Quantitative studies on some living British wetland mollusc faunas

The work described here provides a quantitative basis for die interpretation of fossil assemblages of Mollusca from wetland habitats. Wetlands were sampled for living Mollusca in East Anglia (including an intensive study at Wicken Fen) and Scotland. Within the limited geographical area of Wicken Fen, the mollusc fauna may be used to predict the vegetation and hence to reconstruct the environment. Such a relationship did not continue to hold when scattered sites throughout die East Anglian region were studied. However, the relict nature of these fens should be taken into account. In die central Highlands of Scotland, a better correlation was found between mollusc fauna and flora, though this was inadequate for reconstruction of details of the vegetation. Within the context of wetland, the presence of certain rare species of narrow ecological tolerance is considered the best available measure for the reconstruction of die environment from molluscan assemblages, but their absence is meaningless. Quantitative studies of assemblages of the common species may still prove to be of value at the coarser level of discrimination between wetland, grassland and woodland, but the data are not available. Numerous quantitative studies of fossil assemblages of Mollusca from Quaternary sediments have been made and the results have been interpreted to indicate past environmental and climatic conditions. In previous studies, common species have been placed into ecological categories based on qualitative observations of the occurrence of Mollusca in modern environments, and fossil assemblages have then been interpreted as being formed by transport and accumulation from a variety of different habitats. This may be the case, but equally studies of the living assemblages have shown that the structural complexity of a single habitat may lead to species of very different ecological groups living within the same area of ground. It is simpler to interpret certain fossil assemblages as having been formed in situ in structurally diverse environments, rather than invoking mixing from different environments.