Hydrobia Ulvae Research Articles

Multispecies macrozoobenthic seasonal bioturbation effect on sediment erodibility

Bioturbation in estuarine environments describes all sediment reworking processes implied in sediment transport. However, modelling at large spatial and temporal scales remains a challenge because of the need to consider the fauna at the community level, and because animal behaviour is highly seasonal with non-linear effects of macrofauna functional trait interactions. Bioturbation processes can be linked to the activity of organisms, based on the principle of energy ecology, linking the metabolic rate to the erodibility of a sediment colonised by benthic fauna. This study investigates this postulate by evaluating the erodibility parameters of a sediment subjected to: i) the bioturbation under seasonal temperature variations; ii) the synergistic bioturbation of different species. The experimental design consisted of: i) three temperature levels (winter, spring and summer), ii) three types of species duos (Cerastoderma edule and Macoma balthica; Scrobicularia plana and Hediste diversicolor; Corophium volutator and Peringia ulvae) at 4 different relative densities. Two successive experiments were carried out on the same individuals: measurement of oxygen consumption of fauna then measurement of the erodibility of the colonised sediment in a flume. The oxygen consumption confirmed that the metabolic rate is a good model of the fauna respiration, regardless of species. The erosion results indicated that the metabolic rate in the case of the fluff layer resuspension is an interesting descriptor for 1) the assessment of the bioturbation under variable temperatures and 2) the integration of the two different bioturbator species that could co-occur in the same habitat. In contrast, the effect of bioturbation on the mass sediment erosion threshold cannot be easily modelled by using the metabolic rate and the classification in functional groups is required. Bioturbation models of the fluff layer using metabolic rate is a promising tool for modelling the effects of faunal communities on sediment transport at the scale of an estuary and over the long term, even projected in the context of global warming.

Species diversity and structural features of macrobenthos in coastal lagoon ecosystems, the Kandalaksha Bay, White Sea taken as an example

The Kandalaksha Bay of the White Sea taken as an example, the present study is devoted to its coastal lagoon ecosystems known to differ in their species diversity and structural features, including macrobenthos. Features of the species composition, spatial structure and diversity of macrobenthic sublittoral communities in 4 coastal lagoon ecosystems of the White Sea were studied and analyzed. In the sublittoral of the study lagoons, 39 species of zoobenthos and 4 species of sea weeds and algae (Zostera marina, Cladophora sericea, Ruppia maritima, Salicornia pojarkovae) were found. The lowest indices of species diversity and biomass of macrobenthos were revealed in lagoons significantly fenced off and remote from the sea, where littoral eurytopic small species of zoobenthos (Macoma balthica, Peringia ulvae, Tubificoides benedii, Littorina littorea, Mytilus edulis, Chironomus salinarius) were found to mainly dominate. In the lagoons in which the connection to the sea was stronger, less euryhaline sublittoral invertebrate species prevailed with higher indices of species diversity and total biomass of the macrobenthos community (Nereimyra punctata, Terebellides stroemi, Caprella linearis, Asterias rubens, Molgula griffithsii). Most of the lagoon ecosystems we examined, with the exception of the one most open to the sea, were characterized by low values of ABC indices and a disturbed structure of the macrobenthos community with the predominance of mainly small species of detritophages, this being associated with the negative effects of siltation, carbon loading and salinity (especially in spring or during the times of heavy rain).

Long-term response of coastal macrofauna communities to de-eutrophication and sea level rise mediated habitat changes (1980s versus 2018)

