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The restrictions and the concerted action of the global ban on the use and presence of tributyltin (TBT) in marine applications to protect ecosystems in the marine environment in 2008 was mainly based on the economic impact on shellfish industries and the dramatic extinction of local mollusk populations in the past. In contrast to the vast datasets on effects on mollusks, the knowledge on impacts on species from other taxa remained in the uncertain until almost two decades ago. The assumption on a long-term TBT-mediated pernicious metabolic bottom-up regulation of the crustacean Crangon crangon population was provoked by the outcome of an EU-project 'Sources, Consumer Exposure and Risks of Organotin Contamination in Seafood.' This study reported high TBT body burdens in C. crangon in 2003, at the start of the transition period to the global ban. Experimental research on the TBT impact in C. crangon focused on agonistic interference with natural ecdysteroid hormones at the metabolic pathways regulating growth and reproduction and the biogeochemical distribution of the chemical. In this paper, metabolic, topical and population-relevant biological endpoints in C. crangon and other crustaceans are evaluated in relation to the temporal and spatial trends on TBT's occurrence and distribution in the field during and after the introduction of the tributyltin restrictions and endocrine-related incidents. Arguments are forwarded to relate the German Bight incident on growth and reproduction failure in the C. crangon population, despite the lack of direct evidence, to the pernicious impact of tributyltin in 1990/91 and previous years. The extreme occurrence of TBT in C. crangon from other parts of the southern North Sea and evidence on the high body burdens as dose metrics of exposure also feeds the suspicion on detrimental impacts in those areas. This paper further demonstrates the complexity of distinguishing and assessing the individual roles of unrelated stressors on a population in an integrated evaluation at the ecosystem level.

The “beneficial uses” of dredged sediment are increasingly being explored for habitat restoration and beach nourishment , but beneficial uses must be tempered by evaluating impacts to organisms. We studied a subtidal nearshore deposition site intended to aid beach nourishment where a “thin-layer” sediment deployment method was employed to minimize mounding and disperse sediment within a proscribed area. Baited benthic video landers (BVLs) in a Before-After Control-Impact (BACI) experimental design were used to test the acute effects (within one hour of deposition) of sediment deposition on dominant epifaunal Dungeness crab ( Cancer magister ) and dog whelk (Nucella spp). The effects of sediment deposition depths and the lateral surge (the turbidity front transiting the seafloor) were both considered. Observations revealed sedimentation levels were limited to epifauna . However, video and instrument measurements showed the lateral surge to impact the BVLs as a 1 to 3 m/s sediment-laden front. Crabs were significantly impacted, while gastropods were more resistant to dislodgment. However, the high velocity impact was relatively brief (2 to 7 min). Further, crabs returned to forage at BVLs after a mean lag of about 20 min post-impact. These results indicate an acute but ephemeral impact effect on crab, and support use of the thin-layer deposition method to minimize burial. Our novel use of BVLs in a BACI experimental design were an effective means of evaluating sediment impacts to targeted mobile epifaunal species, and video observations were informative for understanding lateral surge dynamics and the behavioral interactions of organisms.

Nassarius (Plicarcularia) burchardi (Dunker in Philippi, 1849) is a common dog whelk in subtropical and temperate regions of Australia. In April 2009, two shells of this species were found in the central Waitemata Harbour, Auckland. On the 22 June 2009, a live specimen was found at an intertidal site near Henderson Creek on the western central section of the harbour. Between August 2009 and February 2010, a further 21 living specimens in a range of sizes were found across multiple sites in the central Waitemata Harbour. This species is currently adventive and its presence in the Waitemata Harbour suggests accidental introduction from Australia and subsequent survival. If this species becomes firmly established in New Zealand, there may be significant interactions with native species such as Cominella glandiformis (Reeve, 1847), with which it may directly compete for food, and the invasive mussel Musculista senhousia (Benson in Cantor, 1842), which it is known to eat.

This study examined the influence of shell shape on the distribution and movement patterns of three species of Hawaiian hermit crabs: Calcinus elegans , C. laevimanus , and C. latens . Field surveys showed strong differences in shell use depending on habitat. Individuals of C . elegans and C. latens were more frequently in unusual shapes of shells (the cowrie Cypraea caputserpentis and the variable worm shell Serpulorbis variabilis ) when in tide pools and in more standard gastropod shells, such as the dog whelk Nassarius papillosus , when found in the subtidal. In addition, for both C . elegans and C. latens in tide pools, most crabs in unusual shaped shells were out on top of rocks, whereas most crabs in shells that were standard shapes were under rocks. In the laboratory, individuals of C . elegans and C. laevimanus in unusual shells initiated more shell exchanges and when given empty shells crabs readily occupied the standard shaped shells, but crabs did not move into the unusual shaped shells. Mark-recapture experiments in the field showed that C. elegans in standard shaped shells moved out of tide pools and stayed longer when placed on subtidal coral heads, whereas crabs in unusual shaped shells stayed in tide pools and did not stay on subtidal coral heads (in part due to predation). Laboratory tests showed that C. elegans in unusual shaped shells were more readily dislodged by surge than crabs in standard shaped shells. Thus, the difference in movement patterns in preferred vs. unpreferred shell shapes is an important factor influencing the microhabitat distribution of these hermit crabs.

