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Highlights: [•] Larval forms of marine invertebrates are relatively tolerant to BDE-47. [•] Comparative 2-DE based proteomics provide new insights to how larvae might become resistant to BDE-47. [•] C. onyx larvae have adequate proteome plasticity to tolerate BDE-47. [ABSTRACT FROM AUTHOR]

Two primary ciliary bands, the prototroch and metatroch, are required for locomotion and in the feeding larvae of many spiralians. The metatroch has been reported to have different cellular origins in the molluscs Crepidula fornicata and Ilyanassa obsoleta, as well as in the annelid Polygordius lacteus, consistent with multiple independent origins of the spiralian metatroch. Here, we describe in further detail the cell lineage of the ciliary bands in the gastropod mollusc I. obsoleta using intracellular lineage tracing and the expression of an acetylated tubulin antigen that serves as a marker for ciliated cells. We find that the I. obsoleta metatroch is formed primarily by third quartet derivatives as well as a small number of second quartet derivatives. These results differ from the described metatrochal lineage in the mollusc C. fornicata that derives solely from the second quartet or the metatrochal lineage in the annelid P. lacteus that derives solely from the third quartet. The present study adds to a growing body of literature concerning the evolution of the metatroch and the plasticity of cell fates in homologous micromeres in spiralian embryos. [ABSTRACT FROM AUTHOR]

Sibling cannibalism is commonly observed in marine species. For instance, intrabrood cannibalism has been documented in marine gastropods with direct development, suggesting a relationship between embryo behavior and the evolution of life history strategies. However, there has been little effort to document the factors driving sibling cannibalism in marine species. The kin selection theory suggests that the level of relatedness plays an important role in cannibalism patterns. We examined Crepidula coquimbensis, a marine gastropod that broods and encloses its brooded offspring in capsules. Encapsulated embryos show sibling cannibalism and high levels of intracapsular multiple paternity. Given these features, cannibalistic behavior may be driven by kin-relatedness. To test this hypothesis, we constructed artificial aggregations of embryos to mimic three levels of relatedness: high, medium and low. For each category of aggregation, the cannibalism rate and benefits (i.e. size at hatching of surviving offspring) were estimated. In addition, at the end of embryo development, we performed parentage analyses to determine if cannibalism was associated with the relatedness between cannibal and victim embryos. Our results show that the intensity of sibling cannibalism increased in aggregations characterized by the lowest level of relatedness. There were important benefits of cannibalism in terms of hatching cannibal size. In addition, cannibalism between embryos was not random: the variation in reproductive success between males increased over the course of the experiment and the effective number of fathers decreased. Altogether, these results suggest that polyandry may play an important role in the evolution of sibling cannibalism in C. coquimbensis and that kin selection may operate during early embryonic stages in this species. [ABSTRACT FROM AUTHOR]

Sibling cannibalism is commonly observed in marine species. For instance, intrabrood cannibalism has been documented in marine gastropods with direct development, suggesting a relationship between embryo behavior and the evolution of life history strategies. However, there has been little effort to document the factors driving sibling cannibalism in marine species. The kin selection theory suggests that the level of relatedness plays an important role in cannibalism patterns. We examined Crepidula coquimbensis, a marine gastropod that broods and encloses its brooded offspring in capsules. Encapsulated embryos show sibling cannibalism and high levels of intracapsular multiple paternity. Given these features, cannibalistic behavior may be driven by kin-relatedness. To test this hypothesis, we constructed artificial aggregations of embryos to mimic three levels of relatedness: high, medium and low. For each category of aggregation, the cannibalism rate and benefits (i.e. size at hatching of surviving offspring) were estimated. In addition, at the end of embryo development, we performed parentage analyses to determine if cannibalism was associated with the relatedness between cannibal and victim embryos. Our results show that the intensity of sibling cannibalism increased in aggregations characterized by the lowest level of relatedness. There were important benefits of cannibalism in terms of hatching cannibal size. In addition, cannibalism between embryos was not random: the variation in reproductive success between males increased over the course of the experiment and the effective number of fathers decreased. Altogether, these results suggest that polyandry may play an important role in the evolution of sibling cannibalism in C. coquimbensis and that kin selection may operate during early embryonic stages in this species. [ABSTRACT FROM AUTHOR]

Abstract: Females of the calyptraeid gastropod Crepipatella fecunda enclose their fertilized eggs in thin-walled egg capsules. They then brood these capsules for at least several weeks in the mantle cavity, near the gills. Such brooding has the potential to obstruct water flow through the mantle cavity, potentially interfering with particle capture and oxygen uptake. Surprisingly, this study shows that brooding females increase the speed at which particles enter the mantle cavity and in fact increase overall rates of particle capture, although there was no impact on the rate at which particles moved along the gill surface. Brooding females were less able than non-brooding females to retain large-sized food particles (16–20μm), but most of the incoming food particles (2–16μm) were retained equally well by females in both groups. The combination of brooding females and their embryos consumed oxygen faster than non-brooding females. [Copyright &y& Elsevier]

The extant deep-sea fauna is thought to result from recolonisation of this environment by shallow-water organisms following climate-driven mass extinctions. Planktonic larval tolerance to high pressure is considered an important preadaptation for successful deep-sea invasion. In this study, the pressure and temperature tolerance of a species without any known confamilial deep-sea relative were assessed for the first time. Early- and late-veliger larvae of the shallow-water species Crepidula fornicata were subjected to a temperature/hydrostatic pressure regime from 5 to 25 °C and from 0.1 to 40 MPa. Although early and late veliger survived pressures equivalent to 2,000 m water depth or greater at all temperatures, decreased larval activity indicated significant sublethal temperature and pressure effects. Reduced larval activity of early veliger at low temperatures suggests that the bathymetric range of this species may be thermally constrained. A mechanistic model is proposed to explain the emerging pattern of ontogenetic shifts in pressure tolerance of shallow-water benthic invertebrates. [ABSTRACT FROM AUTHOR]

Settlement behavior of molluscan veliger larvae prior to metamorphosis requires cessation of swimming, accomplished by arrest of prototrochal cilia on the margin of the velum (the larval swimming organ). Ciliary arrest in larvae of gastropods is mediated by an action potential that occurs synchronously across the velum as a consequence of electrical coupling between the prototrochal ciliated cells. We developed a preparation for extracellular recording of such ciliary arrest spikes from intact swimming and crawling veliger larvae of the caenogastropod Crepidula fornicata, using a fine wire electrode. Ciliary arrest spike rates during bouts of substrate crawling were significantly higher than those recorded during preceding swimming periods in larvae that were competent for metamorphosis, but not in precompetent larvae. Spike rates were similar on clean polystyrene substrates, and on substrates that had been coated with a natural cue for metamorphosis (mucus from conspecific adults). We used immunohistochemical methods to localize neuromodulators that might regulate the function of velar cilia. Labeled terminals for serotonin, FMRFamide, and tyrosine hydroxylase (an enzyme for catecholamine synthesis) were located in positions consistent with modulatory effects on the prototrochal ciliated cells. Prototrochal ciliary arrest spike rates and beat frequencies were measured in isolated velar lobes from competent larvae, which were exposed to serotonin, FMRFamide, and dopamine (10−5 mol L−1). Serotonin abolished arrest spiking and increased beat frequency; dopamine also increased beat frequency, and FMRFamide depressed it. Competent larvae tested in a small static water column swam to the top of the column when exposed to serotonin, but occupied lower positions than controls when in the presence of dopamine and FMRFamide. The larval nervous system appears to regulate velar functions that are critical for settlement behavior, and is likely to do so by integrating different sensory modalities in an age-dependent manner. [ABSTRACT FROM AUTHOR]

