Hydrobia Ventrosa Research Articles

A history of Pistacia lentiscus and Pinus brutia trees and their ecological changes in the Güllük Bay (Muğla, SW Turkey) during the last 400 years

In this study, we present pollen records together with a multiproxy analysis from a sediment core collected from the Güllük Bay (Bargilya Cove, Muğla, SW Turkey), covering the last 400 years. Pistachio shrubland was occupying around the Güllük Bay between 1613 and 1741 AD. However, after 1741 AD, the vegetation canopy suddenly changed and Turkish pine (Pinus brutia) was established. This supports that the main factor affecting the expansion of Pistacia lentiscus was precipitation rather than temperature after 1741 AD. This change is also indicated by high Sr-Ca values, reflecting arid conditions. Two anthropogenic phases developed in the region. The first phase is marked by Olea europeae between 1613 and 1789 AD. The second is characterized by Plantago, Caryophyllaceae, Cerelia, Rumex, and Sanguisorba minor type suggesting pastoralism and agricultural activities between 1789 and 1964 AD. Macrofaunal communities are also indicative of environmental changes. Abra ovata, Cerastoderma glaucum, Bittium reticulatum, and Skenea catenoides were first settlers between 1572 and 1643 AD. The prominent presence of lagoonal species Abra ovata and Hydrobia ventrosa indicates a lagoonal depositional environment in 1799-1948 AD.

Parasites of Moroccan desert Coptodon guineensis (Pisces, Cichlidae): transition and resilience in a simplified hypersaline ecosystem

Sebkha Imlili (Atlantic Sahara) is a salt flat with over 160 permanent holes of hypersaline water generated in the Holocene and inhabited by euryhaline organisms that are considered to be relics of the past, including the cichlid fish Coptodon guineensis. We surveyed the fish parasites four times over one year, to i) identify the parasites, and ii) determine possible seasonality in infection patterns. Over 60% of the fish were infected by one to three helminths: an acanthocephalan in the intestine and two digenean metacercariae in the kidney, spleen, liver, muscle, and mesenteries. The acanthocephalan Acanthogyrus (Acanthosentis) cf. tilapiae was identified morphologically and molecularly; only one digenean (the heterophyid Pygidiopsis genata) could be identified molecularly. Both identified parasites were present throughout the sampling periods; the unidentified metacercariae were present only in summer and fall. Mean intensities, but not prevalence of infection by the acanthocephalan, reflected a biannual pattern of transmission. Infection accrued with fish size, possibly due to cannibalism. Because the water holes include only a few invertebrates, the intermediate hosts of these parasites can be inferred to be the gastropod Ecrobia ventrosa for the digeneans and either the copepod Cletocamtpus retrogressus or the ostracod Cyprideis torosa for the acanthocephalan. This ecosystem appears stable and provides a window into the past, as the acanthocephalan likely switched from freshwater tilapia to C. guineensis when the Sebkha formed. However, this is a vulnerable environment where the survival of these parasites depends on interactions maintained among only very few hosts.

Relationship between individual metabolic rate and patch departure behaviour: evidence from aquatic gastropods

Individual energy requirements are tightly related to individual resource use and by extension of space‐use patterns and other traits at higher levels of the ecological hierarchy. However, there is still little experimental evidence linking individual energetics and space‐use behaviour. Individual energy requirements scale mainly with body size and temperature, but these do not explain all individual variation. Therefore, studies focused on inter individual variation in resource and space use behaviour can be used to frame foraging dynamics in an energy perspective. We empirically tested the hypothesis of a relationship between individual energetics and patch departure behaviour using as model organisms four small species (body mass ranging from 0.4 to 14 mg AFDW) of aquatic gastropods strongly differing in adult size: Galba truncatula, Bithynia tentaculata, Theodoxus fluviatilis and Ecrobia ventrosa (in descending order of size). Motility tests were performed in controlled microcosm conditions. The tests were designed to classify the specimens as either low motility (not inclined to abandon the patch) or high motility (likely to abandon the patch). The tests entailed measuring the propensity of the individuals to abandon a limited resource patch (2 g DW of conditioned Phragmites australis leaves) within a given amount of time (24 h) when foraging with conspecifics under conditions where competition for food is expected to increase over time due to resource depletion. The individual standard metabolic rate of the tested specimens was measured via open flow respirometry and compared across motility classes at intra‐ and interspecific level. At both levels, we observed that individuals with higher standard metabolic rates were more inclined to abandon the patch. This finding establishes a link between foraging theory and competitive coexistence mechanisms.

