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A joint meeting of
the Conchological Society of Great Britain and Ireland and The Malacological Society of London.

At the National Museum and Galleries of Wales, Cardiff

Saturday 9th November 2002

This was a well attended and lively meeting in the Icons Suite, chaired in the morning by Dr Hefin Jones (University College, Cardiff) and in the afternoon by Professor Robert Cameron (Malacological Society). The discussion continued in the evening in a nearby bar.

Abstracts:

Quantitative survey techniques for investigating freshwater mussel distributions

David C. Aldridge

Aquatic Ecology group, Department of Zoology, University of Cambridge,Downing Street, Cambridge CB2 3EJ.

Choosing an appropriate sampling technique is essential when asking questions about the distribution of organisms. Like many molluscs, freshwater mussels (Bivalvia: Unionidae) are patchily distributed and their abundance varies markedly between sites.; Whilst using real data from freshwater mussel populations, this study addresses some general principles on choosing the most appropriate survey technique depending on the question that is being addressed. For example, how many samples should one collect to be confident of the absence of a particular species? How close together should sample sites be? How many replicate samples are appropriate? Is the efficiency of different survey techniques dependent on the density of the study species? The study concludes by presenting a framework for selecting the most appropriate survey technique for sampling freshwater mussel distributions, based on the question being addressed and the abundance of the study animals within a particular system.


How reliable are our estimates of land mollusc species richness? Scale, statistics and plain common sense

Robert Cameron

University of Sheffield and The Natural History Museum, London.

It is generally accepted that species inventories, whether for atlases or for detailed site studies, may be incomplete. Some recent analyses show that this can be a serious problem, making comparisons of diversity, composition and distribution impossible. In this talk, I look at a range of surveys of land molluscs to see how serious this problem is, and I examine some of the statistical techniques for detecting or correcting it. In many, but not all cases, this examination is reassuring. Some pragmatic rules for sampling are suggested, but no single method will fit all situations.


 

Assessing the small-scale spatial distribution of Mollusca: implications for conservation

Paul Davies, Colleen Wolski, Arrun Denman, Mark Wade, David Hawkins & Chris Grimes

Bath Spa University College

Recent work at Bath Spa University College has concentrated on two themes:

1.n"' small-scale spatial distribution patterns of molluscs in what, to the mollusc sat least, are heterogeneous habitats. 2. the colonisation abilities of mollusc s in developing habitats

Several small-scale distribution studies have been carried out in relic watermeadow systems in central southern England. Results have thus far shown very specific spatial patterning of species-related to changes in vegetation cover and hydrology. Present studies are assessing whether one can usefully define Minimum Viable Habitat (MVH) for given species.

Colonisation studies have concentrated on shaded habitats. Presently, we are assessing the movement of molluscs from established hedgerow habitat into set-aside in which woodland is becoming established; the use of hedgerows and field boundaries as habitat corridors (or as habitat in themselves); and what the term 'woodland' means to molluscs.

All of these studies have conservation implications.


Methods for assessing the marine mollusc microfauna of Rodrigues

Ian J. Killeen Janice M. Light

Malacological Services, 163 High Road West, Felixstowe, Suffolk IP11 991) UK

The micro-gastropod fauna is an element which receives less attention than macro-species in the tropics.Although habitats are recorded for some taxa, many species are known only as shells. In the western Indian Ocean, the microfauna has not been studied in detail.

In October 2001, research was carried out to elucidate the smaller scale local distributions of the mollusc fauna on Rodrigues, in particular the microgastropods associated with a range of habitats and sediment types, and to establish differences between these habitats on the limestone undercut platform and pillow-lava basalt shores.Our initial results from 2000 also indicated that several of the micro-mollusc species may be restricted to one particular type of habitat.

Introduction of a quantitative element poses several problems, not least of which is devising repeatable sampling techniques and having adequate replication. The molluscan communities of the different species of algae, sea grass beds, and short algal/sediment turf habitats were sampled 'quantitatively' using a volume of algae. 2 or n3 replicate samples were gathered. All molluscs from c. 100 samples have been picked out and assigned to morphospeciesThe data have been subjected to multi-variate analysis.


BIOMïR Surveys: Benthic Sampling Programmes in the Irish Sea

Andrew S. Y. Mackie

Marine Biodiversity Section, National Museum of Wales

A brief overview is presented on the Museum's collaborative research programmes in the Irish Sea area.  The aims, methodology and results of our SE Irish Sea surveys (published as BIOMïR 1 Report), SW Irish Sea Survey (SWISS) and the recent Welsh Sandbank Survey are described.  Particular attention is given to the distribution and diversity of the mollusca.


