Xavier de Montaudouin

Does the slipper limpet (Crepidula fornicata, L.) impair oyster growth and zoobenthos biodiversity? A revisited hypothesis

The Prosobranch Gastropod Crepidula fornicata was introduced into Great Britain at the end of the 19th century from North America, upon imported oysters Crassostrea virginica. Since then, it has invaded sheltered coasts of the North West Atlantic and Mediterranean Sea. C. fornicata proliferation has often generated social conflicts due to three main causes: (1) trophic competition with other suspension feeders, e.g. the cultivated oyster Crassostrea gigas; (2) spatial competition with macrozoobenthos; and (3) enhancement of silt and clay sedimentation. The effects of C. fornicata on C. gigas growth and on macrozoobenthic density and diversity have been documented through field experiments in an oyster park of Arcachon Bay (France). Densities of C. gigas and biomass of C. fornicata were manipulated over a period of 247 days within field enclosures at low water level to test: (1) oyster growth, condition index and mortality; (2) zoobenthic community alterations (abundance, biomass, species richness). From this small-scale experiment, it was shown that none of these investigated parameters was significantly affected by the presence of C. fornicata. However, faunal assemblages were modified in enclosures compared to external bare sands, due to adding a hard substrata over a soft sediment.

Trematode communities in cockles (Cerastoderma edule) of the Ria de Aveiro (Portugal): Influence of inorganic contamination

This work aims to assess the trematode parasites infecting the edible cockle Cerastoderma edule, collected in the Ria de Aveiro lagoon, one of the most relevant biodiversity hotspots of the Western Iberia, and evaluate the relationship between the observed patterns and environmental descriptors. A total of 11 of the 16 trematode species known to infect C. edule were identified, including Himasthla continua and Psilostomum brevicolle as new occurrences in this lagoon. Parvatrema minutum was the most abundant and dominant species. Species richness and prevalence were high. The relationship between trematode species abundance, intensity and prevalence, and also environmental variables, showed that most parasites preferred muddy sand areas with euhaline conditions in opposition to areas with contamination and/or distant from the lagoon entrance. This study highlighted the good ecological status of the ecosystem and the transitional biogeographic characteristics of the western Portuguese coast where northern and subtropical faunas can coexist.

Interactive effects of metal contamination and pathogenic organisms on the marine bivalve Cerastoderma edule.

The present study evaluated the interactive effects of cadmium contamination and pathogenic organisms (trematodes Himasthla elongata and bacteria Vibrio tapetis) singularly and in combination during 7 days on the bivalve Cerastoderma edule. Some defense-related activities were analyzed such as genetic expression, metallothionein and immune responses. Trematode metacercarial infection, similar whatever the treatment, induced the strongest responses of immune parameters. Particularly, the interaction between cadmium and parasite exposures induced unusual responses on gene expression and immune responses. No effect of bacterial challenge appeared on bivalve responses, nevertheless a strong mortality of V. tapetis infected cockles occurred between 7 and 14 days. Cadmium bioaccumulation was significantly modulated by both pathogenic organisms. Furthermore, an antagonistic effect of trematodes and bacteria was shown on metal bioaccumulation of co-infected cockles. These results highlighted the importance of considering the multiplicity of perturbation sources in coastal ecosystems to assess the health status of organisms.

Effect of intermediate host size (Cerastoderma edule) on infectivity of cercariae of three Himasthla species (Echinostomatidae, Trematoda)

To understand prevalence patterns of parasites in marine host populations experimental infection studies are required. Bivalves are important host organisms to a variety of trematodes species and in our study area (Wadden Sea) three different Himasthla species co-occur in cockle populations. These species are morphologically very similar but differ with respect to various morphometric dimensions. To study the possible functional importance of differences between Himasthla cercariae (the free-living stage shed from prosobranch snails and encysting as metacercariae in bivalves), we experimentally measured the infectivity of the three congeners in regard to different size groups of juvenile cockles. The smallest species, H. interrupta, has a high infectivity in small cockles (optimum around 4 mm), whereas the two other congeners H. continua and H. elongata exhibit low infection efficiencies in cockles less than 6 mm and higher efficiencies in larger cockles. Behavioural experiments were performed to identify proximate causes underlying the observed infection patterns. Parasite avoidance behaviour of the cockle varies in a host–parasite size-dependent manner so that a large cercaria tend to provoke an avoidance response in a small cockle. The possible consequences of the observed host size preferences in relation to definitive host species (waterbirds) are discussed and it is suggested that one or more of the parasite species are adapted to other host species and that their sympatric occurrence in cockles in our study area is a result of a spinoff from their main cycle mediated through migratory birds.