Since the last decades, previous long-term Wadden Sea studies revealed significant changes in the abundance, biomass and spatial distribution of characteristic macrofauna communities in response to environmental changes and anthropogenic stressors. In this study, we performed statistical community analysis for the East-Frisian Wadden Sea (EFWS, southern North Sea) on two reference datasets across a period with severe climatic and environmental changes (1980s-2018). Therefore, historical macrofauna data from the Quantitative Sensitivity Mapping (1980s, SENSI 1) were reanalyzed and compared with data from the Synoptic Intertidal Benthic Survey (SIBES/SENSI 3) collected in 2018. Our results revealed significant quantitative and spatial changes in the characteristic macrofauna communities between the 1980s and 2018, most likely in response to de-eutrophication and sea level rise mediated habitat changes. Since the 1980s, the total number of taxa remained relatively stable (1980s: 90, 2018: 81), but the total abundance decreased by ca. -31% and the total biomass decreased by ca. -45%, particularly in the eastern regions of the study site probably due to de-eutrophication processes. Thereby, the mean abundances/m2 of ≥ -80% (1980s-2018) in the EFWS of several dominant species decreased: e.g. the gastropod Peringia ulvae, the polychaete Lanice conchilega and the bivalve Mya arenaria. In contrast, the mean abundance/m2 of one dominant species increased by ≥ +80% (1980s-2018): the invasive bivalve Ensis leei. The mean biomass [g/m2] of three dominant species decreased by ≥ -80% (1980s-2018): P. ulvae, L. conchilega and the amphipod Corophium volutator. In contrast, the mean biomass [g/m2] of one dominant species increased by ≥ +75% (1980s-2018): the polychaete Arenicola marina. In the western part of the EFWS, not only higher abundances of A. marina, but also of L. conchilega and P. ulvae were found in 2018, caused i.a. by sea level rise mediated decreasing mud contents and sand accretion on tidal flats. At the community level, the Oligochaeta/Heteromastus community increased in spatial distribution in the western EFWS in 2018 in the vicinity of increasing mussel/oyster beds.

Ecotoxicological tools in support of the aims of the European Water Framework Directive: A step towards a more holistic ecosystem-based approach

The Water Framework Directive (WFD) aims to attain ‘good quality’ status for all European water bodies through the achievement of good ecological status. To this purpose, the WFD advocates the creation of cost-effective monitoring tools to deliver appropriate data that help to create links between chemical and ecological indicators, as those from ecotoxicological research. Here, it was evaluated whether the integration of ecotoxicological tools, as bioassays and biomarkers, did (or did not) strengthen the robustness of the assessment of the ecological status obtained through well stablished biotic indices in two Atlantic estuaries. For that, a battery of in-situ bioassays, including five macroinvertebrate species (the crab Carcinus maenas, the amphipod Echinogammarus marinus, the isopod Cyathura carinata, the snail Peringia ulvae and the polychaete Hediste diversicolor, each one providing complementary information regarding key ecological functions) and a set of biomarkers, was used. In addition, the concentrations of heavy metals in sediments, and in macroalgae (Fucus), were determined, along with sediment granulometric, water physicochemical and nutrients characterization. We show that by interpreting the values of all indicators together, along with environmental components, it is possible to perform a more holistic description of the quality status of a waterbody – and, to begin to allude to factors limiting that quality. Ecotoxicological tools (in situ bioassays and biomarkers) appear to provide an added value of useful information for monitoring programmes regarding the true state - within which, both known and unknown contaminants are potentially present at concentrations sufficient to cause biological effects. Our results support the use of in situ bioassays and biomarkers within protocols aimed at fulfilling the goals of the WFD. In doing so, more complete and informative assessments of the ecological quality status of water bodies can take place.

Analysis of the structural characteristics and spatial organization of macrobenthic fauna in Oualidia lagoon, Morocco

Morocco is a very rich country in terms of wetlands, including bays, estuaries, lagoons, lakes, and rivers, among others. However, many of them need to be well managed and better exploited, thus requiring baseline descriptive studies to assess faunal patterns and trends. Oualidia lagoon is not an exception. In fact, the studies conducted to date in the lagoon mainly focused on its oceanographic features and aquaculture capacities. The present paper presents the first study on the whole macrofaunal assemblages of Oualidia lagoon, having as main objectives analyze the composition and structure of the assemblages, as well as their relationships with the main environmental variables explaining their spatial distribution variability in the enclosed ecosystem of the Oualidia coastal lagoon. The benthic macroinvertebrates of Oualidia lagoon were studied in summer 2013 based on 43 stations spread over the whole lagoon by using a Van Veen grab. Two replicate samples were collected for macrobenthos and one additional replicate for sediment analyses at each station. Also, single water salinity and temperature measurements were recorded at each station. Fifty-one species from seven different taxa were recorded, among which mollusks (37%), polychaetes (25%) and crustaceans (25%) dominated in terms of species number. Peringia ulvae, Abra alba, Sphaeroma serratum, Cerastoderma edule and Corophium sp. accounted for 88% of total abundance. The benthos was structured along a downstream–upstream gradient, showing three assemblages, named according to the IndVal index: (1) Diopatra cf. marocensis, (2) Peringia ulvae, and (3) Cerastoderma edule, while the main factors driving their distribution were granulometry and salinity. The Biotic and Environmental analysis showed that the combination of granulometry and salinity was the major factors controlling the spatial distribution of the macrozoobenthos in the Oualidia Lagoon.

