Testate amoebae are tiny, single-celled organisms that live in a range of wetlands and soils, including in the bogs that we study. The amoeba themselves grow, or make, a shell called a ‘test’, hence the name. Apart from when we are studying samples from the surface of bogs, in which we can find living amoeba, it is these shells that we find in our cores as they can be preserved for many thousands of years. A typical testate amoeba is about 1/20th of a millimetre long and has one aperture, or hole, in its shell out of which it projects itself to move around and feed. There have been thousands of species of testate amoebae recorded globally, but we only find about 50 – 75 different species in a typical bog study. Even within this small number, the diversity of shapes, sizes and colours is quite astonishing, especially when viewed at 400 times magnification.
Each different species of amoeba has a distinctive shell that we can tell apart by looking at features such as the shape and size of the shell and what it is made of. In exactly the same way as plants, different testate amoebae prefer to live in different habitats on the bog surface; wetter or drier spots. So by taking samples back through our cores and counting the proportions of different amoeba in our samples, we can see how the population has changed over time. Because we know that the wetness of the type of bogs we study is controlled by climate, the changes in testate amoebae populations over time can tell us something about how climate has changed, especially when used together with other methods such as plant macrofossils and stable isotopes.