Atlas of the land and freshwater molluscs of Cornwall and the Isles of Scilly

Cornwall has been in the forefront of biological recording in the UK with the develop- ment of computerised databases long before the establishment of biological records centres in other counties. This non-marine mollusc atlas represents the first in a new series of publications and comprises a synthesis of all mollusc records to the end of 1999. This well-presented, softback A4 book has a glossy green cover with a photograph of a living Ashfordia granulata, six pages of introductory text, and a page each for the 122 species recorded from Cornwall. The species' pages comprise a tetrad (2 x 2km) map with records discriminated as pre- and post-1965, a smaller map showing distribution by hectad (10 x 10km), Latin and vernacular names, size, a black and white illustration, and a few lines of text on habitat, modern and sub-fossil records. The national status of species according to the criteria in the British Red Data Book is given. However, there is no mention of those (2) spedes legally protected under Schedule 5 of the UK Wildlife and Countryside Act 1981, for which a license is required for collection.

The non-marine malacofauna of Cornwall is impoverished compared with most of England and this is clearly seen in maps in the national Atlas, (Kerney 1999). This is largely due to absence of calcareous rocks. The freshwater fauna is espedally poor; many species which are abundant further east are absent and even some otherwise ubiq- uitous lymnaeids and planorbiids are uncommon.

The inclusion of a map showing distribution both by hectad in addition to tetrad is very useful and reinforces the value of presenting data on a smaller scale. Distributions not evident from hectad scale are clearly revealed at tetrad scale, e.g. the almost exclusively coastal distribution of helicellids. For others e.g. Zonitoides excavatus, the hectad map (with 24 dots) suggests that the species is common and widespread throughout the county, yet the tetrad map with only 30 dots demonstrates the over-simplification of the larger scale. Comparison of the maps for the two Cepaea species shows that in Cornwall C. nemoralis is considerably commoner than C. hortensis, whereas there is good evidence from other parts of the country that C. nemoralis is declining and C. hortensis is spread- ing. Interpretation of the distributions would have been greatly assisted by the inclu- sion of a coverage map showing the number of spedes recorded from each tetrad. This would show which parts of the county support the most diverse molluscan fauna and highlight areas for which there is the greatest scope for further work. The areas south west of Newquay, the St Ives peninsula and the Helford river valley, appear to support the greatest diversity, but they may well also be the most intensively recorded areas. The eastern part which includes Bodmin Moor appears to be the most impoverished, but it may be that the area has received the least attention.

Regardless of the sparsity of habitats likely to support a diverse molluscan fauna, many species are clearly under-recorded and this is acknowledged by the authors. There are few segregate records for the Arion hortensis and A. circumscriptus complexes. Small species which are tolerant of poorer conditions (e.g. Columella aspera. Vertigo subs- triata) are likely to be more widespread, and with only 11 records for Punctum pygmaeum, there is much scope for sampling woodland leaf litter! As is often the case with mollusc data, Pisidium are under-recorded. However, comparison of the map for P. personatum (30 records), which is a spedes likely to be widespread, with that for Potamopyrgus antipodarum (c. 175 records), suggests that Pisidium are neglected when aquatic habitats have been sampled.

Is there a need for a publication such as this, particularly as it does not represent the results of a detailed or a systematic survey? The opening line of the Foreword states: "This atlas is intended to stimulate interest in non-marine molluscs and is advisedly deemed provisional since there doubtless are more species and certainly more records to be discovered". This not only applies to Cornwall but to many other areas in Britain. It is fair to say that recording non-marine molluscs in this country is at a rather low ebb; a new national atlas has been published which inevitably leads to a belief that work is completed. Also, malacologists involved in county surveys find it difficult to find enough time to maintain the enthusiasm and momentum for such a major undertaking. Any such project should ultimately fulfil the requirements of the end users, i.e. the conservation agencies. These call for up-to-date information on habitats and species of local, national and international importance. Whilst county surveys for their own sake may have less value, systematic small-scale surveying can enable those species and habitats in need of conservation to be identified. In addition to work by malacologists, we need to involve and enthuse the local naturalist community. For example, Cornwall supports a significant number of sites for Lymnaea glabra, a species in severe decline else- where - why not organise a targeted survey? Similarly, most of the British populations of Ponentina subvirescens are in Cornwall and are therefore of national importance. Detailed distributional and ecological surveys would have immense value. Another species, Hygromia cinctella, was not recorded in Cornwall until 1993 and is now spread- ing. An excellent opportunity exists to initiate work to monitor the rate of spread. Such a project is successfully underway in Cardiff, involving local schools. So yes, there is a need for such a work; this atlas should act as a stimulus, not only to continue general non-marine mollusc recording, but also to carry out fieldwork structured towards specific projects.