Temporal and spatial variation of the molluscan community structure in Oualidia Lagoon, Moroccan Atlantic coast

The molluscan assemblages inhabiting the coastal waters of Oualidia Lagoon, Morocco, were studied during winter and summer of 2013. The taxonomic composition and diversity were determined at 43 sample sites. Thirty-four mollusc taxa were recorded in total, including 12 species of bivalves, 20 species of gastropods, 1 species of polyplacophoran and 1 species of cephalopod. Twenty-six of these species are reported here for the first time in Oualidia Lagoon. The gastropod Peringia ulvae and the bivalve Abra alba were the most abundant taxa in both seasons. The deposit-feeder trophic group was highly dominant in both seasons. A classification analysis revealed the existence of three main clusters from downstream to upstream in both seasons: a marine assemblage, a transition assemblage and a lagoon assemblage. Canonical correspondence analyses indicated that the main environmental variables governing the spatial distribution of the molluscs in winter are salinity, temperature and granulometry, whereas in summer they are salinity and granulometry. This study provides a good baseline for future ecological research.

Intraspecific Abundance\u2013Occupancy\u2013Patchiness Relations in the Intertidal Benthic Macrofauna of a Cool-Temperate North Sea Mudflat

The macroecological variable of patchiness (Lloyd’s Ip index of patchiness, P) has recently been shown to be related inter- and intraspecifically to those of abundance (numbers m−2, A), and occupancy (% occurrence in samples, O) in lower latitude seagrass macrofaunas. For the first time in higher latitudes, intraspecific relationships between three spatial variables were investigated in the intertidal mudflat macrobenthos of the Scolt Head barrier island, southern North Sea (53° N, 01° E). Sampling was conducted between early July and late September 2009–2013 using 710-µm mesh for sample processing. Strong positive interspecific A-O and negative interspecific P-O and P-A relationships were present. Two of the most numerous and widespread assemblage components, however, occurred with effectively constant occupancy (Peringia ulvae, 100%, and Tubificoides benedii, 93%) across the whole 20-ha locality and therefore could not show intraspecific relationships of occupancy with other macroecological metrics. These two apart, only one other dominant species failed to show a significant positive intraspecific A-O relationship; no species showed significant P-A relations of any form; and only two showed the negative P-O ones that have been described elsewhere. The intraspecific A-O patterns appear to contrast with those of an earlier study at another North Sea locality (the Dutch Wadden Sea), although differences are more apparent than real, but the Scolt Head fauna showed fewer intraspecific P-O and P-A relations than those characterising similar circumstances in the two lower-latitude localities previously investigated. Neither developmental mode nor variation in local abundance appears to influence these patterns. A-O-P relations therefore seem widespread but may be subject to latitudinal modification.

Multicompartment and cross-species monitoring of contaminants of emerging concern in an estuarine habitat.

The fate of many chemicals in the environment, particularly contaminants of emerging concern (CEC), have been characterised to a limited extent with a major focus on occurrence in water. This study presents the characterisation, distribution and fate of multiple chemicals including pharmaceuticals, recreational drugs and pesticides in surface water, sediment and fauna representing different food web endpoints in a typical UK estuary (River Colne, Essex, UK). A comparison of contaminant occurrence across different benthic macroinvertebrates was made at three sites and included two amphipods (Gammarus pulex & Crangon crangon), a polychaete worm (Hediste diversicolor) and a gastropod (Peringia ulvae). Overall, multiple contaminants were determined in all compartments and ranged from; <LOQ – 386 ng L−1 in surface water (n = 59 compounds), <LOQ – 146 ng g−1 in sediment (n = 39 compounds) and <LOQ – 91 ng g−1 biota (n = 33 compounds). H. diversicolor and P. ulvae (sediment dwellers) showed greater chemical body burden compared with the two swimming amphipod species sampled (up to 2.5 - 4-fold). The most frequently determined compounds in biota (100%, n = 36 samples) included; cocaine, benzyoylecgonine, carbamazepine, sertraline and diuron. Whilst some of the highest concentrations found were in species H. diverscolor and P. ulvae for psychoactive pharmaceuticals including citalopram (91 ng g−1), sertraline (69 ng g−1), haloperidol (66 ng g−1) and the neonicotinoid, imidacloprid (33 ng g−1) Sediment was noted as an important exposure route for these benthic dwelling organisms and will be critical to monitor in future studies. Overall, the analysis of multiple species and compartments demonstrates the importance of including a range of exposure pathways in order to appropriately assess chemical fates and associated risks in the aquatic environment.