Estimates of the average distances by which marine larvae disperse are generally poorly described, despite the central role that larval dispersal plays in the demographic connectivity of populations across geographic space. Here, we describe the population genetic structure and average dispersal distance of the netted dog whelk Nassarius reticulatus (L.) (Mollusca, Gastropoda, Prosobranchia), a widespread member of European intertidal communities, using DNA sequence variation in a fragment of the mitochondrial gene cytochrome c oxidase subunit I (COI). An analysis of 156 individuals from 6 locations spread across approximately 1700 km of the European Atlantic coastline revealed weak and nonsignificant population structure (overall Phi(ST) = 0.00013). However, pairwise Phi(ST) values revealed a slight but significant increase in genetic isolation with geographic distance (IBD), suggesting that populations are not panmictic across the sampled geographic range. If we assume that the isolation by distance is maintained by a stable, stepping stone model of gene flow, then the slope of the IBD is consistent with an average larval dispersal distance of approximately 70 km per generation. The spatial scale of larval dispersal in N. reticulatus is consistent with the life cycle of the species (planktotrophic veliger lasting 30-60 days before competent to settle). A mismatch analysis of the COI sequences revealed a signature of an ancient demographic expansion that began 61 500-160,000 years ago, well before the most recent Pleistocene glaciation event. The greatest levels of genetic diversity occur within the middle latitudes of the whelk's geographic range, consistent with the notion that historic populations of N. reticulatus might have expanded northward and southward from the centrally located Bay of Biscay.

Nucella lapillus appears to be unique within the Muricidae, and indeed the Mollusca, in exhibiting a Robertsonian chromosomal polymorphism. The recorded diploid values range from 2n = 26 to 2n = 36, putatively brought about by fusion of smaller chromosomes to form five pairs of large metacentrics in the 2n = 26 form. In this study, the karyotypes of the numerically extreme forms (2n = 26 and 2n = 36) have been illustrated and described in detail, and a new scheme of nomenclature is proposed for the chromosomal rearrangements observed in N. lapillus. Chromosome numbers and karyotypes were recorded and analysed from 70 sites throughout its wide geographical range, mainly from around the UK coasts but also from sites in Norway, France, Spain, Portugal and the USA, showing remarkable variation in both diploid number and karyotypic configuration. The results provide new evidence that seven chromosomes in the 2n = 26 form can be involved in the Robertsonian rearrangements, but the maximum recorded diploid number remains 2n = 36. Inversions were confirmed in three chromosomes and one population was found to exhibit aneuploidy. Possible explanations for the geographical trends in karyotypic variation are discussed, but despite the advances in the karyology of N. lapillus, a simple solution to this enigmatic phenomenon remains elusive. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 87, 195–210.

Laboratory breeding of the dog-whelk, Nucella lapillus, has established that the male-sterilizing Dumpton Syndrome (DS)—underdevelopment, or non-development (aphally), of the penis, incomplete formation (non-closure) of the vas deferens, resulting in a split prostate—can be readily observed in male F1 progeny. Cultivated under high ambient concentrations of the antifouling agent tributyltin (TBT), DS-carrying females can be recognized by their lesser degree of masculinization (imposex): sterilization is thereby avoided. When Dumpton females are crossed, under high ambient TBT, with individuals from a non-DS-affected population (Bude, North Cornwall) DS is absent from both sexes. Crosses of these F1 progeny result in F2 progeny exhibiting the classic DS symptoms in both sexes. A Mendelian mechanism for DS inheritance is suggested by the data.

Nucella lapillus imposex—superimposition of male characters onto prosobranch (a subclass of gastropod molluscs) females—and organotin female body burden were surveyed on the Portuguese coast, from Vila Praia de Âncora (northern limit) to Praia da Luz (southern limit), at 17 sampling stations, between May and August 2003. The vas deferens sequence index (VDSI), the relative penis size index (RPSI), the percentage of females affected with imposex (%I) and the percentage of sterile females (%S) were used to assess the level of imposex at each site. VDSI, RPSI and %I were 0.20–4.04, 0.0–42.2% and 16.7–100.0%, respectively. Sterile females were found at stations 2 (6.2%), 5 (4.0%) and 7 (5.0%). Tributyltin (TBT) and dibutyltin (DBT) female body burdens were 23–138 and

The netted dog whelk Nassarius reticulatus (Linnaeus, 1758), considered as an extinct benthic species in German Baltic waters, was found again alive in the Mecklenburg Bight during several macrozoobenthic surveys since 1997. All data indicate that the establishment of this marine prosobranch species is connected with the more frequent intrusions of highly saline water from the North Sea into the Baltic that have been observed over the past few years. It is proposed that N. reticulatus is a good bioindicator for the hydrographic status in the western Baltic rather than for other existing potential conditions. Since 1998 a second extinct marine species, the polychaete Scalibregma inflatum Rathke, 1843 was found alive here, too.

