The influence of infections with trematodes Bunocotyle progenetica (Hemiuridae) and Cryptocotyle cancavum (Heterophyidae) onto mortality of littoral mollusks Hydrobia ulvae (Gastropoda: Prosobranchia) after freezing

The mortality of prosobranch snails Hydrobia ulvae uninfected and infected with the parthenites of two species of Trematodes (Bunocotyle progenetica and Cryptocotyle cancavum) after freezing in seawater of different salinity with following thawing has been studied. Reduced salinity exceeds mortality of snails under freezing significant (p < 0.01). The mortality of mollusks increases significant (p < 0.01) with the increase of the exposure time. The mortality of females exceeds the mortality of male significant (p < 0.01) within the group of 2-years individuals. The negative effect of trematode invasion to the vitality of mollusks after freezing was not showed. Trematode infestation registered in March 2004 and in September 2003 is not significant differ (Levakin, 2004). Thus any important differential mortality of individuals H. ulvae infected with parthenites of this Trematodes is not present during a winter time. The conclusion is conformed by the results of our experiments and well accords to features of realization of life cycles of these Trematodes under conditions of the White Sea intertidial zone, where infection is possible only within the worm season.     

The influence of infections with trematodes Bunocotyle progenetica (Hemiuridae) and Cryptocotyle cancavum (Heterophiidae) onto mortality of littoral molluscs Hydrobia ulvae (Gastropoda: Prosobranchia) in condition of extremely high temperature

The effect of invasion of two trematode species, Bunocotyle progenetica (Hemiuridae: Bunocotylinae) and Cryptocotyle cancavum (Heterophiidae) on the host vitality is estimated. The mortality of infected and uninfected individuals of Hydrobia ulvae after different exposure time (3, 6, 9 and 12 hours) under extremely high temperature (+42 degrees C) was compared. The total death of the host was observed after 12 hours of experiment. The death rate of molluscs infected with B. progenetica ranged from 60 to 100% and was significantly higher (p < 0.01) than mortality of individuals infected with C. cancavum and uninfected snails in each case of exposure (3, 6 and 9 hours). At the same time the mortality of individuals infected with C. cancavum was significantly higher (p < 0.05) than the mortality of uninfected snails only after 9 hours of exposure (13.3 and 3.1%, respectively). Difference in pathogen effects B. progenetica and C. cancavum is expressed in different temperature resistance of the host that may be explained by different localisation of redia, their motile activity and manner of feeding. Besides, the invasion by C. cancavum causes the sterilization and accelerated growth of hosts. Low decreasing of the resistance to overheating in snails infected with this trematode could be explained by a compensation effect of this infection. This compensation realizes due to the redistribution of some part of the reproductive energy after the sterilization. An absence of parasitic castration in the case of infection with B. progenetica is a key reason of such considerable declining of their vitality. High lethality of the host appears to be adaptive for the parasite with the monoxenous life cycle.     

Broad-scale patterns of abundance of non-indigenous soft-bottom invertebrates in Denmark

Quantifying the broad-scale distribution and abundance of non-indigenous species (NIS) is necessary to provide accurate estimations on impacts of invasions, to prioritize research, and to guide national management. Sediment grab-sampling is a standardized method for monitoring marine benthos. In Denmark, ~45,000 grab-samples were collected from 1970 to 2005. Using these samples, we compared densities of NIS and native species among 27 broad spatio-temporal groupings. Eight known NIS and one ‘cryptogenic species’ (the polychaete Neanthes succinea) were found in the samples. Most were present in low abundance, but the bivalve Mya arenaria, likely introduced by the vikings from North America, was particularly abundant. M. arenaria was found in ca. 20% of all samples and was among the 10 most common species in all of Denmark. M. arenaria’s high abundance, high filtration capacity and importance in food-web interactions, suggest that this species has dramatically impacted shallow coastal ecosystems in Denmark. The polychaete Marenzelleria viridis, the gastropod Potamopyrgus antipodarum and N. succinea were also widespread and abundant, and they too are likely to have had broad-scale impacts. In conclusion, 28% of grab-samples collected in Denmark over 35 years were affected by some degree of NIS or cryptogenic species, suggesting that centuries of human-mediated transfer of organisms has had a profound impact on the ecology of soft-bottom systems in Denmark.     