Transatlantic discovery of Notocotylus atlanticus (Digenea: Notocotylidae) based on life cycle data.

Digenean parasites feature a series of stages with a distinct appearance, reproduction mode, and lifestyle that together constitute their well-known, complex life cycle. Species descriptions of Digenea have always been based on one of these stages-the marita, or sexually reproducing adult in the final host. However, in some cases, data on the life cycle are essential for the differential diagnosis of closely related species. Here, we present the case of Notocotylus atlanticus, where different stages of its life cycle were discovered for the first time since the species description, and across the Atlantic. We used a material from a naturally infected intertidal marine snail, Ecrobia ventrosa, and several waterfowl species and also carried out infection experiments. For morphological studies, we employed light microscopy, SEM, and CLSM; molecular data obtained include sequences of ITS1 and 28S rRNA gene. We demonstrate that N. atlanticus adult worm morphology is barely sufficient to distinguish it from several other species. Cercariae morphology and identity of the first intermediate hosts provide crucial additional information. According to our preliminary phylogenetic reconstructions, two notocotylid lineages are associated with two major gastropod lineages-the Caenogastropoda and the Heterobranchia. The traditional character to identify notocotylid genera (structure of ventral organs) fails to explain the phylogeny and thus requires reassessment. Further reliable morphological, life cycle and molecular data on other species are likely to reveal more patterns in notocotylid systematics, host specificity, and evolution.

Molluscs and Ostracods of the Qarun Lake: Preliminary Report From FA-1 Core in Faiyum Oasis, Northern Egypt

Abstract A research was conducted on the Holocene lake sediments from the full-cored FA-1 drilling at the southern shore of the Qarun Lake in the Faiyum Oasis in northern Egypt. Altogether 10 taxa of molluscs and 8 taxa of ostracods were identified in the examined deposits, with total amounts of 768 and 2872 individuals, respectively. The fauna was investigated with palaeoecological purpose and allowed for preliminary reconstruction of sedimentary environment in the lake. The occurrence of Valvata nilotica Jickeli, 1874 and Gomphocythere sp. in the lower part of the core and a low proportion of carapaces (2.4-28%) indicated freshwater and higher-energy conditions, respectively. Rapid expansion of Cyprideis torosa (Jones, 1850) at a depth of 18 m could point to very short saline episode in the lake. The increase in salinity and drop of water level were evidenced in the uppermost part of the core (4-3.5 m), when the lake was dominated by Hydrobia ventrosa (Montagu, 1803), Cerastoderma glaucum (Poiret, 1789) and C. torosa. The steady sedimentation in a shallow lake was also supported by considerable amount of complete ostracod carapaces (45%). The faunal assemblage and smooth valves of C. torosa suggested salinity of 14-25‰.

Inter- and intra-specific variation in movement behaviour of benthic macroinvertebrates from a transitional habitat: a laboratory experiment

The movement behaviour of vagile organisms has long been acknowledged as a key determinant of species distribution and biodiversity patterns. Yet, scant information is available for aquatic invertebrates; in addition, the effects of inter-specific differences in morphology and intra-specific variations in body size have been inadequately investigated. In the present study, the movement behaviour of three crustacean species [Proasellus coxalis and Lekanesphaera hookeri (Isopoda) and Gammarus aequicauda (Amphipoda)] and two gastropod species (Ecrobia ventrosa and Bithynia leachii) dominating the macrobenthic assemblage of a Mediterranean transitional habitat (Giammatteo channel estuary, SE Italy) was analysed under resource-free laboratory conditions. The average path length and speed were determined for individuals encompassing a 16-fold range in body sizes. The scale-independent fractal dimension D was used to quantify the tortuosity of their trajectories. In general, significant differences were observed in movement metrics between crustaceans and gastropods; however, species-specific effects were obscured within each taxonomic group by a strong intra-specific variability. All crustacean species were characterized by a significant negative relationship between body size and path tortuosity; specifically, breaks in the slopes of the regression curve were observed, coinciding with sexual maturation. In contrast, negligible relationships were observed for gastropod species. The results of the study suggest that body size may represent a good predictor of movement behaviour for crustaceans but not for gastropods. Specifically, crucial steps of the biological cycle of amphipods and isopods may reflect on considerable variations in movement metrics. The metabolic and ecological implications of these findings are discussed.

