Reproduction and Life Cycle
The life cycle of a mussel is both unique and complex beginning with the release of the male mussel’s sperm into open water. After flowing through the water, the sperm is drawn into the females through their siphons. The eggs are located in their gills and the sperm is brought in through the siphons to fertilize the eggs. Inside the female mussels, the eggs develop into microscopic larvae, also known as glochidia with only 1 out of 1,000,000 glochidia reaching the juvenile stage. In order to complete the reproduction process, the female mussel must infect a host fish with the glochidia. After the glochidia are released from the female, they attach it to the fins, gills, and scales of the host fish (see “fishing page”). On the host fish, the glochidia begin developing a foot, gills, and many internal structures such as the liver, and siphons. Upon being further-developed, the juvenile mussels will drop off their host and start their life. For most mussels, the juvenile stage can last from 2 to 12 years. The last step in the mussel’s life cycle is the sub-adult stage where they will gain the capability to reproduce then restart the cycle. One study claims that the lifespan of a mussel can be as long as 15 years. The spiny mussel habitat has to provide for all transitions the organism goes through, providing all the resources it might need in order to sustain this intricate process. Therefore it is crucial for us to find the right river with perfect conditions for this endangered animal.
When the James River Spinymussel becomes an embryo, it attaches itself to the gills of a fish. This sounds like a simple process, but in reality, there are multiple variables that go into making this stage of the life cycle successful. Although there are plenty of fish species in the watersheds, there are only certain fish species (see Table 1 below) that JRSM embryos can attach to and it is difficult for them to latch onto the gills. Not only are there specific fish that they can latch onto, but the odds of them successfully finding one of these fish at the perfect moment is quite slim. The Spinymussel becomes an embryo externally, meaning they simply sit in the open water waiting for one of the proper fish to swim by. If the fish are not swimming through where the embryo is, or if the water is not moving fast enough to take the embryo to a fish, then the Spinymussel will die before even reaching adulthood. The embryos do not swim, so they cannot go to the fish, the fish have to come to them. If the correct fish species does not make contact with the embryo, then they cannot successfully attach. For an endangered species, successful reproduction is a necessity to replenish the population, and this stage of the life cycle can be very difficult for the mussels to pass.