Different zooplankton structures in the German Bight

In August 1982, a net of 48 stations with altogether 208 samples was investigated in the eastern German Bight with respect to temperature, salinity, as well as the amount and species composition of the mesozooplankton (>80 μm). The data were arranged into different structures by means of a cluster analysis. Four different clusters were found: (a) a “Wadden sea water” with few holoplankton organisms but a higher amount of spionid larvae; (b) a “German Bight water” with a maximum occurrence of turbellaria (Alaurina composita) and medium concentrations of copepods; (c) a mixing area between these two water masses with highest amounts ofOikopleura dioica, Temora longicornis, Acartia sp., mussel larvae and larvae of the spionid worms; (d) a “North Sea water” mass with highest concentrations ofPseudocalanus elongatus, Paracalanus parvus undOithona similis. The differences in the concentrations of the species mentioned between the four clusters were significant on the 0.1%-level.     

Infestation of oysters and mussels by mytilicolid copepods: differences between natural coastal habitats and two offshore cultivation sites in the German Bight

The aim of this study was to determine the macro‐parasitic infestation level of oysters from the southern German Bight focussing on copepods of the genus Mytilicola. Crassostrea gigas, Ostrea edulis and Mytilus edulis were collected at five locations: three nearshore sites in the eastern Wadden Sea and two offshore cultivation sites in the German Bight. To reveal seasonal variations one sampling site was investigated in winter and summer. At the nearshore sites, Mytilicola orientalis was regularly detected in C. gigas. Prevalences ranged between 32.3% and 45.1%, intensity between 3.0 ± 0.6 and 8.2 ± 1.5. Infestation rates of C. gigas within the southern German Bight decreased from west to east: Apparently, M. orientalis has started its range extension along the German coast with gradual retardation eastwards but generally followed the invasion route of its main host, the Pacific oyster. Interestingly, we detected not only M. intestinalis but also M. orientalis as an intestinal parasite in M. edulis, which has sofar not previously been described as host within this region. We conclude that M. orientalis is flexible in its host choice. Furthermore, in the eastern Wadden Sea infestation rates of oysters and mussels by copepods are similar. These results deviate from the patterns observed for the northern Wadden Sea in terms of infestation level and host specificity. No macro‐parasites were found in oysters and mussels from the offshore sites. This absence can be considered as potentially beneficial for aquaculture activities in the open ocean in terms of stamina and physiological performance.     

Contribution to the hydrographical structure of the eastern German Bight

Temperature, salinity, micronutrients, seston components and mesozooplankton were measured on a cruise in the eastern German Bight during November 1976. Three different water bodies and a mixing area which is divided into two subareas could be identified. The water masses differed significantly in regard to temperature, salinity, micronutrients and seston components. In some cases differences in the amounts of mesozooplankton could be found. Temperature and salinity of the water of the Elbe estuary and of the Wadden Sea were relatively low, but amounts of micronutrients and seston were high, whereas the water of the North Sea water body was of higher temperature and salinity with lower amounts of micronutrients and seston. The North Frisian coastal water and a southern mixing area can be regarded as mixing areas between these water bodies.     

The inner German Bight — an ecologically sensitive area as indicated by the bottom fauna

The muddy sediments of the sublittoral area of the inner German Bight are inhabited by a specialized macrofauna with few species. Long-term investigations on community and population dynamics have shown that the majority of this fauna are very susceptible to environmental stress (e. g. oxygen deficiency), and that the impoverishment trend recorded in 1977 has continued. The special hydrographic conditions of the inner German Bight, especially a long flushing time and the possibility of thermohaline stratifications, together with its function as a sediment trap are discussed. It is proposed that such areas should be considered as sensitive, and hence be protected from avoidable additional stress, e. g. introduction of wastes. This proposal is discussed with regard to the dangers arising from the view that muddy areas enriched with organic matter are inhabited by organisms preadapted to the decomposition of additional waste matter.     

