Let's Get Musscular!
How Do Freshwater Mussels Reproduce?
All mollusks reproduce differently, even mussels! Saltwater mussels and freshwater mussels have two incredibly different ways of reproducing, with freshwater mussels even spending a stage of their lives as pesky parasites. So what does freshwater mussel reproduction look like, and how does the environment contribute?
1. Beginning
The reproduction cycle of freshwater mussels begins with the female, who lays eggs and cares for them in her gills. The chambers in the females gills that these eggs reside in are called marsupium, and the eggs stay here until fertilized.
2. Fertilization
Male freshwater mussels release their sperm into the waters of female mussel populated areas so they can be drawn into the females through their siphons. Once the sperm reach the marsupium, they fertilize the eggs. These eggs are now able to become larvae.
3. Larval Stage
Freshwater mussel larvae are called glochidia, and are microscopic. These larvae are unable to stay with the mother, but also unable to move and develop on their own. This is where the host fish come into play.
4. Parasitic Stage
Different freshwater mussel species have different ways of distributing the glochidia to host fish, with some releasing them into open water and others using specialized lure adaptations of tissue ranging from appearing as a simple worm to a detailed crayfish. Once a fish is lured to a female mussel, she contracts her gills, freeing the larvae from her body, and dispersing them amongst the new host fish. The glochidia take shelter in the gills and on the fins of their host fish, settling in for further development. Although labeled as a parasitic relationship, the host fish actually remains unaffected by its hitchikers.
5. Juvenile Stage
The designated host fish's body must encyst the freshwater mussel larvae in order for them to grow into their juvenile stage. Once encysted, the glochidia go through metamorphosis and transform into microscopic juvenile mussels. These juveniles are then able to drop off the host fish and bury in the sediment.
5. Adult-hood
Once buried in the sediment, it takes 2-9 years for the mussels to fully mature into adulthood and become ready to start the cycle all over again.
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Why Is Reproduction So Important?
Freshwater mussels have specific environmental factors that aid them in effective reproduction, with one of these factors being their host fish. Along with being a part of the larvae fostering process, these host fish also aid in richer genetic diversity amongst mussels, as they distribute individuals frrom one population to another during their journeys through the stream. This genetic diversity helpsto keep these species healthy and strong. Without the proper river flows and access to mainstream bodies of water, the host fish are unable to reach areas of mussels. Although different mussels require the use of different host fish species, the niche of host fish in regards to freshwater mussels is ever so important nonetheless. No host fish = no mussels.
What would happen if freshwater mussels disappeared you may ask?
What Do Dams Have To Do With Freshwater Mussel Reproduction Anyways?
With knowing that dams hold back water and split waterways from their original patterns, it can be easily understood that this affects the travelling patterns of many different aquatic species. Amongst these species are fish, including our freshwater friends' buddies, their host fish. The blockage of normal fish migration patterns prevents them from getting to mussel populated waters, leaving no means of reproduction for these species. The removal of these dams could prove hugely beneficial to this dilemma, given that such would open up streams and rivers again, giving the mussels easy host fish access once again. However, there are plenty of other factors that must be taken into account, besides the host fish impacts, before dam removal can be implemented.