Effect of macrofaunal bioturbation on bacterial distribution in marine sandy sediments, with special reference to sulphur-oxidising bacteria

Abstract We have studied the impact of the bioturbating macrofauna, in particular the lugworm Arenicola marina and the bivalve Cerastoderma edule , on abundances and distribution patterns of total bacteria and of bacteria of selected functional groups in sandy intertidal sediments. The selected groups comprised the colourless sulphur-oxidising bacteria and the anoxygenic phototrophic bacteria, which are expected to occupy small zones at the oxygen–sulphide interface in stable (non-bioturbated) sediments. The presence of a wooden wreck buried in the sediment at 10 cm depth within a large area of intertidal sand flat colonised by lugworms provided a unique opportunity to confront field observations with laboratory simulations. The site with the wooden wreck, which was used as control site, was devoid of both A. marina and C. edule , while the composition of the rest of the zoobenthic community was rather similar to that of the surrounding area. In the field, the density of total bacteria was approximately one order of magnitude higher in the control site than in the natural (bioturbated) site. This can be explained by the higher contents of silt and clay particles (higher surface-area/volume ratio) and higher total organic-carbon contents found at the control site. It appears that the presence of macrofauna affects sedimentation processes, which indirectly influence bacterial dynamics. Samples from the control site have been incubated in the laboratory with A. marina and C. edule added (bioturbated core), while an unamended core served as a control. The laboratory experiments contrasted with the field observations, because it was found that total bacteria were actually higher in the deeper layers of the bioturbated core. Moreover, the populations were more homogeneous (less stratified) and colourless sulphur bacteria were on average less numerous in the bioturbated core. In general, laboratory incubations resulted in a decrease of total bacteria with a concomitant increase of colourless and phototrophic sulphur-oxidising bacteria and thus in modifications of the bacterial community structure. Hence, our results demonstrate that care must be taken in extrapolating results from laboratory experiments (e.g. mesocosm research) to field situations.

Digenean trematode species in the cockle Cerastoderma edule: identification key and distribution along the north-eastern Atlantic shoreline.

We describe the digenean fauna of one of the dominant intertidal hosts, the common cockle Cerastoderma edule , in terms of biomass, off north-eastern Atlantic shores. Using published and unpublished literature we have prepared an identification key and provide an up-date of the large-scale distributional patterns of digenean species of the common cockle. At least sixteen digenean species, belonging to seven families, use cockles as intermediate host. Among these species two utilize cockles as first intermediate host only, whereas two species utilize cockles as both first and second intermediate host. The remaining eleven species have cockles as their second intermediate host. Water birds and fish are the definitive hosts to twelve and four species, respectively. Cockles are infected with digeneans along the latitudinal gradient from southern Morocco to the western region of the Barents Sea often with high infection levels. Whereas some of these digenean species occur along most of the latitudinal gradient others show a more restricted northern or southern distribution mostly caused by an underlying latitudinal gradient of host species. Knowledge of digenean species and their large-scale distribution pattern may serve as a baseline for future studies dealing with the effects of climate change on parasite–host systems. For such studies the cockle and its digenean community could be an ideal model system.

Factors involved in growth plasticity of cockles Cerastoderma edule (L.), identified by field survey and transplant experiments

Abstract In Arcachon Bay, a macrotidal coastal lagoon in southwest France, growth rates of cockles Cerastoderma edule (L.) differ greatly between locations. Sampling of populations at different tidal levels showed that the mean shell length was significantly and positively correlated with immersion time, whereas no correlation was found with population density and microphytobenthos biomass. Transplants of cockles between two intertidal sites were used to examine the relative importance of habitat and site of origin for growth rate and condition index. Artifacts due to manipulation were assessed, i.e. the impact of enclosures on growth, conditon index and mortality. During a 5-mo reciprocal transplant experiment, growth rates of the transplanted cockles and the cockles already present were similar, whereas the sites of origin did not affect growth rate. Condition index, however, displayed significant differences in relation to both transplant and origin sites. During a further 6-mo experiment in which cockles were transplanted from one site to four new sites, growth was mainly influenced by tidal level. These results indicate that net growth started when cockles were immersed 30% of the time. It is concluded that, on the scale of Arcachon Bay (156 km2), differences in growth and condition between cockle populations are largely phenotypic. Tidal level (i.e. food supply and emersion stress) accounts for most of these differences, but the existence of genetically or physiologically different populations cannot be excluded.