In the summer of 1995 a massive kill of the dog-whelk, Nucella lapillus, occurred in Bude Bay on the north Cornish coast. High mortality was detectable along 12 km of shoreline. The only other intertidal species affected appeared to be another neogastropod, Ocenebra erinacea. The cause of the kill is unknown but the evidence suggests that it occurred in early July following an extended period of warm, calm weather in June. Possible causes of this event are discussed: algal toxicity may have been responsible since an algal bloom was detected offshore in July in the area. Laboratory experiments exposing gastropods to different species and concentrations of microalgae, designed to test whether N. lapillus is more sensitive than Monodonta lineata and Littorina littorea, gave inconclusive results. No comparable kill has occurred in the Bude area for at least 20 y, but it is suggested that nutrients from a newly-constructed, offshore sewage outfall may now stimulate local algal bloom development during calm weather periods.

The external morphology of the first three larval stages of Nucellicola holmanae is described. These stages were cultured from eggs found with the adults in the viscera of dog whelks collected from Robin Hood's Bay, North Yorkshire. The nauplius develops within the whelk. It moults to a metanauplius which is released as a free-swimming stage. The metanauplius moults to a free copepodid stage which exhibits a combination of characters typical of the first, second and third copepodid stages of other poecilostomatoid copepods. The infective copepodid stage which locates and penetrates the host is visible through the integument of this free-swimming copepodid.

Genetic constitution in the intertidal gastropod Nucella lapillus (L.) influences shell shape, growth rate and physiology. Clinal variation in these traits along a 5 km stretch of coastline in south Devon can be related to environmental variation in temperature and desiccation stress. We have examined mtDNA variation along this shore to investigate whether the cline represents primary or secondary contact. Two distinct mtDNA haplotypes were found which exhibit coincident step clines with karyotypic, allozymic and phenotypic variation and covary with the environmental pressures of temperature and desiccation. These results are interpreted in the context of the wider scale distribution of genetic and phenotypic variation in N. lapillus . It is suggested that the shore studied may represent one of a number of regions of secondary contact within a mosaic hybrid zone in N. lapillus , where coadapted phenotypic variation correlates with habitat and the position of the clines represents an environmental transition.

Several species of the subclass Prosobranchia are considered to be suitable organisms for monitoring long-term effects of triorganotin (TOT) compounds. This study utilized Buccinum undatum and Neptunea antiqua from the North Sea and the Irish Sea. Morphological alterations in the genital system (imposex phenomena), the histological structure of the gut, and the gonads were studied. TOT concentrations in soft body tissue and shells were determined. Females of both species displayed imposex phenomena (pseudohermaphroditism). The percentage of altered females per station ranged from 0 to 90% in B. undatum and from 0 to 29% in N. antiqua. Imposex index values in B. undatum reached 1.09 near Helgoland and 0.86 in N. antiqua sampled at 25 nautical miles from the Scottish northeast coast. Organotin compounds were detected in the soft bodies of snails from all stations. A chi-square analysis revealed a significant correlation between imposex stages and TOT concentrations in B. undatum but not in N. antiqua. Tributyltin (TBT) in B. undatum ranged from 1.0 to 15.9 ng g-1 wet weight (Irish east coast). TBT concentrations in N. antiqua were higher and ranged from 2.2 to 25.7 ng g-1. In both species, organotin compounds in the shells were below detection limits. Despite high TBT concentrations in soft tissues and the occurrence of imposex (offshore and inshore), female gonads were in good shape and no signs of limited reproductive capacity were found. Histological findings indicate that TBT does not contribute considerably to mortality in the common whelk.

The external morphology of the adults of both sexes and of the late male copepodid of Nucellicola holmanae, new genus, new species, parasitic in a gastropod mollusc, Nucella lapillus, is described. A new family within the order Poecilostomatoida is erected to accommodate this monotypic genus. The adult parasite is found within the viscera of the host and is presently recorded only on the North Sea coast of England.

The dog-whelk Nucella lapillus exhibits a number of phenotypic variations and genetic polymorphisms which correlate with habitat-specific environmental pressures, especially those associated with wave action and temperature. This study investigates the relationship between genetic composition (karyotypic and electrophoretic variation) and phenotypic differentiation in N. lapillus sampled at 15 points along an 8 km stretch of coastline. Coincident clinal variation in gene frequencies and shell shape is described; they covary with differences in karyotype and also with growth. Laboratory-reared young show that differences in phenotype (shell shape and growth) are inherited. Experimental evidence is presented that specific shell shapes are adaptive under conditions of thermal stress. Together with the well-established correlations between shell shape and shore exposure, this association provides an argument for a relationship between genetic composition, phenotype and habitat in this species.

Genetic constitution in the intertidal gastropod Nucella lapillus influences variation in shell shape and growth rate which in turn are correlated with such habitat variables as wave action and temperature. We have investigated the response to hyperosmotic stress of samples from a cline in karyotype and allozyme frequencies and shell shape. Animals with a shell shape associated with environments where temperature and desiccation stress are important respond less to hyperosmotic stress than animals living in a high wave energy environment. With regard to the interaction between shell shape, physiology and habitat, animals with elongate shells associated with protected shores are shown to exhibit a reduced response to hyperosmotic stress compared to animals with a more spherical shell shape; this is discussed in relation to the production of an adaptive phenotype.

