Testate amoebae, peat bogs and past climates

Microscopic animals can tell us much about climate change over the last 10,000 years. Testate amoebae (Protozoa: Rhizopoda) are unicellular shelled animals which live in abundance on the surface of most peat bogs. These protozoa have tests made of smooth secreted material, pre-formed plates or cemented particles which are gathered from the surrounding environment. Such particles can include small pieces of silica, pollen grains, fungal hyphae and other organic detritus¹.

Testate amoebae are sensitive indicators of hydrological conditions in peatlands, primarily the depth of the water table². Therefore, if the peat bog has a hydrological regime controlled by precipitation, the fossil testate amoebae preserved in a core sample of peat can be used to decipher past climatic conditions. A statistical approach has been used to reconstruct past climates from fossil assemblages in Canada³, Britain⁴ and Switzerland⁵. However, problems can arise relating to species identification, the lack of modern ecological information for some species and poor fossil preservation.

The following photos are of common contemporary and fossil peatland taxa. The examples are from short cores taken from a number of raised-type peat bogs in the north of Ireland. Samples were prepared for analysis by sieving through a coarse mesh (300μm) and back-sieving through fine mesh (15μm), retaining the residue between the two¹. The sample was centrifuged, the supernatant poured off and the residue stored in glycerol. Identification to species level was achieved using a standard dichotomous key¹. The photos were taken using a Nikon Coolpix 4500 digital camera attached to a Nikon Eclipse E600 binocular microscope.

Wet indicator species
	Amphitrema flavum A wet indicator species with a smooth proteinaceous test which is often amber, brown or yellow in colour. It has a circular aperture at both poles. (Length 45-77 μm)
	Amphitrema wrightianum A species that mostly lives in bog pools and wet hollows. It forms a smooth proteinaceous test which is often yellow in colour. It has distinct collared apertures at both poles. (Length 50-90 μm)
	Arcella discoides type This species mostly lives in very wet conditions, including standing water. It is transparent, circular in shape and is composed of smooth proteinaceous material. It has a circular aperture bordered by a shallow lip. (Length 78-105 μm)
Species living in intermediate/variable conditions
		Euglypha tuberculata type A species indicative of intermediate conditions. It is ovoid in view and is composed of numerous colourless siliceous plates. Its aperture is bordered by finely toothed plates. (Length 45-100 μm)
		Heleopera petricola Lives in variable conditions, is ovoid in shape and is composed of plates and particles. This species has a terminal, slightly convex aperture. Often colourless, brown or violet in colour. (Length 56-150 μm)
		Nebela collaris Mostly found in intermediate to dry conditions, this ovoid shaped species is composed of siliceous plates. The species has a terminal ovoid aperture with a characteristic thin organic collar. (Length 107-184 μm)
Dry indicator species
		Assulina muscorum This species is abundant in dry conditions. It has an ovoid test which is often russet coloured and a terminal oval aperture. (Length 35-60 μm)
		Nebela flabellulum A distinct species which is ovoid in shape and composed of an assortment of siliceous plates. The species is usually colourless and has a terminal aperture surrounded by a thin organic collar. It is generally regarded to be a dry indicator. (Length 76-160 μm)
		Trigonopyxis arcula type This species is a dry indicator which is dark brown in colour and circular in shape. It has a central aperture that can be variable in shape. The species is composed of cemented mineral particles. (Length 123-134 μm)

References

1 Charman, D.J., Hendon, D. and Woodland, W., 2000. The Identification of testate amoebae (Protozoa: Rhizopoda) in peats. Quaternary Research Association Technical Guide No. 9. Quaternary Research Association, London, 147 pp.

Available to buy from http://www.qra.org.uk/technical_guides.htm

2 Woodland, W.A., Charman, D.J. and Sims, P.C., 1998. Quantitative estimates of water tables and soil moisture in Holocene peatlands from testate amoebae. The Holocene, 8: 261-273.

3 Warner, B.G. and Charman, D.J., 1994. Holocene changes on a peatland in northwestern Ontario interpreted from testate amoebae (Protozoa) analysis. Boreas, 23: 270-279.

4 Hendon, D., Charman, D.J. and Kent, M., 2001. Palaeohydrological records derived from testate amoebae analysis from peatlands in northern England: within-site variability, between-site comparability and palaeoclimate implications. The Holocene, 11(2): 127-148.

5 Mitchell, E.A.D., van der Knapp, W.O., van Leeuwen, J.F.N., Buttler, A.J., Warner, B.G., Gobat, J.M., 2001. The palaeoecological history of the Praz-Rodet bog (Swiss Jura) based on pollen, plant macrofossils and testate amoebae (Protozoan). The Holocene, 11: 65-80.