist in North America, and nearly 50 of these reside within Iowa and its border rivers. Most mussels live in rivers, but a few species are abundant in lakes and ponds as well. Despite this surprising diversity, mussels are one of our most imperiled groups of organisms. Nearly two-thirds of mussel species are of conservation concern. In fact, it appears that 36 species of North American mussels may already be extinct.

Freshwater mussels serve many roles in our aquatic ecosystems. Mussels feed by filtering the water, removing algae, protozoa and bacteria—as well as silt. A single mussel the size of a tennis ball can filter over 30 gallons of water a day. Where mussels are abundant, this natural filtration can significantly improve water clarity.

Mussels are also an important food source for other animals. For example, several native fishes eat mussels, including freshwater drum, blue catfish and river redhorse. Mammals like muskrats and raccoons also consume mussels. Some waterfowl ingest thin-shelled species or just their shells as a source of calcium.

Despite appearances, mussels aren’t just living rocks. Pearly mussels have a unique lifecycle involving parasitic larvae that must attach to the gills or fins of a fish. To trick fish into carrying these larvae, some mussel species have developed surprisingly sophisticated lures. Fish striking these lures inhale larvae that attach to their gills. (See opposite page.)

Mussels as a resource

Mussel shells consist mainly of “mother of pearl,” which was the primary raw material for making buttons in the early 1900s. Button manufacturers of that day were lured by Iowa’s abundant pearly mussel population—when areas of some river bottoms were literally covered with shells.

Within a couple of decades, mussel populations had plummeted from overharvest. The U.S. Bureau of Fisheries constructed a research station in 1914 along the Mississippi River at Fairport, where biologists developed methods to artificially propagate mussels. Unfortunately, their efforts coincided with rapid decline of water quality as growing river cities released ever more untreated sewage and industrial waste. Mussel populations continued to drop.

Though plastic buttons eventually replaced shells, a second market wascreated for mussel shells in the 1950s by Japan’s cultured pearl industry. Mussel shells were cut into small cubes, polished into beads and inserted into marine oysters—forming the “seed” for cultured pearls. This market collapsed in the 1990s when the Chinese learned to grow beadless pearls in farm-raised freshwater mussels.

An uncertain future

Mussels face continued threats. Land use has altered the flow in Iowa’s streams, making rivers much less stable. Dams, dredging and channelization cause further damage. Meanwhile, non-native species threaten Iowa’s mussels in a variety of ways: Asian clams by competing for food, black carp potentially using them as food, and zebra mussels by latching onto their shells and inhibiting vital functions, (See box at right.).

In hopes of restoring Iowa’s native mussels and preventing further extinctions, Iowa State University, the University of Iowa, the Iowa DNR and other academic and conservation agencies are working on a variety of conservation projects—including genetic analysis, surveys, stocking artificially propagated juveniles into several of our rivers and public education campaigns—to keep invasive species out of Iowa waters. (See sidebar at right.)

As with the protection of any species, protecting mussels has value beyond the creatures themselves. Strong mussel populations are yet one more important component of a strong, healthy environment.

Iowa's Mussels: Sidebars

"Musseling" in!

Possibly the most amazing feature of mussels is their relationship with fish. Pearly mussels produce parasitic larvae called glochidia, which attach to the gills or fins of a fish. Within days or weeks, the glochidia develop into juvenile mussels (about the size of a pinhead), drop to the bottom of a river or lake, and then grow to adult size. Although glochidia are technically parasites, they do not cause disease and are really more like hitchhikers.

To attract a ride for their larvae, most mussels use lures. In some species the lure is part of the female’s body that resembles a minnow, complete with fins and eye-spots. Fish striking the lure inhale glochidia, which attach to their gills. Other mussels release glochidia in packages that appear like aquatic insects or worms, which break to release glochidia when they are bitten. Anglers may be impressed that a blind shellfish uses such sophisticated fishing tackle!

Restoring Iowa's mussels

A cooperative effort between the Iowa DNR, the US Fish & Wildlife Service, Army Corps of Engineers and others is aimed at recovering the federally endangered Higgins eye pearly mussel. Once ranging across most of the upper Midwest, this species is now in danger of extinction. Over the past several years, the team has placed Higgins eye larvae on the gills of smallmouth bass and walleye, which were then released into the Cedar, Iowa and Wapsipinicon rivers. Results are still being measured.

Keep zebras out of Iowa!

The zebra mussel is a damaging, invasive species that was accidentally imported from Europe into the Great Lakes in the 1980s. It has since spread to many American lakes and rivers, including the Mississippi River. It threatens native mussels, clogs pipes and can dramatically alter an aquatic ecosystem. While native mussels require a host fish to complete their lifecycle, zebra mussels have free-swimming larvae that can attach to almost anything—making transmission from one water body to another all too easy.

Two adult zebra mussels were recently found in Clear Lake. The Iowa DNR plans to use divers to thoroughly search the lake for evidence of a reproducing population. There is currently no known method to selectively eliminate zebra mussels from a water body, so prevention and public education are critical. The Iowa DNR has posted signs at some public boat ramps with tips on how to avoid introducing zebra mussels to new water bodies.

To view a gallery of photos and to recieve more information about mussels click here.

Ecology College

Iowa’s Mussels: How strong are they?

Iowa's Mussels: Sidebars