Response of <i>Sphagnum</i> Testate Amoebae to Drainage, Subsequent Re-wetting and Associated Changes in the Moss Carpet: Results from a Three Year Mesocosm Experiment

<i>Sphagnum</i> peatlands represent a globally significant pool and sink of carbon but these functions are threatened by ongoing climate change. Testate amoebae are useful bioindicators of hydrological changes, but little experimental work has been done on the impact of water table changes on communities.<br> Using a mesocosm experimental setting that was previously used to assess the impact of drought disturbance on communities and ecosystem processes with three contrasted water table positions: wet (–4 cm), intermediate (–15 cm) and dry (–25 cm), we studied the capacity of testate amoeba communities to recover when the water table was kept at –10 cm for all plots. The overall experiment lasted three years. We assessed the taxonomic and functional trait responses of testate amoeba communities. The selected traits were hypothesised to be correlated to moisture content (response traits: shell size, aperture position) or trophic role (effect traits: mixotrophy, aperture size controlling prey range).<br> During the disturbance phase, the mixotrophic species <i>Hyalosphenia papilio</i> dominated the wet and intermediate plots, while the community shifted to a dominance of “dry indicators” (<i>Corythion dubium</i>, <i>Nebela tincta</i>, <i>Cryptodifflugia oviformis</i>) and corresponding traits (loss of mixotrophy, and dominance of smaller taxa with ventral or ventral-central aperture) in dry plots. During the recovery phase we observed two contrasted trends in the previously wet and intermediate plots: communities remained similar where the <i>Sphagnum</i> carpet remained intact but species and traits indicators of drier conditions increased in plots where it had degraded. In the former dry plots, indicators and traits of wet conditions increased by the end of the experiment.<br> This is one of the first experiment simulating a disturbance and subsequent recovery in ex-situ mesocosms of <i>Sphagnum</i> peatland focusing on the response of testate amoebae community structure as well as functional traits to water table manipulation. The results generally confirmed that testate amoebae respond within a few months to hydrological changes and thus represent useful bioindicators for assessing current and past hydrological changes in <i>Sphagnum</i> peatlands.