Invasive Species Conquered Native Mussels Population in Thames River Nearly 100%, New Study Unveils

LONDON, ENGLAND- The population of mussels in the Thames has decreased by up to 95% since 1964, as per studies published on Sunday, Nov 27 in the Journal of Animal Ecology.

The University of Cambridge recreated a 1964 study on a section of the Thames near Wokingham to determine how many mussels were in the river in 2020.

According to the most recent study, mussel levels in the Thames may be about 5% of what they were in the 1960s.

Furthermore, mussel sizes have declined; they are presently 65 to 90% of the highest lengths observed in 1964. The research study was headed by doctoral student Isobel Ollard, who told the Natural History Museum that the depressed river mussel used to be relatively common in the Thames, but their survey analysis found not a single one, raising worries for the species' future.

Threats to Native Mussels

Ollard went on to say that mussels generally are a good indicator of the well-being of the river environment. A significant decrease in mussel volume in the river is also expected to have a knock-on impact on other species, lowering the Thames' total biodiversity. As per co-author professor David Aldridge, the current scenario is a huge drop in native mussel populations is concerning, and they don't know what's causing it.

On the other hand, the International Union for Conservation of Nature Red List of Threatened Species, often abbreviated as the IUCN Red List, classifies 40% of any mussels genus as endangered or near endangered.

As stated by the University of Cambridge's zoology faculty study published in the British Ecological Society, hazards to mussels included pollution problems, climate change, excavation, and dams, as well as upstream operations such as sewage pollutant discharge and fertilizer or pesticide runoff. As per Ollard, each mature mussel can filter up to 40 liters of water daily, eliminating enormous amounts of algae and keeping rivers clean.

(Photo: Isobel Ollard)
One of the mussels gathered in the 2020 survey on the river Thames. Mussel populations in the river Thames in the UK have dropped by as much as 99 per cent between 1964 and 2020.

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The Rise of the Foreign Mussels Species

Aldridge characterized the extinction of native species as "extremely concerning." Although this might appear to be a relatively narrow study of a central site in a particular river in the United Kingdom, it delivers a crucial warning signal concerning the world's freshwaters, as New Scientist reported.

The survey discovered many invasive species, such as the non-native zebra mussel and the Asian clam, which were not present in the 1964 research. According to the experts, the species most likely caught a ride on boats and dropped off as they traveled up the Thames.

They believe the zebra mussel, renowned for thriving on native species and suffocating them to death, is to blame for the reduction. Other potential explanations include shifts in land use near the river and variations in the fishery resources on which mussels rely as part of their life cycle.

Duck mussel populations had declined to 1.1% of 1964 levels, while painter's mussel populations had decreased to 3.2% of 1964 levels.

The experts believe the mussels' slower growth rates reflect the river's return to its natural form following tighter sewage treatment control since the 1960s. They looked at nutrients recorded by the environment agency and discovered that nitrate and phosphate levels had decreased.