International audience; In Europe, the extraction of dyes from marine shells found in archaeological contexts is little known outside the Mediterranean area. Although smaller than the Mediterranean species with dyeing properties, the dog whelk Nucella lapillus and the oyster drill Ocenebra erinaceus canbe indicative of dyeing activities. Theyare regularly found broken in archaeological contexts in France and Ireland, where their presence can indicate an important economic activity of the coastal inhabitants. In this article, I summarize the archaeological data for this activity along the Channel and Atlantic coasts of France, including localization of these deposits and their chronology, composition of the shell middens, typology of fragments of shell, and presence of other activities. The application of biometrics to dog whelks from one site, ZA du Pladreau, yields information on the way in which the shells were selected first on the seashore, and second at the place of pigment extraction.

Nucella lapillus (dog whelk) imposex levels were assessed along the mainland Portuguese coast in 2006 and 2008 and were compared with available data from 2003 for the same area. Given that specimen size has been described as a factor inducing variation in some of the imposex assessment indices, and thus resulting in less reliable results, new monitoring and data analysis procedures are described and applied to study change of imposex levels from 2003 to 2008. A significant decline in imposex intensity was observed in the study area during the study period, and the Portuguese coast ecological status (under the terms defined by the OSPAR Commission) notably improved after 2003, confirming the effectiveness of the Regulation (EC) No. 782/2003 in reducing TBT pollution. Nevertheless, N. lapillus populations are still extensively affected by imposex, and fresh TBT inputs were detected in seawater throughout the coast in 2006. These recent inputs are attributed to vessels still carrying TBT antifoulants applied before 2003, as their presence in vessels was only forbidden in 2008. Considering that Regulation (EC) No. 782/2003 is an anticipation of the IMO global ban entered into force in September 2008, a worldwide-scale decrease in TBT pollution can be expected in the near future.

A study of tributyltin (TBT) uptake, tissue distribution and breakdown in dog-whelks, Nucella lapillus, was carried out using 14C-labelled tributyltin chloride. The compound was introduced into animals by exposure to sea-water, from a diet of labelled mussels and by injection. Measurements of 14C were made on tissue extracts containing total 14C, TBT+DBT and TBT. Organs examined included digestive gland, kidney, mantle, foot, viscera, gonads and blood. Absorption of dissolved TBT occurred primarily via tissues associated with the mantle: autoradiographic evidence showed that of these the ctenidium (gill) and osphradium were probably most important. Of non-reproductive tissues, mantle displayed least evidence of TBT degradation whereas kidney and digestive gland contained lower proportions of 14C as TBT (~60%) than other tissues. By virtue of its more rapid response, initially at least, the kidney had a primary role in degrading dissolved TBT that reached the blood. Dog-whelks feeding on labelled Mytilus edulis absorbed organotins very efficiently via the digestive gland, which then played a major role in TBT breakdown. However, the capacity for degradation is not sufficient to prevent, TBT concentration factors of the order of 100,000 (dry tissue/water) being attained in N. lapillus. Autoradiography revealed surprisingly high grain-counts in nerves, which may be significant in view of evidence in the literature that neurohormones are intermediaries in the chain linking TBT with imposex.

Tributyltin (TBT) pollution has exterminated populations of the dog-whelk Nucella lapillus along most of the north Kent coast (Thames Estuary) but the species survives as a small enclave around the North Foreland. Males in this enclave exhibit an unusual defect involving the non-development or partial development of the genital system: about 10% lack penes, or have undersized penes, and their gonoducts (vas deferens and prostate) are incompletely developed; in some cases, spermatogenesis appears to be retarded. Laboratory-bred animals display the same characters. This deficiency (‘Dumpton Syndrome’) is manifest also in the atypical development of male sex organs on the females (‘imposex’) induced by exposure to tributyltin (TBT). The evidence points to Dumpton Syndrome being a genetic disorder which has lessened the sterilizing effect of imposex and thereby has permitted the survival of this isolated enclave in an area of high TBT pollution.

A massive toxic bloom ofChrysochromulina polylepisoccurred along the Swedish west coast in May and June 1988 with severe effects on most biota in shallow marine habitats. In the present study, the effects on the common dog-whelk,Nucella lapilluswas investigated in the archipelago at the mouth of the Gullmar Fjord.Mortality varied throughout the archipelago, with extinction of populations in the inner parts and survivors found only on the outermost islands. Even on these sites, mortality could be as high as 98­99%. Extensive samples of survivors and dead animals were divided into five age groups dependent on size and wear of the shell. The cohort consisting of 3­4 year old individuals suffered the lowest mortality, while mortality was almost total in younger and older cohorts. In each age group, except the oldest, survivors were significantly larger than the dead.The number of egg capsules laid per female in 1988 seemed normal, but about half of the capsules were empty. The number of young per capsule was significantly lower in 1988 compared to 1989, but the young were significantly bigger.

