Predator exclusion experiments in an intertidal mud flat

The intensity of predation pressure exerted on the macrofauna in muddy sediments was investigated in Königshafen (island of Sylt, eastern North Sea). Tests in aquaria revealed shrimpCrangon crangon, juveniles of the shore crabCarcinus maenas, and gobiid fishPomatoschistus microps as the most important local predators. Their high abundance from July to September led to the hypothesis, that predation pressure on the infauna will be most intense during that period. Cages were set up to protect the infauna against these predators. No protective effect was achieved with cages constructed of 20-mm mesh nylon net; however, cages with screen wire and gauze of 5-mm mesh and smaller resulted in a considerable increase of the infauna. In cages of 1-mm mesh gauze, set up from March to June, the macrofauna reached an abundance of four times the control density. In the period from July to October, the factor of increase was as high as 23. Species density was 28 400 cm^–2, as compared with only 7 in the control. Species which colonized the mud flat during spring and early summer established dense settlements inside the cages, but failed to do so in uncaged mud-flat areas. It is concluded that predation by young crabs, shrimp and gobies determines to a large extent the structure and dynamics in the local intertidal macrofauna.     

Modeling the influence of a young mussel bed on fine sediment dynamics on an intertidal flat in the Wadden Sea

Mussel beds are known to affect fine sediment dynamics and morphology on mudflat scale, a clear example of ecosystem engineering. Current research into possible ecological engineering applications of mussel beds makes quantitative modeling desirable. In this study a process-based model of the interaction between a young mussel bed and fine sediment was set up for use in the hydrodynamic and morphological model Delft3D-FLOW. The model encompasses the hydraulic roughness of the mussel bed, active capture of suspended sediment by filter feeding and changed bed properties due to biodeposited matter. The mussel bed implementation in Delft3D-FLOW was applied in a test case: a Wadden Sea intertidal mudflat model. It was concluded that a combination of active deposition via filtration and slow down of the flow due to increased roughness leads to high net deposition in the mussel bed. In addition, the ability of young mussels to quickly climb on top of deposited material results in rapid trapping of large amounts of fine sediment. In the wake of the mussel bed, deposition is also high because of reduced flow velocities. The effects of different existing mussel bed patterns were also evaluated. Patchiness and specifically striped patterns cause mussel beds to experience less sedimentation than uniformly covered beds of the same size and may therefore be favorable to mussels.     

Variations in the sulfide regime and the distribution of macrofauna in an intertidal flat in the North Sea

Sulfide concentrations were measured in the inner and outer Königshafen (Sylt, Wadden Sea) from November 1990 to December 1991 to assess the fluctuations of sulfide levels in natural tidal habitats. Three different areas were compared: (1) muddy sediment (2) fine-medium sand, and (3) a mussel bed. Other abiotic factors such as Eh, pH, temperature, grain size and organic content were measured. After assessment of the macrofaunal distribution, an attempt was made to relate the distribution to the sulfide concentrations in the benthic habitat. Sulfide concentrations varied between sites throughout the year with considerable differences ranging from below 5 μM (limit of detection) to about 1 mM (Oct. 1991). The faunal composition (Table 2) at the different sites hardly varied; it was always dominated by annelids: The cirratulidTharyx marioni was the most abundant species in the upper layers of all sites, where it occurred at low sulfide concentrations (<50 μM).Heteromastus filiformis was commonly found in the deeper sediment layers of the muddy site where it was regularly exposed to sulfide levels around 75 μM and peak concentrations in autumn up to 1 mM.Capitella capitata, Tubificoides pseudogaster andTubificoides benedii were very common in the upper sediment layers where sulfide levels were about 150 μM in autumn. These species also occurred, however, in the deeper layers with higher sulfide concentrations. These results document not only the wide annual range of sulfide concentrations at different depths in a tidal flat, they also emphasize that under natural conditions tidal flat annelids are exposed to considerable concentrations of hydrogen sulfide.     

