The Thames is not well, you can also tell from its mussels

Reading is a small town not far from London, on the road leading to Bristol, in the Thames valley. It has recently been the subject of a study that analyzed its own how many mussels there were in the most famous of English rivers. Yes, in fact, as two researchers from the University of Cambridge recount, Isobel Ollard And David C. Aldridge, studying the mussels in the river is one way to take a snapshot of the health of the Thames. And the snapshot that emerges tells of an ecosystem with signs of “substantial degradation”, reads the pages of the Journal of Animal Ecology.

Actually in general freshwater bivalves are not doing well overall. Factors such as pollution, invasive species, habitat modifications and climate change – needless to say – have put these molluscs in crisis, with the result, the authors recall, that today about 45% of species are extinct or endangered. And considering that the bivalves filter the water, feed on algae and provide habitats for the development of other species, inevitably the ecosystems that host them, or once hosted them, change.

To understand how the bivalves of the Thames were doing, Ollard and Aldridge sampled an area of ​​the river near Reading, analyzing the abundance of species and their size, and comparing the results with those gathered from a survey which had concerned the same site in 1964. Over half a century later all the species analyzed have declinedat very low levels in some cases – just 1% – and one was not detected (the so-called depressed river mussel, the Pseudanodonta complanata). All have also shrunk: they grow from 65% to 90% compared to the size they had at the time. In the meantime, new, invasive ones have appeared, perhaps brought by the boats that ply the river, such as the Asian clam or the zebra mussel (Corbicula fluminea And Dreissena polymorpha). “This reduction in native mussel populations is really concerning, and we’re not sure why,” Aldridge said in a university statement. In fact, we are talking about a biomass of just 7.5% compared to that estimated in 1964.

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There are some hypotheses, and he points the finger first of all at the invasive species, as changes in the fish population interact with the larvae. Another hypothesis – less probable however, explain the authors – indicates the variation in nutrient levels as another cause, since by influencing the growth of algae they would consequently also have influenced that of the mussels. The nutrients are of anthropic origin and today they are more contained thanks to regulations: in this sense, therefore, the decrease in the growth of mussels could be interpreted as a return to a more natural state, write the authors.

However, the fact remains that, however significant, the one analyzed is only one site, they conclude, and the bivalves can also vary greatly from area to area. Expanding analysis like this will help to better understand what is happening.