8/13/01

Contacts:
John Downing, Animal Ecology, (515) 294-2734
Kelly Arbuckle, Iowa Department of Transportation, (515) 233-7863
Ross Harrison, Iowa Department of Natural Resources, (515) 294-5973
Susan Thompson, Communications Service, (515) 294-0705

IOWA STATE RESEARCH SHOWS DECLINE IN IOWA MUSSEL POPULATIONS

AMES, Iowa -- A century ago large freshwater mussels, sometimes called clams, were so abundant in Iowa's waterways that the state was a world center for mussel diversity, and the home of a lucrative shell industry. But an Iowa State University study shows a dramatic decline both in Iowa's freshwater mussel population, and in the number of mussel species found in the state's interior rivers and streams.

The study looked at 118 stream sites where mussel counts were done in 1984-85 and repeated 15 years later. In the first count, there was an average of a little more than five species found at each site with a maximum of 22 at one site. The average fell to just less than two species with a maximum of 12 in 1998. Sites with no living mussels increased from 6 percent in the first count to 47 percent in 1998. A few sites showed slight increases.

"We knew mussel populations were declining worldwide, but the rates of decline we've seen in Iowa are alarming," says Kelly Arbuckle, the former graduate research assistant in the Iowa State animal ecology department who traveled around Iowa to do the mussel counts.

"Other scientists have projected 123 of the 297 known species of mussels will be extinct within the next century," says John Downing, the Iowa State animal ecology professor who directed the research. "These local declines are how these extinctions occur."

Downing says mussels are important because they help keep freshwater bodies clean and clear. "They feed on particles that are suspended in the water. Under some conditions, a single mussel can filter all the particles out of several quarts of water each hour," he says. As a result, mussels also are indicators of stream health. 

The researchers found the number of mussel species declined least dramatically at sites where wooded stream banks shaded the streams. And mussel biodiversity was lower in rivers with higher levels of agricultural nutrients such as nitrogen and phosphorus.

Downing says the survey indicates land-disturbing activities near streams adversely impacts mussel habitat and therefore, mussel communities. But a number of other factors also may be involved in the decline, such as mussel harvesting, the availability of host fish (mussel larvae attach to host fish during development), stream flow rates and sedimentation.  

The research was funded by the Iowa Department of Natural Resources (DNR). Marion Conover, chief of the DNR's fisheries bureau, agrees many factors are involved. "Mussels are relatively long-lived and have a complex life cycle, so the factors causing the rapid decline experienced in the 15 years studied may have been set in motion many years ago," he says.

Conover says the agency would like to establish reference sites to monitor mussel populations on a regular basis. "We will be moving forward to list additional species on our threatened and endangered list, plus proposing rules that prohibit taking mussels for catfish bait or general interest," he says. "With additional funding, we would like to look at ways to recover species through reintroduction."

The Iowa State researchers, Arbuckle and Downing, say the study provides valuable tools for use in future mussel conservation and restoration work.

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