A population study of the shrimp Crangon allmanni in the German Bight

The only reproducing population of Crangon allmanni within the German Bight is in the Helgoland Trench (HTR), a depression of more than 50 m depth south of Helgoland. In coastal and shallower offshore waters the shrimp is much rarer and is recorded in higher numbers only in early spring when the water is still cold. The life cycle of the HTR population lasts for about 1.5 years maximum. Recruitment takes place in summer, and these recruits form the reproducing population of the next year. The shrimps are sensitive to environmental stress and are therefore good indicators of environmental changes. Electronic Publication     

A seafloor crater in the German Bight and its effects on the benthos

 In 1963 a deep crater was formed about 65 m below sea level in the western part of the German Bight, due to a gas eruption caused by drilling carried out from the platform ’Mr. Louie’. The study area is situated in a sandy to muddy bottom area inhabited by an Amphiura filiformis association (sensu Salzwedel et al. 1985). The crater, sometimes called ’Figge-Maar’, functions as a sediment trap, concentrating particles and organisms from the water column, thus leading to extreme sedimentation rates of about 50 cm, on average, per year. Crater stations, compared with stations situated in the vicinity, show enrichments of juveniles. Echinoderms, especially the subsurface-dwelling heart urchin Echinocardium cordatum and ophiuroids are responsive to enrichment. Other species that are typical of the Amphiura filiformis association are shown to be unable to cope with the special conditions in the crater. Received: 12 June 1998 / Accepted:16 September 1998     

The fate of an immigrant: Ensis directus in the eastern German Bight

We studied Ensis directus in the subtidal (7–16?m depth) of the eastern German Bight. The jack-knife clam that invaded in the German Bight in 1978 has all characteristics of a successful immigrant: Ensis directus has a high reproductive capacity (juveniles, July 2001: Amrumbank 1,914?m^?2, Eiderstedt/Vogelsand: 11,638?m^?2), short generation times and growths rapidly: maximum growth rates were higher than in former studies (mean: 3?mm?month^?1, 2nd year: up to 14?mm?month^?1). Ensis directus uses natural mechanisms for rapid dispersal, occurs gregariously and exhibits a wide environmental tolerance. However, optimal growth and population-structure annual gaps might be influenced by reduced salinity: at Vogelsand (transition area of Elbe river), maximum growth was lower (164?mm) than at the Eiderstedt site (outer range of Elbe river, L _∞?=?174?mm). Mass mortalities of the clams are probably caused by washout (video inspections), low winter temperature and strong storms. Ensis directus immigrated into the community finding its own habitat on mobile sands with strong tidal currents. Recent studies on E. directus found that the species neither suppresses native species nor takes over the position of an established one which backs up our study findings over rather short time scales. On the contrary, E. directus seems to favour the settlement of some deposit feeders. Dense clam mats might stabilise the sediment and function as a sediment-trap for organic matter. Ensis directus has neither become a nuisance to other species nor developed according to the ‘boom-and-bust’ theory. The fate of the immigrant E. directus rather is a story of a successful trans-ocean invasion which still holds on 23?years after the first findings in the outer elbe estuary off Vogelsand.     

A multiannual outbreak of the turbellanan Alaurina composita Mecznikow 1865 in the German Bight

The plankton time series of ‘Helgoland Roads’ hasshown a multiannual population change in the abundance of theturbellarian Alaurina composita Mecznikow 1865. From the 1970sto the mid-1980s, the summer population increased by two ordersof magnitude; since then, it has fallen by about one order ofmagnitude. As limnetic investigations in related species show,A.cornposita must be considered a key predator of the NorthSea pelagial. Knowledge regarding the biology and ecology ofthe species is only rudimentary.     

Importance and abundance of the recently established speciesCoscinodiscus wailesii Gran & Angst in the German Bight

