Spatial variability in structural and functional aspects of macrofauna communities and their environmental parameters in the Jade Bay (Wadden Sea Lower Saxony, southern North Sea)

Spatial distribution and functional structure of intertidal benthic macrofauna in relation to environmental variables in the Jade Bay (southern North Sea) were studied and compared with other intertidal areas of the Wadden Sea. A total of 128 stations covering the whole Jade Bay were sampled in summer 2009. A total of 114 taxa were found. Highest species numbers occurred in the subtidal areas, whereas highest mean abundances were found in the upper intertidal areas. Based on species abundance data, six significantly distinct macrofauna communities in the Jade Bay were identified and evaluated with multivariate statistics, univariate correlations and canonical correspondence analysis. Differences in these community patterns were caused by the response of the dominant species (Hydrobia ulvae, Tubificoides benedii, Pygospio elegans, Caulleriella killariensis, Scoloplos armiger, Urothoe poseidonis, Microprotopus maculatus) to prevailing environmental conditions along the gradient from the lower and exposed sandy intertidal areas via intermediate mixed sediments to the upper mudflat areas. Distribution patterns in relation to tidal zonation were best explained by variability in submergence time, Chlorophyll a (chl a) content and sediment composition (mud content), which are proxies for hydrodynamic conditions and food availability. Species inventory and species richness were comparable with other intertidal areas of the Wadden Sea, but the Jade Bay differs from these areas regarding dominant species. Differences in sediment composition and morphological characteristics (macrotidal versus mesotidal Wadden Sea areas) are discussed for comparison of regional differences.     

Major Changes in the Ecology of the Wadden Sea: Human Impacts, Ecosystem Engineering and Sediment Dynamics

Shallow soft-sediment systems are mostly dominated by species that, by strongly affecting sediment dynamics, modify their local environment. Such ecosystem engineering species can have either sediment-stabilizing or sediment-destabilizing effects on tidal flats. They interplay with abiotic forcing conditions (wind, tide, nutrient inputs) in driving the community structure and generating spatial heterogeneity, determining the composition of different communities of associated species, and thereby affecting the channelling of energy through different compartments in the food web. This suggests that, depending on local species composition, tidal flats may have conspicuously different geomorphology and biological functions under similar external conditions. Here we use a historical reconstruction of benthic production in the Wadden Sea to construct a framework for the relationships between human impacts, ecosystem engineering and sediment dynamics. We propose that increased sediment disturbances by human exploitation interfere with biological controls of sediment dynamics, and thereby have shifted the dominant compartments of both primary and secondary production in the Wadden Sea, transforming the intertidal from an internally regulated and spatially heterogeneous, to an externally regulated and spatially homogenous system. This framework contributes to the general understanding of the interaction between biological and environmental control of ecosystem functioning, and suggests a general framework for predicting effects of human impacts on soft-bottom ecosystems.     

The Influence of Dry-season Conditions on the Bottom Dwelling Fauna of an East Australian Sub-tropical Estuary

Spatial patterns in benthic infaunal community structure of Port Curtis estuary (north-eastern Australia) were determined from quantitative grab samples and examined in relation to environmental variables. A total of 149 riverine, estuarine and open coastal stations were sampled during the winter survey, and 5744 individuals from 466 species identified. Filter-feeding organisms (primarily polychaetes, molluscs and crustaceans) dominated the benthos, and accounted for 50% of the total species abundance and 30% of the total species richness. Most taxa were uncommon, and 98% of species individually represented less than 2% of the total abundance. Distributional patterns in total species richness and abundance were highly correlated, and both parameters varied significantly with sediment grain size. Numbers of species and individuals were typically highest in coarse-sand and gravel sediments, and were lowest in fine, well-sorted, sands. Cluster analysis of species abundance data revealed nine community groupings characterised by small species sub-sets with restricted distributions. These groupings were primarily related to sediment grain size, sediment organic carbon content, salinity and depth. Not all variation in community structure was explained by these environmental variables, and it is likely that other unmeasured factors play an important role in determining benthic faunal composition in the estuary.     

