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In the current context of environmental change, ocean acidification is predicted to affect the cellular processes, physiology and behaviour of all marine organisms, impacting survival, growth and reproduction. In relation to thermal tolerance limits, the effects of elevated pCO2 could be expected to be more pronounced at the upper limits of the thermal tolerance window. Our study focused on Crepidulafornicata, an invasive gastropod which colonized shallow waters around European coasts during the 20th century. We investigated the effects of 10 weeks' exposure to current (380 μatm) and elevated (550, 750, 1,000 μatm) pCO2 on this engineer species using an acute temperature increase (1 °C 12 h -1) as the test. Respiration rates were measured on both males (small individuals) and females (large individuals). Mortality increased suddenly from 34 °C, particularly in females. Respiration rate in C.fornicata increased linearly with temperature between 18 and 34 °C, but no differences were detected between the different pCO2 conditions either in the regressions between respiration rate and temperature or in Q10 values. In the same way, condition indices were similar in all the pCO2 treatments at the end of the experiment, but decreased from the beginning of the experiment. This species was highly resistant to acute exposure to high temperature regardless of pCO2 levels, even though food was limited during the experiment. Crepidulafornicata appears to have either developed resistance mechanisms or a strong phenotypic plasticity to deal with fluctuations of physicochemical parameters in its habitat. This suggests that invasive species may be more resistant to future environmental changes than its native competitors. [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]

Although the phenomenon of multilocus heterozygote deficiencies in numerous taxonomically diverse molluscs has been studied for over 30 years it has resisted general explanation. Here we describe a case in Crepidula onyx Sowerby, a common protandrous slipper limpet on the Pacific coast of southern California. Spatial and temporal differentiation at 16 polymorphic allozyme loci were examined in samples of adult snails from three or four seasons and six localities in Mission Bay, San Diego. The populations were highly polymorphic (proportion of polymorphic loci PL=0.65–0.69; mean individual heterozygosity HO=0.13–0.29) and although there were slightly more changes in allele frequency between autumn and winter than between winter and spring, statistically significant spatial and temporal change or patterning was not detected. If the larvae are passive dispersers the lack of population structure is attributable to the fact that during any three-week period that they are in the plankton, the waters of Mission Bay are completely mixed by tidal currents. In marked contrast, statistically significant heterozygote deficiencies were found in all samples (locality and season) and subsamples (males and females). At each locality and season, deficiencies were as pronounced in males as in females. Furthermore, at each locality, there was no increase in level of multilocus deficiency between males in one season and females in a subsequent season. We conclude that the heterozygotes had been lost in the larval planktonic stage or at the time of metamorphosis and settlement. Several hypotheses to explain the heterozygote deficiencies in adults are discussed: inbreeding, self-fertilization, presence of null alleles, allele scoring bias, aneuploidy, parental imprinting, spatial and temporal Wahlund effects, age-effects, and direct natural selection on the marker loci. Although we can reject some of these hypotheses, others like inbreeding, require testing with markers with greater statistical power. Wahlund effects due to inadvertent mixing of two cryptic species and/or micro-spatial population genetic structuring due to reproductive asynchronies appear unlikely causes. Natural selection against heterozygotes in the larval phase of life may account for the observations, but selection does not appear to operate directly on any of the individual loci studied. An hypothesis is offered to explain the general selection against heterozygotes during the pelagic larval stage, and for the reverse during the sessile adult stage. Selection coefficients would, however, have to be unusually high and we conclude that we are unable satisfactorily to explain our observations. [ABSTRACT FROM PUBLISHER]

Epibionts of mussels can have detrimental effects on their basibionts, such as reduced growth rates, lower fecundity, increased mortality and an enhanced risk of dislodgement of the overgrown bivalves due to stronger hydrodynamic forces. In blue mussels Mytilus edulis, the epibiotic American slipper limpet Crepidula fornicata reduces growth and survival. In a field experiment we tested the hypothesis that an enhanced byssus thread production with high energetic costs for the mussels due slipper limpet epibionts is the underlying mechanism for the epibiont burden. Byssus thread production in overgrown mussels was twice as high as in unfouled M. edulis (11 ± 0.9 and 5.4 ± 0.6 byssus threads/mussel/day, respectively). A control experiment revealed intermediate byssus thread production (8.4 ± 0.8 byssus threads/mussel/day) in mussels cleaned of C. fornicata at the beginning of the experiments, indicating that C. fornicata is responsible for the effects observed. We conclude that increased byssus production in fouled M. edulis is a functional response to higher drag caused by epibionts and that it is associated with increased energy expenditure that reduces allocation of resources for other processes such as growth, reproduction and survival. Such indirect effects of epibionts, mediated by an enhanced byssus production, may be widespread in byssus-producing bivalves, with important implications for their population dynamics. [ABSTRACT FROM AUTHOR]