Abstract: Understanding the processes that drive the recruitment of invasive non-native species is of critical importance in evaluating their potential to colonise previously unoccupied habitats. The slipper limpet Crepidula fornicata has spread rapidly into most European waters since its first introduction from the North West Atlantic in the late 19th century. Its invasion success is thought to have been aided by its long larval phase and its tolerance towards a wide range of environmental conditions. The Milford Haven Waterway in Wales, U.K. supports a population with highly variable densities in the intertidal as well as the subtidal zone. In the present study, we tested a series of existing models to investigate the roles of larval supply, larval habitat selection and post-settlement mortality in determining the final distribution of C. fornicata in the intertidal zone of the Milford Haven Waterway. During the main reproductive season of 2011, data on total settlement rates and recruitment were collected by deploying slate panels for varying durations in the low intertidal zone, and data on larval abundances were obtained by taking frequent plankton samples at two sites with contrasting adult densities: Beggars Reach (~15±13indm−2) and Pennar (~343±360indm−2). Total larval densities were much higher at Pennar, but densities of late-stage larvae (i.e. larval supply) were similar at both sites, indicating that local hydrodynamics may have resulted in the spatial homogenisation of supply of late-stage, metamorphically competent larvae, despite the higher larval production at the high adult abundance site. Settlement rates also did not differ between sites. Seasonal recruitment was overall low, indicating that post-settlement mortality, likely as a consequence of exposure to intertidal conditions, is very high. The lack of a relationship between adult abundance and settlement rates indicates that the final distribution of C. fornicata in the intertidal may be a result of differential post-settlement mortality. Understanding recruitment patterns in non-native species is essential for developing management strategies for potentially harmful invaders such as C. fornicata. [Copyright &y& Elsevier]

Adelphophagic development, where embryos consume sibling embryos or nurse eggs, is particularly common in marine caenogastropods and some families of polychaetes. When exogenous nutrition is provided before hatching, egg size and hatching size can be uncoupled, but advantages and constraints of adelphophagic development compared to development from large eggs are unknown. Here we examine temperature-mediated plasticity in offspring size, brooding duration, and fecundity in the adelphophagic marine gastropod Crepidula cf. onyx. We use these data combined with previously published data on two planktotrophic Crepidula and two Crepidula species that develop from large eggs to test hypotheses about the consequences of adelphophagic development and patterns of variation in offspring size. In Crepidula cf. onyx, egg size shows no significant effect of temperature. Hatching size is significantly larger at 28 °C than at 23°C but proceeds from fewer eggs per capsule at 28 °C. Hatching size is therefore decoupled from both egg size and the number of eggs per capsule. Although development is faster at the higher temperature, broods are produced roughly every 26-27 days at both temperatures. Increased rate of development has been cited as a potential advantage of adelphophagic development in muricids, but the adelphophagic C. cf. onyx did not develop more quickly than C. atrasolea or C. ustulatulina, species that produce similarly sized hatchlings from large eggs. Comparisons across calyptraeid species support the role of adelphophagy in increasing variance in offspring size. This increased variability is primarily expressed within broods or among broods from the same female, not among females. [ABSTRACT FROM AUTHOR]

The establishment and spread of a non-native species in an introduced range depends to a large extent on the performance of the species under the prevailing environmental conditions. The spawning, larval and spatfall periods of the invasive gastropod Crepidula fornicata were monitored in the intertidal zone at its northernmost range in Wales, UK, between February 2010 and January 2011. The duration of the reproductive season was similar to that recorded from more southerly European populations. Spawning and larval release occurred throughout most of the year even at low seawater temperatures of <7 °C, but benthic recruitment was observed over a much shorter period at seawater temperatures >16 °C. Recruitment was low and likely controlled by post-settlement mortality. These observations suggest that C. fornicata's northwards spread in Welsh waters will not be limited by seawater temperature negatively affecting reproduction, but by processes acting after larval release. These data show the importance of incorporating settlement and post-settlement processes into studies on recruitment success when aiming to predict the potential spread of a potentially harmful invader such as C. fornicata. [ABSTRACT FROM AUTHOR]

Abstract: In Europe, the gastropod Crepidula fornicata is an invasive species characterized by a long reproductive period (from February to November). Thus, its larvae are exposed to variations in available food sources (in terms of quantity and quality). We aimed to investigate if bacteria could contribute to larval food both in presence or absence of phytoplankton, and to compare these results to seasonal variations of bacteria and phytoplankton abundances at a coastal site in the English Channel. First, ingestion of fluorescent beads of 0.5 to 2μm diameter, showed that larvae were able to ingest particles of typical bacterial size. Then we used a dual stable isotope labeling approach which consisted in labeling a bacterial pelagic community with 15N and a diatom (Chaetoceros gracilis) culture with 13C, and supplying larvae with 15N-labeled bacteria, 13C-labeled diatoms, and both labeled sources. This technique has, to our knowledge, never been applied to invertebrate larvae. After 24h of experiment, larvae were significantly enriched in all treatments: +21.5‰ (∆δ13C) when supplied with diatoms, +1364‰ (∆δ15N) when supplied with bacteria, and +24‰ (∆δ13C) and +135‰ (∆δ15N) when supplied with the two mixed sources. These results indicated that bacteria can contribute to the larval nutrition in C. fornicata, even in the presence of phytoplankton. Our results however suggested that larvae of C. fornicata preferentially used diatoms and showed that the supply of free bacteria did not alter the uptake of diatoms. Considering the seasonal variations of bacteria and phytoplankton abundances at the study site, these results suggested that bacteria may constitute a complementary resource for the larvae of C. fornicata when phytoplankton is abundant and may become a substitute resource when phytoplankton is less available. This approach offers promising perspectives to trace food sources and assess nitrogen and carbon fluxes between planktotrophic larvae and their preys. [Copyright &y& Elsevier]