Patterns in biogeochemical properties of sediments and benthic animals among different habitats in mangrove forests

Abstract Determining interactions between biological and physical structure of intertidal sediments and their relationships to ecological functioning is vital for improving our understanding of these complex habitats. If spatial and/or temporal variations in the benthos are related to properties of the sediment, one can infer that sediments should vary and change at similar scales to the benthos. The mangrove forests of Sydney Harbour, Australia consist of distinct subhabitats (termed MH1‐3, representing a change from open mudflat to canopied mangrove forest), which might affect benthos and, independently, properties of the sediment. This study tests the model that the benthos and sediment would respond to environmental differences between MH1–3 similarly in different locations and thus show consistent patterns of difference among habitats. Although general patterns of sediment properties and benthos were relatively similar, detailed patterns varied among locations. The relative importance of the different sedimentary properties varied in unpredictable ways among habitats in the different locations. Out of all the variables, only total carbohydrate was consistently important in driving differences among habitats in all three locations, but only between MH1 and MH2. That there were no other strong consistent differences between the different microhabitats in terms of the measured properties of the sediments indicates that there is more driving these patterns than a simple relationship to different habitat formed by mangrove forests and/or feedbacks between sediment properties and benthos. With respect to the benthic assemblage, in all bays MH1 and MH3 were the most different. The benthos showed stronger patterns relating to the different subhabitats than did the sediment, suggesting that there are important differences affecting these habitats that were not revealed by our suite of biogeochemical measurements of the sediment.     

Benthic primary production in the Ems-Dollard estuary during 1975

Summary Primary production measurements of benthic micro-algal vegetations were carried out with samples from six permanent plots. These permanent plots were assumed to cover the range of salinities and sediments in the estuary. A modification of the standard¹⁴C-procedure (COLIJN and VAN BUURT, 1975) was used throught this study. The sensitivity and reliability of the modified method, based on combustion of the filtered sediments and subsequent scintillation counting, is discussed. The method proves to be a fast one, and reliable with recoveries over 95%. Moreover, counting efficiences can be based on one quench curve only for all sediment samples. The method is also applicable for planktic primary production. To make a direct comparison of the six permanent plot possible, the potential primary production was measured under saturating light intensities. The incubation temperature corresponded with the temperature during sampling.The results show a spring peak in both production and chlorophyll-a values on all permanent plots. Daily fixation rates were calculated, using daylength and tidal emersion data. No corrections for respiration during the dark period have been made. Production over 1975 was calculated, using 7 to 12 measurements per permanent plot. The results are given in Table I, which also shows the relative sediment composition and exposure time for the six permanent plots. The sediment composition is given as the mean extinction at 430 nm of a partly settled sediment suspension (SCHRÖDER, 1976).Partial correlation coefficients of primary production with five variables (station, level, chlorophyll-a, salinity and temperature) were computed. Only chlorophyll-a showed a positive significant correlation coefficient (r=0.683; n=53). In contrast to the results of CADÉE and HEGEMAN (1974) in the western Wadden Sea no correlation could be found between primary production and temperature. The absence of a spring peak in the western part of the Wadden Sea is another striking difference with our results, for which no explanation can be given.More measurements are needed over a longer period to model the benthic production of micro-algal vegetations. Such a model is needed to predict the primary production under changing environmental conditions.     