东海表层沉积物纯培养与非培养细菌多样性

于2011年7月采集了浙江舟山沿岸海底沉积物样品(122°10′41″E,29°49′7″N),通过埋片原位观察、荧光显微计数、纯培养菌分离以及非培养细菌构建克隆文库的方法,分析和研究了东海表层沉积物细菌群落结构及其多样性.埋片原位观察和荧光显微计数法的结果表明:沉积物样品中细菌的细胞数量为(9.30±3.44)×107 cells/g;通过分离纯化共获得313株细菌,分属于20个属,4种培养基对细菌的分离效果依次为RO＞M l＞Zobell 2216＞MR2A;常规形态学与生理生化鉴定结果显示芽孢杆菌属(Bacillus)和海球菌属(Marinococcus)从数量和种类上皆为优势菌属,分别占分离菌株总数的21.08％和17.25％;对73株典型海洋细菌进行16S rDNA分子鉴定发现,厚壁菌门(57.5％)、γ-变形杆菌纲(32.9％)、黄杆菌纲(4.1％)和放线菌纲(5.5％)等为主要类群.非培养细菌克隆文库序列分析发现:细菌克隆子主要属于厚壁菌门和变形杆菌门,而芽孢杆菌纲和γ-变形杆菌纲是上述两个门的优势类群.综合纯培养与非培养数据得出东海海域表层沉积物细菌多样性丰富,具有进一步开发研究的价值.     

Effects ofFucus vesiculosus covering intertidal mussel beds in the Wadden Sea

The brown algaFucus vesiculosus formamytili (Nienburg) Nienhuis covered about 70% of mussel bed (Mytilus edulis) surface area in the lower intertidal zone of Königshafen, a sheltered sandy bay near the island of Sylt in the North Sea. Mean biomass in dense patches was 584 g ash-free dry weight m^?2 in summer. On experimental mussel beds, fucoid cover enhanced mud accumulation and decreased mussel density. The position of mussels underneath algal canopy was mainly endobenthic (87% of mussels with >1/3 of shell sunk into mud). In the absence of fucoids, mussels generated epibenthic garlands (81% of mussels with <1/3 of shell buried in mud). Mussel density underneath fucoid cover was 40 to 73% of mussel density without algae. On natural beds, barnacles (Balanidae), periwinkles (Littorina littorea) and crabs (particularly juveniles ofCarcinus maenas) were significantly less abundant in the presence of fucoids, presumably because most of the mussels were covered with sediment, whereas in the absence of fucoids, epibenthic mussel clumps provided substratum as well as interstitial hiding places. The endobenthic macrofauna showed little difference between covered and uncovered mussel beds. On the other hand, grazing herbivores — the flat periwinkleLittorina mariae, the isopodJaera albifrons and the amphipodsGammarus spp. — were more abundant at equivalent sites with fucoid cover. The patchy growth ofFucus vesiculosus on mussel beds in the intertidal Wadden Sea affects mussels and their epibionts negatively, but supports various herbivores and increases overall benthic diversity.     

Predation on barnacles of intertidal and subtidal mussel beds in the Wadden Sea

Balanids are the numerically dominant epibionts on mussel beds in the Wadden Sea. Near the island of Sylt (German Bight, North Sea), Semibalanus balanoides dominated intertidally and Balanus crenatus subtidally. Field experiments were conducted to test the effects of predation on the density of barnacle recruits. Subtidally, predator exclusion resulted in significantly increased abundances of B. crenatus, while predator exclusion had no significant effects on the density of S. balanoides intertidally. It is suggested that recruitment of B. crenatus to subtidal mussel beds is strongly affected by adult shore crabs (Carcinus maenas) and juvenile starfish (Asterias rubens), whereas recruits of S. balanoides in the intertidal zone are mainly influenced by grazing and bulldozing of the very abundant periwinkle Littorina littorea, which is rare subtidally. Thus, not only do the barnacle species differ between intertidal and subtidal mussel beds, but the biotic control factors do so as well. Electronic Publication     

Effects of herbivorous birds on intertidal seagrass beds in the northern Wadden Sea