Parasites on an intertidal Corophium-bed: factors determining the phenology of microphallid trematodes in the intermediate host populations of the mud-snail Hydrobia ulvae and the amphipod Corophium volutator

The phenology of microphallid trematodes within their intermediate hostpopulations has been studied on an intertidal mud flat. The parasites usethe mud snail Hydrobia ulvae and the infaunal amphipod Corophium volutatoras first and secondary intermediate host, respectively. Migratory shorebirdsact as final hosts. Our results show a general trend of decline in thedensity of infected intermediate hosts during both spring and autumn, whichcould mainly be ascribed to shorebird predation. During summer the densityof both infected snails and infected amphipods increased considerably, witha culmination in June within the snail population (1000 infectedm-² and in August within the amphipod population (40 000infected m-². This time lag in parasite occurrence could berelated to (1) the development time of larval trematodes within the snails,(2) higher ambient temperatures in late summer increasing parasitetransmission between snails and amphipods during this period, and (3) ageneral increase in the Corophium population during late summer. Fromsamples collected between 1990 and 1995 it is shown that microphallidtrematodes occasionally may give rise to mass mortality in the amphipodpopulation. The prerequisites for such an event are a high parasiteprevalence within the first intermediate host population and unusually highambient temperatures, facilitating parasite transmission to the secondaryintermediate host, C. volutator.     

Evidences of habitat displacement between two common soft-bottom SW Atlantic intertidal crabs

The intertidal burrowing crab Chasmagnathus granulatus Dana is the dominant species in soft sediments and vegetated intertidal areas along the SW Atlantic estuaries (southern Brazil 28°S to the northern Argentinean Patagonia 41°S) where it produces dense and extensive burrowing beds. The mud crab Cyrtograpsus angulatus Dana coexists with Ch. granulatus in this area, but it also inhabits areas to the south (northern and central Argentinean Patagonia). A survey covering both areas showed that C. angulatus rarely live in burrows when coexisting with Ch. granulatus, but form large burrowing beds when not coexisting with Ch. granulatus. When both species coexisted, burrowing beds of C. angulatus are restricted to sandy-muddy areas. Only rarely are burrows of C. angulatus found within Ch. granulatus beds. However, when Ch. granulatus were experimentally excluded within their burrowing beds, new settlers of C. angulatus made burrows and maintained them until they reached large size. Paired (inside and outside Ch. granulatus burrowing bed) sampling during high tide using beach nets showed that C. angulatus rarely venture inside the Ch. granulatus crab beds. Other field experiments showed that adults Ch. granulatus always displace C. angulatus from burrows. Furthermore, in several sites located south of the limit of distribution of Ch. granulatus at the Patagonian coast, soft bare intertidals are dominated by burrowing beds of C. angulatus mixed with the congener C. altimanus Dana. Together, these evidences suggest that the mud crab C. angulatus is displaced from soft bottom areas by the burrowing crab Ch. granulatus. It is an example of competitive exclusion through aggressive interference in soft-bottom habitats when the shared resource is the access to sediment surface, a two-dimensional well-defined resource.     

Study of phosphagens in two trematodes

Extracts from the adults of two trematodes Fasciola gigantica and Paramphistomum explanatum have been shown to contain three phosphagens, phosphoarginine, phosphocreatine, and phosphoglycocyamine. The three phosphokinases involved in the transphosphorylation of these phosphagens in both worms were inhibited by EDTA and mercuric ions while iodoacetate had no effect.     

