…a guest blog written by ecologist and field technician, Fay Jolly
Hidden in the clear, lime-rich water of Malham Tarn lives one of Britain’s rarest residents – the Malham Sedge (Agrypnetes crassicornis), a caddisfly so picky it is found nowhere else in the UK. This fussy little insect builds intricate underwater cases from tiny pieces of vegetation, but its entire British population clings to existence in just this single lake. It’s a precarious situation. One catastrophic event – pollution, disease or climate change – and this species could vanish from Britain forever.
Malham Tarn isn’t just any lake. It’s what scientists call a “marl lake” – a rare type of freshwater habitat with exceptionally clear water and sediments rich in calcium carbonate. Marl lakes are ecological jewels, supporting unique communities of plants and animals specially adapted to their alkaline, mineral-rich waters.
However, marl lakes are incredibly vulnerable. When fertilisers and other nutrients wash in from surrounding farmland, they trigger algal blooms that cloud the water and disrupt the delicate chemistry that makes these habitats special. What was once gin-clear can become murky and overloaded.
That’s where researcher Fay Jolly from the University of Stirling comes in. Fay investigated whether Loch Baile a’ Ghobhainn on the Isle of Lismore in western Scotland, might offer a potential second home for our endangered caddisfly. But how could you tell if the loch was suitable without decades of observation?
The solution was ingenious – read the history of the loch written in its sediment layers. Like tree rings or pages in a diary, each layer of mud at the bottom of the loch tells a story about past conditions – what plants grew nearby, which insects lived there, and how clean the water was.
The findings revealed that Loch Baile a’ Ghobhainn has changed over the past century, showing similar patterns to Malham Tarn. While the loch has experienced some nutrient enrichment over time, it still retains many characteristics that could support the Malham Sedge.
The research suggests that with some careful restoration work to improve water quality and boost marl formation, Loch Baile a’ Ghobhainn could become a vital second refuge for Britain’s rarest caddisfly. Establishing a new population would dramatically reduce the species’ extinction risk.
Caddisflies play vital roles in freshwater, being crucial for breaking down dead vegetation. They’re also a crucial food source for fish, birds, and other wildlife. When we lose species like the Malham Sedge, we lose threads in nature’s intricate web – threads whose importance we often only discover once they’re gone.
And there’s a bonus: marl lakes themselves are climate allies. Their chalky sediments lock away carbon for centuries, making them important natural carbon stores. Protecting and restoring these rare habitats helps wildlife and climate action at the same time.
Thanks to Fay’s detective work, this rare caddisfly may soon have the safety net it desperately needs. Proof that creative science can offer hope even for our most endangered species.
About the Author:
Fay Jolly, an ecologist and field technician originally from Manchester but moved to Stirling for her Degree, uses paleoecology among other techniques to aid species recovery projects. Her research exploring A.crassicornis was awarded the research based learning prize at the University of Stirling for an innovative and novel piece of research that has gone on to inform the restoration of Marl lakes and the recovery of A.crassicornis.