During autumn migration (September to December), brent geese (Branta b. bernicla) and wigeon (Anas penelope) feed on the seagrass Zostera noltii in the nearshore, upper tidal zone leeward of the island of Sylt (eastern North Sea). To graze on leaves and shoots above the sediment and on rhizomes and roots below, these birds reworked the entire upper 1 cm layer of sediment eight times within this 3-month period. In addition, brent geese excavated pits 3–10 cm deep by trampling in order to feed on below-ground phytomass. About 12% of the seagrass beds became pitted to an average depth of 4.5 cm. Using net exclosures, it was estimated that birds removed 34 g dry weight m^–2 of above-ground and 28 g of below-ground phytomass. This corresponds to 45% of the phytomass in September. Of the overall loss of phytomass from September to December, 63% was caused by birds. Roughly half of the leaves fell off anyway until December and the other half were taken by the birds. Below the ground, phytomass remained almost constant where birds were excluded, while with birds phytomass of rhizomes and roots was halved. In spite of this strong effect, in the next vegetation period the blade density was lower at former exclosure sites compared to the ambient seagrass bed. The underlying process seems to be a self-inhibition of dense overwintering seagrass by mud accretion. Assuming our experimental results can be scaled up to the entire seagrass bed, we hypothesize that in the sheltered upper intertidal zone, seasonal erosion caused by herbivorous geese and ducks is necessary for the persistence of Z. noltii. Received: 7 January 1999 / Received in revised form: 23 August 1999 / Accepted: 25 August 1999     

Monitoring the Wadden Sea — an introduction

The Wadden Sea is an ecotone of far-reaching importance. Its nature is continuously changing, and ecological monitoring is needed to identify and analyse trends, and to inform the general public about accelerated change caused by human impact. Sustained ecological research with a diversified monitoring program is essential to overcome the ‘immature phase’ of short-term and single-site studies in ecological science. Long-term and wide-scale phenomena are of increasing relevance to human welfare. Ecological monitoring includes retrospective and ongoing recordings of physical, chemical and biological parameters on a regional scale. It improves our understanding of natural patterns and processes, and of the distortions caused by man. It may provide early warnings. It is a necessary precondition for translating the principle of anticipatory action into practical policy, and it also documents the effects of actions taken. Monitoring the Wadden Sea will help to protect its great variety of flora and fauna, and will also prevent it from deteriorating into a gray coastal backwater, serving for utility purposes only.     

An evaluation of small-scale genetic diversity and the mating system in Zostera noltii on an intertidal sandflat in the Wadden Sea

Background and Aims

The dwarf eelgrass, Zostera noltii, is a predominant inhabitant of soft-bottom intertidal regions along the coasts of northern Europe. It is a monoecious, protogynous angiosperm in which the potential for self-fertilization and inbreeding are high, especially if clone sizes exceed pollen dispersal distances. The aim of the present study was to determine the relationship between mating system and clonal structure, examine the relative roles of geitonogamous selfing and biparental inbreeding, measure pollen availability (multiple paternities) and estimate pollen dispersal.

Methods

A 100-m² plot was established in a large, intertidal Z. noltii meadow on the island of Sylt in the German Wadden Sea. A total of 256 adult shoots was sampled: one from the centre of 100 fixed 1-m² quadrats (large scale resolution) and an additional 156 from within eight randomly selected 1-m² sub-quadrats (small-scale resolution). DNA was extracted from seeds and leaf tissue of all samples and genotyped with nine microsatellite loci.

Key Results

Mating system analysis revealed high multilocus and single locus outcrossing rates. Average pollen dispersal distance was nearly the same as the average genet (clone) size. Multiple paternity was common and 20–30 % of mature seeds originated from matings within the plot. Among inbred seeds, most resulted from geitonogamy rather than biparental inbreeding.

Conclusions

Moderate disturbances intrinsic to the intertidal habitat appear to facilitate seed recruitment by gap formation. Pollen dispersal distances are sufficient to maintain outcrossing and high clonal diversity.     

Expanding the known diversity and environmental distribution of cultured and uncultured bacteria

Microorganisms represent the largest component of biodiversity in our biosphere. Traditional methods of bacterial identification depend on their culture on laboratory media and the comparison of their phenotypic characteristics. They include cellular morphology, motility, staining reactions of cell walls, ability to grow on different media and biochemical tests. These methods have many limitations and only a very small fraction of microorganisms have been cultivated. To date, molecular methods based on 16S rRNA sequences and their phylogenetic analysis are widely used for reliable identification, particularly for hard-to-culture microbial pathogens. These so-called < molecular methods > do not require laboratory culture of isolated organisms, and many novel non-described phyla have been detected, improving our view of bacterial diversity. Novel strategies for culturing the < uncultivated > are now under development, which are leading to the complete characterization of these new bacteria. More recently, meta- or ecogenomics, based on the complete sequencing of clones containing cosmids or bacterial artificial chromosomes with inserts, addresses the genetic potential of a sample irrespective of whether the microorganisms can be cultured or not. This has considerably extended our view of microbial diversity at the genomic level and the probability of finding new genes and their products suitable for the biotechnological and pharmaceutical industry.     

