The effects of aperiodic desiccation on the diversity of benthic desmid assemblages in a lowland peat bog

The lowland minerotrophic “Swamp” peat bog, located in the Czech Republic, is one of the most important European sites of desmidiacean diversity. The hydrological regime of the bog is driven by the water level of a nearby ancient manmade pond. Therefore, the bog experiences severe aperiodic drying events related to the pond draining. In this study, we investigated the drought-related response of the benthic desmid assemblages of the bog. The samples were taken bimonthly from 12th May 2008 to 19th May 2010, including the 8-month drying out period between October 2008 and June 2009. In addition to the species frequency data, morphometric methods were used to analyse the disparity, morphological turnover and surface-to-volume (S:V) ratios of Desmidiales. The drying event influenced the species composition, biovolume and S:V ratio data of the more species-rich pool, but its influence was less conspicuous in the species-poor acidic site. Accordingly, the species-rich site had generally higher species or morphological turnover between successive samples. The indicators based on the morphometric data were generally more sensitive than the species data. Therefore, we propose that the biovolume, S:V ratios or disparity measures of desmidiacean assemblages might be of benefit for future studies of peat bog microphytobenthos. Desmid assemblages at both sites recovered rapidly following the re-wetting of the bog, and they attained the pre-disturbance diversity, species composition and disparity values. We conclude that the drying event of the bog did not irreversibly influence its valuable desmid assemblages.