1999 Annual Award Winner, Dr Richard Meyrick

Land snails are common in calcareous sediments of Holocene age and are ideally suited for providing detailed palaeoenvironmental data. Tufa, a calcareous spring precipitate, is one of the best types of sediment for preserving successions of land snail assemblages. Where tufa accumulation was rapid, the temporal resolution of each sample can be on a centennial scale or less.

The primary aim of my Ph D was to extend the coverage of well-dated Late-glacial and Holocene molluscan successions in Europe. In addition to one site in Britain, sequences were examined from two tufa deposits in Germany, one in Luxembourg and three in Sweden. Detailed faunal and environmental histories were produced for each site, where possible with associated radiocarbon chronologies. Individually, the sequences from the continental mainland provided the first quantitative Holocene molluscan records from their respective regions and collectively represented a 1200 km south-north transect of faunal assemblages across north-west Europe.

Local mollusc assemblage zones were defined for each of the sites on the basis of significant changes in faunal composition. These were then combined with limited information available from the literature to propose regional mollusc zones for Northamptonshire, the Rheinland (Luxembourg and western Germany), Skåne (southernmost Sweden) and south-central Sweden. Broad similarities in the development of molluscan faunas during the Late-glacial and Holocene across north-west and central Europe were demonstrated.

In north-west Europe, Late-glacial and early Holocene open-ground assemblages were dominated by Vallonia and Trichia, together with a few shade-demanding elements. The Late-glacial was characterised by the presence of Vertigo genesii and Abida secale, depending on the depositional environment. Catholic elements became increasingly important at the start of the Holocene, whilst the expansion of shade-demanding taxa, most notably Carychium tridentatum, reflected the onset of wooded conditions. As this woodland became more established, the boreo-alpine species Discus ruderatus was replaced by its congener, D. rotundatus, which has a more southerly modern distribution. Similar deciduous forest-optimum faunas developed at approximately the same time in the southern England and Rheinland, although these were characterised by different defining species: Spermodea lamellata and Leiostyla anglica in the former and Platyla polita, Sphyradium doliolum and Perforatella incamata in the latter. Such assemblages became progressively more impoverished with increasing latitude. For example, in Skåne (southernmost Sweden) such assemblages are a restricted combination of the English and Rheinland faunas, characterised by P. polita and Spermodea lamellata. The reappearance of open-ground faunas from ~5000 yr BP reflects widespread anthropogenic clearance.

The relative timing of such key biostratigraphical events was used to evaluate the dispersal of terrestrial molluscs from glacial refugia during the last 13,000 years. Molluscan faunas characteristic of a certain biome (although not necessarily represented by exactly the same assemblage) seem to develop first in central Europe. A time lag of about 500 years then occurs before similar faunas are observed in western Europe (Rheinland and southern England). For example, woodland becomes established here by ~9700 yr BP, the replacement of D. ruderatus by D. rotundatus occurs at ~8500 yr BP and deciduous forest optimum faunas appear at -7500 yr BP. As these faunas move northwards into Scandinavia, rates of dispersal decrease and become more variable. For example, the establishment of deciduous forest optimum faunas does not occur until at least 5000 yr BP in Skåne and perhaps as late as historical times in Östergötland (south-central Sweden).

It appears that during the Late-glacial and earliest Holocene, the majority of dispersal routes passed through central Europe, although whether the molluscan refugia were located in the Balkans, further east, or a combination of the two, is not yet known. The forest optimum assemblages of central Europe and the Rheinland remain similar and probably represent dispersal from the former region into the latter. However, the corresponding fauna from southern England has a more western and oceanic character and probably originated from the Iberian Peninsula, where relict populations of Spermodea lamellata and Leiostyla anglica still occur, or from refugia located off the modern west coast of Europe. Despite the apparent late arrival of most elements of the Scandinavian malacofauna, it is interesting that during the Holocene Thermal Optimum (loosely defined as the period 9000-5000 yr BP by the Intergovernmental Panel on Climate Change) several taxa had more northerly ranges than they now occupy (e.g. Vertigo moulinsiana, D. rotundatus and V. angustior).

Since completing my PhD, my research activities have been quite diverse. I have extended my investigation of molluscan faunal history in the Rheinland, to include the examination of a sequence deposited during the last glacial period (approximately 20,000 yr BP). I have also been involved in an archaeological excavation near Cambridge, providing an appraisal of the local environment at the time of occupation. Furthermore, last summer I had the opportunity to work in Canada for several months, examining two Holocene sequences from southern Ontario.

More recently, I have been appointed head of Quaternary molluscs at the 'Forschungsstation fur Quartärpaläontologie' in Weimar, Germany, which has just become part of the Senckenberg Research Institute. This position provides an unparalleled opportunity to expand my research both temporally, by examining sequences from earlier episodes of the Quaternary, and specialty, by investigating molluscan successions from Central Europe and further east. Moreover, I am already involved in a number of collaborative projects, including one examining the faunal and environmental history of central Germany at the end of the last interglacial and another investigating variations in the morphology of land snail shells (and other faunal elements) during glacial-interglacial transitions, together with French scientists.