I’ve been learning a lot about mussels this week, in particular about the Zebra mussel (Dreissena polymorpha). This invasive mollusc is native to the Caspian and Black Seas, spread from there to western Europe during the 19th century, and was first noted in Britain around 1824. By the 1970s it had spread extensively, through rivers and other waterways, around the coastline, into lakes and harbours. According to Cardiff University’s Professor Steve Ormerod, Cardiff ‘Bay has somewhere between 10 and 35 million of them covering every hard surface.’

The reason I have been learning about Zebra mussels is because of the Coot in my photographs and my curiosity about what it had found and was eating. I asked the question on Twitter and information came pouring in, in particular thanks to Steve Ormerod, who confirmed the identification and provided a link to a research paper he co-authored about the rapid colonisation of Cardiff Bay by these mussels when the Bay was first formed (see details and link below). Steve was able to tell me that Tufted ducks are the ‘classic predators’ of these mussels, and he was a little surprised to see a Coot also predating them, though did say that the mussels are ‘a lipid, protein and calcium-rich source for waterfowl’.

As for my Coot, it seemed to have worked that out for itself. Having dived for the mussel, it swam over to the water’s edge and proceeded to pull off all the vegetation and, presumably, any smaller mussels attached to the big one and ate all that. It then bashed the bigger one on the rocks like a Song thrush smashes snails on a stone, and down the hatch that went too. Happy Coot, and happy me, after watching and learning about something new!

Alix, Muriel, Richard J. Knight & Steve J. Ormerod, ‘Rapid colonisation of a newly formed lake by zebra mussels and factors affecting juvenile settlement‘, Management of Biological Invasions, 2016, Volume 7, Issue 4, pp. 405-18.