There is evidence of recovery from symptoms of imposex in populations of dogwhelks Nucella lapillus (L.) from study sites on the Isle of Cumbrae (Scotland) and, in particular, on shores adjacent to the town of Millport. RPSI scores and the numbers of ‘penisbearing’ females have decreased, and the numbers of dogwhelks on the shore have increased, between 1988 and 1993. Dogwhelks were not found at all at one site at Millport in 1988 but were abundant there by 1992–1993.

The toxicity of cadmium, zinc and cadmium/zinc mixtures at concentrations ranging from 1000 to 50000μg/l were investigated against cercariae and metacercariae of Parorchis acanthus obtained from the dog whelk Nucella lapillus. Cercarial encystment at concentrations of 25000μg/l or higher was significantly impaired by all test metals; however, at lower concentrations only zinc demonstrated toxicity. Mixtures of cadmium and zinc had a synergistic effect compared with single metal toxicity but only at 50000μg/l. Excystment in vitro was only significantly affected by cercariae exposed to cadmium/zinc mixtures whilst encysting. Twenty-four h exposures of fully formed cysts had no effect on excystment in vitro. Effects on in vitro excystment rates over a 2h period demonstrated widespread effects for cercariae-exposed P. acanthus. No effects were evident on excystment rates of cyst-exposed parasites.

cited By 49; International audience; Sediment and water samples have been collected between 1992 and 1995 for evaluating butyltin contamination in two marinas from the coastal area in The Netherlands, two years after the ban of TBT. Sediments extracts were analysed by capillary gas chromatography-inductively coupled plasma-mass spectrometry. Sediment concentrations for TBT showed no trend of decrease between 1992 and 1995 and were extremely high in the marina secluded from tidal action; 17.5 ± 8.0 μg g-1 and much lower for the marina with tidal action; 0.117 ± 0.073 μg g-1. High ratios between TBT and DBT in the sediments indicate that degradation mechanisms in the sediments are of minor importance. Dissolved butyltin compounds were analysed in water by means of gas chromatography-atomic absorption spectrometry. Water concentrations of TBT showed no clear trend of decrease between 1992 and 1995 and were high in the marina secluded from tidal action; 139 ± 166 ng litre-1 but much lower for the marina with tidal action; 48 ± 98 ng litre-1. An active degradation mechanism during summer periods was indicated by low (< 1) TBT/DBT ratios in the water phase of the marina secluded from tidal action.

Nucella lapillus (L.) is a marine gastropod mollusc widely used as a bioindicator of TBT pollution in the North Atlantic coastlines. The species reproductive cycle and the male penis length seasonal/spatial variation were studied at a single site at Aveiro seashore (NW Portugal) between December 2005 and June 2007. The main objective of this work is to assess if the "Relative Penis Size Index" (RPSI)--an important imposex assessment index--varies seasonally and spatially in the same sampling site and how this can affect results obtained in imposex monitoring programmes. Animals able to reproduce were found every month but a seasonal pattern in N. lapillus reproductive cycle was evident. Female gametogenic maturation varied seasonally and a decrease in capsule gland volume and condition factor occurred in late summer/early autumn. The gametogenesis in males did not show a significant seasonal variation as in females but the condition factor, penis length, amount of sperm and prostate volume also diminished in late summer/early autumn. On the other hand, males that were close to egg capsules clusters had larger penises than those far away from clusters. The temporal and spatial male penis length variation introduces a bias on imposex assessment results when using RPSI and the magnitude of the error involved is evaluated for different TBT pollution levels scenarios. We consider that RPSI provides interesting and complementary information that should not be excluded from monitoring programmes, but temporal or spatial comparisons of imposex should be based on other more reliable imposex indices like the VDSI. published

Caging studies have been previously reported to be useful for providing valuable information on biological effects of mollusks over short periods of time where resident species are absent. The degree of imposex in caged dog whelk (Nucella lapillus), was measured using the vas deferens sequence index (VSDI) and the Relative Penis Size Index (RPSI) and the extent of shell thickening in caged Pacific oyster (Crassostrea gigas) was investigated at t = 0 and t = 18 weeks. Nucella lapillus, when provided with mussels as a food source at the control site at Omey Island on the west Irish coast, did not demonstrate imposex features, whereas those transplanted to port areas did. Dunmore East exhibited the highest level of imposex (3.25 VDSI and 2.37 RPSI). Shell thickening was evident in C. gigas transplanted to Dunmore East, with low effects evident at the control location, Omey Island, and Dublin Bay at t = 18 weeks. Dry weight whole-body concentrations of organotins were most elevated in all species held at Dunmore East compared with other locations. Greatest delta15N and delta13C enrichment was observed within the tissues of the predatory N. lapillus in all three test sites. Increased assimilation in the Dublin Bay oysters might have been influenced by the presence of more nutrients at this location. Surficial sediment organotin levels were most elevated in the Dunmore East

Metacercariae of the microphallid trematode Maritrema arenaria are found in the shore barnacle Semibalanoides balanoides which is heavily predated by the dog whelk, Nucella lapillus. This study demonstrated that, under experimental and natural conditions, M. arenaria metacercarial cysts were ingested by N. lapillus and the metacercariae retained their viability while passing through the molluscs' digestive systems. Dog whelks are a known food source for numerous bird species, leading to the conclusion that they may act as paratenic hosts of M. arenaria. The strategic importance of the adoption by M. arenaria of N. lapillus as a paratenic host is discussed.

