Baltic hard bottom mesocosms unplugged: replicability, repeatability and ecological realism examined by non-parametric multivariate techniques

The similarity percentage breakdown procedure (SIMPER) establishes the species principally responsible for these differences. Considering abundance data Theodoxus fluviatilis is always an important discriminator between groups, mostly accompanied by Mytilus edulis and either Idotea spp. (replicability) or Gammarus spp. (realism). For biomass data Mytilus and Idotea are the most important overall discriminators, followed by Lymnaea spp. (repeatability and realism) and Cerastoderma glaucum (realism). Finally the factors and processes restricting mesocosm performance are outlined and their consequences are briefly discussed. It is concluded that the degrees of replicability, repeatability and ecological realism are too low for straightforward use of these and probably most other mesocosms in predictive risk assessment or in extrapolation of results to natural ecosystems. (C) 1999 Elsevier Science B.V. All rights reserved.