Most large freshwater mussel species (Bivalvia: Unionoida) are temporary obligate parasite on fish. As part of a general long and complicated life cycle, the mussel larvae attach to fish fins or tissue where they metamorphose to juvenile mussels, taking from a few days to about one year. Host fish use varies considerably between generalist mussels using a variety of fish species or host specialist having one or two suitable hosts. During parasitism fish serve as carries for mussel distribution. A lack of suitable host fish therefore does affect mussel distribution and can impair mussel recruitment, affecting population density, potentially leading to extinction. Anthropogenic habitat alteration has been causing a multitude of threats to freshwater mussels such as changes in host fish composition, habitat modification, water pollution, land-use change, exotic species introductions and overharvesting. Today, freshwater mussels are one of the most threatened groups of organisms on earth.
The thick-shelled river mussel (Unio crassus), target species of my doctoral studies, is one of the most threatened freshwater mussel species in Europe. The relationship between U. crassus and its host fish species is particularly interesting as this mussel species is able to parasite different fish species in a community but not all. So far, few studies have been addressing this question. However, it has been shown that the host fish use varies between different drainage areas. Which fish species, U. crassus is able to parasite in Swedish streams is in focus of my research.
Here, I conduct host fish mapping in the mussels’ distribution area. Additionally, I follow the question if the host fish use follows coevolutionary adaptations in the host-parasite system and if certain fish species serve as suitable hosts in general, for example. My research may help to establish suitable conservation strategies for both, U. crassus and its host fish. Knowledge about the organism’s interaction and their ecology is fundamental for adapting stream restoration activities to the organism habitat preferences as well as for re-introduction measures of U. crassus in streams with mussel extinction.
European LIFE project: UnioCrassusforLIFE: www.ucforlife.se
Länsstyrelsen i Skåne, Blekinge, Jönköping, Östergötland, Södermanland
Gustafsson, S., Osterling, M., Skurdal, J., Schneider, L.D., Calles, O. 2013. Macroinvertebrate colonization of a nature-like fishway: The effects of adding habitat heterogeneity. Ecological Engineering. 61, 345-353
Olsson, I., Bergengren, J., Schneider, L., Österling, M. 2013. Den tjockskaliga målarmusslans återkomst. Sötvatten 2013. Om miljötillståndet i Sveriges sjöar och vattendrag. Havs och Vatten myndigheten.