Abstract: It is well known that interactions with conspecifics can affect the size and timing of sex change but the potential effects of other environmental influences on sex change are rarely examined. Sex allocation theory predicts that increased mortality rates should decrease the optimal size at sex change. Therefore we examined how stress (early starvation and exposure to desiccation) affects the size at sex change in Crepidula cf. marginalis a protandrous marine snail. Our results showed significant effects of early starvation on sex change: animals responded to early starvation by losing male characteristics earlier and at smaller sizes, remaining longer in the transitional phase, and becoming female at larger sizes than animals that were provided adequate food throughout. Desiccation on the other hand, decreased the size at which the female reproductive morphology was attained but no other effects were detected. The results of the desiccation treatment are consistent with theoretical predictions that higher mortality rates should decrease size at sex change. The starvation treatment seems to indicate that animals reduce the allocation to reproduction under extreme stress by entering a non-reproductive transitional stage earlier. Instead of regaining the male phase when conditions improved, they grew and rapidly completed the transition to the female phase. [Copyright &y& Elsevier]

Protandrous hermaphrodites are predicted to change sex from male to female when relative reproductive fitness of females surpasses that of males. How size at sex transition varies with population, mating group and individual parameters was investigated for five populations of the protandrous hermaphrodite slipper snail, Crepidula fornicata. The populations varied for density, size distribution, average mating group size and sex ratio. Size at sex-change was correlated with the population sex ratio. Comparisons of multiple hypotheses revealed that variables predicting the sex of a snail vary among positions in the mating group. The variables included body size, the relative size of the snail sitting atop the focal snail and population density. Our data support the conclusions that size at sex-change (and by inference, the size at which one sex has relatively greater fitness) is not fixed for these hermaphrodites and that individual size, social conditions and population differences all influence variation in relative fitness. [ABSTRACT FROM AUTHOR]

Many marine gastropod species brood their embryos in thin-walled capsules to protect them during development. Despite its beneficial effects, encapsulation has two major constraints, nutrition and oxygen supply, which affect embryo development and larval survival. Developing embryos usually rely on intracapsular food sources provided by the mother, in the form of yolk, nurse eggs and intracapsular fluid. However, it is still not clear if they are able to feed on extracapsular sources that may cross the capsule wall. We investigated this possibility in the calyptraeid species Crepidula fornicata. In this species, the internal capsule wall thickness sharply decreases during embryonic development, which might change wall permeability to small organic molecules, thus providing embryos with external dissolved organic matter. To test this hypothesis, encapsulated and excapsulated embryos of C. fornicata were placed for 48 h in a 13C-enriched amino acid (l-alanine) solution. Excapsulated embryos were enriched in 13C (+5.75‰), which suggested that they were able to assimilate the labelled amino acid. In contrast, encapsulated embryos were weakly enriched (+0.75‰), suggesting that encapsulation greatly reduces the potential for the use of extracapsular amino acids and that encapsulated embryos mainly rely on maternal food. [ABSTRACT FROM PUBLISHER]

The article discusses a study that showed marine gastropods Crepidula plana and Crepidula convexa specimens displayed immunity from trematode larvae, unlike gastropods that serve as intermediate hosts. Some 114 specimens of C. plana and 103 of C. convexa from Rhode Island and Massachusetts showed no parasitic infection although 264 Littorina littorea specimens, periwinkles, from the same sites were infected. The results are similar to those from two studies on C. fornicata of the same genus.

Background: Animals with a spiral cleavage program, such as mollusks and annelids, make up the majority of the superphylum Lophotrochozoa. The great diversity of larval and adult body plans in this group emerges from this highly conserved developmental program. The 4d micromere is one of the most conserved aspects of spiralian development. Unlike the preceding pattern of spiral divisions, cleavages within the 4d teloblastic sublineages are bilateral, representing a critical transition towards constructing the bilaterian body plan. These cells give rise to the visceral mesoderm in virtually all spiralians examined and in many species they also contribute to the endodermal intestine. Hence, the 4d lineage is an ideal one for studying the evolution and diversification of the bipotential endomesodermal germ layer in protostomes at the level of individual cells. Little is known of how division patterns are controlled or how mesodermal and endodermal sublineages diverge in spiralians. Detailed modern fate maps for 4d exist in only a few species of clitellate annelids, specifically in glossiphoniid leeches and the sludge worm Tubifex. We investigated the 4d lineage in the gastropod Crepidula fornicata, an established model system for spiralian biology, and in a closely related direct-developing species, C. convexa. Results: High-resolution cell lineage tracing techniques were used to study the 4d lineage of C. fornicata and C. convexa. We present a new nomenclature to name the progeny of 4d, and report the fate map for the sublineages up through the birth of the first five pairs of teloblast daughter cells (when 28 cells are present in the 4d sublineage), and describe each clone's behavior during gastrulation and later stages as these undergo differentiation. We identify the precise origin of the intestine, two cells of the larval kidney complex, the larval retractor muscles and the presumptive germ cells, among others. Other tissues that arise later in the 4d lineage include the adult heart, internal foot tissues, and additional muscle and mesenchymal cells derived from later-bornprogeny of the left and right teloblasts. To test whether other cells can compensate for the loss of these tissues (that is, undergo regulation), specific cells were ablated in C. fornicata. Conclusions: Our results present the first fate map of the 4d micromere sublineages in a mollusk. The fate mapreveals that endodermal and mesodermal fates segregate much later than previously thought. We observed little evidence of regulation between sublineages, consistent with a lineage-driven cell specification process. Our results provide a framework for comparisons with other spiralians and lay the groundwork for investigation of the molecular mechanisms of endomesoderm formation, germ line segregation and bilateral differentiation in Crepidula. [ABSTRACT FROM AUTHOR]

The article focuses on a study on the impact of rising coastal seawater temperatures on the reproductive output of Crepidula (C.) fornicata, an invasive gastropod. It notes that the nature and the structure of a habitat get to be modified by the abundance of C. fornicata species to their advantage. Findings show extended periods of brood presence and greater intensity in the reproductive activity of C. fornicata population in Bourneuf Bay, France during the 2006-2007 period than the 2000-2001 period in which the former posted higher water temperature. Results also indicate that the species exhibited greater intensity of gametogenesis amid higher water temperatures and chlorophyll (chl) α values.