Quantifying both land snail diversity and factors that can influence it in Mediterranean landscapes

F. Magnin

Institut MZditerranZen d'Ecologie et de PalZoZcologie, CNRS, Aix-Marseille

It is generally established that the Mediterranean area harbours the highest land snail richness in Europe.  This is mainly a consequence of Late Cenozoic history and of geomorphology.  One of the consequences of such diversity is a very complex spatial pattern of snail communities.  The purpose of this talk is not to discuss the reliability of field and statistical techniques applied to estimate molluscan diversity, nor to undertake an account of snail biodiversity in Mediterranean France.  I will just present (1) field methods we have used to record at the same time land snail communities and environmental data, mainly in open habitats, and (2) statistical tools which can be used to explain patterns of diversity from environmental and historical factors.


Towards a standardized protocol for land mollusc sampling: molluscan ecology in south Iberia

Alex Menez 

The University of Wales, Cardiff and The Gibraltar Museum, Gibraltar.

Why sample land molluscs?  The answer to this question is the starting point for decisions in planning a sampling methodology.  The requirements of a collector or atlas-worker are different to those of an ecologist.  I concentrate on the methods for sample collection that are necessary for quantitative ecological work and that will allow subsequent objective data analyses.

It is argued that a standardized sampling and data analytical protocol is necessary to allow comparisons to be adequately made in an ecological study.  Data from current work in south Iberia are used to illustrate a protocol recommended for use in land mollusc ecology.


What can a snail do to the reliability of our results?

Beata M. Pokryszko

Museum of Natural History, Wroclaw University

Species lists for large areas (a country, a province etc.) are more complete and reliable than those for small areas, since many factors affecting our results are negligible when dealing with the former but very important when studying the latter.  The estimate of relative abundance is an additional small-area problem.  Some gastropod species are capable of "escape" from species lists in some spatial and temporal situations.  Some of the escape-responsible factors are directly related to life cycles and/or microhabitat preferences, e.g.: clustered distribution (close association with a plant species, dead timber etc.), small areas occupied by populations, short life cycles involving drastic seasonal changes in abundance, preferences regarding shelter under extreme weather conditions.  Standard methods of sampling and their drawbacks are discussed in this context, based on life history and micro-ecology studies.


Small sample sizes and Biodiversity analysis from land-snail surveys in South Africa

Mary Seddon, Dai Herbert & Peter Tattersfield

University of Sheffield and The Natural History Museum, London.

A study of land-snail diversity was undertaken to investigate the faunas of different forest types in KwaZulu Natal, South Africa.  The methods used were a variation on the standard protocols used in East Africa and focused on Direct search (fixed-time and fixed-area) and litter sampling.  Data are presented on the differences between these forest types, showing that species richness were highest in the Scarp forests.  However, discussion will focus on the differences in various Diversity Indices and the effects of uneven sample sizes in our data sets



Posters

Truncatella subcylindrica
(Linnaeus, 1767) in Ireland

J.D. Nunn', P. Anderson2 and S.M. Smith3

1Ulster Museum, Botanic Gardens, Belfast BT9 5AB, UK

2School of Agriculture,Queen's University,Belfast BT9 5PX, UK

3Woodleigh, Townhead, Hayton, Cumbria CA4 9JH UK

In July 2000, two colonies of the brackish-water gastropod Truncatella subcylindrica (L.) were located in Galway Bay.  These were the first live records for Ireland.  The only apparent previous record was a shell from Bundoran in the mid 19th century, considered by later workers to be in error.  Prior to the discovery in Ireland, the species had only been recorded from the extreme south-west and south of England in Britain.  The colonies in Galway are currently the most northerly in the world.

A project was undertaken in 2001, supported by a grant from the Praeger fund of the Royal Irish Academy, to study the ecology and associated fauna and flora of Truncatella subcylindrica, and to search for further colonies.  A total of 50 site visits was made in August and November to Counties Galway, Clare, Mayo, Kerry and Wexford, with more detailed work undertaken at the two known colonies at Rincarna and Carrowmore.

The presence of Truncatella subcylindrica at Rincarna and Carrowmore was confirmed, and the extent of the colonies elucidated.  Three shells of Truncatella subcylindrica were also found in shell sand from Rine Point, Co. Clare.  A search at 47 other sites in the counties listed failed to find new colonies with live shells.