长江口及东海春季底栖硅藻、原生动物和小型底栖生物的生态特点

利用Ludox-QPS方法并结合沉积环境因子的综合分析,研究了2011年4月采自长江口及东海10个站位以底栖硅藻、纤毛虫和异养小鞭毛虫为代表的微型底栖生物及小型底栖生物的组成、丰度和生物量、分布及生态特点。结果表明,底栖硅藻的丰度 (5.92 ? 104 ind/10 cm2) 和生物量 (83.29 ?g C/10 cm2) 远高于纤毛虫 (丰度为1036 ind/10 cm2,生物量为3.33 ?g C/10 cm2)、异养小鞭毛虫 (丰度为4451 ind/10 cm2,生物量为2.51 ?g C/10 cm2) 和小型底栖生物 (丰度为1947 ? 849 ind/10 cm2,生物量为49.01? 22.05 ?g C/10 cm2)。在鉴定出的11个小型底栖生物类群中,线虫占小型底栖生物总丰度的90%和总生物量的37%。底栖硅藻生物量在长江口及东海海域呈由近岸向外海逐渐降低的分布特点,而底栖纤毛虫、异养小鞭毛虫及小型底栖生物的分布则正相反。在垂直分布上,76%的硅藻和80%的线虫分布在0–2 cm沉积物表层,仅1%的硅藻和6%的线虫分布在5–8 cm分层。统计分析表明,底栖硅藻的现存量与沉积物中叶绿素a含量呈极显著的正相关,与底层水温度呈弱的正相关;该海域底栖原生动物和小型底栖生物的分布受多个因子而非单一环境因子的共同作用。对比分析表明,长江口及东海单位体积沉积物中的硅藻丰度较水体中的硅藻丰度高2个数量级,沉积物中相当部分的叶绿素a含量可能系底栖硅藻所贡献;表层8 cm沉积物中纤毛虫的丰度约是上层30 m水柱中纤毛虫丰度的30倍,生物量约是后者的40倍。尽管纤毛虫在生物量上远小于小型底栖生物,但其估算的生产力约是后者的3倍;而异养小鞭毛虫由于个体更小,其周转率可能较纤毛虫更高。长江口及东海陆架区原生动物和小型底栖生物的高现存量及生产力预示着其在该海域生态系统中的重要作用。     

Temporal variations in microbenthic metabolism and inorganic nitrogen fluxes in sandy and muddy sediments of a tidally dominated bay in the northern Wadden Sea

Factors controlling seasonal variations in benthic metabolism (O₂ flux) and dissolved inorganic nitrogen (DIN) fluxes were examined during a 12–14 month period at three intertidal Wadden Sea stations. Since the flux measurements were made as small-scale laboratory core incubations, the results are primarily related to the microbenthic community (microalgae, bacteria, micro-, meio- and small macrofauna) and cannot be considered representative of the total benthic community in the Wadden Sea. Furthermore, it has to be emphasized that light intensity during day-time simulations were constant and saturating at all times. Benthic primary production and oxygen uptake appeared to be temperature dependent with a ‘seasonal Q₁₀’ of 1.7–1.8 and 2.7–4.3, respectively. Inundation had no effect on oxygen fluxes as evidenced by similar sediment respiration with and without water cover. A stronger temperature dependence of primary production in muddy than in sandy sediment indicated that the overall control in the latter may be complex due to factors like macrofaunal grazing and nutrient availability. Benthic respiration may not be controlled by temperature alone, as sedimentary organic matter content correlated significantly with both temperature and benthic respiration. Annual gross primary production in high intertidal sandy sediment was 10 and 50% higher than in low intertidal sandy and muddy sediments, respectively. Since annual benthic community respiration was 2 times higher in muddy than sandy sediments, the annual net primary production was about 0 in the former and 17–19 mol C m^?2 yr^?1 in the latter. However, heterotrophic contribution by larger faunal components as well as removal of organic carbon by waves and tidal currents, which are not included here, may balance the budget at the sandy stations. There was no or only weak relationships between (light and dark) DIN exchange and factors like temperature, sedimentary organic content, and oxygen fluxes. Factors related to nutrient fluxes, such as denitrification and nutrient concentration in the overlying water, may have hampered any such relationships. In fact, DIN fluxes at all three stations appeared to be strongly controlled by DIN concentrations in the overlying water. On an annual basis, the sediment appeared to be a net sink for DIN.     

Temporal and vertical distribution of ciliophoran communities in the benthos of a small eutrophic loch with particular reference to the redox profile

