The freshwater polychaete Manayunkia speciosa is the intermediate host for two myxozoan parasites (Ceratomyxa shasta and Parvicapsula minibicornis) that infect and cause mortality in out-migrating juvenile salmon in the Klamath River. Studies have established that the polychaete populations in the lower Klamath River are patchily distributed but concentrated below Iron Gate Dam, where they are usually associated with organically-rich fine sediments that accumulate within beds of Cladophora and other macrophytes, or in epilithic biofilms (Stocking and Bartholomew 2007, Wilzbach and Cummins 2009). Increased abundance of the worm below Iron Gate Dam, particularly in the stretch of river between the Shasta and Scott Rivers, coincides with the section of river that has been found to be highly infectious for salmonids (e.g. Bartholomew et al. 2007, Hallett and Bartholomew 2006). Polychaete densities have been found to be highly variable among seasons and years, and are likely strongly affected by hydrologic events and sediment transport. M. speciosa is small, reaching a maximum body length of only 4 mm, and it lacks morphological structures for directing its movement within the water column or for anchoring itself to the substrate. Because of its small size and morphological features, the polychaete is likely susceptible to displacement at high flows and mortality from bedload movement or sediment abrasion.
Recognition of the probable importance of flow and sediment dynamics in affecting distribution and abundance of polychaete populations has generated keen interest among scientists and managers in the potential for using flow and sediment manipulations as a strategy for reducing polychaete populations to enhance salmon survival. Reduction in densities of infected polychaetes would result in reduced production of the parasitic actinospores that are infectious to fish, and thus disrupt disease dynamics. One strategy that has been proposed for impacting polychaete populations has been gravel augmentation. Gravel would be introduced upstream of dense patches of polychaetes where increased flows would move the bedload over the patches. Flow and sediment manipulations, however, are likely to be effective only if polychaetes are killed by the manipulations rather than simply re-distributed as viable animals elsewhere within the system. Effects of varying velocities and particle sizes of transported sediments on viability and displacement of the polychaete are unknown.