Grids of 17 to 50 stations in the German Bight were sampled 18 times within the framework of the multidisciplinary programmes ZISCH and PRISMA in winter and spring of 1988/89 and from April 1991–April 1992. The frequent abundance ofCoscinodiscus wailesii Gran & Angst, a recently established large diatom, was noteworthy, as it dominated the phytoplankton biomass over long periods (e.g. 12/88–3/89 and 8/91–11/91). The bulk of the phytoplankton carbon during these periods (up to 90%) could be attributed to this species. Blooms ofCoscinodiscus wailesii producing up to 1400 μg carbon 1⁻¹, were recorded in early spring of 1989 and autumn of 1991. The potential consequences for the whole ecosystem refer to the huge size of this organism, which may cause reduced exploitation of its primary production by native consumers. Furthermore, sedimentation and remineralisation processes may be affected. ForC. wailesii, a doubling of biomass in 70 h could be estimated on the basis of data from four successive surveys in 1991. Results from laboratory cultures under comparable conditions confirm this rate. In the survey area, no increase in biomass was recorded for the relatedCoscinodiscus granii Gough, although there was sufficient silicate supply for growth. Field data showed 8–10 times lower copper and 10–20 times lower cadmium and zinc accumulation inC. wailesii, compared to concentrations found in native phytoplankton species. Subsequent laboratory tests suggested that one reason for the remarkable success ofC. wailesii, mainly in inshore regions, may be derived from its tolerance of higher doses of heavy metals due to very low sorption.     

The macrofauna of a stony sand area in the German Bight (North Sea)

The sublittoral macrofauna of the Steingrund, a stony area east-northeast of Helgoland, was investigated from May till October 1991 using a van Veen grab and a small dredge. The diverse endo- and epifauna of the sandy bottoms, pebbles and boulders of this Saalian end moraine comprised 289 taxa, whereby the polychaetesMagelona papillicornis, Lanice conchilega andSpiophanes bombyx dominated in terms of abundance. Species rare in the German Bight, such as the spongeLeucandra fistulosa, the sea urchinEchinus esculentus, and the sea anemoneHaliplanella lineata, were also found. The two sample sets were processed separately with multivariate techniques, and differentiated on the basis of occurrence and numbers of the abundant species. The analysis of the grab samples revealed two types of theTellina-fabula-community. These associations were differentiated by the presence of species of the coarse-sand-inhabitingGoniadella-Spisula-community and were related to the distribution of the grain size of the sediment. Likewise, two epifaunal assemblages were distinguished. Sandy bottoms were characterized byOphiura albida, Liocarcinus holsatus andPagurus bernhardus, while boulders and pebbles were covered by a varied sessile and mobile epifauna dominated by the sessile bryozoanFlustra foliacea and the mobile pantopodeAechelia echinata. Numerical density, biomass and annual production estimates are in the range of values determined for the macrobenthos of the German Bight, while annual P/B ratios mounted up to 5.     

On the occurrence of Diogenes pugilator in the German Bight (Crustacea: Decapoda Diogenidae)

The occurrence of Diogenes pugilator in the German Bight has been examined since 2005. The steady onshore and offshore presence confirms that this southern species has established sustaining populations. The morphometric features are comparable to that of other populations in the adjacent Atlantic Ocean.     

Comparison of trace heavy-metal levels from monitoring in the German Bight and the southwestern Baltic Sea

Since 1973, monitoring for selected trace heavy metals has been performed in the German Bight (North Sea) and the western Baltic Sea. This paper deals with a set of filtered and unfiltered samples from a network of 22 stations covering the whole German Bight based on a cruise with RV “Gauss” in May 1974, and a similar series of samples taken at different depths at 18 stations in the Baltic Sea in October 1974. The metals Cd, Cu, Fe, Mn, and Ni were determined by flameless atomic absorption spectrometry. Data comparison is facilitated since sampling and analytical methods were identical. Distributions of metal-content data have been calculated from unfiltered and filtered samples. Qualitative and semi-quantitative aspects of the major differences or similarities between the histograms obtained from both sea areas are discussed.     

Experiments with artificial nests on predation in reed habitats

We performed nest predation experiments with artificial nests in reedbeds investigating whether nest predation pressure is different at the water-reed edge and the grassland-reed edge compared with the reed interior. Furthermore, we tested the effects of vegetation structure (reed density, height and thickness) and the effect of other nest site characteristics (distance from edge, water depth) on the success of artificial nests. The experiments were completed 3 times during the breeding season in 2001 at Lake Neusiedl, Austria. Each artificial nest resembled Great Reed Warbler (Acrocephalus arundinaceus) nests and contained one plasticine and one Quail (Coturnix coturnix) egg and the predators were identified by marks left on the eggs. The potential predators were birds, probably the Marsh Harrier (Circus aeruginosus), gulls (Larus spp.) and reed warblers (Acrocephalus spp.). Nest survival data were analysed using the Mayfield method, and we performed a discriminant analysis for the data of vegetation and nest site characteristics. The nest predation was higher at the edges than in the reed interior, and was most pronounced in April, before the new reed sprouted. The reason for this finding was probably that after May the new reed contributed to greater concealment of the nests through the higher reed density and height.     