SUMMARY. The ciliate communities occurring at three benthic sites in a small eutrophic loch have heen investigated over a 2-year period. Two characteristics of the community were studied in detail, the pattern of vertical distribution within the sediment and the temporal distribution of ciliates occurring in the surface sediment. The relationships between ciliate distributions and the environmental factors recorded were analysed by multiple regression. Significant relationships were revealed between vertical distribution of ciliates and the sediment redox (Eh) profile, the larger ciliate communities being associated with regions of higher potential. Other factors such as sediment density, organic matter, temperature and daylength, combined with other indicators of benthic metabolism (sulphide ion activity (Es^2?), pH, oxygen flux) were selected in the regression analysis as accounting for much of the variation in the depth distribution of ciliates. In analysing the temporal distribution of ciliates in the surface sediment, numbers were inversely related to Eh, Es^2? and oxygen flux, a result of the upwards migration of reducing conditions and greater microbial activity in the sediment surface during the summer. Daylength, temperature, organic carbon and benthic chlorophyll-a were also selected as accounting for much of the variation in ciliate number. It is proposed that the large increases in number and biomass of surface-sediment cilates in the summer months resulted from an intolerance of reducing conditions developing immediately beneath the surface and the increased productivity of the benthos as a whole during this period. Methods are also described for the construction, calibration and operation of electrodes used in measuring Eh, Es^2? and oxygen flux in the freshwater benthos. Data recorded for these three variables revealed similar seasonal patterns at each site in each of two consecutive years.     

Diversity and abundance of Gram positive bacteria in a tidal flat ecosystem

Gram positive bacteria recently have been identified as important components of freshwater ecosystems and are also present in marine environments. However, their quantitative significance and possible role in the latter systems is still little studied, in particular in coastal regions. Therefore, we investigated the abundance and composition of Gram positive bacteria in the Wadden Sea, a tidal flat ecosystem in the German Bight of the North Sea. Applying fluorescence in situ hybridization we found that Actinobacteria constitute 4-7% of total bacteria in the Wadden Sea and slightly higher proportions in a freshwater drainage channel connected to the sea by a sluice. The application of denaturing gradient gel electrophoresis of 16S rRNA gene fragments after amplification by an Actinobacteria-specific primer set and subsequent sequencing showed that the composition of the actinobacterial community in the Wadden Sea was distinctly different from that in the freshwater system. A bacterial clone library of 111 clones yielded eight Gram positive phylotypes which are related closely to other marine phylotypes including the Marine Actinobacteria Clade but also to freshwater phylotypes. We applied dilution cultures, enriched with various biopolymers, Marine Broth and Fucus vesiculosus extracts, for isolating bacteria from the bulk water, suspended aggregates, the oxic surface and oxic/anoxic transition zone of the sediment. Fifty-three isolates affiliated to seven families of the order Actinomycetales and nine isolates to the family Bacillaceae. The salinity range (1-45 per thousand NaCl) and growth optimum of 14 strains from various families showed that all except one strain exhibited a rather broad range of sustained growth from 1 per thousand to >or= 20 per thousand NaCl and several strains exhibited an optimum of > 10 per thousand NaCl. The results indicate that the Gram positive bacterial community in the Wadden Sea is surprisingly diverse and consists mainly of indigenous species which appear to be well adapted to the environmental conditions of this coastal ecosystem.     

Late Holocene stratigraphic evolution of a back-barrier tidal basin in the East Frisian Wadden Sea, southern North Sea: transgressive deposition and its preservation potential

The late Holocene stratigraphic evolution of a back-barrier tidal basin in the East Frisian Wadden Sea, southern North Sea, was investigated on the basis of a conceptual model relating the rate of sea-level rise to the rate of sediment supply. For this purpose, more than 20 vibra-cores and box-cores were evaluated, complemented by ¹⁴C ages of in situ peats and historical charts. In spite of interspersed short regressive events, the late Holocene stratigraphy generally reveals upward-coarsening grain-size trends indicative of transgressive deposition in the course of sea-level rise rather than erosion and redeposition by migrating channels. A particular feature is the general absence of down-core bioturbation traces, which stands out in sharp contrast to the intensely burrowed modern surface layer. Thus, in the Wadden Sea, high sediment turnover in the course of rapid transgression evidently obliterates most bioturbation traces and other tidal signals such as minor regressive deposits, thereby emphasising the importance of preservation potential.     