Effects of organic pollution and physical stress on benthic macroinvertebrate communities from two intermittently closed and open coastal lagoons (ICOLLs)

Benthic macroinvertebrate communities and environmental conditions were studied in two intermittently closed and open coastal lakes and lagoons (ICOLLs), located in southern Algarve (Foz do Almargem e Salgados), with the purpose of evaluating the effects of organic pollution, originated mainly from wastewater discharges, and the physical stress caused by the irregular opening of the lagoons. Most of the year, lagoons were isolated from the sea, receiving the freshwater inputs from small rivers and in Salgados, also from the effluents of a wastewater plant. According to environmental and biotic conditions, Foz do Almargem presented a greater marine influence and a lower trophic state (mesotrophic) than Salgados (hypereutrophic). Benthic macroinvertebrate communities in the lagoons were distinct, just as their relations with environmental parameters. Mollusca were the most abundant macroinvertebrates in Foz do Almargem, while Insecta, Oligochaeta and Crustacea were more relevant in Salgados. Corophium multisetosum occurred exclusively in Salgados stations and, just as Chironomus sp., other Insecta and Oligochaeta, densities were positively related to total phosphorus, clay content and chlorophyll a concentration in the sediment, chlorophyll a concentration in water and with total dissolved inorganic nitrogen. Abra segmentum, Cerastoderma glaucum, Peringia ulvae and Ecrobia ventrosa occurred only in Foz do Almargem, with lower values of the above mentioned parameters. Both lagoons were dominated by deposit feeders and taxa tolerant to environmental stress, although in Salgados there was a greater occurrence of opportunistic taxa associated to pronounced unbalanced situations, due to excess organic matter enrichment.

Substratum preferences in two notocotylid (Digenea, Notocotylidae) cercariae from Hydrobia ventrosa at the White Sea

Notocotylids are digeneans with a two-host life cycle. Their cercariae encyst on underwater substrata, and final hosts (mostly water birds) get infected by consuming encysted metacercariae. The aim of this study was to assess whether notocotylid cercariae have encystment substratum preferences. We used Cercaria Notocotylidae sp. No 11 Deblock, 1980 (presumably Paramonostomum alveatum Mehlis 1846) and C. Notocotylidae sp. No 12 Deblock, 1980 associated with mudsnails Hydrobia ventrosa at the White Sea. Three series of experiments were performed in which distribution of cysts across different combinations of substrata was measured. The results suggest that C. Notocotylidae sp. No 11 cercariae encyst almost exclusively on the leaves of green plants without any plant species preferences. C. Notocotylidae sp. No 12 cercariae use shells of living molluscs and plant substrata equally often but avoid empty shells. These preferences are probably adapted to the feeding habits of the final hosts and this may enhance the transmission of the studied notocotylid species. Mechanisms of the observed preferences might be associated with the ability of cercariae to recognize substrata features: either chemical cues or surface structure. Substratum selectivity in cercariae is considered as a first step towards downward incorporation of the second intermediate host into the life cycle.

Biotic interactions affect the colonization behavior of aquatic detritivorous macroinvertebrates in a heterogeneous environment

It has previously been suggested that macroinvertebrates actively search for suitable patches to colonize. However, it is not well understood how the spatial arrangement of patches can affect colonization rates. In this study, we determined the importance of the environmental factors (distance, connectivity and resource availability) for patch colonization in an experimental system using Gammarus aequicauda (Amphipoda), Lekanesphaera hookeri (Isopoda) and Ecrobia ventrosa (Gastropoda). Furthermore, we also assessed how the relative importance of each of these environmental factors differed in interactions between the three species. The single species experiments showed that distance was the most important factor for G. aequicauda and E. ventrosa. However, while E. ventrosa preferred patches close to the release point, G. aequicauda strongly preferred patches further from the release point. High resource availability was a strong determinant for the patch colonization of G. aequicauda and L. hookeri. Connectivity was only of moderate importance in the study system for L. hookeri and E. ventrosa. The effects of the environmental factors were strongly affected by interspecific interactions in the multispecies experiments. For G. aequicauda, the distance preference was lowered in the presence of E. ventrosa. Moreover, while for L. hookeri the effect of resource availability was ruled out by the species interactions, resource availability gained importance for E. ventrosa in the presence of any of the other species. Our results suggest a strong link between environmental factors and biotic interactions in the colonization of habitat patches and indicate that the effect of biotic interactions is especially important for species sharing similar traits.