Abstract: Within estuaries of New York, USA, recurrent harmful brown tides (Aureococcus anophagefferens) have contributed toward the collapse of two major bivalve fisheries (bay scallop, Argopecten irradians and northern quahog or hard clam, Mercenaria mercenaria), while populations of the Atlantic slipper limpet Crepidula fornicata have persisted in the presence of these blooms. Rates of suspension feeding by C. fornicata and M. mercenaria in the presence of different strains of A. anophagefferens and wild brown tide blooms were quantified to assess the potential impact of brown tides on slipper limpet and hard clam populations. Slipper limpets were capable of clearing all strains of A. anophagefferens at biomass-specific rates similar to an ideal food source (Isochrysis galbana), whereas clearance rates of M. mercenaria fed toxic clones of A. anophagefferens were significantly lower than when fed I. galbana or non-toxic clones of A. anophagefferens (p <0.01). During brown tide blooms (104–106 cells mL −1) on the south shore of Long Island during 2008 and 2009, clearance rates of C. fornicata when fed bloom water were an order of magnitude greater than those of M. mercenaria (p <0.001). Finally, during mesocosm experiments, C. fornicata reduced bloom densities of A. anophagefferens (106 cellsmL−1) by an order of magnitude in 3–4 days, whereas densities of A. anophagefferens in mesocosms stocked with equal or greater biomasses of M. mercenaria were unchanged. These results demonstrate that C. fornicata can actively feed in the presence of A. anophagefferens and suggest that this species could serve as a top-down control of blooms in shallow, poorly flushed estuaries. [Copyright &y& Elsevier]

Abstract: Coastal bays provide habitats for juveniles and adults of many marine species. Mont Saint-Michel Bay (MSMB, France) hosts a highly diversified fish community and constitutes one of the most important nursery grounds for many commercially exploited marine species, such as sea bass, flatfish, clupeids and rays in the English Channel. Besides, MSMB also suffers from the massive invasion of an exotic mollusc, the American slipper-limpet (Crepidula fornicata, L.). This species arrived four decades ago and now represents the main filter-feeder biomass in the bay (150 Mt), an order of magnitude larger than local farmed and natural shellfishes. Recent analyses underlined the impact of this small gastropod on the trophic structure of this bay and its negative influence on juvenile sole densities in the nursery grounds. The present study uses a geostatistical approach to explore the effect of the extension of the slipper-limpet on flatfish (common sole Solea solea, L.; plaice Pleuronectes platessa, L.; brill Scophthalmus rhombus, L. and flounder Platichthys flesus, L.) spatial distribution. Data collected during survey of the MSMB at the end of the 1970s and three decades later have been used to build interpolated maps of (1) slipper-limpet and (2) flatfish spatial distributions. Slipper-limpets were concentrated in a small area, in the western part of the MSMB, in the 1970s while today they occupy half of the bay. This rapid proliferation led to the decrease of available surface for flatfishes, which previously occupied the whole bay and are now restricted to its eastern part. The present study highlighted that the negative influence on fish habitat in MSMB is apparently more related to changes in the substratum than to trophic interactions. This invasion has possible consequences on flatfish population renewal at a large scale and may also damage other benthic or demersal species, such as rays. [Copyright &y& Elsevier]

Abstract: Marine larvae that experience some sub-lethal stresses can show effects from those stresses after metamorphosis, even when they seem to recover from those stresses before metamorphosis. In this study we investigated the short and long-term effects of exposing the larvae of three calyptraeid gastropods (Crepidula fornicata, Crepidula onyx, and Crepipatella fecunda) to temporary reductions in salinity. Larvae of all three species showed slower larval growth rates, longer time to metamorphic competence, and substantial mortality after being stressed in seawater at salinities of 10, 15, and 20 for less than 48h. Larval tolerance to low salinities varied widely within and among species, but longer stresses at lower salinities were generally more harmful to larvae. However, larvae in nearly all experiments that were able to metamorphose survived and grew normally as juveniles; there were no documented “latent effects.” For all three species, starving larvae in full-strength seawater was not as harmful as exposing larvae to low salinity stress, indicating that detrimental effects on larvae were caused by the salinity stress per se, rather than by an indirect effect of salinity stress on feeding. C. fornicata that were stressed with low salinity as juveniles were more tolerant of the stress than larvae: all stressed juveniles lived and showed reduced growth rates for no more than 3days. Our data suggest that even though reduced salinity is clearly stressful to the larvae of these 3 gastropod species, metamorphosis seems to generally provide individuals with a fresh start. [ABSTRACT FROM AUTHOR]

Abstract: In gregarious species with copulation and internal fertilization, male–male competition and female cryptic choice may affect reproductive success of both sexes. We carried out a molecular analysis to study paternity and sperm use by females in the protandrous marine brooding gastropod Crepidula coquimbensis. In the field, a single female inhabits an empty hosting shell with up to six males. This gregarious behavior may promote intra-brood multiple paternity if females can store sperm from several consecutive copulations with the surrounding males. To study female sperm usage, the males sharing shelters with five different adult females were collected and preserved for paternity analysis. Females were transported alive to the laboratory and isolated for six months. After that, an additional male was offered to each of the five study females. Once the females had laid capsules, a total of 528 embryos from the five females were assigned paternity based on five microsatellite loci. Paternity analysis showed that every male sharing the empty hosting shell of a female as well as the additional male were assigned fatherhood of embryos laid by this specific female. Females can thus use sperms from multiple males including sperms stored for at least six months. In addition, in four out of the five offspring arrays, a similar contribution of each male to the brood was observed, a pattern associated with the close relationship between the number of fathers observed and the effective paternity index calculated. These results contrast with those of paternity analyses carried out in another species of the same genus, C. fornicata which is characterized by a stacking behavior in which the closest male to the female achieves the highest reproductive success. Male reproductive success may be largely influenced by the aggregation pattern and male mating opportunities in the Crepidula complex, a hypothesis to be examined further by studying other species exhibiting different grouping behavior. [Copyright &y& Elsevier]

Abstract: In many marine benthic invertebrates, the larval stage is the main vector of dispersal. Selective metamorphosis of larvae into an appropriate habitat is then essential to the survival of the benthic adult, with profound implications for population dynamics. Within this context, the identification of causal external factors triggering larval metamorphosis is of primary interest. In the widely invasive marine species Crepidula fornicata (L.), adult conditioned seawater is an effective inducer but the inducer has not yet been chemically characterized. In the present study, we experimentally tested the inductive ability of dibromomethane (DBM), a halogenated compound naturally-produced by red algae of the family Corallinaceae that co-occur with C. fornicata in the field. Through a series of three experiments, we demonstrated that DBM effectively induces metamorphosis of C. fornicata larvae, with a strong dose–response effect. Positive responses were observed for the four tested concentrations (5, 50, 500 and 5000ppm), 5000ppm being the most effective at inducing rapid metamorphosis. At this concentration, larvae became responsive at least five days before they became responsive to excess KCl, a chemical commonly used to test for competence in C. fornicata. Whether DBM could be an effective natural inducer would require further studies to quantify DBM and other halogenated compounds in the vicinity of C. fornicata beds, where they could influence larval behaviour even in the absence of other settlement cues. [ABSTRACT FROM AUTHOR]

The article presents research on the variation and repeatability of egg size among broods from a single female from two gastropods, Crepidula atrasolea and ustulatulina. It says that egg size was measured from three to seven broods per female and females were raised from hatching under under invariant temperature in incubators during the preliminary experiment. The females were raised under changing temperatures on the laboratory bench top in the second experiment. It suggests that there were differences in egg size among broods from each female and in females from the bench top under both conditions. The estimates of repeatability were reduced when among brood variation was included in the calculations. It adds that brood order and female do not contribute to intraspecific variation.