Crepidula fornicata L. (mollusque, gastéropode) en baie de Marennes-Oléron : cartographie des fonds par sonar à balayage latéral et estimation du stock

Abstract Extensive and detailed subtidal ground mapping of the Marennes-Oleron Bay and Fouras-Aix areas was performed with a side-scan sonar. Side-scan sonographs gave a comprehensive view of sedimentological bottom environments and also allowed us to outline locations of grounds colonised by the gastropod mollusc Crepidula fornicata L. with a precise estimate of their surface. A sedimentological map of the centre of the Marennes-Oleron Bay is given, describing spatial organisation of the following four types of sediment: pure mud, fine sand, coarse sand and rocks. Crepidula beds were also recognised on sonographs and were estimated to cover 181 hectares in the Fouras-Aix area and 615 hectares within the Marennes-Oleron Bay. Standard sampling methods were then combined with the side-scan sonar mapping results, allowing an estimate to be made of the stocks of Crepidula fornicata (live specimens and dead shells). A stratified sampling procedure was performed in April–May 1995, including 80 stations sampled with a Smith McIntyre grab (two grabs per station). The live stock of Crepidula was estimated to be 2 494 ± 3 344 tons at Fouras-Aix and 2 644 ± 1 137 tons within the bay of Marennes-Oleron. This latter estimate is similar to the previous one performed in this bay in spring 1984, i.e. 1 800 ± 900 tons, due to the overlap of 95 % confidence intervals. These comparable estimates within the Marennes-Oleron Bay give no evidence to suggest that dredging operations (1 000–1 500 tons-yr −1 ) performed in the bay for 15 years are not efficient. However, annual landing operations of slipper limpet cannot prevent further spread of the species, as pointed out by the large development of a new Crepidula ground in the north-western centre of the bay (north Lamouroux sand bank). Both natural processes (current action and bed load transport) and bottom-trawl activities can facilitate spread of the species in the bay, as revealed by side-scan sonar image analysis.

Prevalence, intensity, and aneuploidy patterns of disseminated neoplasia in cockles (Cerastoderma edule) from Arcachon Bay: Seasonal variation and position in sediment

The present report presents the first evidence of disseminated neoplasia (DN) in cockles Cerastoderma edule from Arcachon Bay (France). Aneuploidy of neoplastic cells allowed the use of flow cytometry (FCM) to diagnose and stage DN. A 1year survey (2007) of the prevalence and intensity (% of aneuploid circulating cells in neoplastic cockles) was conducted. Prevalences ranged from 2.2% (June) to 13.6% (May), and disease intensity ranged from 18.7% (June) to 95.5% (September). These percentages were not correlated with seawater temperature, but rather showed unexplained oscillations over the year. Prevalence and intensity of DN were higher in cockles found at the surface of sediment compared to those buried normally (11.8% vs. 6.7% and 53.0% vs. 40.6%, respectively, p<0.05). DN could thus be one mechanism leading to unexplained presence of cockles at the surface of the sediment in Arcachon Bay. Ploidy characteristics of neoplastic cells were also investigated using FCM, revealing an unusual, broad continuum of ploidy distribution from 1.6 to 9.6n. Ploidy values were not in whole numbers in contrast to the rounded values reported in other studies. Ploidy varied according to DN intensity, with the ploidy distribution of neoplastic cells from lightly-diseased cockles being unimodal (3.7n median). In contrast, highly-diseased cockles showed a bimodal ploidy distribution (3.0n and 4.7n medians). This suggests that, in cockles from Arcachon Bay, mechanisms leading to aneuploidy are complex, developing during disease progression.

Metazoan parasites in an intermediate host population near its southern border: the common cockle ( Cerastoderma edule ) and its trematodes in a Moroccan coastal lagoon (Merja Zerga)

The metazoan parasite community of Cerastoderma edule was studied in the southern geographical range of the host (the coastal lagoon Merja Zerga, Morocco). A total of 11 metazoan species was found in cockles. Nine of these were trematodes using cockles as either first intermediate host (three species) or second intermediate host (six species). In addition, two other endo-metazoan species ( Pinnotheres pisum and Paravortex cardii ) were recorded from cockles in the studied lagoon. All the observed metazoans in cockles from Merja Zerga have previously been recorded at sites north of Africa. Up to 10% of the cockles in the studied size-groups were first intermediate hosts to castrating parasites ( Gymnophallus choledochus , Labratrema minimus and Monorchis parvus ). Among trematodes having metacercariae in cockles (second intermediate host) Meiogymnophallus minutus was the most widespread as it was observed in all cockles from all the examined habitats in the lagoon and it occurred in record high intensities. Different sub-communities of the trematode fauna using cockles as second intermediate host could be identified (subtidal vs intertidal associations). The richness and species composition of the macroparasite community in cockles from Morocco are discussed in relation to patterns seen in cockles from other sites along their geographical range. Migratory fish and waterbirds (final hosts) are generally responsible for the large scale spread (latitudinal spread) of trematodes. However, the distributional patterns of involved intermediate hosts in the life-cycles of the different trematode species in cockles are determining the richness and species composition patterns seen in cockles at shallow water sites along the east Atlantic shoreline.