Testate amoebae

Testate amoebae are unicellular organisms that create a shell, or ‘test’. Testate amoebae are commonly found in the sediments of wet environments, and particularly Sphagnum peat bogs. In Sphagnum bogs, testate amoebae, living near the surface, strongly reflect the local humidity conditions. As peat bogs are typically characterised by an assemblage of wetter and drier sections, within a single peatland often 20-40 taxa of amoebae can be found. In contrast to vegetation, however, testate amoebae have the potential to quickly adapt to changes in environmental conditions, owing to their high reproductive rate of weeks to months.

In order to understand the environmental preferences of each taxon, we study testate amoeba ecology by sampling surface vegetation of a number of peat bogs. For a solid image of amoeba ecology, care must be taken to collect vegetation from both wet and dry sections of multiple peat bogs. At the same time, the local water table depth is recorded as a measure for local humidity. In the laboratory, amoebae can be extracted from the vegetation by gently boiling the vegetation and sieving to isolate the finer fraction of the sediments. After identification and counting using a high-powered microscope, a series of statistical analyses are undertaken to build an image of optimal and tolerated water table levels for each taxon found, also called ‘transfer function‘ – the first of its kind in southern South America.

In analysis of peat cores, testate amoebae are counted at regular intervals, with the different assemblages representing changes in humidity conditions through the peat bog’s history. The different taxa identified for each level are expressed as a percentage of the total assemblage. These data can then be entered into the transfer function to obtain a water table depth reconstruction for the counted level, thus reconstructing changing water table depths over time. As ombrotrophic bogs receive all their water and nutrient inputs from precipitation, they are a strongly governed by prevailing climate, and therefore water table depth reconstructions based on testate amoebae data can be interpreted as a proxy for climatic variability. Within the PATAGON project, identification, analysis and interpretation of testate amoebae data is the responsibility of Dr Simon Van Bellen. Microscopic photographs of testate amoebae found during the project can be seen here.