MOLLUSCAN FORUM - NOVEMBER 2ND 2000

ABSTRACTS OF PRESENTATIONS (in alphabetical order)

The influence of the Mediterranean element in the marine molluscan fauna of the Azores.

SÉRGIO P. ÁVILA

Secção de Biologia Marinha, Departamento de Biologia, Universidade dos Açores, 9500 Ponta Delgada, Açores, Portugal.

The biogeographical relationships of the shallow-water ( <50m ) marine molluscs of the Azores were established by Ávila ( 2000 ). In that study, the malacofauna of the Azores was compared with similar lists from Scandinavia, Belgium, British Isles, Gulf of Biscay to Galicia, Portugal, Western Mediterranean, Morocco and Mauritania, Madeira , Porto Santo, The Desertas, Selvagens, Canary Islands, Cape Verde, Ascension Island, St Helena and the Caribbean. The Mediterranean, the Madeiran Archipelago and the coasts of mainland Portugal had the highest number of shared species with the Azores, whereas St Helena and Ascension shared only a small number of species. Complementary data is provided which reinforces the importance of the Mediterranean as a source of colonists to the Azores, and emphasises the importance of the sea-mounts located between the south of Portugal and the Madeiran Archipelago.

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Ageing mucus trails and their role in the nutrition of Littorina littorea.

JANINE BLACKWELL

Ecology Centre, Sunderland University, Sunderland, SR1 3SD, UK

Littorina littorea is an important member of the intertidal community. Davies & Beckwith (1999) reported the use of L. littorea pedal mucus in feeding, in an artificial laboratory environment. Here, this work is extended in a more thorough investigation in the field. Mucus trails were exposed at different sites of exposure, for different periods of time. On trails exposed for 1 and 2 tidal cycles, trail following occurred over ~ 1/3 of the trail compared to 17% of the trail after 1 week. Tracker snails moved significantly faster off the mucus trail than on. The mean chlorophyll a density was 10 x greater on the mucus trail than off. L. littorea seem able to modify their feeding behaviour on encountering old trails. The results are discussed in terms of the ecology of L. littorea and its effects on micro-benthic communities

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The importance of side-channels as refuges from river management for a population of freshwater mussels (Bivalvia: Unionidae).

THOMAS BURDITT

School of Geography and Environmental Management, University of the West of England, Coldharbour Lane, Bristol, BS16 1QY

Routine river management operations such as weed cutting and dredging can have a severe impact on freshwater mussel populations. This study looked at the numbers and sizes of 4 species of mussels (Anadonta anatina, A. cygnea, Unio pictorum and Pseudanodonta complanata - a red data book species with a Species Action Plan) in the main channels, side-channels and side-channel mouths of two canalised lowland waterways. In a heavily dredged river (the River Brue), mussel populations are over twice as dense in the side-channel mouths as in the main channel, though the side-channels themselves were not found to be significant habitats for mussels. This is particularly true of P. complanata. Sizes of mussels at the side-channel mouths were no t statistically different from those in the main channel, but had an equally diverse range of ages, indicating populations from which re-colonisation of the main channel might be possible. The existence of these island populations is linked to the inaccessibility of dredging equipment (drag-lines) to the areas in front of side-channel mouth sluices.

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Larvae of the tropical oyster Crassostrea belcheri are induced to settle in the presence of pheromone from the adults.

SOMCHAI BUSSARAWIT

Phuket Marine Biological Centre, Phuket, Thailand

Pediveliger larvae of the tropical oyster Crassostrea belcheri ( Sowerby ) were allowed to settle under different conditions. Three types of seawater were used for the experiments: aged seawater ( one month ), fresh natural seawater, and aged seawater conditioned by the presence of adult oysters for 24 hours. Ten different substrates were used in each of the three water types. The highest settling was found in conditioned seawater, followed by fresh seawater and aged seawater respectively. The settling reached a maximum within 24 hours in the conditioned seawater. The fact that larvae are induced to settle by pheromones released by the adults is an important mechanism for explaining the gregariousness of the oysters in nature.

