Influence of environmental features on polychaete host morphology: Implications for salmonid risk of ceratomyxosis

Background/Question/Methods

The freshwater polychaete, Manayunkia speciosa, is the invertebrate host of Ceratomyxa shasta, an important parasite of salmonids. Polychaete population structure and individual morphology may be influenced by environmental conditions, which may have implications for parasite transmission and in turn, disease risk to fish. Large M. speciosa are characterized by larger and more numerous feeding structures than small individuals and presumably filter larger quantities of material. Consequently, larger M. speciosa may offer increased transmission opportunities than smaller individuals as a function of relatively more surface area for parasite spore contact and. However, relationships between environments, environmental features, and M. speciosa morphology have not previously been described.   We measured body and feeding palp lengths of polychaetes collected from different habitats including pools, eddies, and runs, and tested individuals for C. shastainfection.

Results/Conclusions

In general, polychaetes from eddy habitats were larger than those from other habitats; however the magnitude of variation was temporally variable.  In contrast, feeding palp length was correlated with substrate and velocity conditions at the local scale.  Environmental conditions provide the context in which hosts and parasites interact and may ultimately determine the outcomes.  Our results suggest that polychaete host morphology is influenced by both coarse and fine scale river features and we suggest each may influence C. shasta transmission dynamics by a different mechanism.