Populations of the common dog-whelk Nucella lapillus (L.) are declining or have already disappeared at many sites on rocky shores around the United Kingdom (Bryan et al. 1986). There is conclusive evidence that this is caused mainly by tributyltin (TBT) compounds leached from ships' antifouling paints (Bryan et al. 1987). These compounds impose male sexual characters (or imposex) on female N. lapillus. Other stenoglossan gastropods including Nassarius obsoletus Say (Smith, 1981a) and Ocenebra erinacea (L.) (Féral & Gall, 1982) are similarly affected by TBT. The intensity of expression of imposex in N. lapillus can generally be related to the sea water concentration of TBT. The appearance of a small penis and the partial development of a vas deferens first occurs at TBT concentrations below 0.5 ng/1 (as tin), although reproduction appears to be unaffected at this level. At 1–2 ng Sn/1 penis size is markedly increased and in some females proliferation of vas deferens tissue overgrows the genital papilla, thus sterilizing the animal. At slightly higher concentrations virtually all females become sterilized and at around 10 ng Sn/1 oogenesis is suppressed and spermatogenesis initiated (Gibbs, Pascoe & Burt, 1988). Since development is direct and there is no planktonic stage, N. lapillus has a very limited capacity for dispersion: thus the sterilization of females heralds the almost certain decline of so affected populations (Gibbs & Bryan, 1986).

European populations of the common dog-whelk, Nucella lapillus (L.), usually show a neat and precise pattern of shell shape variation with the exposure of their habitat to wave action. Whilst this is the case along much of the west coast of Scotland, there are a number of instances where unusually elongated shells occur, somewhat reminiscent of the form described for the Severn Estuary. There are no obvious environmental or geographical correlates to explain the occurrence of these forms and a genetical interpretation is sought.

Populations of the common dog-whelk, Nucella lapillus (L.), usually show a gradation in mean shell shape related to the exposure of the shore on which they live. Enclaves from exposed headlands have shorter, squatter shells than do their compatriots in shelter. This paper describes the pattern of shell-shape variation shown by populations in the Isles of Scilly and on the north coast of Wales. In both places a gradation is present, but it is not numerically similar, the Welsh population being more elongated. It is concluded that the selective agents are the same in both places. Wave action always eliminates the most elongate-shelled whelks first, and crabs always find it easier to take the animals with the widest apertures to their shells. The reason for the observed differences between the patterns described here lies in the genetic differences between the populations: Scillonian whelks do not have the option of being as elongated as the Welsh ones, which, in turn, cannot show very short squat shells in exposure.

The term ‘imposex’ was coined by Smith (1971) to describe the superimposition of male characters onto unparasitized and parasitized females of gonochoristic gastropods. In Nassarius obsoletus (Say) the development of imposex results in the female having one or more of the following characters: (1) a penis with a duct leading to (2) a vas deferens which passes back to the ventral channel of the capsule gland and (3) convolution of the normally straight gonadial oviduct (Smith, 1980). Imposex in the similarly gonochoristic Nucella lapillus (L.) was first noted by Blaber (1970) who found females with penis-like outgrowths in Plymouth Sound populations. Subsequent studies (Bryan et al. 1986; Gibbs & Bryan, 1986) have demonstrated that the incidence and intensity of imposex have since increased markedly in the same populations and that the phenomenon is widespread around south-west England.

Four populations of the predatory gastropodNucella lapillus were sampled at sites around the South West Peninsula of England in 1986, and analysed for allozyme variation at 18 enzyme loci. Two of these loci, αGpd-1 andHk-1, exhibited sex-specific phenotypes. An absolute locus association was observed between two other loci,Mdh-1 andEst-3. This association was only found at one site (Prawle), and it is suggested that the presence of chromosomal polymorphisms could explain this finding. As a measure of overall similarity, Nei's genetic identity statistic,I, was calculated; the mean for all populations was 0.989, with values ranging from 0.981 to 0.997. Although similar on this gross level, considerable interpopulation variation was evident. Observed mean heterozygosity (per locus) ranged from 0.043 to 0.104 (mean 0.074). Populations differed also in the loci at which significant heterozygote deficits were seen (of the seven deficits recorded only those at thePep-1 locus were consistent across sites) and in the presence of rare alleles undetected elsewhere. The variation observed showed no correlation to shell morphology or geographical distance and confirmed the conclusion that species of the genusNucella show considerable disjunct variation.