Mass mortality associated with koi herpesvirus in wild common carp in Canada

Koi herpesvirus (KHV) was identified as being associated with more than one mortality event affecting common carp in Canada. The first was an extensive mortality event that occurred in 2007 in the Kawartha Lakes region, Ontario, affecting Lakes Scugog and Pigeon. Fish had branchial necrosis and hepatic vasculitis with an equivocal interstitial nephritis. Several fish also had branchial columnaris. Subsequent mortality events occurred in 2008 in additional bodies of water in south-central Ontario, such as Lake Katchewanooka and outside of Ontario in Lake Manitoba, Manitoba. Koi herpesvirus was detected in fish submitted for examination from all of these lakes by polymerase chain reaction (PCR), and sequence of the PCR product revealed 100% homology to KHV strains U and I. Real-time PCR analysis of KHV-infected wild carp revealed viral loads ranging from 6.02×10(1) to 2.4×10(6) copies μg(-1) host DNA. This is the first report of KHV in Canada.     

Recruitment of marine invertebrates: the role of active larval choices and early mortality

Summary Spatial variation in the recruitment of sessile marine invertebrates with planktonic larvae may be derived from a number of sources: events within the plankton, choices made by larvae at the time of settlement, and mortality of juvenile organisms after settlement, but before a census by an observer. These sources usually are not distinguished.A study of the recruitment of four species of sessile invertebrates living on rock walls beneath a kelp canopy showed that both selection of microhabitats by settling larvae and predation by fish may be important. Two microhabitats were of interest; open, flat rock surfaces, and small pits and crevices that act as refuges from fish predators.The polychaete Spirorbis eximus and the cyclostome bryozoan Tubulipora spp. showed no preference for refuges, but settled apparently at random on the available substrata. Tubulipora was preyed upon heavily by fish, while Spirorbis was relatively unaffected. The bryozoans Celleporaria brunnea and Scrupocellaria bertholetti both recruited preferentially into refuges. Scrupocellaria were preyed upon, while Celleporaria juveniles seemed unaffected. Predation by fish modified the spatial distribution (Tubulipora), abundance (Tubulipora), or size distribution (Scrupocellaria) of the juvenile population, or had relatively little effect (Celleporaria, Spirorbis).All of the above events occur within three weeks of settlement. Since inferences about the effect of larval events on the population dynamics of adult organisms are often based on observations of the patterns of recruitment after one or two months, they are therefore likely to be misleading.     

Cd transfer in the deposit-feeder Prosobranch Hydrobia ulvae (Pennant) from benthic diatoms: the kinetics of rapid Cd assimilation and efflux

The kinetics of Cd trophic transfer from benthic diatoms to the Prosobranch mud snail Hydrobia ulvae was described experimentally in microcosms using Cd contaminated microalgae (0.71, 3.63 and 8.54 μg Cd mg Chl a⁻¹). The depurated mud snails (2 ind. cm⁻²) were allowed to feed on the stable Cd pre-contaminated benthic diatoms at the concentration of 2 mg Chl a dm⁻³ to ensure that the algal food availability was not a limiting factor. Weight-specific ingestion rate (IR) and assimilation efficiency (AE) were calculated by an indirect mass-balance method on the basis of metal residues in the snail tissues, and metal loss (efflux rate, Δe) was estimated for the time intervals when a decrease or no change in the tissue metal concentrations occurred.A similar pattern of consumption was observed in all experiments: ingestion was rapid over the first 4 h, followed by slower ingestion period (between 4 and 16 h). The feeding behaviour of H. ulvae was not affected by the different diatom Cd concentrations. An analogous two-phasic pattern was observed in the tissue Cd concentration changes. Net accumulation of Cd in the snails was observed for the two highest exposures, indicating that the Cd threshold concentration in food above which metal is retained in the body, lies between 0.71 and 3.63 μg Cd mg Chl a⁻¹. The respective 16-h AEs were 0.024% and 0.004% potentially due to rapid gut-passage of microalgae and/or diminished nutritional value of the food. The efflux rates, calculated for the last 12 h of exposure, were positively related to the concentration of Cd in the snail tissues and microalgae. This study demonstrated that trophic transfer should be considered as a source of Cd accumulation in snails and the ability of H. ulvae to enhance their rate of Cd elimination in response to elevated metal concentrations in the ambient environment is relevant for models predicting metal bioaccumulation and toxicity in coastal and estuarine systems.     