Abiotic factors affect microhabitat selection and community dynamics in a sandy-bottom lotic chironomid midge assemblage

Research has established that there is a relationship between lotic macroinvertebrates and environmental variables; however, the sample is frequently large with a coarse mesh size, or sampling is broad in scope. My working hypothesis was that microhabitat variability affects habitat choice and community structure of larval chironomid midges, examined at a scale close to organismal size. Small benthic cores were taken monthly and divided vertically into 1?cm sections. Midge larvae were extracted from each section, and 14 environmental variables were assessed for each section. Partial canonical correspondence analysis indicated that a number of species showed unique microhabitat preferences. The species?Cenvironment relation was strong, in which several environmental variables contributed significantly to patterns of midge habitat structure, most notably current, depth in the sediment, and certain sediment fractions. This research demonstrated that small macroinvertebrates are selective in choosing microhabitats, measured at the rarely examined small scale close to organismal size, in a simple homogeneous sandy environment. Precision in defining an organism??s microhabitat can help us better to understand species habitat choices with a view to improve understanding of species interrelationships.     

Relationships between benthic macrofauna and biogeochemical properties of sediments at different spatial scales and among different habitats in mangrove forests

In muddy intertidal sediments, there are reported complex interactions between the biological, physical and chemical properties of the sediment and the benthos that live in and on it. These are expected to be reflected in strong relationships between benthic animals and particular properties of the sediment, although some research has shown these relationships to be relatively weak. This study investigates the relationships between benthic macrofauna and biogeochemical properties of sediments within and among different habitats in multiple mangrove forests in a temperate estuary, in order to address the generality of any such relationships. Matched samples of benthos and sediment were collected from three habitats, which differed with respect to shading, the amounts of algae and leaf litter and the presence of pneumatophores. The sediment was sampled for water content, grain size, organic matter, chlorophylls a and b and colloidal and total carbohydrate.Spatial variation in sediment and benthos were significantly correlated across habitats in two of the three bays, but the sediment properties that contributed to differences between habitats and those that best correlated with the benthos varied among bays. In all bays, the single taxon that best correlated with the sediment was spionid polychaetes, but correlations were generally weak. There was no generality in the patterns of variation among the benthos or sedimentary properties among habitats. The benthos differed significantly among bays in all habitats, with large variation within and among sites. The sediment varied significantly at small scales in all habitats, but significant differences among bays were only found in two habitats. All spatial scales contributed to the total amount of variability in the sediment and there was little predictability from the patterns shown in one habitat to those in other habitats, or from one component of sediment to other components. Such variability suggests that there may be structural redundancy in this fauna, with different components of the benthos contributing to similar functions in different places. Such variability must be considered in experiments designed to understand relationships between ecological structure and function in these complex habitats and in any sampling studies to identify environmental impacts in these habitats.     

Variations in the mussel population of the Dutch Wadden Sea in relation to monitoring of other ecological parameters

The pattern of distribution of intertidal mussel beds is relatively constant over a number of years although their surface area can vary greatly. The abundance of mussels shows much greater fluctuations. In the western part of the Dutch Wadden Sea, west of the Terschelling tidal divide, the amount of mussels on natural beds fluctuated between 1 and 24 million kg fresh weight during the years 1949 to 1988. In the eastern part of the Dutch Wadden Sea the biomass varied between 5.5 and 180 million kg. The influence of the mussels on the ecosystem therefore can be very different between years. When many mussels are present the whole watermass can be filtered every few days. In years with few mussels present the filtering may take one month. It is argued that monitor programmes for a.o. nutrients, chlorophyll and growth rates of benthic organisms are of limited value if there is no indication about the total amount of mussels in the area. Presented at the VI International Wadden Sea Symposium (Biologische Anstalt Helgoland, Wattenmeerstation Sylt, D-2282 List, FRG, 1–4 November 1988)     

Marine fungal communities in water and surface sediment of a sea cucumber farming system: habitat-differentiated distribution and nutrients driving succession

The planktonic and benthic fungi in a sea cucumber farming system were simultaneously investigated on three sampling dates. Analyses of SSU rRNA gene libraries of four samples revealed 131 fungal operational taxonomic units, of which 58 % were potentially novel. Chytridiomycota, Blastocladiomycota and Monoblepharidomycota were detected only from sediment, whereas ascomycetes and basidiomycetes dominated in sediment and water, respectively. Cryptomycota phylotypes were detected in both water and sediment samples. Based on terminal-restriction fragment length polymorphisms, distinct succession and contrasting community structure were found between planktonic and benthic habitats. Redundancy analysis indicated that the concentration of dissolved silicate in surface water and N:P in porewater were the most significant abiotic variables shaping the planktonic and benthic communities, respectively. This study indicates that plankton and benthos are distinct habitats for fungal distribution even in shallow coastal systems, and nutrients and stoichiometric ratios play important roles in driving succession of fungal communities.     