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Thermal stress of a tropical intertidal limpet: Cellana toreuma, in Hong Kong

ROSE M. Y. CHAN1 & Maurizio De Pirro2

1 Department of Ecology & Biodiversity, The University of Hong Kong, Hong Kong.

2 Dipartimento di Biologia Animale e Genetica, Università degli Studi di Firenze, Italy.

Cellana toreuma is a common, semi-exposed shore limpet which experiences heavy mortality during tropical Hong Kong summers, resulting in a predominantly annual life span. Limpets in the mid shore experience higher body temperat ures (1-2° C) during daytime emersion than ambient air (31.0° C) or rock (34.0° C) temperatures, and there is a positive correlation between heart rate and rock temperature. Laboratory experiments support this relationship but with increased temperature and duration, an upper threshold to heart rate is recorded. Desiccation rates in the laboratory increased with substrate temperature and duration, limpets losing up to 10 % body water at 40° C after 60 minutes. C. toreuma appears unable to control water loss as a means of alleviating thermal stress, or to regulate heart rates as has been recorded in higher shore species suggesting that C. toreuma is not capable of physiological thermoregulation, which may account for the recorded summer mass mortalities.

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Variation in the growth and morphology of freshwater mussels ( Bivalvia: Unionidae ) in the River Thames.

CATHERINE FOWLER, Stephanie Riach and David Aldridge.

Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK

Three species of freshwater mussel, Anodonta anatina, Unio tumidus and Unio pictorum, were sampled from sites in the River Thames below Abingdon. There were significant differences in growth-rates and shell morphology between sites for all three species, and the paper examines possible causes for these differences, including temperature, nutrient availability and current velocities. It appears that these unionids aare constrained in their growth patterns by the nature of the flow-re gime, and they probably show phenotypic plasticity in their response to such regimes.

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Designing a computer-based information system for marine Antarctic Mollusca: a database for biogeographic analysis in biodiversity and ecology.

HUW GRIFFITHS, Katrin Linse and Alistair Crame

British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET

The aims of our project are to (1) establish comprehensive databases of the distribution, shell morphology and selected ecological characters of Antarctic molluscan taxa, (2) analyse the databases and derive patterns, and (3) interpret the results and display them on interactive maps. The database will hold distribution records ( Lat., Long., Depth, Substrate ) for every gastropod species found in the Southern Ocean as well as other detailed information on each species, for example on shell size, shell features, colour, reproductive method and feeding habits. The database can be expanded to include areas outside the Southern Ocean for comparisons. The combination of a Microsoft Access 2000 database, using Oracle as a data store, and a link to ARCV iew for creating the maps seems to be the best solution in terms of easy data entry and obtaining meaningful reports.

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Intraspecific variation in the freshwater pearl mussel Margaritifera margaritifera, and its possible consequences for conservation.

ANNA HOLMES

BIOSYB, National Museum of Wales, Cathays Park, Cardiff CF10 3NP, UK

Margaritifera margaritifera is an endangered species in Britain, and threatened throughout its European range. There has been a 95% decline in central Europe since the beginning of the 20th Century, with similar effects in England and Wales, which now have only three recruiting populations between them. There has recently been the loss of a population of c. 5000 individuals in N. Wales due to a land drainage scheme. Shells less than 20mm long were present, suggesting that it was a recruitin g population. Conservation agencies decided to collect and translocate living individuals to a site downstream. 342 individuals were moved, but only 40 have survived for a year. Amongst the possible reasons for failure, the differences between populations which are geographically close, but which originated in areas separated during the Pleistocene are considered.

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The diets of two Littoraria species in Hong Kong mangroves

OLIVE H. K. LEE

Department of Ecology & Biodiversity, The University of Hong Kong, Pokfulam, Hong Kong

Littoraria melanostoma and L. ardouiniana (Littorinidae) are the most common littorinids found on the leaves and trunks of Hong Kong mangroves. Mangrove littorinids of this genus feed on plant cells, algae and fungi, however, the fee ding habits of the Hong Kong species are unknown. To investigate their diets, monthly gut content analysis and stable isotopic investigations of the littorinids and their potential food items were undertaken. The gut contents of these littorinids mainly consisted of plant cells, whilst fungi, algae and cyanobacteria were also found and their diets were similar and didn’t vary over the year. Stable isotope analysis, however, suggested they might feed on mixed diets, probably composed of plant cells and phylloplane fungi of mangroves. The nutritional value of their potential food items didn’t appear to be related to the diet composition, suggesting these littorinids are generalists simply consuming the food items available from the mangrove substrate non-selectively.