In many invertebrates there is a tendency for habitat preferences to become narrower close to the northern range limits.  At Rincarna and Carrowmore, Truncatella subcylindrica is confined to muddy gravel near the top of the shore, on shingle spits impounding brackish lagoons, often in gravel under large boulders.  The gravelly habitat is probably inundated only at spring tides but is kept constantly moist by the impoundment of the lagoon which leaches through the spit back into the sea.  It has been observed on or in Vaucheria inside an inundated lagoon, and can stand immersion in fully saline water for some days although it is primarily amphibian or terrestrial.  Densities of up to 500 animals per square metre were recorded on the Vaucheria.  From observations, it is clear that that T subcylindrica requires constant moisture, high (near fully marine) salinity, and gravelly or bare rock surfaces which serve to absorb the sun's heat.

The Rincarna and Carrowmore sites are possibly unique in Ireland, although there is a slight chance that similar sites may exist in Co. Kerry.  Both lagoons are small, and very vulnerable to disturbance.  There has already been some dumping of rubbish at the western end of Rincarna Lagoons.  It is suggested that these two sites be considered for maximum protection under available conservation legislation in Ireland.


Ensuring accurate estimates of population size in the field: an example using Achatina fulica in dense vegetation

PaulCraze

School of Biological Sciences, University of Plymouth,

Drake Circus, Plymouth.  PL4 8AA

Email: paul...@care4free.net

There is sometimes a justifiable tendency to accept low accuracy in fieldwork since to do otherwise involves an unreasonable amount of time and effort.  Now and then an opportunity arises to test some of the assumptions used to justify this acceptance.  One, sometimes subconscious, assumption when using quadrats to estimate population size and distribution is that those individuals not encountered due to physical inaccessibility will not significantly affect the results.  Recently, an opportunity arose to test this assumption on Ile aux Aigrettes (IAA) off the coast of Mauritius.  The surface of IAA has been marked out with a permanent grid of quadrats.  In an on-going programme, these quadrats are being cleared of non-native vegetation one at a time.  This means that counts of molluscs before and after clearance can be compared and the effect of dense, inaccessible vegetation on the counts can be estimated.

The introduced land snail Achatina fulica was used as the model organism for this study since it is abundant, relatively conspicuous and any information on its distribution would be useful in planning its eradication from IAA.  Four methods were used to generate estimates of snail numbers using the pre-clearance counts.  Predicted number of snails was then estimated for any quadrat on the island using a GIS interpolation.  Comparing these predictions with actual counts allowed for an assessment of the accuracy, precision and bias associated with each of the four estimation methods.

Assuming the same density of Achatina fulica in accessible and inaccessible parts of quadrats gave the most accurate, unbiased estimate.  Ignoring the unsearched parts of quadrats gave the worst estimate and shows that, for accurate fieldwork on poorly mobile organisms such as molluscs, the effect of physical accessibility on the probability of encountering an individual can be a significant factor


A checklist, atlas and bibliography for the marine Mollusca of Ireland

J.D. Nunn1, S.M. Smith2, B.E. Picton1 & D. McGrath3

1Ulster Museum, Botanic Gardens, Belfast BT9 5AB, N. Ireland

2Woodleigh, Townhead, Hayton, Cumbria CA4 9JH, England

3Galway-Mayo Institute of Technology, Galway, Ireland

The most recently published checklist for the marine Mollusca of Ireland was in 1900 by A.R. Nichols, former keeper of Natural History at the National Museums of Ireland.  In 1992, a project was initiated to update and extend this checklist, and to compile an atlas of the species distribution.  Fieldwork for other purposes had been carried out between 1974 and 1991, including Galway Bay (1974-76), north coast of Ireland (1986), Strangford Lough (1986-92), Mulroy Bay (1986-95), and Lough Hyne (1990-97).


The region under study is within 550 30'N to 500 30'N and 50W to 160W.  Each recording 'square' is 6' x 12'.  Of the 2303 'squares' for recording Mollusca in the area, 245 include the littoral zone.  Since the inception of this project, a further thirteen major surveys have taken place around the coast of Ireland.  There is a clear requirement for uniform coverage and recording effort to avoid the impression of relative rarity. 96% of the littoral recording 'squares' of Ireland have been surveyed, and a further 2% are inaccessible except via boat.  Recording from the sublittoral zone is considerably less comprehensive, being dependent upon availability of diving and/or dredging facilities, and financial support.