Benthic Communities of Coastal Water Bodies at Different Stages of Isolation from the White Sea in the Vicinity of the White Sea Biological Station, Moscow State University, Kandalaksha Bay, White Sea

Communities of macrozoobenthos in the White Sea coastal water bodies that have partially or completely lost connection with the sea as a result of postglacial land uplift, are studied. As the degree of isolation from the sea increases, stable vertical stratification with a tendency to meromixis and gradual dilution of seawater provide the conditions for the formation of an unusual composition of macrofauna and succession, from a normal or slightly depleted marine biome to a completely freshwater ecosystem. Data collected in the years 2012–2017 present the macrozoobenthos community of five marine lagoons and four meromictic lakes in comparison with the marine communities of Kislaya Inlet, which connects the two water bodies studied, and with the freshwater lakes of the Kindo Peninsula. The typology of the water bodies was carried out according to the degree of isolation, taking into account the hydrological regime and differences in fauna lists. A naturally determined change in bottom communities occurs as the degree of isolation of the water body from the sea increases. In marine lagoons, regularly flooded by tides, there is a community of Macoma balthica (L. 1758)–Pontonema vulgare (Bastian 1865) Filipjev 1916, widespread in the marine littoral. In more isolated lagoon-type water bodies with a similar set of species, Mytilus edulis L. 1758 and Mya arenaria L. 1758 make up a significant share in biomass in addition to M. balthica. The populations of the gastropod mollusk Hydrobia ulvae (Pennant 1777) are much developed here. Even at this stage, the fauna comprises more littoral eurybionts (H. ulvae, M. balthica, M. arenaria, M. edulis, Arenicola marina (L. 1758), Tubificoides benedeni (d’Udekem 1855), chironomids, etc.) and less sublittoral stenohaline forms. At the next stage, H. ulvae dominates by biomass, and the share of the chironomid Chironomus gr. salinarius and oligochaete T. benedeni increases as well. Insects and their larvae (beetles, chironomids, and other dipterans) settle in shallow areas. In meromictic lakes, where a salt aerobic layer is preserved under the pycnocline, the fauna of the mixolimnion mainly comprises insect larvae, while only a few euryhaline forms remain from the marine fauna, namely, the amphipod Gammarus duebeni Lilljeborg 1852 and the chironomid Ch. gr. salinarius. At the stage of complete isolation from the sea, conditions are anaerobic below the pycnocline and, despite the suitable salinity, there is no marine fauna. In such water bodies, the benthos is represented exclusively by freshwater forms, mainly insects and mollusks. In completely freshwater bodies, chironomids make up the majority of the biomass; each lake has its own set of species, which changes from year to year. In the fresh water of Nizhnee Ershovskoe Lake, the population of G. duebeni remains in the part of the lake closest to the sea. The species diversity decreases as the water body is isolated from the sea; the maximum number of species was found in marine lagoons near Sonostrov Island (23–34 species); in Kislo-Sladkoe Lake, 10–15 species are found per survey. In Bol’shie Khruslomeny Lake, the aerobic part of the monimolimnion has a critical salinity and the species diversity is minimal (6–10 species). The number of species increases again after a stable fresh layer appears in the water body. The quantitative characteristics of the macrobenthos change in a similar way. The maximum abundance were noted in marine lagoons; in Kislo-Sladkoe Lake, the average abundance is significantly lower. In the meromictic water bodies with a fresh mixolimnion, the maxima of abundance and biomass are observed in the upper 0.5-m water layer, while in marine lagoons the maxima are located in the depth range of 1.0–2.5 m; in addition, in less isolated water bodies, the maximum biodiversity is observed in deeper layers than in more isolated ones. This layer is characterized by the highest content of dissolved oxygen, and often by supersaturation. The benthos abundance varies greatly in freshwater bodies.