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Subtidal distribution and shell morphometry in Margarella antarctica ( Lamy, 1905 ) on Adelaide Island, Antarctica.

KATRIN LINSE, Peter Enderlein and Andrew Clarke.

British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET

Margarella antarctica is a common representative of the malacofauna in the shallow waters (0-36m) of the Antarctic Peninsula and the Scotia Arc. This small Trochid grazes on benthic diatoms and microalgae which cover rocks and seaweed. For distribution and density studies, the numbers of Margarella in 50x50cm quadrats were counted, and the distances between each snail measured. Six different sites with six depth levels ( 5, 10, 15, 20, 25 and 30m ) were compared and their substrata noted. Animals found were collected for morphometric analysis. Height/diameter relationships are directly proportional. Frequencies of shell heights show three peaks which may represent successive cohorts. Fresh egg-capsules and just-hatched juveniles can be found in summer. This suggests that as in many other Antarctic benthic marine invertebrates, oocyte maturation and egg development can each take over one year.

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The potential impact of the Asian clam Corbicula fluminea on the Norfolk Broads

STEPHAN MÜLLER

Department of Zoology, University of Cambridge, Cambridge CB2 3EJ

The Asian clam Corbicula fluminea arrived in the Norfolk Broads about five years ago. The source of the invasion, original means of transport and current mechanism of spread are unknown. An outline is given of the studies designed to elucidate the source of the founding individuals, the mechanisms of invasion through the Broads, and the potential impact on key ecological functions of this important wetland area. An important aspect of projects like this is the involvement of a large number of different agencies, organisations and individuals utilising and sharing responsibility for the area affected by the invasion. The widely differing interests and requirements of these groups necessitate a multidisciplinary approach to tackling the problem of biological invasions in the Norfolk Broads.

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Mollusc stratigraphy of Quaternary deposits at Cape Tolstik, NW Russia.

JAN K. NIELSEN

Geological Museum, Øster Voldgade 5-7, DK-1350, Copenhagen K, Denmark

Recently, a 4 Km long and 20m high section was rediscovered at Cape Tolstik on the south-western White Sea coast. The section contains three till units in superposition, each overlain by sorted sediments. The lower till unit contains marine molluscs and barnacles of which many are well preserved and therefore subject only to limited reworking. Assemblages of the overlain units above this are progressively more degraded, suggesting repetitive reworking. Although no absolute datings are presently ava ilable, the stratigraphical position above the Eemian ( last interglacial ) seems clear. The assemblage of the lower till is characterised by boreal components (e.g. Arctica islandica, Astarte sulcata, Cerastoderma edule ). These components, which in other areas occur in undisturbed Eemian sediments of the Boreal Transgression, are not known from any other Late Cainozoic marine sediments in this region. Thus, a post-Eemian age for the three tills is implied, i.e. locally at least three glaciations within the Weichselian.

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Speciation of Osilinus ( Trochidae ) at the Mediterranean- Atlantic interface.

JO PRESTON

Marine Biodiversity and Ecology Division, University of Southampton, Boldrewood Biomedical Sciences Building, Bassett Crescent East , Southhampton, UK.

The species of the Trochid genus Osilinus have apparently undergone adaptive radiation and population fragmentation at the Mediterranean- Atlantic interface. The Atlantic islands ( Madeira, Canaries and Selvagens ) and upwelling pockets along the Portuguese Atlantic coast are of particular interest because of the isolation and divergence that may have occurred there. Investigation of the phylogeographic relationships between populations and species will hopefully serve to elucidate this cur rent taxonomic confusion. This paper will describe the application of morphological and morphometric approaches complemented by molecular techniques ( most notably DNA sequencing ) to resolve the phylogeny of Osilinus and to understand its evolut ionary history through the use of a model system. This paper will present the current situation, my ongoing research, and preliminary phylogenetic results for comment.

