December 18, 2009
Ask someone to name a threatened species that makes its home in the Klamath River, and odds are the answer you'll hear will be "salmon," followed by "suckerfish" or "sturgeon." While it's true that Klamath populations of these fish species are facing severe threats stemming from human activity, fish aren't the only aquatic creatures in danger of extinction. In fact, the majority of the organisms threatened by human impact on freshwater ecosystems like the Klamath are invertebrates. One of the least-known but most important Klamath invertebrate groups may be the freshwater mussels. And, until 2007, the Klamath's mussels were almost entirely unknown to Western science! Mussels, which are North America's most endangered group of organisms, are an important bio-indicator of aquatic ecosystem health and a cultural resource for indigenous peoples worldwide.
Unlike the Eastern U.S., where the majority of mussel diversity is found, the West is home to only seven freshwater mussel species belonging to three genera. The West's mussels are just as critical to the healthy functioning of freshwater ecosystems as their Eastern counterparts. Yet despite their importance, knowledge of mussel distribution and ecology lags in the West and so, therefore, do efforts to conserve their populations and habitat.
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Freshwater mussels play key roles in the West's riverine ecosystems. Mussels are filter feeders, drawing particles out of the water and depositing them as excreta on the river bottom, thereby making many nutrients available for other invertebrates. As filter feeders, mussels are essentially nature's water purifiers, reducing river turbidity and maintaining water quality. Because they are sedentary, long-lived (up to 100 years) filter feeders, mussels can provide cumulative indication of environmental conditions at a site of interest.
Fascinatingly, mussels depend on fish, including some salmon and trout species, to complete part of their life cycle. They must pass through a larval stage as parasites on host fish, during which they grow and metamorphose into juvenile mussels before dropping off to settle onto the substrate. Without the right host fish, mussels can't pass out of the larval stage to adulthood; therefore, conservation of mussel species is very much dependent on the conservation of the host fish they parasitize.
In the Klamath Basin, freshwater mussels historically comprised an important element of the diet of all the Tribes along the Klamath River. Mussels offered utility beyond a source of easily harvestable protein: their shells could be used as utensils such as spoons, made into jewelry, or sharpened to provide tools. Women traditionally used large mussel shells as utensils for consuming acorn soup, and the shells were also used as thumb protectors for drawing fiber for cordage from iris plants.
So far, the mussel project has concentrated on examining the presence, absence, and distribution of mussel species within the river, as well as some factors related to their habitat preference. Field crews snorkel-surveyed 40 sites between Weitchpec and Irongate Dam in 2007 and 60 sites in 2009. Surveys in 2009 began to incorporate study of the mussel population age structure: studying the relative proportions of old vs young mussels in the population will tell researchers whether or not the mussel populations are successfully reproducing. The project also has a cultural component, including interviews with elders and review of ethnohistorical literature.
Three species have been identified by mussel researchers in the Klamath. The most common and well-distributed by far is Gonidea angulata, the Western Ridged Mussel. Little is known about G. angulata, including which host fish it needs to reproduce. Margartifera falcata, the Western Pearlshell, is also found in the Klamath, although in far fewer numbers. M. falcata thrives best in cold, clear water and can live up to 120 years. It requires salmonid species, such as steelhead, Chinook, and coho, to reproduce. The third species of mussel in the Klamath is an unidentified species in the genus Anodonta, found sporadically only at sites upriver of Seiad Valley and most common just below Irongate Dam. Anodonta are short-lived and have a high tolerance for stagnant water and pollution. Although there is no way of knowing if mussel populations are in decline, since there is no data on populations from before 2007, there is certainly no shortage of mussels in the Klamath. Some mussel beds contain tens of thousands of mussels; the largest found so far contained an estimated 25,000.
The Karuk Tribe's Water Quality Department collected mussels for tissue analysis in 2007. Alarmingly, they found levels of microcystin, a liver toxin produced by the blue-green algae blooms in the reservoirs behind the Klamath dams, more than 100 times in excess of the World Health Organization's established levels for safe human consumption. Freshwater mussels are thus unsafe for human consumption, at least at some times of year; this is a concern both for tribal members who consume mussels and for how the microcystin is affecting the mussels themselves.
The next time you go down to the riverbank, take a look around for mussel shells. The next time you see a salmon, imagine the microscopic mussel larvae hitching a ride to their destination on its gills, and take a minute to think about all those thousands of unsung mussels, doing the important task of filtering the Klamath through their bodies day in and day out. If we persevere, with knowledge, care, and the right conservation strategy, freshwater mussels will ideally continue to thrive in the Klamath watershed for many generations to come.
For more information: www.mkwc.org
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TOC for Forest & River News, Winter 2009