Recent developmental and genomic research focused on "slipper snails" in the genus Crepidula has positioned Crepidula fornicata as a de facto model system for lophotrochozoan development. Here we review recent developments, as well as earlier reports demonstrating the widespread use of this system in studies of development and life history. Recent studies have resulted in a well-resolved fate map of embryonic cell lineage, documented mechanisms for axis determination and D quadrant specification, preliminary gene expression patterns, and the successful application of loss- and gain-of-function assays. The recent development of expressed sequence tags and preliminary genomics work will promote the use of this system, particularly in the area of developmental biology. A wealth of comparative information on phylogenetic relationships, variation in mode of development within the family, and numerous studies on larval biology and metamorphosis, primarily in Crepidula fornicata, make these snails a powerful tool for studies of the evolution of the mechanisms of development in the Mollusca and Lophotrochozoa. By bringing a review of the current state of knowledge of Crepidula life histories and development together with some detailed experimental methods, we hope to encourage further use of this system in various fields of investigation. [ABSTRACT FROM AUTHOR]

Offspring size is a key characteristic in life histories, reflecting maternal investment per offspring and, in marine invertebrates, being linked to mode of development. Few studies have focused explicitly on intraspecific variation and plasticity in developmental characteristics such as egg size and hatching size in marine invertebrates. We measured over 1000 eggs and hatchlings of the marine gastropods Crepidula atrasolea and Crepidula ustulatulina from two sites in Florida. A common-garden experiment showed that egg size and hatching size were larger at 23 °C than at 28 °C in both species. In C. ustulatulina, the species with significant genetic population structure in cytochrome oxidase I (COI), there was a significant effect of population: Eggs and hatchlings from the Atlantic population were smaller than those from the Gulf. The two populations also differed significantly in hatchling shape. Population effects were not significant in C. atrasolea, the species with little genetic population structure in COI, and were apparent through their marginal interaction with temperature. In both species, 60–65% of the variation in egg size and hatching size was a result of variation among females and, in both species, the population from the Atlantic coast showed greater temperature-mediated plasticity than the population from the Gulf. These results demonstrate that genetic differentiation among populations, plastic responses to variation in environmental temperature, and differences between females all contribute significantly to intraspecific variation in egg size and hatching size. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99, 489–499. [ABSTRACT FROM AUTHOR]

Abstract: Crepidula fornicata, the slippershell snail, while native to New England, has now become a successful invasive species along coastlines in many other parts of the world. This study considers the possible control of native populations by several common predators: the invasive shore crab Hemigrapsus sanguineus, one species of pagurid hermit crab (Pagurus longicarpus), and juveniles of the drilling gastropods Nucella lapillus and Urosalpinx cinerea. In the laboratory, juveniles of C. fornicata were especially vulnerable to the two crustacean predators tested, and to a lesser extent vulnerable as well to predation by the oyster drill U. cinerea; in choice tests, young oyster drills ate barnacles and mussels rather than slippershell snails, but ate C. fornicata when offered no other choice. Juveniles of two other Crepidula species (C. plana and C. convexa) were less susceptible to predation by hermit crabs, probably due to differences in juvenile shell morphology and growth trajectories. Remarkably, juvenile dogwhelks (N. lapillus) ate no Crepidula prey over several months in the laboratory, even in the absence of alternative food and although they readily consumed blue mussels. Additional work is needed to determine the role of crustacean and other predators in regulating the growth of native populations of C. fornicata in the field and to determine the extent to which the explosive growth of at least some invasive Crepidula populations reflects escape of juveniles from native predators. [Copyright &y& Elsevier]

Abstract: Benthic faunal activity and density play an important role in determining the rates of benthic nutrient fluxes, which enrich the water column and contribute to phytoplankton growth. The intensity of nutrient fluxes in the Bay of Brest depends on the density of the invasive gastropod, Crepidula fornicata. In order to study the impact of benthic fluxes on phytoplankton dynamics, realistic daily nutrient inputs simulating various densities of C. fornicata were added to six enclosures during three weeks. The increase in fertilization intensity influenced the phytoplankton biomass. A succession from Chaetoceros spp. to Pseudo-nitzschia spp. and Leptocylindrus danicus was observed in all enclosures, but the dynamics of successions were different. Pseudo-nitzschia spp. was favored in the three more fertilized enclosures, while Chaetoceros spp. persisted longer in less enriched enclosures. Despite an apparent nitrogen limitation, the quantum efficiency of PSII (Fv/Fm) was high (>0.5) and stable in all enclosures. The maximal photosynthetic capacity (PBmax) was also invariable and oscillated around an average value of 2.23mg C (mgChl a)−1 h−1. The stability of Fv/Fm and PBmax observed at different nutrient input intensities demonstrates that the daily inputs maintained the physiological balance of the microalgae. The maximal light utilization efficiency (α) and the light saturation parameter (Ek) were also quite stable after day 8, which reveals that photosynthetic parameters were driven by growth constraints due to nutrient availability and not by incident light or species successions. We suggest that our results correspond to an “Ek independent variation” regulation. We propose that such regulation of photosynthetic parameters appears when there are frequent nutrient additions which do not allow replete nutrient conditions to be reached but lead to physiological equilibrium. Thanks to our results we can understand how even low benthic fluxes, by supporting their cellular physiological status, allowed diatoms to dominate the phytoplankton community in the six enclosures. These results confirm the importance of daily benthic inputs as much as the amount of nutrient inputs. However, we suggest that high benthic fluxes have a buffering effect on nutrient availability, thereby limiting the consequences of short-term events which can entail a sudden increase of nutrient input, and are known to promote Dinophyta bloom formation. [Copyright &y& Elsevier]

Abstract: In diverse invertebrate species characterized by a biphasic life cycle, metamorphosis represents a fundamental biological transition which determines the fate of benthic population dynamics through settlement and recruitment. Within this context, nitric oxide (NO) is thought to act as an endogenous inhibitor of metamorphosis. While attention has been focused on the mechanisms of this inhibitory pathway with pharmacological agents and immunohistochemistry tools, relatively few studies have investigated transcriptional process at the origin of NO synthesis. In this paper, we report the isolation of a 218-bp cDNA fragment of an ortholog of the neuronal nitric oxide synthase (nNOS) gene in the invasive marine species Crepidula fornicata. By the use of quantitative real-time PCR, we examine the transcription of this gene throughout larval development and in response to two inducers [K+ excess (20 mM), dibromomethane (DBM) (1000 ppm)] that are known to potentiate metamorphosis in invertebrate species. The level of transcription increased constantly during the larval development, suggesting an increased repressive effect over metamorphosis as larvae aged. Interestingly, maximum values were reached 6 h post-treatment, before declining within 20 h for all the tested conditions. Overall, our results are in agreement with the involvement, at a molecular level, of the NO signalling pathway in metamorphosis. The decrease in nNOS gene transcription post-induction could support the inhibitory effect of NO upon the onset of metamorphosis in competent larvae, although further studies are needed to fully describe the pathways triggered by K+ ions and DBM induction. Furthermore, results indicate that metamorphosis could occur after termination of endogenous inhibition, bringing support to the hypothesis of spontaneous metamorphosis. [Copyright &y& Elsevier]