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Genetic variability in the mollusc Bradybaena fruticum ( Gastropoda: Pulmonata ).

INGRIDA SATKAUSKIENE

Department of Biology, Vytautas Magnus University, Daukanto 28, Kaunas, Lithuania

The aim of this programme was to examine genetic variability in wild and laboratory populations of the land snail Bradybaena fruticum. Protein polymorphisms and isoenzymes ( non-specific esterases and malic enzyme ) were analysed by PAGE, es tablishing the amount of polymorphism, mean number of alleles per locus and heterozygosity. Wild populations had more polymorphisms, but lower levels of heterozygosity than laboratory stocks. Features of the natural environment which might affect heterozy gosity are discussed.

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The autecology of the two EUHSD listed land snail species Vertigo angustior and V. geyeri ( Gastropoda: Stylommatophora) in Wales

EVA SHARLAND

National Museum of Wales, Cathays Park, Cardiff CF10 3NP

Only 41 of the total 632 protected plants and animals listed in Annex II of the EC Species and Habitats Directive occur in Britain and of these, five are British mollusc species. Two of these molluscs species are Vertigo angustior and Vertigo geyeri, which are both considered vulnerable throughout Europe and are consequently protected under this agreement. In addition, both species are classified in the British Red Data Books as RDB1 (endangered). There are threats of further decline in existing populations due to habitat loss, particularly from the drainage of wetlands. The aim of this project was to provide recommendations for a practical monitoring strategy. This will be used to enable conservation agencies to fulfil their monitoring requirements under the UK Biodiversity Action Plan and EC Habitats and Species Directive.

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Using introns to investigate the phylogeny of a marine snail

BOB SIMPSON

School of Biology, Leeds Univerity, Clarendon Way, Leeds LS2 9JT, UK.

The analysis of genetic polymorphisms in groups of organisms leads to understanding of the processes which structure populations. Littorina is one of the best known invertebrate genera in phylogenetic terms with Reid (1996) having developed a detailed taxonomic analyses of the genus, first using morphological and then molecular-based cladistic investigations. This tree shows a number of polychotomies that are still unresolved. Using sequence data from a rapidly evolving region of DNA (i.e. non coding regions, introns) within the highly conserved calmodulin gene we aim to gain a clearer picture of what is happening in some of these species and therefore develop a greater understanding of the evolutionary processes involved. Discussed here are the preliminary, incomplete trees highlighting the complicated and intriguing nature of the variation within the calmodulin gene family when compared to the accepted phylogeny.

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Microhabitat selection in tropical high shore Littorinids.

RICHARD STAFFORD

Ecology Centre, University of Sunderland, Sunderland SR1 3SD, UK

In Hong Kong, The high shore littorinids Nodilittorina trochoides and Nodilittorina radiata have contagious distributions over small spatial scales ( several centimetres ). This presentation explores the role of surface topography in shaping these distributions. High numbers (up to 99% ) of littorinids are found aggregating in microhabitats such as cracks and crevices which only occupy around 5 to 10 % of the total area. Temperature and desiccation stress are reduced in these microhabitats, and littorinids occupying them have a higher water content than those on bare rock. A manipulative experiment was performed to test the hypothesis that such microhabitats would be selected less often if physical stress was reduced. Results obtained do not support the hypothesis, and reasons for this are discussed.

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Pheromonal influence on reproduction in Biomphalaria glabrata (Say, 1818), an intermediate host of Schistosoma mansoni

JACQUELINE TRIGWELL

Ecology Research Group, Canterbury Christ Church University College, North Holmes Road, Canterbury CT1 1QU, UK.

