Snail Hydrobia Ulvae Research Articles

Digenean larvae in Hydrobia ulvae from Belfast Lough (Northern Ireland) and the Ythan Estuary (north-east Scotland)

In this study the digenean parasites in the mud snail Hydrobia ulvae at two sites were compared for a period of one year. The sites were the north shore of Belfast Lough (Northern Ireland) and the Bend of Tarty on the Ythan Estuary (north-east Scotland). Samples of snails were collected monthly from which 13 species of digenean larvae were recorded at Belfast Lough. Two of these species were absent at the Bend of Tarty. Overall digenean prevalence was very similar at each site indicating that the respective bird communities were composed of ecologically equivalent species. Differences in the prevalence of individual digenean species are discussed in relation to the abundance of definitive and/or secondary intermediate hosts at each of the sites. Both sites displayed similar seasonal patterns of parasite prevalence with sharp increases to around 25% in the summer months. Snail shell heights were greater at Belfast Lough than at the Bend of Tarty and a positive correlation between snail shell height and infection by trematode parasites was recorded at both sites. Increased parasite prevalence in larger snails was attributed to factors such as age-related susceptibility and/or parasitic castration of the snails.

Use of an in Ovo Technique to Provide Adults of Levinseniella sp. no. 17 That Were Identified as Levinseniella minuta (Trematoda: Microphallidae)

Metacercarial cysts identified as Levinseniella sp. no. 17 (Deblock, 1980) were found in the mud snail Hydrobia ulvae. These larval trematodes had never been allied to a known species of adult worm. They were chemically excysted and cultured for 120 hr on the chorioallantoic membranes of chicken embryos. The resulting adult worms were observed by light and scanning electron microscopy and details of their anatomy and topography were compiled. Their morphometric measurements were compared with those of adult worms taken from the scientific literature. A very high degree of similarity was discovered between anatomical details of the worms produced in this study and those provided for Levinseniella minuta. It was concluded that Levinseniella sp. no. 17 is the larval stage of L. minuta.

Kinetics of tidal resuspension of microbiota:testing the effects of sediment cohesiveness and bioturbation using flume experiments

Resuspension of the top few sediment layers of tidal mud flats is known to enhance planktonic biomass of microbiota (benthic diatoms and bacteria). This process is mainly controlled by tidal shear stress and cohesiveness of mud, and is also influenced by bioturbation activities. Laboratory experiments in a race track flume were performed to test the interactive effects of these factors on both the critical entrainment and resuspension kinetics of microbiota from silt-clay sediments from the Marennes-Oleron Bay, France. The marine snail Hydrobia ulvae was used to mimic surface bioturbation activities. As expected, the kinetics of microbial resuspension versus shear stress were largely controlled by the cohesiveness of silt-clay sediments. However, our results indicate that the effect of surface tracking by H. ulvae on microbial resuspension was clearly dependent on the interaction between sediment cohesiveness and shear velocity. Evidence was also found that microphytobenthos and bacteria are not simultaneously resuspended from silt-clay bioturbated sediments. This supports the theory that diatoms within the easily eroded mucus matrix behave actively and bacteria adhering to fine silt particles eroded at higher critical shear velocities behave passively.

Diet, prey‐size selection and intake rates of Black‐tailed Godwits Limosa limosa feeding on mudflats

This paper describes aspects of the winter feeding ecology of Black‐tailed Godwits Limosa limosa on an intertidal mudflat in the Tagus estuary, Portugal. Their diet consisted mainly of the bivalve mollusc Scrobicularia plana, which represented 88% of the ingested biomass. The remaining 12% was the worm Nereis diversicolor and, occasionally, the snail Hydrobia ulvae. Ingested Scrobicularia varied between 10 and 20 mm in length, and all size classes of Nereis present in the sediment, except those smaller than 20 mm, were preyed upon. A change in dietary composition occurred over the winter, probably in response to changes in the availability of Nereis and small Scrobicularia. Intake rates averaged 74.9 mg dry weight per minute, which corresponded to a net energy intake of 1.21 kJ per min.

Migratory rhythms of drifting juvenile molluscs in tidal waters of the Wadden Sea

After initial spatfall, some species of bivalves and juvenile mud snails may re-enter the water column and thus undergo secondary dispersal. Uslng continuous plankton net records of the number of drifting organisms over a period of 4 mo in summer 1991, rhythms of migratory activity were analysed on a tidal flat area near the Island of Sylt, eastern North Sea. All abundant species showed a clear diurnal pattern. The mud snail Hydrobia ulvae was more abundant in the water column during daytime than in the dark, while the reverse was true for the bivalves observed. In addition, cockles Cerastoderrna edule and razor clams Ensis directus displayed a semilunar rhythm of drifting activity, and in clams Macoma balthlca there was a 10 d periodicity not closely linked to lunar phases. In most species, the quantitative effect of these longer periodicit~es was stronger than that of the diurnal component The pattern of migratory activity, resulting from these diurnal and lunar rhythms together with a seasonal component, was distorted by weather conditions in a species-specific way. As a consequence, records of drifting young molluscs may be severely biased unless these rhythms of migratory activity are taken into account.

