‘I am so happy to see them!’: fan mussels are back in Europe’s waters – but can scientists keep them alive?

After a series of mass mortality events, it is more common to find these huge Mediterranean clams dead. Which is why the species' biggest fangirl of all', Susan Smillie, is thrilled to see a thriving population in Greece

I swim and I stare as my shadow causes panic on the seabed below. Shells snap shut, one, two, three. Alive, alive, alive. I am so happy to see them: noble pen shells, all improbably but indisputably alive. These giant Mediterranean clams are a species on the verge of extinction, with so few left that it is rare to find one living anywhere in Europe.

Often known as fan mussels, the moniker is a suitable one for this beautiful bivalve, its pearlescent point dug into the sand, fanning up to a rounded posterior. I'm in the Amvrakikos Gulf on the west coast of Greece, where I have the privilege of watching these creatures grow. Their presence is such good news that Spanish scientists have flown in to see the clams for themselves as part of an EU project focused on trying to rescue, and hopefully expand, what is left of the pen shell population.