Trematode prevalence-occupancy relationships on regional and continental spatial scales in marine gastropod hosts

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 490:147-154 (2013) - DOI: https://doi.org/10.3354/meps10381 Trematode prevalence-occupancy relationships on regional and continental spatial scales in marine gastropod hosts David W. Thieltges1,*, David J. Marcogliese2, Christopher A. Blanar3, Robert Poulin4 1Marine Ecology Department, NIOZ Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg, The Netherlands 2Aquatic Biodiversity Section, Watershed Hydrology and Ecology Research Division, Water Science and Technology Directorate, Science and Technology Branch, Environment Canada, St. Lawrence Centre, 105 McGill Street, Montreal, Quebec H2Y 2E7, Canada 3Division of Math, Science, and Technology, Farquhar College of Arts and Sciences, Nova Southeastern University, 3301 College Avenue, Fort Lauderdale, Florida 33314, USA 4Department of Zoology, University of Otago, PO Box 56, Dunedin 9054, New Zealand *Email: david.thieltges@nioz.nl ABSTRACT: The positive inter-specific relationship between local abundance and large-scale spatial occupancy is one of the most universal patterns in the distribution of species. However, evidence for the validity of this relationship in the marine realm is still scarce, especially for parasites. Using data from published studies, we investigated this relationship in trematode parasites infecting several marine gastropod species. On a regional spatial scale (<100 km between any pair of sites), we found a positive relationship between mean local prevalence (percentage of infected individuals in a population) and large-scale site occupancy among trematode species in all 4 gastropod host species investigated (Littorina obtusata, L. saxatilis, Hydrobia ventrosa, Ilyanassa obsoleta), although this was not significant in the case of L. saxatilis. Similar positive relationships were observed on a continental scale (>1000 km between the most distant sites) in 2 host species (L. littorea, H. ulvae). Further analyses pointed to the role of dispersal by the definitive hosts in shaping these prevalence-occupancy relationships as we found a significant interaction between definitive host type and mean local prevalence affecting the spatial occupancy of the trematodes infecting H. ulvae. While trematode species that use highly dispersive birds as definitive hosts exhibited a significant positive relationship, the ones that use less dispersive fish did not. Our results indicate that a positive relationship between local abundance and large-scale distribution also holds true for marine parasites, and they suggest a strong role of definitive host dispersal in linking local epidemiological infection patterns of parasites with their large-scale biogeographic distributions. KEY WORDS: Parasitism · Macroecology · Biogeography · Species distributions Full text in pdf format Supplementary material PreviousNextCite this article as: Thieltges DW, Marcogliese DJ, Blanar CA, Poulin R (2013) Trematode prevalence-occupancy relationships on regional and continental spatial scales in marine gastropod hosts. Mar Ecol Prog Ser 490:147-154. https://doi.org/10.3354/meps10381 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 490. Online publication date: September 17, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

How lonely they are? A degree of isolation among macrozoobenthos species in the Marine Protected Area, the Bay of Puck, the Southern Baltic

Abstract Extensive sampling (450 grabs) was performed all over the inner part of Puck Bay (105 km2 area) in summers of 2007–2009. The GIS-based analysis of samples was performed to assess in detail the distribution of 32 benthic species. The minimum area of occurrence was less than 1 km2 for Lekanosphaera rugicauda and the maximum was 83 km2 for Cerastoderma glaucum. The material reveals that species with the pelagic larval stage were most widespread, with the least distance between individuals and the highest average density (e.g. Cerastoderma glaucum, Hydrobia ventrosa). The most isolated and the least dense species within the studied area were discretely mobile, non-larval crustaceans (e.g. Gammarus oceanicus and Lekanosphaera rugicauda), present at single sites with the largest distance from each other. We conclude that analysis of species distribution helps in understanding the threats to populations of marine invertebrates and marine spatial planning, through locating the isolated species and populations.