Reproductive strategies and parental effects play a major role in shaping early life-history traits. Although polyandry is a common reproductive strategy, its role is still poorly documented in relation to paternal effects. Here, we used as a case study the invasive sessile marine gastropod Crepidula fornicata, a mollusc with polyandry and extreme larval growth variation among sibling larvae. Based on paternity analyses, the relationships between paternal identity and the variations in a major early life-history trait in marine organisms, that is, larval growth, were investigated. Using microsatellite markers, paternities of 437 fast- and slow-growing larvae from 6 broods were reliably assigned to a set of 20 fathers. No particular fathers were found responsible for the specific growth performances of their offspring. However, the range of larval growth rates within a brood was significantly correlated to 1) an index of sire diversity and 2) the degree of larvae relatedness within broods. Multiple paternity could thus play an important role in determining the extent of pelagic larval duration and consequently the range of dispersal distances achieved during larval life. This study also highlighted the usefulness of using indices based on fathers' relative contribution to the progeny in paternity studies. [ABSTRACT FROM AUTHOR]

The article examines the proposed two-dimensional, depth-averaged, hydrodynamic and reactive-transport model that has been specifically developed for the estuaries and the Bay of Brest. The proposed model, accordingly, includes an explicit representation of the benthic-pelagic coupling which is stimulated by the increasing density of the slipper limpet Crepidula fornicata. The testing of proposed model reveals that the benthic nutrient dynamics are highly variable and strongly depend on the local conditions.

Crepidula convexa, a calyptreid gastropod with direct embryonic development, changes sex from male to female in the course of its lifetime (protandry). Under sex-allocation theory, male reproductive success should be independent from age and size (a proxy used for age). However, this may be counterbalanced by female cryptic choice or gregarious behaviour. Eleven polymorphic microsatellite loci were thus developed to examine paternity of embryos and larvae. This set of loci appears suitable to carry out paternity analyses due to the high exclusion probability of unrelated males given the maternal genotype. [ABSTRACT FROM AUTHOR]

Cell lineage studies in mollusk embryos have documented numerous variations on the lophotrochozoan theme of spiral cleavage. In the experimentally tractable embryo of the mud snail Ilyanassa, cell lineage has previously been described only up to the 29-cell stage. Here I provide a chronology of cell divisions in Ilyanassa to the stage of 84 cells (about 16 hours after first cleavage at 23°C), and show spatial arrangements of identified nuclei at stages ranging from 27 to 84 cells. During this period the spiral cleavage pattern gives way to a bilaterally symmetric, dorsoventrally polarized pattern of mitotic timing and geometry. At the same time, the mesentoblast cell 4d rapidly proliferates to form twelve cells lying deep to the dorsal ectoderm. The onset of epiboly coincides with a period of mitotic quiescence throughout the ectoderm. As in other gastropod embryos, cell cycle lengths vary widely and predictably according to cell identity, and many of the longest cell cycles occur in small daughters of highly asymmetric divisions. While Ilyanassa shares many features of embryonic cell lineage with two other caenogastropod genera, Crepidula and Bithynia, it is distinguished by a general tendency toward earlier and more pronounced diversification of cell division pattern along axes of later differential growth. [ABSTRACT FROM AUTHOR]

The degree to which larvae of the invasive American slipper limpet (Crepidula fornicata) and the Japanese oyster (Crassostrea gigas) may compete for food was examined during 2003 in the laboratory. Larval microalgae uptake, growth and mortality were compared for larvae fed each of six species of unicellular algae, ranging in length from 2 to 10 μm. Tested diets included the two flagellates Tetraselmis chui (Prasinophyceae) and Isochrysis affinis galbana (T-ISO, Haptophyceae), one member of the Chlorophyceae (Nannochloris atomus), and three diatom species (Chaetoceros calcitrans forma pumilum, Chaetoceros gracilis, Skeletonema marinoï). We found that the limpet larvae ingested phytoplankton over a wider range of cell sizes and ate at higher rates on each diet than did the oyster larvae. For example, oyster larvae consumed 2216 cells h-1 of N. atomus, while limpet larvae consumed the same phytoplankton cells at approximately twice that rate, 5159 cells h-1, on the same diet. Larvae of both species grew more quickly on a mixture of flagellates than on any of the diatom alone (12 versus 7 μm d-1 for oyster larvae and 41 versus 28 μm d-1 for limpet larvae). Our results suggest that in the Bay of Mount Saint-Michel (France, Western Channel), where larvae of both species co-exist in the summer, intensive grazing by limpet larvae can potentially deplete phytoplankton concentrations to cause competition with oyster larvae, particularly for smaller sized phytoplankton species. [ABSTRACT FROM AUTHOR]