Features of the Species and Spatial Structure of Macrobenthos in the Green Cape Lagoon (Kandalaksha Bay, White Sea)

Features of the species and spatial structure of macrobenthic sublittoral communities in a lagoon ecosystem on the Green Cape (the White Sea) were studied. 31 invertebrate species and 3 species of sea grasses and algae (Zostera marina, Cladophora sericea, and Fucus vesiculosus) were found in the sublittoral of the surveyed lagoon. The data on the species composition, diversity and spatial structure of macrobenthos communities indicate the predominance of littoral brackish-water and marine euryhaline macrobenthos species (Hydrobia ulvae, Tubificoides benedii, Chironomus salinarius, and Macoma balthica) in the coastal region of the lagoon, marine euryhaline littoral and sublittoral species (mainly polychaetes Heteromastus filiformis, Polydora ciliata, and Capitella capitata) in the central deeper region, and marine sublittoral less euryhaline species (Pontoporeia femorata, Anonyx nugans, Nereimyra punctata, Terebellides stroemi, Astarte montagui, Micronephthys minuta, and Atylus carinatus) at the exit from the lagoon. The ecosystem of the Green Cape lagoon belongs to lagoons significantly fenced off from the sea with depleted specific fauna (many littoral species) and largely influenced by carbon load and salinity. The reduced connection of the lagoon with the sea due to the continued rise of the White Sea coast (4 mm per year in this area) will contribute to a decrease in the species diversity and the predominance of few small eurytopic invertebrate species resistant to organic load, oxygen deficiency, and desalination.

Impact of Chronic and Massive Resuspension Mechanisms on the Microphytobenthos Dynamics in a Temperate Intertidal Mudflat

AbstractMicrophytobenthos (MPB) resuspension is a key mechanism in the transfer of organic matter from productive intertidal mudflats to terrestrial and marine systems. In this study, we infer on the contribution of physical and biological factors involved in the MPB resuspension. We use a physical‐biological coupled model forced by realistic meteorological and hydrodynamical forcings to simulate chronic (without any concomitant sediment resuspension) and massive (driven by bed failure) resuspension over a year. The model simulates mud surface temperature, MPB growth, and grazing by the gastropod Peringia ulvae. The model suggests that MPB resuspension is the highest in spring tides and at the flood beginning due to high current velocity and low water heights that promote waves‐sea bottom interactions. The seasonal export of MPB biomass is the highest in spring, up to threefold higher than in summer when the export is the lowest. The simulated seasonal dynamics of MPB resuspension results from the MPB biomass concentration in the sediment, physical disturbances, and the bioturbation activity by P. ulvae. Annually, 43% of the simulated MPB primary production is resuspended. The MPB resuspension (60.8 g C·m−2·yr−1) exceeds the loss by P. ulvae grazing (41.1 g C·m−2·yr−1). The model suggests that chronic and massive resuspension events are important in the synoptic to seasonal MPB dynamics in temperate intertidal mudflats. Accounting for such processes in the carbon budget assessment in the land‐ocean interface could bring new insights to our understanding of the role played by MPB in the coastal carbon cycle.

Elevation gradient affects the development of macrozoobenthic communities in the Wadden Sea: A field experiment with artificial islands

Tidal flats are subject to dynamic processes, characterized by sedimentation and erosion, which become more important in times of climate change. To investigate impacts of elevation levels on ecosystem functioning, we focused on macrozoobenthos as an essential ecosystem component that links trophic levels and determines sediment structure. Therefore, three elevation levels of six experimental islands (each 2 × 6 m) and six natural reference sites (nearby tidal flats) were sampled for species richness, abundance and biomass in the back-barrier system of the island of Spiekeroog (German Wadden Sea, southern North Sea) from 2014 to 2016. Reference sites had constant biodiversity and abundance over time that were higher compared to the three elevations of the experimental islands. At the lowest elevation, the community became more diverse over time, including marine and terrestrial taxa. At the middle elevation, community shifted from a marine species inventory over an opportunist-dominated assemblage to a less diverse community dominated by Enchytraeidae (Oligochaeta). The community of the highest elevation mostly remained constant, resembling the second, opportunistic community from the middle elevation that was dominated by the snail Peringia ulvae (Pennant, 1777) and the oligochaetes Enchytraeidae spp. and Tubificoides benedii (d'Udekem, 1855). Correspondingly, food web structure was more complex and comprised more trophic interactions at the lowest elevation compared to the other elevations mainly inhabited by deposit feeders. Results demonstrate negative impacts of increased sediment elevation on macrofaunal biodiversity and functional diversity, originating from reduced inundation and vegetation establishment.