Component community of larval trematodes in the mudsnail Hydrobia ventrosa: temporal variations in prevalence in relation to host life history

Temporal variations in the prevalence of larval trematodes in the short-lived prosobranch mudsnail Hydrobia ventrosa (Montagu) were investigated in relation to host life history and season for 4 successive years in temperate windflats of the southern Baltic Sea. The component community of trematode larvae in H. ventrosa comprises at least 10 species; families (and species) represented include Notocotylidae (1), Echinostomatidae (1 or 2), Heterophyidae (2), Monorchidae (1), Microphallidae (3 or 4), Psilostomatidae (1), and Hemiuridae (1). The notocotylid Paramonostomum alveatum was the most prevalent species, followed by the microphallids Maritrema subdolum and Microphallus sp. Trematode prevalence in H. ventrosa fluctuated seasonally. Prevalence usually peaked in summer between July and September-October and decreased in late winter-early spring. This seasonal change is chiefly explained by the life history patterns of the semelparous snail host. Hydrobia ventrosa has a maximum life span of about 2 yr and reproduces between June and November of its second calendar year. The first trematode infections appeared annually in May when the most abundant cohort of H. ventrosa, the second-calendar-year snails, mature. The prevalence continued to increase until August-September, throughout the reproductive period of the second-calendar-year snails, Prevalence decreased during winter, when most of the second-calendar-year snails died after reproduction. On the basis of longterm laboratory experiments, it has been shown that the late autumn-winter mortality was not the result of trematode infections. Seasonal patterns of prevalence were similar among the trematode species except for the monorchid Asymphylodora demeli, the only one using fish definitive hosts. Species-specific differences in the seasonal occurrence of prepatent infections and the predominance of certain larval stages in winter are interpreted as different strategies of the trematode species to survive the harsh winter conditions, or to survive the death of the first intermediate host in autumn-winter, or both.     

Family of CNP neuropeptides: common morphology in various invertebrates

Neuropeptides expressed in the command neurons for withdrawal behavior were originally detected in the the central nervous system (CNS) of the terrestrial snail Helix (command neurons peptides, CNP). The family of CNP-like neuropeptides bears a C-terminal signature sequence Tyr-Pro-Arg-X. Using antisera against two of them, we have studied the CNS of various invertebrates belonging to the phyla of mollusks, annelids and insects. The immunoreactive neurons were detected in all studied species. Stained neurons were either interneurons projecting along the CNS ganglia chain, or sensory neurons, or neurohormonal cells. Beyond common morphological features, the immunoreactive cells had another similarity: the level of CNP expression depended on the functional state of the animal. Thus, the homologous neuropeptides in evolutionary distant invertebrate species possess some common morphological and functional features.     

Comparative life histories of two diplostomid trematodes, Ornithodiplostomum ptychocheilus and Posthodiplostomum minimum

A lack of comparative studies limits our understanding of interspecific variation in parasite life histories, especially for species that incorporate asexual and resting stages into their life cycles. Ornithodiplostomum ptychocheilus and Posthodiplostomum minimum are sympatric diplostomid trematodes that share the same first (pond snail, Physa gyrina) and second (fathead minnow, Pimephales promelas) intermediate hosts within lakes in Alberta, Canada. Interspecific differences in the body sizes of adults, cercariae, and metacercariae were evaluated from parasites recovered from laboratory-raised chickens, snails, and minnows, respectively. Differences in adult worm fecundity and cercariae production were estimated from chickens and snails exposed to known numbers of parasite larvae. Posthodiplostomum minimum adults, metacercariae, and eggs were 97, 86, and 5% larger than those of 0. ptychocheilus, respectively. The average numbers of eggs produced per day by P. minimum was 3 times higher than for O. ptychocheilus, and P. minimum produced approximately twice as many cercariae per day. Although the larger of the 2 species had higher egg and cercariae production, conclusions regarding covariation between adult worm size and the reproductive rates of other life cycle stages require further studies on related species.     