Strategies for biomass control are actively sought in response to proliferation of the introduced, suspension-feeding gastropod Crepidula fornicata along European coasts. Among these, dredging, crushing and on-site rejection may only be envisaged if the risk of further dissemination through the release of gametes and of excapsulated embryos/larvae is found to be nil or extremely low. This study evaluates such risk using three approaches: (1) determination of the periods of brood presence/absence, (2) external fertilizations of gametes obtained by gonad stripping, (3) cultures of mechanically-excapsulated embryos and larvae. A period of near- or total brood absence was observed between September 2006 and January 2007. The few zygotes (1.5% to 7.5%) obtained from external fertilizations did not proceed beyond the 4-cell stage. Excapsulated young embryos and mid-stages died in less than 4 days of culture. Despite their ability to swim, grow and feed, excapsulated veligers all died before metamorphosis. No juveniles were obtained from external fertilizations and excapsulated cultures, indicating that the release of crushed catches directly at sea could not present a dissemination risk from the standpoint of gamete or prematurely-excapsulated larval dispersal. Furthermore, by carrying out the crushing operations during the period of brood absence, the dissemination risk becomes nil. Negative ecological impact of such operations could be offset by attraction of motile predators, as yet unaccustomed to this introduced species, and their subsequent generalization to live slipper limpets and invasive feral Crassostrea gigas. At the very least, this biomass reduction approach would concentrate bottom habitat unavailability to restricted zones, freeing up the rest of the subtidal for other, formerly displaced species, as well as reducing the pressure on the trophic carrying capacity of affected habitats. La prolif?ration des cr?pidules, Crepidula fornicata gast?ropode suspensivore, le long du littoral europ?en, a stimul? de nombreuses strat?gies de contr?le de sa biomasse. Parmi elles, le dragage, broyage et relargage sur site des cr?pidules sont envisageables ? condition que le risque de diss?mination additionnel, li? au rejet de gam?tes et/ou d''embryons/larves excapsul?s, soit nul ou extr?mement faible. Trois ?tudes sont effectu?es pour ?valuer ce risque?: (1) la d?termination des p?riodes de pr?sence/absence de pontes, (2) les f?condations externes de gam?tes obtenus par scarification des gonades, (3) les cultures d''embryons et de larves m?caniquement excapsul?s. Une p?riode d''absence totale de ponte est observ?e entre novembre 2006 et janvier 2007. Les quelques zygotes obtenus (de 1,5?% ? 7,5?%) ? partir des f?condations externes ne survivent pas au-del? du stade 4 cellules. Les jeunes embryons et les stades interm?diaires excapsul?s sont morts en moins de quatre jours de culture. Malgr? leur capacit? ? nager, cro?tre et se nourrir, toutes les larves v?lig?res excapsul?es sont mortes avant la m?tamorphose. Aucun juv?nile n''a donc ?t? obtenu ? partir des f?condations externes et des cultures de propagules excapsul?es, indiquant que le relargage de cr?pidules broy?es en mer pr?senterait peu de risques de diss?mination par les gam?tes et par les larves pr?matur?ment excapsul?es ? partir du site de rejet. De plus, en effectuant les op?rations de broyage hors des p?riodes de ponte, le risque de diss?mination serait extr?mement faible. Les impacts ?cologiques n?gatifs g?n?r?s par de telles op?rations pourraient ?tre compens?s par l''attraction de pr?dateurs, encore non accoutum?s ? cette esp?ce introduite, sur les sites de rejet, pouvant stimuler leur pr?dation par l''abondance de cr?pidules vivantes et d''hu?tres sauvages Crassostrea gigas. De plus, le rejet de broyats pourrait ?tre concentr? sur des zones d?limit?es, permettant ainsi de lib?rer des habitats, du reste de la zone subtidale, pour d''autres esp?ces autrefois d?plac?es et de r?duire la pression trophique exerc?e par la cr?pidule sur les habitats infest?s. [ABSTRACT FROM AUTHOR]

A population of the invasive slipper limpet (Crepidula fornicata) has been spreading in the Bay of Mont-Saint-Michel (Western English Channel) for 40 years. Sidescan sonar, underwater video and quantitative sampling were conducted in 1996 and 2004 to document the widening geographic spread of the species over the bay. The limpet population grew by 50% during this period, to reach a fresh biomass of about 150 000 t. This local study analyses causes and effects of the spread and provides a typical example of the limpet spreading process. This population increase has significant effects on the environment in the most densely colonized area (modification to the sediment and biodiversity), leading to the emergence of a new benthic community. Anthropic dredging activities are among the causative factors of the spread but are also adversely affected by the invasion. Depuis 40 ans, la population de cr?pidules (Crepidula fornicata) prolif?re en baie du Mont Saint-Michel (Manche Ouest). Deux ?tudes r?alis?es en 1996 et 2004 ont permis de cartographier et d'estimer le stock de la population gr?ce ? des moyens similaires?: sonar ? balayage lat?ral, vid?o sous-marine et pr?l?vements quantitatifs ? la benne. Durant cet intervalle de temps, la biomasse a augment? de 50?% pour atteindre 150?000?t dans la baie en 2004. Cette ?tude comparative a permis d'analyser les causes et les effets d'une telle prolif?ration et d'en montrer le processus g?n?ral. Dans les secteurs fortement colonis?s, les effets sur l'environnement sont particuli?rement n?fastes (modification du s?diment et de la biodiversit?) et aboutissent ? une nouvelle communaut? benthique. Les activit?s de p?che aux engins tra?nants (dragues et chaluts) sont ? la fois les principales responsables et les victimes de cette prolif?ration. [ABSTRACT FROM AUTHOR]

For dioecious species, choosing a mate of the same sex can have reproductive costs. For sex-changing animals, however, a lack of sex recognition may not carry a reproductive cost, as pairs that were initially same-sex can become opposite-sex pairs as one partner changes sex. The strength of sex discrimination in sex changers, then, should depend on the duration of mating associations and whether the time of sex change is influenced by social situation (“flexible” sex change). We studied two species of marine snails that change sex from male to female, one with flexible sex change and long-term or permanent mating associations ( Crepidula fornicata) and one with short-term pairings and relatively fixed time of sex change ( Crepidula convexa), to determine whether either species exhibits sex recognition and whether members of C. convexa show stronger sex discrimination. In laboratory experiments, small males, the choosing animals, were placed with either a male or a female conspecific (no-choice experiments) or given a choice of a male or female (choice experiments). We controlled for shell length in all experiments, as relative size may influence sex change or choice. Males of both species paired more often with females than males, but, as predicted, males of C. convexa showed stronger discrimination: When given a choice, no C. convexa male paired with another male. In contrast, some C. fornicata males always chose other males even when given the choice of a female. These results suggest that sex recognition can be adaptive even for sex changers but demonstrate that the level of sex recognition will depend on other aspects of reproductive behavior. [ABSTRACT FROM AUTHOR]

Osmotic pressure and major ions (Cl−, Na+, Mg2+, Ca2+) of the egg capsule fluid in the slipper limpet Crepidula fornicata were investigated in relation to embryonic development. Calcium permeability of the capsule wall was studied at oviposition, by dipping freshly laid egg capsules in 45Ca as a tracer. This study also determined total calcium content of the embryos at different developmental stages. Osmolarity and major ion concentrations in egg capsule fluid were higher than seawater at uncleaved and trochophore stages, and then dropped to the same level as sea water at veliger stage. Concentrations of Cl− and Na+ were relatively high at oviposition, peaked at trochophore stage, and finally dropped close to concentrations of seawater at hatching. In contrast, concentrations of Mg2+ and Ca2+ decreased steadily during capsular development. Radiotracer permeability experiments in freshly laid egg capsules confirmed that the capsule wall is impermeable to this ion at that stage. However, because of the dissolution of the inner layer of the wall during the final part of capsular development, the wall becomes permeable to calcium and probably to the rest of the major ions studied. [ABSTRACT FROM AUTHOR]

