It’s a famous quote from Jackie Kennedy.
“Pearls are always appropriate.”
Indeed. A piece of jewellery so fine and yet so simple that it can be worn with anything to any occasion. In the world of fashion and value, real pearls really can be priceless. However, the idea that ‘pearls are always appropriate’ is where a certain problem lies. As we know, pearls are not just a gem that can be found merely anywhere. No, because the purest pearls have to be produced by a very special organism. A bivalve mollusc. Ok, so bivalve mollusc sounds anything but glamorous doesn’t it? But it’s the truth. Typically, when someone says pearl, we think oyster. But here in the UK, we hold a different kind of pearl producing bivalve mollusc. A highly endangered bivalve mollusc, whose populations are extremely endangered across the world. In fact, their global stronghold is Scotland and one of the reasons that they are now so endangered is due to that valuable little gem that they can produce. Of what are we talking? The freshwater pearl mussel.
Margaritifera margaritifera. For some reason I am now reading margherita margherita and thinking of pizza. That’s how my mind works apparently. Anyway! The freshwater pearl mussel. A seemingly uninspiring mollusc, a little lacking on the cute factor and therefore a little lacking in general public awareness. Of course, not everyone is unaware of them, but if I said red squirrel and freshwater pearl mussel, I would be willing to wager that most would know the red squirrel, but not the pearl mussel. But delve a little deeper into the history of this mussel and his story is rather fascinating.
Our history lesson of the freshwater pearl mussel begins millennia ago and we find ourselves in the time of the Romans. Indeed, the first documented reference to the mussel in Britain comes from Suetonius, the biographer of Julius Caesar, who claimed that Caesar loved pearls so much, that it played a part in the first Roman invasion of Britain in 55BC! Sounds a little odd, but then again, so did a lot of things the Romans did. Fast forward a little and in 12th century Scotland, pearls were also a big part of the UK’s history, with Alexander I, King of Scots, claiming to have the very best collection of pearls than any other living man. As the pearl mussel was once widely distributed through our lands, no doubt some, if not all of these pearls, came from the freshwater pearl mussel. However, come the 18th century and we begin to see the first claims of declines in the freshwater pearl mussel. Since then, this decline has increased at an alarming rate and not just in the UK, but globally, with most of the remaining populations across the world being small, fragmented and extremely fragile.
But why so threatened? What is it that could make a little bivalve mollusc so vulnerable? And why do we care? Well, as we’ve already mentioned, we humans love a good pearl. They’re pretty, they’re a bit of a status symbol and they can be worth a bit of cash. Pearl fishing has been a long standing and significant threat to the pearl mussel, but the species now has full protection and yet their decline continues. So what else? Well, unfortunately for the pearl mussel, they are not very easily pleased. And why should they be! They require the substrates of river beds to be highly specific, they need a high standard of water quality, little disturbance and, very importantly, they need fish. Hang on a minute, fish?! What, are they partial to a bit of seafood? A few prawns? An octopus maybe? No no, but they do in fact have a parasitic stage in their life-cycle, where pearl mussel glochidia (microscopic larvae) attach themselves to the gills of salmon and brown trout. After a few months of living in the highly oxygenated environment, they then drop off the fish and onto the river bed, where they grow and become adults. Unfortunately, these fish species have also experienced declines and the freshwater pearl mussel finds itself with a reduced number of hosts. Pollution, eutrophication, disturbance from dam building, management to watercourses and natural events such as flooding, have all had a negative impact on this fragile species. Water quality is simply not good enough and there are now very few areas where the species can go undisturbed by humans and river management.
So, why do we care? Well, the pearl mussel has more talents than its ability to produce pearls. It thought that the pearl mussel may also provide vital ecosystem services. Like all mussels, they are filter feeders, so they essentially clean our waters as they go, cycling through gallons of water per hour. They can capture particles and leave behind cleaner and more nutrient rich waters, therefore, providing fresh water for the rest of us. And that’s not just humans, with the pearl mussel also benefitting other aquatic and riverine species from its filter feeding behaviour.
So, ladies and gentlemen, I give you the freshwater pearl mussel. Loved by the most famous Roman general we have ever known, adored by Kings and a species that has been present and part of our country’s biodiversity for many centuries. Unfortunately, his popularity as a pearl producer has been something of his downfall, but it’s not too late just yet! The next chapter in the life history of this bivalve mollusc is still being written, with any luck and a bit of conservation magic that next chapter will not be titled ‘Extinct.’
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