Effects of digenean trematodes and heterotrophic bacteria on mortality and burying capability of the common cockle Cerastoderma edule (L.)

Population dynamics of marine invertebrates is controlled by a variety of abiotic and biotic factors. Among these, some have received lesser attention from marine ecologists because of their ‘discrete’ nature. This is the case of parasitism and bacterial load. In the present study, we focused on the role that both digenean trematodes and heterotrophic aerobic bacteria might play in the mortality and burying behaviour of cockles, Cerastoderma edule.The bivalves were sampled monthly during 1 year from two sites in Arcachon Bay (French Atlantic coast). Mortality rates were assessed after transferring in the laboratory normally buried and unburied (i.e. found lying at the sediment surface at low tide) cockles. Their digenean and bacterial loads were determined for both positions (normally buried and unburied). Mortality rate was significantly higher for cockles found out of the sediment at low tide, suggesting that this abnormal position was a prelude to cockles' death. Comparison of digenean load of cockles showed no significant difference between buried and unburied bivalves. In contrast, bacterial load was significantly higher in unburied cockles than in normally buried animals. The effect of high concentration of a marine bacterial strain (Pseudomonas fluorescens) on cockles' burying behaviour and mortality was tested in the laboratory. Results showed that these bacteria could trigger the emergence of animals from the sediment but did not cause cockles' death. These field observations and laboratory experiments suggest that bacteria, rather than digenean trematodes, could play a role in the emergence of cockles and, hence, affect their survival in the wild.     

Gene flow between populations of two invertebrates in springs

1. Using allozymes, we analysed genetic structure of the freshwater gastropod Bythinella dunkeri and the freshwater flatworm Crenobia alpina. The two species are habitat specialists, living almost exclusively in springs. The sampled area in Hesse (Germany) covers a spatial scale of 20 km and includes two river drainages. From the biology of the two species we expected little dispersal along rivers. However, the possibility exists that groundwater provide suitable pathways for dispersal. 2. In B. dunkeri heterozygosity decreased from west to east. For some alleles we found clines in this geographic direction. These clines generated a positive correlation between geographic distance and genetic differentiation. Furthermore patterns of genetic variation within populations suggested that populations may have been faced with bottlenecks and founder effects. If populations are not in population genetic equilibrium, such founder effects would also explain the rather high amount of genetic differentiation between populations (10%). 3. For C. alpina the mean number of alleles decreased with increasing isolation of populations. Genetic differentiation between populations contributed 19% to the total genetic variation. Genetic differentiation was not correlated to geographic distance, but compared with B. dunkeri variability of pairwise differentiation between pairs of populations was higher in C. alpina. 4. Overall B. dunkeri appears to be a fairly good disperser, which may use groundwater as dispersal pathway. Furthermore populations seem to be not in equilibrium. In contrast C. alpina forms rather isolated populations with little dispersal between springs and groundwater seems to play no important role for dispersal.     

Experimental differences in mortality patterns between European minnows, Phoxinus phoxinus, infected with sympatric or allopatric trematodes, Diplostomum phoxini

A factorial experiment was conducted to examine if the digenetic trematode parasite Diplostomum phoxini influences minnow growth and survival negatively and if different parasite populations differ in their effects on hosts. Juvenile full-sibling minnows from a lake located at the northern edge of the Swiss Alps were infected experimentally with D. phoxini from either their own or another lake. When exposed to sympatric parasites, the minnows survived a low and a high infection dose more or less equally, but with allopatric parasites mortality increased with infection dose. Parasites did not reduce host growth and minnows exposed to a low infection dose grew quicker than either non-infected ones or ones exposed to a high infection dose. Thus, the results show different patterns of pathogenicity between two parasite populations and suggest that (1) the observed differences are at least partially genetic and that (2) the co-evolved, sympatric host-parasite association has reached a degree of low pathogenicity. Differences between the findings presented here and those of a previously published study are discussed.     