Irish molluscan records have also been obtained from museum collections including the Ulster Museum, National Museum of Ireland, National Museums of Scotland and the National Museums & Galleries of Wales.  Records from major surveys have also been incorporated (e.g. Northern Ireland Sublittoral and Littoral Surveys; BIOMAR survey (Republic of Ireland), BIOMïR and SWISS surveys (southern Irish Sea)).  Additional records have been supplied by government departments, agencies, universities, consultants, individuals and a comprehensive collection of literature.

Data have been incorporated into a computer database, which will generate the distribution maps.  Currently there are 96,400+ records of Mollusca for the island of Ireland stored on the database representing 19,600+ visits to sites.  Of these, 39,000+ records were obtained from 1700+ site visits by fieldwork specifically for this project.  A bibliography of 1350+ references for marine Mollusca in Ireland has been compiled.  From this dataset, a provisional checklist has been compiled of 892 taxa (live/dead, all dates), with an additional 59 species of uncertain status.  Many records new to Ireland or to Sea Areas have been observed.


The atlas and checklist will published as a CD:

Title:The marine Mollusca of Ireland: checklist, atlas and bibliography

Authors: Julia Nunn; Shelagh Smith; Bernard Picton; David McGrath

Publication date: 2003

Format: CD-ROM with accompanying instructions and notes as a sleeve.

Content : Text & distribution map for each species; photographs of marine biotopes in Ireland; photographs for 200+ species; historical background; ecology & description of the coast/sublittoral where relevant to Mollusca etc.


Problems in assessing distribution trends of slug species, both historical and recent

Roy Anderson

Department of Agricultural & Environmental Science, Queen's University, Belfast BT9 5PX

The reliable identification of slugs for distribution mapping schemes, applied experimental studies and, particularly, the assessment of historical changes in distribution, represents a pervasive and ongoing problem.  Questions arise such as, where did the notorious pest, Arion vulgaris Moquin-Tandon (lusitanicus auctt. nec Mabille) originate?  What is its current distribution?  We do not know.  Even the name is controversial.

What hope then of resolving such questions?  The answer lies partly in more detailed studies of development and reproduction.  These can finally resolve, for instance, how many species of the genus Arion occur in the British Isles, a question that is currently not answered, at least in the available literature.  Much headway has been made by detailed studies such as those of Davies (1977, 1979, 1987) but the large Arion species remain intractable.  Currently four or five large Arion species are recognised in Europe but there is persuasive evidence that there are at least seven or eight.  When such matters are finally resolved it may be possible to look back in time and see whether material figured and described in early accounts of the European fauna are identifiable.

In the present study I have examined cases for the early occurrence of several slugs, now widespread, in Ireland.  This has been done primarily from the work of R F Scharff who monographed the Irish slug species in 1891.  It can be demonstrated, notwithstanding a description of a yellow slug which he described as occurring in woodlands, that Scharff's description refers to the Mediterranean Limacus flavus (L.) and not the east European L. maculatus (Koleniczenko).  Some controversy surrounds the origins of this slug but it is very likely to be an import of recent origin and is certainly still expanding both in numbers and in range in Ireland.  It can also be inferred that among the large Arion species present in eastern Ireland in Scharff's time were at least Arion ater (L.), Arion rufus (L.), Arion flagellum Collinge and possibly Arion vulgaris. Taylor (1907) provides a hint that vulgaris was in Britain as he figures a spermatophore clearly belonging to that species but labelled ater var. rufus.  The drawing was abstracted from Moquin-Tandon (1855) so does not provide final proof that he recognised it from his own material.  Taylor (1907) and Scharff (1891) also figure 'varieties' of Arion ater which today can be recognised with some confidence (unpublished observations) as colour forms of Arion rufus (L.). This is distinct from the Continental 'rufus' referred to by Taylor and by all modern Continental authors.  The name A. empiricorum Ferussac can be justified for that taxon which has a distinct spermatophore and ligular anatomy.  Scharff (1891) refers to the difference in size between Irish and Continental large Arion species, commenting upon the large red forms which were abundant in German forests.  It seems unlikely from both Taylor's and Scharff's accounts that Arion empiricorum was present in Britain or Ireland at that time, or if present, recognised as distinct from reddish forms of related species.  It is widespread on the Continent and should occur, at least in the Channel Islands.


Discussion of the meeting continuing in a nearby bar: Richard Preece, Barry Colville, Robert Cameron and Beata Pokryszko.

Illustrations to follow


 

 

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