Invertebrate species list of coastal lagoons in the Balearic Islands

1 - Coastal lagoons are particular ecosystems, since they are ecotones between terrestrial, freshwater and marine ecosystems, being characterized by a high temporal variability. Because of these characteristics, coastal lagoons have very peculiar abiotic and biotic conditions that require investigation if we are to understand their complex ecological functions. In this study, a list of invertebrate species from coastal lagoons in the Balearic archipelago is provided in order to enhance the knowledge of their aquatic fauna. This study reports on the existence of 123 species, from 135 genera and 24 families.The most common taxa were Chironomus spp. (Meigen, 1803) and Halocladius spp. (Hirvenoja, 1973) (Diptera, Chironomidae), Hydrobia ventrosa (Montgau, 1803) (Gastropoda, Hydrobiidae), Cyprideis torosa (Jones, 1850) (Ostracoda, Cytherideidae), Lekanesphaera hookeri (Leach, 1814) (Isopoda, Sphaeromatidae) and Naididae (Oligochaeta).

Ecrobia grimmi in brackish Lake Sawa, Iraq: indirect evidence for long-distance dispersal of hydrobiid gastropods (Caenogastropoda: Rissooidea) by birds

Ecrobia grimmi in brackish Lake Sawa, Iraq: indirect evidence for long-distance dispersal of hydrobiid gastropods (Caenogastropoda: Rissooidea) by birds

New data on Microphallus breviatus Deblock &amp; Maillard, 1975 (Microphallidae: Digenea) with emphasis on the evolution of dixenous life cycles of microphallids

Infection by intramolluscan stages of Microphallus breviatus Deblock & Maillard, 1975 are common in Hydrobia ventrosa mudsnails in Iceland. Cercariae encyst inside the daughter sporocysts and develop there into metacercariae that become infective for the definitive hosts which are probably charadriiform waders. The adult stage was obtained in 1-day-old chicks that were experimentally infected with metacercariae from naturally infected hydrobians. New data are presented on the morphology and biology of the cercariae, and the adult is described for the first time. Comparisons are made between M. breviatus and closely related species. Differential diagnosis of M. breviatus is given. The morphological specializations in larvae of the hermaphroditic generation of the microphallids accompanying transition from trixenous life cycles to dixenous ones are considered, and the applicability of the term "life-cycle truncation" to microphallids with dixenous life cycles is discussed. Also, reasons for the broad distribution of dixenous life cycles within the family Microphallidae are reviewed.

A loss of fecundity in a population of mudsnails Hydrobia ventrosa caused by larval trematodes does not measurably affect host population equilibrium level

Host snail demography and trematode parasitism were followed for one host generation in a shallow brackish lagoon of the western Baltic Sea. In addition, a laboratory experiment was simultaneously conducted to quantify the effects of parasitic infection on host fecundity. Hydrobia ventrosa of the cohort of 1996 had a maximum life-span of up to 2 years and reproduced between May and November of their second calendar year in 1997. Snails died after reproduction. The first trematode infections appeared in May 1997 when the snails started to mature. Total trematode prevalence peaked in summer and declined during winter to the lowest level in early spring 1998. Eight taxa of larval trematodes were found. Egg production of females with trematode infections was significantly reduced. Among females with pre-patent infections, about 20% were still able to produce eggs. Among females with patent infections merely 9% could lay eggs, compared to an average of about 51% in uninfected females. Taking into account a summer prevalence of about 25%, parasitic infections caused an overall reduction in egg production of the snail host population of about 15%. The reduction in host fecundity as a result of larval trematode infection did not measurably affect the population dynamics of H. ventrosa, because other environmental factors, especially winter severity and available food supply, were concluded to be much more relevant.

Abundance, Population structure and Production of Hydrobia ventrosa (Gastropoda: Prosobranchia) in a Mediterranean brackish lagoon, Lake Ichkeul, Tunisia