Interactive effects of co-occurring anthropogenic stressors on the seagrass, Zostera noltei

Abstract Coastal ecosystems are subjected to multiple co-occurring anthropogenic stressors which potentially interact to produce complex impacts on the structure and functioning of biological communities. Seagrass meadows are among the most rapidly declining coastal habitats on Earth. In particular, high nutrient loadings, enhanced sedimentation and competition from blooming seaweeds, like the invasive red alga Gracilaria vermiculophylla, are claimed to be associated with this decline. In this study, we tested for individual and potential interactive impacts on the intertidal seagrass Zostera noltei of these three stressors using a factorial field experiment. We measured seagrass shoots density and biomass (both above and below ground seagrass biomass) as proxies of seagrass physical condition. We also examined changes in fauna assemblages. The study suggested that sediment loading had the most detrimental impacts on health of the seagrass meadows. The effect of seaweed addition was negative and denso-dependent. Deleterious effects of nutrient enrichment were less evident. Non-additive interactions were also noticeable for some of the structural traits measured. Particularly, nutrient enrichment changed the effect of the other stressors for some of the responses measured. The effect of the treatments was also perceptible in the associated fauna assemblages. The ubiquitous grazer Peringia ulvae was more abundant in treatments with sediment loading, but those sediment effects in the density of the small grazer were modulated by nutrient and seaweed addition levels. Finally, we suggest that more studies should test for synergistic effects of co-occurring stressors to better understand the direction and intensity of changes triggered by human activities in natural ecosystems.

Macrofaunal spatial distribution and community structure in a lagoon without a river discharge (the Oualidia lagoon, NW Morocco)

AbstractThe assemblage structure and spatial distribution patterns of macrobenthic communities according to environmental conditions were analysed through five samplings carried out at 14 intertidal soft sediment stations in the Oualidia lagoon (NW Morocco). A total of 89 macrobenthic taxa were collected, amounting to 55.188 specimens. Molluscs, polychaetes and arthropods were the most species‐rich groups. The snail Peringia ulvae was the most dominant species, especially abundant in the mid‐ and upper lagoon sections (nearly 64% of the total specimens gathered), followed by the mollusc Scrobicularia plana (10%). Diversity values were generally low (&lt;3 bit) pointing out the high dominance by few species. Multivariate analyses clearly distinguished three distinct macrobenthic assemblages, successively distributed from lagoon inlets towards inner parts. Nevertheless, each assemblage was found in particular habitat types and had a specific species composition in response to different environmental characteristics. (a) The Scolelepis fuliginosa community occupied sandy substrates at the lower section of the lagoon with stronger marine influence and, (b) the P. ulvae community lived in sandy‐muddy substrates, including two sub‐communities dominated, respectively, by Cerastoderma edule, S. plana and Tritia pfeffeiri inhabiting the middle section and S. plana the upper section. The combination of salinity, temperature, pH and silt content was identified as the major environmental variable subset with the highest correlation with the observed macrofaunal patterns and silt fraction as the single best correlated variable. The results demonstrated significant spatial differences in macrobenthic assemblage structure and composition along environmental gradients in spite of the absence of direct freshwater river inflow.

