Background/Question/Methods Testate amoebae are a group of moisture-sensitive, shell-producing protozoa that have been used widely in paleoecology and environmental monitoring.   In these applications, testate amoebae assemblages have been used as indicators for mean water-table depth.  However, it is likely that seasonal moisture variability also influences community composition. The objectives of this study were to assess the influence of seasonal moisture variability on the composition of testate amoeba communities.  Testate amoebae and surface-moisture conditions, including hourly measurements of relative humidity within the upper few centimeters of Sphagnum, were examined throughout the growing season at 78 microsites within eleven peatlands of Pennsylvania and Wisconsin.  Non-metric multidimensional scaling (NMS) was used to describe patterns of community composition, and these patterns were compared to environmental variables to assess controls on testate amoebae assemblages. 
Results/Conclusions Results indicated that testate amoeba communities are sensitive to the average-moisure conditions experienced during the growing season as well as the magnitude of seasonal-moisture variability. Particular species (e.g., Hyalosphenia subflava, Arcella discoides) were more frequent and abundant in highly variable environments.  Other species with apparently wide ecological niches with respect to average water-table depth (e.g., Assulina muscorum), only occurred abundantly at the edges of their environmental distribution when seasonal conditions were highly variable.  Differences in life-history traits, such as rates of encystment and reproduction, likely explain the observed community responses to seasonal moisture variability. Results suggest that seasonal-moisture variability should be considered when using testate amoeba community composition as an indicator of paleoenvironmental or environmental conditions.