Effect of population density and presence of a potential competitor on the growth rate of the mud snail Hydrobia ulvae (Pennant)

The mud snail Hydrobia ulvae (Pennant) and the amphipod Corophium arenarium Crawford were used in a series of laboratory and field experiments to investigate the hypothesis that natural populations of such deposit-feeders live under conditions of resource limitation. Growth rates of Hydrobia confined at several different densities within cages in the field and in laboratory microcosms indicated that density-dependent reduction of growth rate and increased mortality occurred at densities found in natural populations. Similar experiments failed to provide any evidence that Corophium mortality or behaviour was modified by the presence of Hydrobia or members of its own species; nor did the presence of Corophium cause a reduction in growth rate of Hydrobia.

Effects of macroalgal mats on the ecology of intertidal mudflats

The standing biomass and distribution of the invertebrate fauna of mudflats covered by macroalgal mats has been determined and compared with that of mudflats unaffected by algae. The faunal biomass of algal-covered mud was consistently higher than uncovered mud, mainly due to the presence of large populations of the snail Hydrobia ulvae. The structure of the faunal composition of algal-covered mud was altered and the numbers of at least one species of polychaete worm markedly reduced. The effect of these changes on the bird population exploiting the mudflats is discussed.

In-situ investigations on the echinodermAsterias rubens as a predator of soft-bottom communities in the western Baltic Sea

In-situ investigations on the life of the common sea star (Asterias rubens L.) were carried out in 1976, employing the Underwater Laboratory “Helgoland“ in Lubeck Bay (Western Baltic Sea). The abundance ofA. rubens amounted to 2–31 m−2 on sediment (fine sand), and to 324–809 m−2 on mobile algal carpets drifting over the bottom. Actual population parameters (abundance, size class distribution) are influenced by both substrate quality and drifting. Stomach investigations revealed prey-size selectivity: Small sea stars feed mainly on the snailHydrobia ulvae when living on the sediment, but on mussel brood(Mytilus edulis) in the phytal. The principal food items of larger sea stars are the sand-dwelling clamMacoma baltica and the phytal-living isopodIdotea baltica respectively.A. rubens is very adaptive to the food available; the diversity of its diet corresponds to the species diversity found in its environment. A change of biotope during active or passive migrations causes switching. The sea star is able to catch motile animals and to dig out infaunal clams. It exhibits a diurnal feeding pattern related to light periodicity; the activity decreases at night. The average frequency of feeding is highly dependent on predator body size; it declines with growth. In-situ experiments indicate an exponential relationship between the feeding duration uponM. baltica and the quotient of clam size to logarithm of sea-star size. An approach is made toward a rough estimate of macrofauna consumption byA. rubens on sediment. The sea star seems to be an important predator and thus a competitor of demersal fishes on soft bottoms of the western Baltic Sea.

Benthic invertebrates as indicators of organic pollution in the Western Baltic Sea

AbstractThe quantitative distribution of some important benthic invertebrates in a shallow inshore area of Kiel Bay (Western Baltic Sea) is described. This region is partly polluted by domestic sewage from the municipality of Kiel. Three groups of species are distinguished with reference to their densities and other population parameters in the different subareas: Progressive species of the 1st and 2nd order indicate a high and moderate to slight degree of pollution respectively by high population numbers. Regressive species are adverse indicators, absent or occurring in exceptionally low numbers in affected areas. In many cases the examination must be concentrated on sand bottom, because a series of species normally dwelling on aufwuchs build up dense populations in sand, if it is organically enriched.The polychaetes Capitella capitata, Nereis diversicolor and Polydora ligni are regarded as progressive species of the 1st order. The amphipods Corophium insidiosum and Gammarus salinus, the mussel Mytilus edulis, the polychaete Pygospio elegans, the snail Hydrobia ulvae, and some other invertebrates belong to the group of indicators for slight organic pollution. The main regressive species are the amphipod Bathyporeia sarsi and the mite Copidognathus fabriciusi.

Resource partitioning on basis of hydrolytic enzymes in deposit-feeding mud snails (Hydrobiidae) : II. Studies on niche overlap.

Crude extracts of hydrolytic enzymes from the related mud snailsHydrobia ulvae, H. ventrosa andH. neglecta are compared by use of six different methods and 18 natural carbohydrates. Synthetic substrates for linkage specific carbohydrases and trypsin-like activity were studied in addition to lysozyme-like activity.A significant hydrolysis was only observed with the reserve carbohydrates amylose, glycogen and laminaran. Many algal carbohydrates were, however, digested to some extent.The qualitative spectra are almost identical for the three species but significant quantitative differences were found. The findings are discussed in relation to information on the chemical composition of potential food items and it is concluded that the commonly observed coexistence of the snails can in part be explained by selection for microalgae and detritus particularly meeting their enzymatic potentials.