Determining How Functionally Diverse Intertidal Sediment Species Preserve Mudflat Ecosystem Properties After Abrupt Biodiversity Loss

Hale, H.; Jacques, R.O., and Tolhurst, T.J., 2019. Determining how functionally diverse intertidal sediment species preserve mudflat ecosystem properties after abrupt biodiversity loss. Journal of Coastal Research, 35(2), 389–396. Coconut Creek (Florida), ISSN 0749-0208.As a result of anthropogenic climate change, extreme climatic events have increased in frequency, severity, and longevity. The consequences for community structure after a catastrophic event have been well studied. However, changes in ecosystem functioning that occur after such an event, including ecosystem recovery, are still uncertain. A catastrophic event was simulated in an intertidal sedimentary habitat. Postevent sediment replicates were assigned to one of four recovery scenarios: (1) no recovery, (2) migration recovery, and recovery by differential opportunistic colonisation by (3) the polychaete worm Hediste diversicolor and (4) the mud snail Peringia ulvae, two locally dominant infauna species. These are compared with a control scenario not subjected to the event. The simulated extreme event caused a shift in habitat state due to a reduction in mobile macrofauna abundance and an increase in microphytobenthos biomass. Migratory recovery of species and the simulated opportunistic expansion of a single species ameliorated this shift and, for some metrics, functional compensation for the loss of other species and the preservation of certain ecosystem functions was observed. The dominant species identity during postevent habitat recovery can have considerable effects on important ecosystem processes and functions with consequences that may result in functional regime shifts in a habitat and alter coastal stability.

The role of invasive marine plants for macrofauna nutrition in the Wadden Sea

Wadden Sea macrozoobenthos has access to food sources of different quality. In addition to microphytobenthos (MPB) and macroalgae (e.g. Fucus vesiculosus Linnaeus, 1753), the invasive C4 grass Spartina anglica C.E. Hubbard has become an abundant primary producer in the Wadden Sea. To elucidate the role of different primary producers for the nutrition of typical Wadden Sea consumers, we conducted a mesocosm experiment with four food treatments (S. anglica, F. vesiculosus, MPB and all three resources together) under a simulated tidal cycle. We used consumers of different feeding types—the omnivorous polychaete Hediste diversicolor (O.F. Müller, 1776), the interface-feeding bivalve Limecola balthica (Linnaeus, 1758) and the surface deposit-feeding snail Peringia ulvae (Pennant, 1777)—and analyzed their biomass, δ13C and δ15N stable isotope values and fatty acid (FA) profiles. After 4 weeks, the biomass of H. diversicolor increased in treatments that contained F. vesiculosus, but decreased in the treatment with MPB. δ13C values of H. diversicolor reflected those of the food sources provided and FA profiles varied strongly between the treatments, indicating feeding on copepods and bacteria as well as macrophytes. The biomass of P. ulvae significantly increased in treatments with S. anglica and all three resources. However, δ13C values of P. ulvae differed significantly between the treatments and were unrelated to the food sources except for MPB. FA profiles confirmed the assimilation of MPB in this species. δ13C values and FA composition of L. balthica were similar in each of the treatments and did not resemble the resources provided. Instead, the high proportion of respective marker FAs indicated feeding on plankton. δ15N values of the consumer species declined significantly in the order H. diversicolor > L. balthica > P. ulvae in each of the treatments. These results indicate different strategies in food source use of the three consumer species with the performance of the generalist feeders H. diversicolor and P. ulvae exceeding that of the selective feeder L. balthica.

Using a mesocosm approach to evaluate marine benthic assemblage alteration associated with CO2 enrichment in coastal environments

The effects of acidification related to the CO2 enrichment in the coastal environments on marine macrobenthic abundance, diversity and richness were analyzed in a medium- term (21 days) using mesocosm experiments. Two sampling sites located in the Bay of Cadiz – SW, Spain were selected and tested at pH values ranged from 7.9 to 6.0 (± 0.1). Moreover, variations in the concentrations of metals in the sediment samples were analyzed at the end of each experiment. The results showed low variation in the concentrations of metals in the sediment among the pH treatments. A significant decrease (p < 0.05) in the abundance, diversity and richness of assemblages were measured between the control and the lowest pH level in both sampling sites tested in this study (Rio San Pedro and El Trocadero). The majority of species were found in all samples except in pH 6.0 which only two species were found (Hydrobia ulvae and Scrobicularia plana,) in Rio San Pedro sediment fauna. In general, the results of cluster analysis showed 60% and 40% similarity in all replicated tests in El Trocadero and Rio San Pedro of sediment fauna, respectively. The results of the Principal Component Analysis (PCA) showed that both sediment parameters and pH reduction can interfere in the benthic assemblage indices. Although the assemblages’ indices have shown decreases only in the lower pHs, the organisms also could be impacted by chronic effects. Therefore, the extension of this study is important in order to improve the knowledge about the risks associated with CO2 enrichment in on marine organisms.