Mass and temperature dependence of metabolic rate in litter and soil invertebrates

Metabolic scaling theory provides a framework for modeling the combined mass and temperature dependence of metabolic rate. The theory predicts that whole-organism metabolic rate should scale with body mass raised to the 3/4 power as a consequence of the physical characteristics of internal distribution networks. Metabolic rate is predicted to vary with absolute body temperature, T, according to the Boltzmann factor, e(-E/kT), where E is the apparent activation energy of biochemical reactions, 0.2-1.2 eV, and k is Boltzmann's constant. I evaluated those predictions, using a compilation of published data on the metabolic rates of litter- and soil-dwelling earthworms, isopods, oribatid mites, springtails, and spiders. Earthworms, oribatid mites, springtails, and spiders had mass-scaling exponents that were statistically indistinguishable from the expected value of 0.75. The scaling exponent for terrestrial isopods, 0.91, was significantly greater than expected. All taxa had apparent activation energies within the predicted range of 0.2-1.2 eV. Activation energies for isopods, oribatid mites, springtails, and spiders were not significantly different from the average expected value of 0.6 eV, while the activation energy for earthworms, 0.25 eV, was significantly lower than 0.6 eV. Updated equations for estimating metabolic rate from body mass and environmental temperature are given for investigations into the ecological energetics of litter and soil animals.     

Development in vitro of the neuromusculature of two strigeid trematodes,Apatemon cobitidis proterorhini and Cotylurus erraticus

Confocal microscopy interfaced with cytochemical procedures has been used to monitor development of the major muscle systems and associated serotoninergic (5-HT, 5-hydroxytryptamine) and peptidergic (FaRP, FMRFamide-related peptide) innervation of the strigeid trematodes, Apatemon cobitidis proterorhini and Cotylurus erraticus during cultivation in vitro. Sexually undifferentiated metacercariae were successfully grown to ovigerous adults using tissue culture medium NCTC 135, chicken serum and egg albumen. Eggs were produced after 5 days in culture but had abnormal shells and failed to embryonate. 5-HT and FaRP (the flatworm FaRP, GYIRFamide) were localised immunocytochemically in both central and peripheral nervous systems of developing worms. During cultivation, the central serotoninergic and FaRPergic neuronal pathways of the forebody became more extensive, but retained the same basic orthogonal arrangement as found in the excysted metacercaria. Longitudinal extensor and flexor muscles of the hindbody provide support for the developing reproductive complex. The male reproductive tracts were established in advance (day 3) of those of the female system (day 4); completion of the latter was marked by the appearance of the ootype/egg chamber. The inner longitudinal muscle fibres of the female tract appeared prior to the outer and more densely arranged circular muscles. Circular fibres dominate the muscle complement of both alimentary and reproductive tracts. 5-HT- and GYIRFamide-immunoreactivities were demonstrable in the central nervous system (CNS) and subtegumental parasympathetic nervous system (PNS) throughout the culture period, but innervation of the developing reproductive structures was reactive just for 5-HT. Only at the onset of egg production was FaRP-IR observed in the reproductive system and was expressed only in the innervation of the ootype, a finding consistent with the view that FaRPs may regulate egg assembly in platyhelminths.     

Massive mortality of marine invertebrates: an unprecedented event in northwestern Mediterranean

An unprecedented mass mortality event has been observed at the end of the summer 1999 along the coasts of Provence (France) and Ligury (Italy). This event has severely affected a wide array of sessile filter-feeder invertebrates from hard-substratum communities, such as sponges (particularly the keratose sponges Hippospongia and Spongia), cnidarians (particularly the anthozoans Corallium, Paramuricea, Eunicella and Cladocora), bivalves, ascidians and bryozoans. Along the Provence coasts, the outbreak spread from east to west. Exceptionally high and constant temperatures of the whole water column (23-24 degrees C, for over one month, down to 40 m) could have determined an environmental context favourable to the mass mortality event. Like the thermal anomaly, the mortality is limited in depth. However, we cannot ascertain whether temperature had a direct effect on organisms or acted in synergy with a latent and/or waterborne agent (microbiological or chemical). Taking into account the global warming context in the NW-Mediterranean, monitoring programs of physical-chemical parameters and vulnerable populations should rapidly be set up.