Mechanisms of cross-shore distribution pattern of the intertidal mud crabMacrophthalmus japonicus

In the intertidal mud crabMacrophthalmus japonicus, most large crabs occurred in the upper sandy areas. Mechanisms of the size-dependent distribution were interpreted experimentally. In the lower muddy area, food was more abundant and crab density was much higher than in the upper area. Under the high density conditions, interaction among large crabs became severe and more large crabs abandoned their burrows. In the experiment on burrowing-site selection, large crabs burrowed only in the muddy side under the low density, but also in the sandy side under high density conditions. The burrowing in the upper sandy area may be advantageous for large crabs, though food availability is lower, because of less competition and higher survivorship under the low crab density.     

波罗的海放线菌的多样性

摘要:【目的】为了探索海洋放线菌的多样性,为发现新的药物先导化合物提供新菌源,我们分析了波罗的海的放线菌多样性及生物活性。【方法】采集100 份底泥样品,用7 种培养基分离放线菌809 株;去掉相同菌株后,选择280 株代表菌进行了初步分类鉴定;采用琼脂扩散法,检测了它们对5 种细菌、真菌的抗菌活性;用API ZYM system 测定了21 种酶的活性。【结果】用海藻糖-脯氨酸培养基和HV 培养基分离的放线菌中,稀有放线菌占60% 和63% ;波罗的海的放线菌有15 个属,其中3 个属是首次从海洋中分离     

Macrofauna distribution and bioturbation on tidal confluences of the dutch Wadden Sea

Macrofauna density and bioturbation intensity (measured with X-ray radiography), were studied in the Dutch Wadden Sea near Ameland and in Mok Bay, Texel, in September 1988. The bivalveMacoma balthica and the polychaeteHeteromastus filiformis were widely distributed in the areas studied. The cockleCerastoderma edule and the polychaeteScoloplos armiger did not occur in areas with high clay content, while the molluscsHydrobia ulvae andMya arenaria preferred fine sediments. The polychaeteNereis diversicolor preferred the higher parts of the intertidal. In the Ameland area disturbance of primary sediment structures was highest near the shore and near the middle of the tidal confluence where physical reworking was low. The sheltered Mok Bay sediments were completely reworked by deposit-feeders. Bioturbation intensity and deposit-feeder (bioturbator) density were, however, not highly correlated. A number of stations showed higher bioturbation towards the surface and this may be related to the high abundance of near surface dwelling macrofauna, due to eutrophication and organic enrichment of the sediments in recent years.     

Long-term changes of intertidal and subtidal sediment compositions in a tidal basin in the northern Wadden Sea (SE North Sea)

Wadden Sea tidal flats are highly dynamic regarding the spatial distribution and the grain size composition of their sediments. From 2003 to 2006 surface sediments have been surveyed in an intertidal and a subtidal area within the tidal inlet Königshafen (south-eastern North Sea, northern Wadden Sea, island of Sylt) with the goal to gain information on short-term development trends in the grain size composition. The average grain size (Mean) becomes finer in the sheltered part of the intertidal survey area whereas a coarsening tendency can be observed in the more exposed part of the intertidal and especially in the subtidal survey area. The trend of the most frequent grain size (first Mode) shows the same spatial distribution pattern but is far less distinct. Thus, the changing Mean must be related to an increase in the deposition of fines in the sheltered part of the intertidal Königshafen as well as a general removal of fine-grained material in the exposed intertidal and subtidal Königshafen. In order to see long-term trends the surveys of 2003–2006 were compared to earlier studies conducted in 1932/1933, 1981 and 1989. A significant depletion of mud can be observed in the entire survey area. It is concluded that primarily changed hydrodynamics that may accompany ongoing climate change are responsible for this. However, the loss of fine-grained sediments is additionally amplified by a reduced vegetation cover and coastal protection measures.     