Abundance, growth and production of the mud snail Hydrobia ventrosa (MONTAGU) were studied in the Ichkeul wetland, northern Tunisia. H. ventrosa occurred at annual mean densities (biomass) from 370 ± 78 individuals/m 2 (0.17 ± 0.03 g ash-free dry mass/m 2 ) in the macrophyte-free area to 23 475 ± 9 876 individuals/m 2 (9.86 ± 3.48 gAFDM/m 2 ) in the macrophyte covered areas. Mean aboveground macrophyte biomass was maximum in September followed by a complete breakdown of the Potamogeton pectinatus L. meadow from October onward due to high salinity. Only the meadow of Ruppia cirrhosa (PETAGNA) GRANDE at Tinja remained in place. Abundance and biomass of H. ventrosa were positively related to the macrophyte biomass (p < 0.001). Age class I was recruited twice: in May-June and in September. The first recruited cohort reached a mean length of 2.03 ± 0.04 mm in November. In the second recruited cohort, no growth was found after November, and their mean length remained around 1.29 ± 0.02 mm. Maximum length of age class II rarely exceeded 2.85 mm (mean = 2.78 ± 0.07 mm) and the average life span is approximately 13-15 months. The mean annual production of Hydrobia ventrosa for the whole lagoon (90 km 2 ) was 11.86g AFDM/m 2 (3.51 g C/m 2 , 0.34g N/m 2 ) i.e. 85 % at Sejnene area (30.5 km 2 ), 1% in the Centre (49.6 km 2 ), 4% at Tinja area (3.0 km 2 ) and 11% at Joumine area (6.9 km 2 ). The annual P/B ratio was about 3. On the basis of this value, H. ventrosa consumed 23 % of the energy income from the macrophytes during the study period and a third (36 %) of the secondary production was available to the next trophic level, which is suggestive of the importance of Hydrobiids in lagoonal ecosystems.

Factors influencing the distribution of digenetic trematode infections in a mudsnail (Hydrobia ventrosa) population inhabiting salt marsh ponds in Iceland.

This study analyzed the influence of several abiotic and biotic variables on the distribution of digenetic trematode infections in a mudsnail, Hydrobia ventrosa, population inhabiting 12 ponds on the Melabakkar salt marsh in Iceland, the northwestern limits of the geographical distribution. Nine trematode species were found to infect the snail population, which included Microphallus pirum, Microphallus breviatus, Microphallus claviformis, Maritrema subdolum (Microphallidae), Cercaria Notocotylidae sp. 11 Deblock, 1980, C. Notocotylidae sp. 12 Deblock, 1980, C. Notocotylidae sp. 13 Deblock, 1980 (Notocotylidae), Cryptocotyle concavum (Heterophyidae), and Psilostomum brevicolle (Psilostomatidae). Correlations between biotic variables (snail density in the ponds and vegetation cover), abiotic variables (distance of each pond from the sea, pond elevation above chart datum, size, average depth, salinity, and some characters of the littoral zone and sediments), and trematode infections were analyzed. These variables indirectly affected the trematode infections because some determined how attractive the ponds were for the final hosts, which were various species of marine and shore birds. We propose that their habitat use and defecating habits are the main determinants of the trematode distribution in the area.

Spatial and Temporal Variations in the Trematode Component Community of the Mudsnail Hydrobia ventrosa in Relation to the Occurrence of Waterfowl as Definitive Hosts

Spatial and Temporal Variations in the Trematode Component Community of the Mudsnail Hydrobia ventrosa in Relation to the Occurrence of Waterfowl as Definitive Hosts

Spatial and temporal variations in the trematode component community of the mudsnail Hydrobia ventrosa in relation to the occurrence of waterfowl as definitive hosts.

The component community of larval trematodes infecting the mudsnail Hydrobia ventrosa (Montagu) was examined in coastal lagoons of the southern Baltic Sea among different host subpopulations in relation to the structure of the waterfowl community. The 10 trematode species observed represent the families Notocotylidae (1), Echinostomatidae (1 or 2), Heterophyidae (2). Monorchidae (1). Microphallidae (3 or 4), Psilostomatidae (1), and Hemiuridae (1). Eight of these species infect waterfowl as adults. The structure of the trematode communities was similar between sampling sites. Seven trematode taxa were commonly found at all sampling sites. Prevalence values of the 6 most abundant taxa, which infect birds as final hosts, were significantly different between neither sampling sites nor across year. Overall trematode prevalence in H. ventrosa fluctuated seasonally. Prevalence usually peaked in summer between July and September or October. Low prevalences were observed in late winter and early spring. In contrast, the seasonal maximum in waterfowl numbers differed between areas because of significant spatial differences in the bird community structure. The species composition of the component trematode community of H. ventrosa in the coastal lagoons of the southern Baltic Sea is more or less independent of the species composition of the waterfowl community. This independence presumably results from the lack of host specificity in most of the observed trematode species. Otherwise, the low host specificity in combination with the enormous waterfowl diversity in the coastal lagoons might explain the stability of the prevalence pattern of the component trematode community.

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.