(jat1@canterbury.ac.uk)

Biomphalaria glabrata is an hermaphrodite freshwater snail that self-fertilises when isolated but outcrosses when paired. B. glabrata’s choice of sexual role when mating has been shown to be affected by the copulat ory history of the mating pair. This may be due to entrainment, levels of available sperm, or an effect of pheromonal cues. It is possible that pheromones from conspecifics influence egg production. When previously isolated snails are paired with, but s eparated by a water permeable membrane from, other sexually mature snails, egg mass production increases significantly, even though there is no physical contact between the two snails. Pheromonal cues from sexually mature B. glabrata may also affect the onset of sexual maturity in immature snails. Preliminary experiments have shown that when hatchling snails are raised in the same water as, but separated from, sexually mature conspecifics, they reach sexual maturity earlier than those raised in i solation.

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Extensive homoplasy in a complex morphological character in Greek Clausiliidae ( Gastropoda: Pulmonata )

DENNIS R. UIT DE WEERD

Kaiserstraat 63, 2311 GP, Leiden, the Netherlands

( University of Leiden)

Shells of Clausiliid snails are characterised by a clausilial apparatus ( CA ), a structure to block the aperture of the shell by a movable plate. Two types of CA are recognised: the open type has a bypass-canal next to the clausilial plate supported b y two parallel lamellae; the closed type lacks this bypass-canal, and is considered the apomorphic condition. Despite the fact that the closed type has obviously arisen several times independently within the family, it has been used as an important taxono mic character state. Both types of CA are found in a group of closely related Greek and Turkish clausiliids. Based mainly on the CA-type, three genera have once been recognised within this group: Albinaria, Isabellaria and Sericata. This classification conflicts with overall shell morphology and geographical distribution. In our study CO1 sequences of species from the three alleged genera were obtained and analysed. The results are more consistent than the traditional classification, and ind icate extensive homoplasy in the CA type. Thus even at lower taxonomic ranks, the value of the CA type as a character may be low.

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Divergence in the face of gene flow: AFLP analysis of parapatric morphs of Littorina saxatilis.

CRAIG WILDING

School of Biology, University of Leeds, Leeds LS2 9JT, UK.

On rocky shores around the U.K. coastline, two morphs of Littorina saxatilis are often found parapatrically. On high shore cliffs and boulders this species is thin shelled, wide apertured and females typically brood low numbers of large embryos. On mid-shore boulders and bedrock the animal is thick shelled with a small aperture and embryos are numerous but small. Previous work suggests that these animals mate assortatively, and that there is evidence for some form of reproductive barrier between them. We wish to know whether there is molecular genetic evidence for this reproductive barrier. To this end we have applied the technique of Amplified Fragment Length Polymorphism (AFLP) analysis to five U.K. populations of Littorina saxatilis, four where the high shore (H) and the mid shore (M) are found, and one where M only occurs. Using 4 primer pairs we have scored 306 bands. FST values for these 306 AFLP loci have been compared with the distribution of FST estimated from a simulation model using realistic values of mutation and migration. We find that about 5% of these loci show evidence of the effects of selection across the cline, either direct or indirect through linkage. This is consistent wit h expectations from sympatric speciation models which propose an initial divergence of a small part of the genome driven by strong disruptive selection.

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Visiting the Mollusca Section at the National Museum of Wales, Cardiff.

HARRIET WOOD

National Museum & Galleries of Wales, Cathays Park, Cardiff, CF10 3NP.

The Mollusca Section at the NMW, Cardiff holds one of the largest mollusca collections in Europe. Our dry collection, comprising of some 180,000 lots, is rich in scientifically and historically important material and is made up of m any different collections. Of particular importance is the Melvill-Tomlin collection which was donated to us in 1955 and contains material from over 850 sources. Our wet collection includes material from many of our recent collecting expeditions.
The section has excellent visitor services facilities: Before arriving at the museum you can browse or search 60% of our collection on the museum website. Whilst using the collection first hand the user can take advantage of our extensi ve historical molluscan library, reprints and journals. If you are unable to visit the collection in person we operate a loan service (subject to status).
The current projects carried out in the section by our museum staff illustrate how our expertise are used in a variety of areas, ranging from local biodiversity surveys to alpha taxonomy and training projects abroad.