Temporal variability of ecological niches: a study on intertidal macrobenthic fauna

The determination of temporal niche dynamics under field conditions is an important component of a species’ ecology. Recent developments in niche mapping, and the possibility to account for spatial autocorrelation in species distributions, hold promise for the statistical approach explored here. Using species counts from a landscape‐scale benthic monitoring programme in the western Dutch Wadden Sea during 1997–2005 in combination with sediment characteristics and tidal height as explanatory variables, we statistically derive realised niches for two bivalves, two crustaceans and three polychaetes, encompassing predators, suspension and bottom feeding functional groups. Unsurprisingly, realized niches varied considerably between species. Intraspecific temporal variation was assessed as overlap between the year‐specific niche and the overall mean niche, and this analysis revealed considerable variation between years. The main functional groups represented by these species showed idiosyncratic and wide variability through the study period. There were no strong associations between niche characteristics and mean abundance or body size. Our assessment of intraspecific niche variability has ramifications for species distribution models in general and offers advances from previous methods. 1) By assessing species’ realized niches in the multivariate environmental space, analyses are independent from the relative availability of particular environments. Predicted realized niches present differences between years, rather than annual differences in environmental conditions. 2) Using spatially explicit models to predict species habitat preferences provide more precise and unbiased estimates of species–environment relationships. 3) Current niche models assume constant niches, whereas we illustrate how much these can vary over only a few generations. This emphasizes the potentially limited scope of global change studies with forecasts based on single‐time species distribution snapshots.     

Benthic–pelagic coupling: a comparison of the community structure of benthic and planktonic heterotrophic protists in shallow inlets of the southern Baltic

1. The taxonomic composition, abundance and biomass of heterotrophic protists (ciliates, heterotrophic flagellates (HF), rhizopods and actinopods) in the sediment and water column of shallow inlets of the Southern Baltic was studied under a variety of environmental conditions during 1996–1997. A shallow, highly eutrophic station and a deeper, less eutrophic station were compared.
2. Community biomass ranged from 0.12 to 0.34 μg C cm?3 in the water column and from 1.5 to 105 μg C cm?3 in the sediment. Heterotrophic protists dominated zooplankton biomass at both stations (73% and 84% mean contribution), while they were of minor importance within the zoobenthos. Expressed per unit area, benthic biomass contributed a significant part (44% and 49%) to the total heterotrophic protistan community at both stations.
3. Although the methodology for counting ciliates and HF was focussed on a high taxonomic resolution, the results reveal some general trends in the distribution of heterotrophic protists: protozooplankton biomass was dominated by flagellates (80% mean biomass contribution) at the shallow station and by ciliates (73% mean biomass contribution) at the deep station. In the benthos at both stations, ciliates were the dominant protozoans, followed by the hitherto little‐studied rhizopods (25% and 35% mean biomass contribution) and flagellates.
4. The degree of benthic–pelagic coupling differed between taxonomic groups. Benthic and pelagic communities of ciliates showed little taxonomic overlap. In contrast, many heterotrophic flagellate species were found both in the benthos and in the pelagic. These benthic–pelagic species contributed significantly to the biomass of HF in the water column. The planktonic rhizopod community consisted of a subset of those species found in the benthos.
5. The abundance of benthic and pelagic protists was positively correlated at the shallow station, but taxonomic data indicate that the direct exchange between benthic and pelagic communities was only partly responsible.     