La population de N. lapillus a beaucoup decline sur les cotes britanniques au cours des vingt dernieres annees,a la suite de l'utilisation d'une peinture antifoulage,le TBT, pour la coque des bateaux de plaisance.Des individus survivants,resistants au TBT sont encore signales.On etudie une possible correlation entre la resistance au TBT et une morphologie particuliere de la coquille

Shell shape and colour variation is common in littoral molluscs. As far as shape is concerned, exposure to wave action acts as a strong agent of natural selection, but only speculation seems to have been directed towards elucidating the determinants of colour variation. In the dog-whelk (Nucella lapillus (L.)) diet may play some part in producing the pigment for colour. However white and banded forms are often found in otherwise coloured colonies. This study describes the classification for colour and banding of 83,524 whelks from 444 areas around the British Isles and west Atlantic coast. Colour and banding were significantly correlated r=0.45±0.05). Because of the possible involvement of diet in shell colour, attention has been confined to banded forms. No obvious pattern in distribution could be discerned. Possible factors affecting the occurrence and incidence of banding are: climate; geology; exposure to wave action; predation; intra- or interspecific competition; cryptic genetical factors; or intraspecific recognition. The only one which was definitely associated with banding frequency was exposure (r= 0.33±0.05), but there were so many exceptions to the correlation (e.g. highly exposed populations which were entirely unhanded), that this is unlikely to be causal. The most probable explanation seems to be the local spread of mutant forms (probably linked to fitness traits), which have not attained equilibrium frequencies–even though N. lapillus has apparently occurred in large colonies round much of the British coast since the end of the Pleistocene.

Predation of the barnacles Balanus balanoides and Elminius modestus by the common dog-whelk, Nucella lapillus was studied in the laboratory. Greater numbers of B. balanoides were taken as prey unless the whelks had been previously subjected to an extensive period of starvation.Selective predation is discussed in the light of similar studies on Nucella and related predatory species. The effects of prey selection on the competitive interactions of the prey species are also considered.The method of predatory attack involves either a drilling or a prizing technique. The latter is used predominantly when Nucella attacks E. modestus, whereas drilling is employed to a far greater extent when attacking B. balanoides. Attacks using the drilling technique are usually made at the occludent margins of the opercular valves.

The shell of the Common dog-whelk (Nucella lapillus (L.)) is white and unbanded at most places around the British Isles. However, high frequencies of banding occur on the Buchan coast, around Anglesey and the Menai Straits, on the Cower Peninsula, around the Devon–Somerset border in the Bristol Channel, and especially on the north Cornish coast (reaching a peak between Newquay and Padstow). The frequency of banding is significantly less in older than younger whelks in the same locality, and this change is uncorrelated with the selection against shell shape variation that takes place on exposed shores. It is concluded that banding is a pleiotropic manifestation of physiological variation, and that a study of such variation in different morphs could indicate the importance of different physiological stresses at different stages of the life history of N. lapillus.

In Nucella lapillus there is usually a progressive gradation in mean shell shape from short squat individuals on exposed headlands to more elongated ones in shelter. This pattern has been attributed to the differential selective effects of wave action and crab predation, although it would almost certainly be an oversimplification to imagine these as the only significant forces involved, especially near the limits of the species' distribution. However, whilst this pattern of shell-shape variation with exposure is generally true over most of the animal's range in both Europe and North America, there are exceptions. There are occasional enclaves with much more elongated shells than would normally have been expected. Sometimes these are so abundant, as in the Severn Estuary, that all dog-whelk enclaves are unusually elongated, regardless of the exposure of their habitat. In other areas, such as south-eastern England, the Solway Firth and the area around the mouth of the Conway the shells are not unusually elongated, but the enclaves show very little variation: a normal sheltered-shore form is seen wherever the species occurs. Shetland samples appear to be a combination of this pattern (predominating) with the ‘normal’ one showing the full range of shellshape variation. Nucella appears in the Atlantic fossil record at the end of the Pliocene without any antecedent forms. It is assumed to have colonized from the Pacific and exploited the vacant niche before the onset of the Ice Age. Successive advances and retreats of the ice, with attendant changes in sea level, will have served to break up and recombine those dog-whelk populations that were not eliminated. It is postulated that the modern Nucella lapillus is a combination of several genetically distinct populations, some of which show the full range of variation and may respond to the selective effects of crabs and waves, and some of which do not and show little variation.

In most parts of southwestern Europe the shape of dog-whelk shells varies in a predictable manner with the exposure of the shore on which the animals are living. As the same relationship also applies on shores near Mongstad in Norway, it was thought that it might be true in Sullom Voe (Shetland) which is at about the same latitude. In fact the relationship only holds for some west coast samples. Exposed shores are indeed colonised by the short squat form expected of such places but the more elongated form, usually associated with very sheltered shores, is also found on all but the really exposed sites: there is accordingly very little difference in the shape of dog-whelk shells on Shetland shores. The species is consequently of little or no use in the assessment of exposure.

Plants and animals were investigated to ascertain theirγ- radioactivity values on both dune sites (machair) and inter-tidal sites on the western coast of Barra, Outer Hebrides, UK. Material in both habitats was clearly contaminated. The accumulation ofγ-radioactivity through food webs to organisms such asNucella lapillus (dog whelk) in the inter-tidal sites and in sheep and cattle in terrestrial sites is described.