Adaptation of benthic invertebrates to food sources along marine-terrestrial boundaries as indicated by carbon and nitrogen stable isotopes

Frequent environmental changes and abiotic gradients of the Wadden Sea require appropriate adaptations of the local organisms and make it suitable for investigations on functional structure of macrozoobenthic communities from marine to terrestrial boundaries. To investigate community patterns and food use of the macrozoobenthos, a transect of 11 stations was sampled for species number, abundance and stable isotope values (δ13C and δ15N) of macrozoobenthos and for stable isotope values of potential food resources. The transect was located in the back-barrier system of the island of Spiekeroog (southern North Sea, Germany). Our results show that surface and subsurface deposit feeders, such as Peringia ulvae and different oligochaete species, dominated the community, which was poor in species, while species present at the transect stations reached high abundance. The only exception was the upper salt marsh with low abundances but higher species richness because of the presence of specialized semi-terrestrial and terrestrial taxa. The macrozoobenthos relied predominantly on marine resources irrespective of the locality in the intertidal zone, although δ13C values of the consumers decreased from −14.1±1.6‰ (tidal flats) to −21.5±2.4‰ (salt marsh). However, the ubiquitous polychaete Hediste diversicolor showed a δ15N enrichment of 2.8‰ (an increase of about one trophic level) from bare sediments to the first vegetated transect station, presumably due to switching from suspension or deposit feeding to predation on smaller invertebrates. Hence, we conclude that changes in feeding mode represent an important mechanism of adaptation to different Wadden Sea habitats.

The Weierstrassian movement patterns of snails.

Weierstrassian Lévy walks are the archetypical form of random walk that do not satisfy the central limit theorem and are instead characterized by scale invariance. They were originally regarded as a mathematical abstraction but subsequent theoretical studies showed that they can, in principle, at least, be generated by chaos. Recently, Weierstrassian Lévy walks have been found to provide accurate representations of the movement patterns of mussels (Mytilus edulis) and mud snails (Hydrobia ulvae) recorded in the laboratory under controlled conditions. Here, we tested whether Weierstrassian Lévy walks and chaos are present under natural conditions in intertidal limpets Patella vulgata and P. rustica, and found that both characteristics are pervasive. We thereby show that Weierstrassian Lévy walks may be fundamental to how molluscs experience and interact with the world across a wide range of ecological contexts. We also show in an easily accessible way how chaos can produce a wide variety of Weierstrassian Lévy walk movement patterns. Our findings support the Lévy flight foraging hypothesis that posits that because Lévy walks can optimize search efficiencies, natural selection should have led to adaptations for Lévy walks.

Small-scale removal of seagrass (Zostera marina L.): effects on the infaunal community

ABSTRACTEelgrass meadows are a common feature in shallow waters along the Norwegian coast, where they provide a habitat for a diverse infaunal community. Recreational boat anchoring and moorings physically scour seagrass and may affect the ecosystem functioning and resilience of the system to natural and anthropogenic disturbances. A small-scale eelgrass (Zostera marina) removal experiment was conducted to study the effects on macro- and meiofauna. Entire plants, including the rhizomes, were removed from 4 m2 patches in three eelgrass meadows in the inner Oslofjord in October 2010. Core samples were taken after a recovery period of 10 months, from the removed patches as well as from the surrounding meadow. Macrofauna (>500 μm) and meiofauna (63–500 μm) in the sediment were investigated for possible effects of the eelgrass removal. Macrofauna and meiofauna composition were site specific and therefore location was identified as the main determinant for the infaunal community. The eelgrass did not regrow within the recovery period and bare sediment patches with only single eelgrass shoots were present during the sampling. Our analyses support an influence of the removal on individual species, but not the complete community. In particular one species, the gastropod Peringia ulvae, was encountered in higher numbers in samples from the removed patches than in control samples. From a management perspective, such minor removal of eelgrass, on the scale of square metres, appears to have no long-lasting detrimental effect to the infaunal community in sheltered meadows with muddy sediments.