Written by Kelsey Crowley under the direction and review of David Kringen and Alison Coulter, Assistant Professor, SDSU Department of Natural Resource Management.
To reproduce, freshwater mussels rely on fish to carry their young into new areas and disperse them when they are old enough. Reproducing adult mussels will create hundreds of larval mussels which will be sent out into the water column. As mussels cannot walk and only shift small distances, they must devise a way to ensure their young survive. These infant mussels have no control of where they are going, as they rely only on the flow of water to carry them. As they are being carried, they inevitably will be carried into a fish (also known as a host fish) and most times, attach to the gills and fins. The reason for the attachment is that it allows for the infant mussels to receive oxygen, nutrients as a result of the fish's diet, and safety from predators. Additionally, the fish will travel further away from the adult mussels, which allows mussels to spread out and inhabit new areas. After about two weeks to two months, depending on the mussel species, these infant mussels grow into juveniles and are ready to drop off. They detach from the fish and implant into sediment. There, they remain until they grow into adults to continue the reproductive life cycle.
As one can imagine, there are complications to this process that make conserving mussels difficult. Each mussel species has a preference for certain host fish. Some mussels are generalists, meaning they can use a variety of host fish (some up to 20!) while others are specialists, meaning they are very selective and use few host fish (1-3). Generalist mussels are much easier to conserve since they can reproduce with many different hosts. Meanwhile, specialists can be difficult to manage since they rely on so few host fish. If the fish habitat changes and the limited host fish species that specialist mussels rely on disappear, they will then have no available host fish to carry their young.
To complicate matters, host fish ranges can change drastically depending on environmental and human factors. One particular issue is the implementation of dams and reservoirs, which separate host fish from reaching mussels downstream. This reduces both species richness and abundance of host fish available for mussel reproduction. Fish can also change their habitat ranges based on increasing temperatures, catastrophic weather, and pollution. By conserving suitable fish habitat, it also allows us to indirectly conserve mussels by providing necessary resources for mussels to reproduce.