The development of male characters, notably a penis and a vas deferens, on the female (the phenomenon of ‘imposex’) of the dog-whelk, Nucella lapillus, is described. Three stages are recognized: an ‘early’ stage involving the formation of a vas deferens and a small penis, an ‘intermediate’ stage characterized by the enlargement of the female penis to a size approaching that of the male and a ‘late’ stage during which the female opening (vulva) is occluded by overgrowth of vas deferens tissue. This blockage of the pallial oviduct prevents the release of egg capsules and renders the female sterile. The extent and cause of such reproductive failure is evident from the high incidence of females containing aborted capsules in declining populations close to sources of tributyltin (TBT) contamination. These same populations comprise fewer females than expected and it would appear that the accumulation of aborted capsules within the pallial oviduct eventually causes the premature death of the female.

ABSTRACI The mucous trails secreted by certain species of intertidal limpets serve as adhe sive traps for the microalgae that are their primary food resources. The mucous trails of two solitary homing limpets, Lottia gigantea and Coiisella scabra, also stimulate the growth of microalgae. In contrast, the mucous trails of an aggregating limpet, Coiisella digitalis, and the carnivorous dog whelk, Nucella emarginata, do not stim ulate microalgal growth. These results may be explained by differences in the behav ior of these gastropod species. Homing species can capitalize on the production of a food enhancing mucus because they have restricted home ranges and retrace their own mucous trails. The persistence time of mucus in the field varied with gastropod species, mucus type (i.e., mucus produced by moving or stationary limpets), and tidal height. Field studies suggest mucous trails can, but may not always, persist long enough to allow algal enhancement. Biochemical analyses suggest that the ability of mucous trails to trap microalgae adhesively is correlated with carbohydrate content. The ability of mucous trails to stimulate microalgal growth is correlated with higher total organic content of mucous secretions and an ability to stimulate bacterial growth. A bacterial film may be impor tant in the stimulation effect.

Nucella lapillus is a common and widely distributed carnivorous gastropod of North Atlantic rocky sea shores. Populations of this animal usually show variation in shell shape according to the exposure of their habitat to wave action, with individuals from exposed sites having a short squat shell and a wide aperture as compared with a more elongated form seen in shelter. The same pattern of variation is seen over most of the species European range, but there are some exceptions. One of these has been described in Sullom Voe (Shetland) and this prompted an investigation of Faroese populations to ascertain whether they behaved in a similar manner. It is shown in this paper that Faroese populations vary in shell shape with exposure in the usual way (and not like those in Shetland) and moreover show such a fine and precise reflection of minor alterations in environmental conditions that measurement of dog-whelk shells may prove to be the best way of ‘measuring’ exposure in Faroe.

A survey of the gastropod Nucella lapillus around the south-west peninsula of England has revealed that the incidence of ‘imposex’, the induction of male sex characters in the female, is widespread, that all populations are affected to some degree and that the phenomenon is most prevalent along the south (Channel) coast. Populations close to centres of boating and shipping activity show the highest degrees of imposex, especially those within the vicinities of the Helford, Fal, Salcombe and Dart estuaries and in Plymouth Sound and Tor Bay. Within Plymouth Sound the degree of imposex increased markedly between 1969 and 1985, coinciding with the introduction and increasing usage of antifouling paints containing tributyltin (TBT) compounds.

Past attempts to age classify dog-whelks are revised briefly. The most satisfactory method is a system which relies upon familarity of morphological characteristics with which to separate population samples into five different classes. An attempt has been made to quantitate this system. Definite standards have been suggested as the criteria with which to separate the five age classes, and a series of simple methods have been demonstrated which, when followed give finite values for each of these standards. The standards suggested are: (i) the lower limits for shell-length in mature individuals; (ii) the lip-thickness coinciding with maturity; (iii) the upper limits for shell-length in juvenile crevice dwellers. The methods of estimate for values for these standards are illustrated in practice with population samples from Blackrock, Sussex. The values thus obtained and the methods used in each estimation are discussed with view to their validity. It is reasonable to suspect that the quantitative age classification system can be used to classify dog-whelks from any shore provided large enough population samples are collected to estimate the values for each standard. Use of the system is further demonstrated by classification of animals from the shore at Martin's Haven, Pembrokeshire.

By examination of samples of Purpura lapillus from the whole of their European range, it appears that the species can exhibit quite as wide variation within a relatively small region such as that studied in the Dorset-Devon-Cornwall area, as it can over its whole geographic range. Population samples were taken from seventy-six localities, mostly in the south-west of England, and covering a wide range of environmental conditions, and the variations in these shells were studied in relation to two primary environmental factors, degree of exposure to wave-action and diet.

The amount of stabilizing selection undergone by a population of animals at different times of its life can be estimated by comparing the variances of different age samples. This paper describes an investigation into the intensities of selection experienced by populations of the common dog-whelk, Nucella lapillus (L.) exposed on different shores to different degrees of wave action. It was found that the variance of more exposed populations was reduced during life by up to 90%. There was a positive correlation between the intensity of stabilizing selection and the amount of wave action experienced by the whelks. Most of this selection took place during the first year or two of the life of the animals.