This study demonstrates that the timing of larval starvation did not only determine the larval quality (shell length, lipid content, and RNA:DNA ratio) and the juvenile performance (growth and filtration rates), but also determine how the latent effects of larval starvation were mediated in Crepidula onyx. The juveniles developed from larvae that had experienced starvation in the first two days of larval life had reduced growth and lower filtration rates than those developed from larvae that had not been starved. Lower filtration rates explained the observed latent effects of early larval starvation on reduced juvenile growth. Starvation late in larval life caused a reduction in shell length, lipid content, and RNA:DNA ratio of larvae at metamorphosis; juveniles developed from these larvae performed poorly in terms of growth in shell length and total organic carbon content because of “depletion of energy reserves” at metamorphosis. Results of this study indicate that even exposure to the same kind of larval stress (starvation) for the same period of time (2 days) can cause different juvenile responses through different mechanisms if larvae are exposed to the stress at different stages of the larval life. [ABSTRACT FROM AUTHOR]

The size-advantage model and sex-allocation theory are frequently invoked to explain the evolution and maintenance of sequential hermaphroditism in many taxa. A test of current theory requires quantitative estimates of reproductive success and knowledge of the relationship between reproduction and size for each gender. Reproductive success can be difficult to measure. In species where polyandry occurs, it can be quantified only by determining paternity of offspring. We employed microsatellite loci to establish paternity for 12 families of Crepidula fornicata, where a family is defined as a single female, her brood, and the males stacked on top of her. Genetic data were analyzed and paternity was assigned to a single potential father for more than 83% of the offspring tested. Estimates of reproductive success revealed that one male within the family fathered the majority of offspring and that he was usually the largest male and the one closest to the brooding female. The dominant male's success also tended to decrease as the number of mature males within the family increased. Our results suggest that sperm competition could be a driving force in determining male reproductive success and the timing of sex change in C. fornicata. [ABSTRACT FROM AUTHOR]

This paper concerns the role of nitric oxide (NO) in controlling metamorphosis in the marine gastropod Crepidula fornicata. Metamorphosis was stimulated by the nitric oxide synthase (NOS) inhibitors AGH (aminoguanidine hemisulfate) and SMIS (S-methylisothiourea sulfate) at concentrations of about 100-1000 µmol l-1 and 50-200 µmol l-1, respectively. Metamorphosis was not, however, induced by the NOS inhibitor L-NAME (L-Ng-nitroarginine methyl ester) at even the highest concentration tested, 500 p, mol l-1. Moreover, pre-incubation with L-NAME at 20 and 80 µmol l-1 did not increase the sensitivity of competent larvae to excess K+, a potent inducer of metamorphosis in this species; we suggest that either L-NAME is ineffective in suppressing NO production in larvae of C. fornicata, or that it works only on the constitutive isoform of the enzyme. In contrast, metamorphosis was potentiated by the guanylate cyclase inhibitor ODQ (1H-[1,2,4]oxadiazolo[4,3, -a]quinoxalin-l-one) in response to a natural metamorphic inducer derived from conspecific adults. Because NO typically stimulates cGMP production through the activation of soluble guanylate cyclase, this result supports the hypothesis that NO acts as an endogenous inhibitor of metamorphosis in C. fornicata. The expression of NOS, shown by immunohistochemical techniques, was detected in the apical ganglion of young larvae but not in older larvae, further supporting the hypothesis that metamorphosis in C. fornicata is made possible by declines in the endogenous concentration of NO during development. [ABSTRACT FROM AUTHOR]

Larvae of the slipper limpet Crepidula onyx metamorphose in response to marine biofilms. In this study, we investigated how the percentage of larval metamorphosis in this species was affected by biofilms that differed in certain attributes. To manipulate bacterial and diatom cell densities and community composition, we developed biofilms in the laboratory (1) at different temperatures (16, 23 and 30°C) and salinities (20, 27 and 34‰), (2) with or without addition of antibiotics, and (3) in the light or in the dark. We also allowed biofilms to develop at three field sites with different prevailing environmental conditions so as to generate biofilms with different, but natural, attributes. Bacterial and diatom community composition in biofilms were determined using a DNA fingerprinting technique and microscopic examination, respectively. The effects of biofilms on metamorphosis were investigated in laboratory assays. The percentage of larval metamorphosis correlated with bacterial and diatom cell densities in only one of the three experiments conducted, but was substantially affected by differences in bacterial and diatom community composition in all three experiments. It also appears that metamorphosis of C. onyx depends on the simultaneous presence of both bacterial and diatom communities in biofilms. [ABSTRACT FROM AUTHOR]

Abstract: The effects of season and qualitative selection capacity on trophic relationships between two sympatric invasive suspension-feeders, Crepidula fornicata and Crassostrea gigas, were investigated in Bourgneuf Bay (France) from January 2003 to June 2004. Carbon and nitrogen stable isotopic deviations, δ 13C and δ 15N, of common Atlantic slippersnails and Pacific oysters were analysed relative to isotopic composition and availability of end-members. Slippersnail deviations were less variable over the sampling period compared with those of oysters. Significant differences between δ 13C and δ 15N of C. fornicata and C. gigas were found from winter to early summer, and linked to major isotopic changes in oysters. We identified three distinct seasonal periods: January to March when oysters were 15N-enriched compared to slippersnails and to themselves at other times of the year, April to June–July when oysters showed a 15N-depletion and a more marked 13C-depletion compared to slippersnails and to themselves at other times of the year, and July–August to December when both species presented similar carbon and nitrogen deviations. Species-specific differences in qualitative selection capability may explain these seasonal differences in isotopic deviations. Whereas the isotopic composition of the indiscriminate suspension-feeding slippersnails reflects the composition of the seston throughout the year, the oyster is capable of qualitative selection. The oyster isotopic compositions are consistent with a facultative activation of selection mechanisms under conditions of qualitative and quantitative food limitation, notably the preferential ingestion and assimilation of the dominant organic source in the suspended pool. We conclude that C. fornicata and C. gigas are trophic competitors only in winter and spring at this site, where detrital end-members are major POM components. These results underscore (1) the importance of long-term (annual) studies in the evaluation of potential trophic competition, and (2) the necessity to include the qualitative selection capacities of suspension-feeders in future interpretations of trophic relationships in marine coastal ecosystems. [Copyright &y& Elsevier]

Abstract: This study focussed on the determination of the main trophic subsidies for three dominant filter feeding molluscs of the benthic community, namely, Crassostrea gigas (Thunberg), Mytilus edulis (L.) and Crepidula fornicata (L.), cultivated or naturally occurring in the Bay of Mont Michel (France). δ 13C and δ 15N values revealed that the diet of these filter feeders was primarily based on marine plankton together with a lower contribution of the organic matter derived from salt marsh phanerogames, as estimated through the isotopic mixing equations (Isosource). The microphytobenthos inhabiting the intertidal flat and the salt marshes do not contribute significantly to the diet of cultivated and naturally occurring C. gigas and M. edulis. Hence, in this bay, the major trophic pathways differ from previous results obtained in several coastal systems devoted to shellfish culture. This could result from ecological particularities and/or strong hydrodynamic conditions in the Bay of Mont Michel. [Copyright &y& Elsevier]