Effects of rewetting measures in Dutch raised bog remnants on assemblages of aquatic Rotifera and microcrustaceans

Published source details Van Duinen G.A., Zhuge Y., Verberk W.C.E.P., Brock A.M.T., van Kleef H.H., , R. S.E.W., van der Velde G. & Esselink H. (2006) Effects of rewetting measures in Dutch raised bog remnants on assemblages of aquatic Rotifera and microcrustaceans. Hydrobiologia, 565, 186-200.
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Summary

A previous comparative study on aquatic macroinvertebrates between water bodies created by rewetting measures and water bodies which had not been subject to restoration showed that species assemblages differ considerably between these rewetted and non-rewetted sites, with the larger species diversity and more characteristic and rare species in the non-rewetted sites. As Rotifera and microcrustaceans generally have a high dispersal capacity and a low dependence on habitat heterogeneity for the completion of their life cycle, compared to macroinvertebrates, the occurrence of these microinvertebrate species, including characteristic raised bog species, was expected to be similar between rewetted and non-rewetted sites in bog remnants.

Study sites: Aquatic microinvertebrate species assemblages of Rotifera and microcrustaceans (Copepoda and Cladocera) were sampled in 20 sites, situated in 7 Dutch raised bog remnants throughout the eastern Netherlands; 10 sampling sites were created by rewetting and 10 were remnants of former peat cuttings, or trenches used in buckwheat culture (50 + years old) not subject to bog restoration measures. In both groups, water bodies sampled differed in age, size, water and substrate quality and vegetation structure.

Sampling: All sites were sampled in the period of 1 April to 6 May 2002. At each sampling site two sets of subsamples were taken. Each set consisted of pooled subsamples collected at different spots in the water body. One set of subsamples was taken by means of two plankton nets with 45 and 115 micrometer mesh size, respectively, and was fixed immediately by adding formaldehyde. The other set of subsamples was taken using only a plankton net with 45 micrometer mesh size, was not fixed and was examined under the microscope to identify illoricate Rotifera.

Environmental variables: Surface water and sedimented organic matter were sampled and analysed for concentrations of various ions and elements. Electric conductivity and dimensions of the water bodies (length, width and depth) were assessed at the sites and pH, alkalinity and turbidity of surface water samples were measured in the lab within 24 h after sample collection.

Classification of microinvertebrates: Species were considered to be characteristic for raised bogs when they are listed as typical of bogs or acidophilous species (preferring acid water bodies) in literature.

A total of 129 species (Rotifera 108, Cladocera 15, Copepoda 6 species) were found. The species assemblages, total numbers of species and numbers of characteristic raised bog species did not differ between the 10 rewetted and 10 non-rewetted sites. The dominant pattern in the variation in microinvertebrate assemblages could be explained by the presence or absence of open water and variation in physico-chemical variables of surface water and organic matter. Furthermore, the species assemblages of water bodies situated in the same area were on average more similar to each other than to assemblages from other areas. These differences between areas may be due to differences in environmental conditions of water bodies, and possibly also to differences in the local species pool and the subsequent immigration sequence of species.

Conclusions: In contrast to what was found for aquatic macroinvertebrates in a previous study, species assemblage and species richness of micro-crustaceans and rotifers (including bog-associated species) did not differ between rewetted and non-rewetted sites in Dutch bog remnants. As microinvertebrates have a less complex lifecycle, they may have less strict demands on their environment (regarding e.g. vegetation structure, combination of habitat elements). In addition, high (passive) dispersal rate of micro-crustaceans and rotifers (easy dispersal by wind and animal vectors), may explain this difference in the response of macroinvertebrates and microinvertebrates to rewetting of bog remnants. The authors conclude that differences in the life cycles of species, as well as differences in their dispersal capacity could explain their differential response to restoration measures in bog remnants and other landscape types as well.

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http://www.springerlink.com/content/l1720630804817w7/fulltext.pdf