How realistic are outdoor microcosms? A comparison of the biota of microcosms and natural ponds

Abstract

This study investigated the extent to which aquatic plant and macroinvertebrate assemblages in small outdoor microcosms (cylinders 1.25-m diameter x 1.25 m deep) resembled assemblages found in natural ponds in Britain. Comparisons were made in terms of community structure, species richness, and numbers of uncommon species. Multivariate analysis indicated that, although the microcosms had no exact natural analogues, their plant and animal assemblages were most like those of deep, circumneutral ponds. Unlike natural ponds, the microcosms supported relatively species-poor invertebrate assemblages, lacking uncommon species. Among individual taxa, microcosms supported similar numbers of species of Gastropoda, Isopoda, Amphipoda, and Odonata as natural ponds but significantly fewer Coleoptera, Hemiptera, and Trichoptera species. This was most likely due to the absence of a shallow littoral area in the microcosms. Because of their vertical sides, the microcosms supported no marginal wetland plants, but submerged and floating-leaved plant assemblages were similar in community type and species richness to natural ponds. Refinements to microcosm and mesocosm designs are identified that would enable experimental systems to more closely replicate the assemblages found in natural ponds. In particular, the incorporation of natural margins would be likely to lead to experimental communities that were closer analogues of natural ponds.

Aquatic Risks of Pesticides, Ecological Protection Goals, and Common Aims in European Union Legislation

“…Few studies have compared assemblages in model streams and natural streams, but those that have indicate that Biever et al (1994) (outdoor microcosms) assemblages in model streams are representative of the natural streams from which they are derived (Belanger et al 1995;Wong et al 2004). Model ecosystems that simulate lentic aquatic ecosystems, however, usually contain species that are characteristic of the deeper parts of freshwater ponds and often lack the species assemblages that are typical of littoral zones (Williams et al 2002). However, it appears from several model ecosystem experiments with insecticides that threshold levels for effects may be very similar between lentic test systems that differ considerably in complexity, at least when they contain representatives of sensitive taxonomic groups (in this case, arthropod populations; Tables 4 and 5).…”

Opinion of the Scientific Panel on Plant protection products and their residues (PPR) related to the aquatic risk assessment for cyprodinil and the use of a mesocosm study in particular

“…Some uncertainty remains about the extrapolation from mesocosm results to natural water bodies. Model ecosystems that simulate lentic aquatic ecosystems usually contain species characteristic of deeper parts of freshwater ponds and often lack the species assemblages typical for littoral zones (Williams et al, 2002). On the other hand, it appears from several model ecosystem experiments with insecticides, that threshold levels for effects may be very similar between lentic test systems that differ considerably in complexity, at least when they contain representatives of sensitive taxonomic groups (Brock et al, in press).…”

An indoor pelagic mesocosm facility to simulate multiple water-column characteristics

“…Spivak et al (2011) concluded that results from mesocosm-scale experiments on micro-algae probably are relevant to large-scale processes, such as eutrophication. On the other hand, Williams et al (2002) found that freshwater pond mesocosms showed lower biodiversity than corresponding natural ponds. Mesocosms in a mesotrophic and a eutrophic lake showed the same water chemistry as the surrounding water, but most biological variables diverged from the surrounding water (Dzialowski et al 2014).…”