A study into freshwater pearl mussels


[MUSIC] My name is Louise Lavictoire, I am a PhD student. Andy Ramsey is my Supervisor and I’m working with the freshwater pearl mussel to better understand captive breeding of the species. So that we could re-introduce them into the wild and hopefully save them from extinction. These mussels are one of only a handful of freshwater mussels that we have in the UK. They’re critically endangered because of things that humans have done so declining with their habitat because of practices like forestry and intensification of land use, farming and that kind of thing. And, as well as trying to sort of improve general water quality for other species. Improving it for the pearl mussel will be of benefit to humans as well because they provide an environmental service and that they filter our water. So the adult mussels can filter up to 50 liters a day and help remove things like algae and small particles and things like that. So if we can get the conditions right for them, it will help other species as well sort of helping us to keep our waters clean. They’re sort of fairly important for river clarity and that kind of thing. I’m working with the scanning electron microscope here at Derby University to try and see if there are any differences in biology of juvenile mussels at different ages. So working with mussels which are really a few weeks old and working up to about three, three and a half years old. To see what happens when they switch between modes of feeding so they start out as pedal feeders where they use their foot ancillary action to pump water into their shells. And when they’re roughly about 18 months old, they go through a transformation where they switch from pedal feeding to filter feeding. So they then start to use their gills as the primary pump of water into the valves. And so I’m looking at the differences that the gills undergo between the pedal feeding and the filter feeding stage. To try and understand if it’s a source of mortality for juvenile mussels, and just to try and understand what happens to the gills during that period. The gills are, I guess the best way to describe it, is they’re kind of triangular and semi-hollow. So the female mussels brood the glochidia within the gills and then as the temperature starts to rise, the females because they use their gills to breathe as well as to brood and to feed. They start to sort of go into stress because they can’t breathe with all of these glochidia inside of them. So they release them as a stress response and it just so happens to coincide with the perfect time that the fish are around to assist the glochidia. So it’s all very synchronous and timed well. Even the really young mussels have cilia that on their gills, which I wasn’t expecting. I guess they can act like a rudimentary filter cuz the cilia kind of help sort particles that they feed on. So they feed on algae and bacteria, so that’s one thing. So even the youngest mussels have fairly complex cilia. The older mussels have quite organized gills and definitely by three years old they’ve got sort of a fully functional sorting mechanism. [MUSIC] The Freshwater Biological Association who I work for as well as doing this part time PhD. We’ve got a captive breeding program for the species with a view to releasing them when they get to a stage where they’re a bit more robust and able to handle life in the wild. Trying to get them to about ten years old, that they are able to sort of handle less than ideal conditions. So we’ve got some eight year olds and then we’re planning to try and reintroduce them in 2017/18 time. And we’re still breeding from six different populations, trying to breed new juveniles every year. So they are really fascinating species in terms of reproductions. Not only do they use their gills for feeding but they also use them for breathing like we would use or lungs for breathing but they also use them for brooding. The life cycle is pretty complex that you’ve got male and female mussels. The male mussels release sperm into the water, which the females then inhale and then they use the sperm to fertilize their eggs. And then they brood the eggs for about six weeks or so, and then they release the larvae into the water column. So every female mussel, it’s estimated, can release anything from 4 to 60 million larvae in one grow, in one season. The larvae go into the water column which then it has to find a salmon or a trout to complete its life cycle. So, as the salmon and trout are swimming around, the larvae which are called glochidia have snap on to their gills. So as the fish takes in water to pass over its gills to breathe, the glochidia recognizes that it’s in a fish and starts to snap, and it snaps onto the gills of the fish. As sort of a defense mechanism, the fish creates this cyst around the glochidia, and then the glochidia stay on the fish for about nine months, ten months, depending on temperature. And then once the temperature starts to rise again, in following spring, the juvenile mussels drop off of the fish into the gravel and then start to grow as juveniles here. So the captive breeding program needs adult mussels, fish and then we collect the juvenile mussels as well. So it’s really convoluted and complex, the work couldn’t be done without the SCM scanning electron microscope. So it’s a great resource and it feeds really well into the project that I’m doing which looks at both the behavior side of things as the juvenile mussels as well as the biology. So it mixes the two quite nicely. [MUSIC]

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