Testate amoeba functional traits and indicator taxa are important tools for tracking peatland restoration effectiveness.

Restoring degraded peatlands is vital for sustaining their capacity as carbon sinks and long-term carbon stores. Microbial assemblages serve as valuable indicators for monitoring environmental change and assessing the success of ecosystem restoration efforts. Testate amoebae are a group of unicellular shelled protists that are commonly used for Holocene palaeohydrological reconstruction in peatlands. While progress is being made, the use of testate amoebae for biomonitoring in peatland restoration is still in its early stages. The aim of this study is to assess testate amoebae response to restoration measures (drain blocking) across three lowland raised bogs in Northern Ireland. To accomplish this, Sphagnum samples were collected from each site using a before-after control-impact (BACI) experimental design. After peatland drainage ditches were blocked, subtle yet significant responses in testate amoebae were observed: (1) key unambiguous wet-indicator taxa became more abundant in samples adjacent to blocked dams; (2) a widespread increase in the abundance of taxa with sub-spherical tests was observed, most notably in samples near to blocked drains. The findings of this study demonstrate the reliable response of testate amoebae to wetter conditions across all sites after restoration. Functional trait analysis paired with an indicator-taxa based approach, demonstrate the value of testate amoebae as contemporary bioindicators for tracking peatland restoration success, even when detailed hydrological monitoring data is not available. However, testate amoebae should be used with some degree of caution for peatland biomonitoring until long-term assemblage-level response to restoration is better understood.