A method for rapid abundance estimation of semiplanktonic meiofauna

Many meiofaunal copepods and plathelminths enter the tidal waters at night thus exhibiting a life-style intermediate between benthic and planktonic. At the same time, ostracods may leave their interstitial dwelling and move across the sediment surface. In laboratory experiments, the percentage of plathelminth populations emerging from the sediment varied with the species, temperature, light conditions, and the dimensions of the sediment cores studied, but not with tidal level, season, ambient density of conspecifics, or the sediment composition. Therefore, the swimming activity may be utilised for extraction of semiplanktonic meiofauna provided that the extraction procedure is standardised with respect to temperature, light and core size. For free-living plathelminths from the Wadden Sea intertidal a robust standard procedure is as follows: sediment cores 1.6 cm in diameter (2 cm² surface area) and 3 cm deep are fitted into cylindrical containers and submerged into aquaria containing filtered seawater (ambient salinity, room temperature, darkness) for 24 h. The sediment containers are then removed and the aquarian water filtered through appropriate meshes; the residue contains the emergent faunal component. For plathelminths, this procedure reduces sorting time by some 90% compared with the standard shaking–decantation method and thus makes it possible to process a high number of samples in a short time. Similar procedures may be developed for copepods and epibenthic ostracods. Received in revised form: 28 August 2000 Electronic Publication     

The microphytobenthos of Königshafen—spatial and seasonal distribution on a sandy tidal flat

A microphytobenthic species composition of a tidal flat in the northern Wadden Sea was analysed regarding cell numbers and biomass (in carbon units). The three sampling sites differed in tidal inundation from 15 cm to about 90 cm water depth at high tide. The sediment was sandy at all three stations. A cluster analysis revealed a separation of the benthic diatoms into three areas: aNereis-Corophium-belt, a seagrass-bed and theArenicola-flat. Small epipsammic diatoms were most abundant and dominated the microalgal biomass. A microphytobenthic “spring bloom” even started beneath the ice cover of the flat in January. Lowest values of cell numbers and biomass of benthic microalgae were found in summer. Highest values were measured in the uppermost area (Nereis-Corophium-belt), and only here was an autumnal increase of benthic microalgae found. Further cluster analysis within each of the three areas revealed seasonal differences although the majority of species were present all year round. Many species were most abundant in spring, and some showed a bimodal distribution (spring-autumn) in the year of investigation.     

Dispersal Ability Determines the Role of Environmental,Spatial and Temporal Drivers of Metacommunity Structure

Recently, community ecologists are focusing on the relative importance of local environmental factors and proxies to dispersal limitation to explain spatial variation in community structure. Albeit less explored, temporal processes may also be important in explaining species composition variation in metacommunities occupying dynamic systems. We aimed to evaluate the relative role of environmental, spatial and temporal variables on the metacommunity structure of different organism groups in the Upper Paraná River floodplain (Brazil). We used data on macrophytes, fish, benthic macroinvertebrates, zooplankton, periphyton, and phytoplankton collected in up to 36 habitats during a total of eight sampling campaigns over two years. According to variation partitioning results, the importance of predictors varied among biological groups. Spatial predictors were particularly important for organisms with comparatively lower dispersal ability, such as aquatic macrophytes and fish. On the other hand, environmental predictors were particularly important for organisms with high dispersal ability, such as microalgae, indicating the importance of species sorting processes in shaping the community structure of these organisms. The importance of watercourse distances increased when spatial variables were the main predictors of metacommunity structure. The contribution of temporal predictors was low. Our results emphasize the strength of a trait-based analysis and of better defining spatial variables. More importantly, they supported the view that “all-or- nothing” interpretations on the mechanisms structuring metacommunities are rather the exception than the rule.     

Fundamentals of an applied ecosystem research project in the Wadden Sea of Schleswig-Holstein

The aims, content, and organisatory structure of a proposed interdisciplinary ecosystem research project in the Wadden Sea of Schleswig-Holstein (W. Germany) are briefly presented. The project will include research on both fundamental as well as applied aspects of the Wadden Sea ecosystems and their interaction with local human activities. In contrast to most of the other completed or currently running ecosystem research projects on tidal coasts, a considerable part of the scientific work will also deal with aspects of ecosystem management and protection of the various marine and semiterrestrial habitats of the Wadden Sea. Considerable attention is paid to theoretical and methodological aspects of research on ecosystems and landscape units. In particular, the adoption of a hierarchical view of complex biological and environmental systems is recommended. Presented at the VI International Wadden Sea Symposium (Biologische Anstalt Helgoland, Wattenmeerstation Sylt, D-2282 List, FRG, 1–4 November 1988)