Today we’re going to look back at some slightly warmer days in August, when Dave Horne of the Queen Mary University of London paid the loch a visit. I’ll let him explain further…
I have been working through some samples I collected in Loch Leven in August, picking out specimens of ostracods, which are tiny crustaceans, typically around one millimetre long that live in all manner of aquatic habitats. Why am I doing this? The fossil remains of ostracods (their calcium carbonate shells) can tell us a great deal about past environments and climates. I use them to reconstruct the winter and summer temperatures experienced by early humans in the British Isles, focusing on archaeological sites spanning the past million years or so. To do this I need to calibrate the temperature ranges of living ostracod species by comparing their geographical distribution with a climate model in a GIS (Geographical Information System). One species of particular interest, Cytherissa lacustris, is widespread in the colder parts North America and Europe, and is often considered to be a cold climate indicator when found in fossil assemblages.
Distribution of C. lacustris
Until recently I knew of only two British sites where it can be found living, one in northern England and one in NW Scotland. Then, on a visit to the Discovery Museum in Newcastle upon Tyne to study a large archive of ostracods collected by the 19th-Century naturalist George Brady, I came across a microscope slide containing ostracods collected from Loch Leven in June 1890, among which were several specimens of Cytherissa lacustris (on the slide they are listed, in Brady’s handwriting, as “Cytheridea lacustris” which is how it was known at that time); in some I could see appendages protruding from between their shells, a clear indication that they had been alive at the time of collection.
slide from Discovery Museum in Newcastle
I was keen to find out whether the species still lives in Loch Leven, and after a few email exchanges I found myself on a boat on the loch in the company of three wardens, a shepherd and two sheepdogs, heading for St Serf’s Island on a gorgeous August day.
Much sunnier weather than today!
While sheep were being rounded up I was able to wade around part of the island’s shoreline, netting ostracods among the submerged plants, sand and mud. A quick look at my samples with a hand lens confirmed that I had collected lots of ostracods – indeed there were some “large” (2mm!) green ones visible to the naked eye – but to find out if they included Cytherissa lacustris would require systematic work back in the laboratory at Queen Mary University of London’s School of Geography where I work.
The freshwater ostracods shown here (Cypris pubera & Herpetocypris reptans) were imaged in a microaquarium, but they are representative of what I found in my Loch Leven samples.
Now I can report that the expedition was successful, as I have indeed found Cytherissa lacustris alive in Loch Leven – only one specimen so far, but that is sufficient to put a new dot on my distribution map, and I have plenty more material to sort through. Thank you Therese, Jeremy and Gus for making my fieldwork possible. I hope to make some high-magnification Scanning Electron Microscope images of the specimen later this week.
If you want to find out more about ostracods and Dave’s research then see here. So that’s another species we know we have here at Loch Leven NNR, another species that enjoys our clean, nutrient rich waters. Today the ostracods may not be enjoying our water so much as some of it has actually frozen.
Frozen harbour
Anyway, I’ll post later on in the week with updates on wildlife sightings, what we’ve done throughout the week, and anything else that might be of interest to you!
Loch Leven National Nature Reserve 
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