Management of the Wadden Sea

The Wadden Sea situated along the North Sea coasts of Denmark, the Federal Republic of Germany and The Netherlands represents one of the world's largest bar-built type of estuaries. The area is a typical sedimentation and mineralization basin, with a large influx of organic matter from the adjoining North Sea, consequently a delicate oxygen balance and a rich benthic macrofauna, poor in species, which serves as food for juveniles of some commercially important North Sea fishes and for large numbers of migrating and wintering waders and waterfowl. Past and present activities of the human society in the area include fisheries (mainly for shrimp and mussels, semi-culture), shipping, land reclamation, recreation, dredging for sand and shells, and waste discharge from industries and human communities. Until the present these activities, although sometimes conflicting, did not fundamentally affect the area and its biota (pollution excluded), but future claims, including the construction of large deep-sea harbours, drilling for natural gas and oil, large-scale land reclamation and increased industrialization etc., might gradually induce degradation. For instance, area reduction by continued land reclamation could lead to irreversible losses of specific biotopes (e. g. salt-marshes, mud-flats), which could affect the size of bird and fish populations in a much wider region. Increased pollution, which has already inflicted damage on bird and seal populations, could reduce the fauna and hence the value of the area as a natural sanctuary. In the event of a proposal for a new human activity in the area, the present standing practice in the countries concerned requires an evaluation of its safety and economic aspects and its environmental impact. However, the various plans are considered separately and there is a general need for integrated management of the area.     

Influence of light quality and gassing on the vertical migration of diatoms inhabiting the Wadden Sea

Diatoms inhabiting the Wadden Sea show a rhythmic migration pattern, which is superimposed by the tidal rhythm. In addition to light intensity, light quality has a pronounced influence on the upward-directed migration, thus giving some information on the nature of the relevant photoreceptors. Maximum diatom migration occurred when sediment surfaces were illuminated with blue light. The cell densities in blue light exceeded those of white light control experiments 1.8-fold. Furthermore, we registered a minor peak in the red light region, which reached approximately 60% of the white light controls. Cryptochrome and/or phototropin may thus be involved and act as photoreceptors for the vertical migration pattern. Flushing sediment surfaces of freshly mixed Wadden Sea sediments with air, O₂, CO₂ or N₂ did not show a significant influence of O₂ on the upward migration. The disappearance of diatoms from sediment surfaces which were flushed with CO₂ is most probably caused by the acidification of the sediment bed.Communicated by E. Rachor     

Geochemistry of mercury in an intertidal flat of the Scheldt estuary

Sediments were sampled on the ‘Groot Buitenschoor’, an intertidal flat located at about 60 km from the Scheldt's river mouth. Hg concentrations ranged from 30 to 1756 ng g⁻¹. The concentrations were strongly correlated with fine grain fraction, organic matter content and sulphide concentrations. Incubation experiments were performed in order to determine the potential methylation rate of Hg as well as biotic and abiotic factors influencing this transformation. About 1 to 2% of the added inorganic Hg is converted into methylmercury. This conversion rate points to the same equilibrium ratio as was observed in natural sediments, indicating an equilibrium between methylation and demethylation reactions in the sediments. Incubation of a sterilised sediment sample significantly decreased the methylation rate, but the methylmercury concentrations observed are still ten times higher than the natural (unspiked) sediment. This result could be due to a chemical (non-enzymatic) methylation of mercury. Sulphate reducing bacteria are the main species responsible for the methylation of Hg at this site. Addition of Na₂MoO₄, a specific inhibitor of sulphate reducing bacteria, decreased the methylation rate to the abiotic level (sterilised sediment). High sulphate reduction rates, however, lead to lower methylation rates. Increased formation of sulphides due to microbial sulphate reduction leads to enhanced HgS formation and this reaction competes with the methylation process. HgS is in fact the major product formed by the reaction of sulphate reducing bacteria with Hg species. About 50% of the Hg spiked to the sediments is transformed into HgS during the incubation experiments, and that compound is practically unavailable for methylation in contrast to other bound forms of Hg.