Larvae of uncommon caridean decapods in the German Bight: Species composition,distribution and abundance

Typically, the most abundant group of shrimp larvae in the German Bight is formed by representatives of the family Crangonidae. Larvae of the remaining species have been largely ignored, and only scarce information concerning their ecology is available. Thus, the purpose of the present study was to determine the species composition, distribution and abundance of noncrangonid shrimp larvae in the German Bight in July 1990, after the mildest winter of the century. The material is based upon plankton samples collected at 77 stations, covering the entire German Bight. Eight species were identified, as well as larvae of Palaemonidae andProcessa-juveniles.Processa nouveli holthuisi (53.0%) andP. modica (31.3%) were predominant in the collection. The distribution of the two species was clearly separated: the main concentration ofP. nouveli holthuisi (peak concentration of 1.94 larvae per m³) was confined to the northwest corner of the German Bight, while a majority ofP. modica larvae (peak concentration of 0.54 larvae per m³) occurred at the southwesterly stations. The spatial distribution ofCaridion steveni andEualus occultus around Helgoland indicates the presence of an adult population at the only rocky island in the study area. Other taxa, such as larvae of Palaemonidae and juvenilePandalina brevirostris were collected exclusively in estuarine habitats. Based upon both the results of the present study and comparable data, we conclude that developmental stages of ten non-crangonid species, as well as representatives of Palaemonidae, can be expected to occur in the plankton of the German Bight. The extremely mild temperatures of the preceding winter may have been, in part, responsible for the relatively high densities of some taxa encountered during our plankton survey. We assume that warm winter temperatures favour the immigration, reproduction and survival of cold-sensitive species.     

Seasonal occurrence and abundance of caridean shrimp larvae at Helgoland,German Bight

Plankton samples were collected from January 1985 to January 1986 three times per week at Helgoland to study seasonal occurrence and abundance of caridean shrimp larvae. A total of eleven species were obtained. Ninety-one % of all larvae collected during the sample period belonged toCrangon crangon L. andCrangon allmanni Kinahan, 6% toPhilocheras trispinosus Hailstone and 3% to the remaining eight species. Collections were generally dominated byC. crangon larvae. However,C. allmanni larvae were most abundant in June coinciding with hatching activities of the population near Helgoland.C. allmanni was observed to have the highest density of all species with approximately 8 larvae per m³. Larvae ofEualus occultus (Lebour),Eualus pusiolus (Kroyer),Hippolyte varians Leach andAthanas nitescens Leach were most likely released by populations inhabiting the rocky intertidal zone around Helgoland. The presence ofProcessa modica Williamson & Rochanaburanon andProcessa nouveli holthuisi Al-Adhub & Williamson in the German Bight was verified by observations of a series of different developmental stages. Larvae of the rare speciesCaridion steveni Lebour were also recorded. The observed shrimp species were placed into three different groups with respect to their seasonal occurrence. Possible advantages of the timing of larval dispersal relative to predation and food availability are given. The results on seasonal occurrence and relative abundance are discussed in relation to environmental factors (temperature, salinity) as well as to the geographical distribution of the species.     

Insights into the ecology of Schizosaccharomyces species in natural and artificial habitats

The fission yeast genus Schizosaccharomyces contains important model organisms for biological research. In particular, S. pombe is a widely used model eukaryote. So far little is known about the natural and artificial habitats of species in this genus. Finding out where S. pombe and other fission yeast species occur and how they live in their habitats can promote better understanding of their biology. Here we investigate in which substrates S. pombe, S. octosporus, S. osmophilus and S. japonicus are present. To this end about 2100 samples consisting of soil, tree sap fluxes, fresh fruit, dried fruit, honey, cacao beans, molasses and other substrates were analyzed. Effective isolation methods that allow efficient isolation of the above mentioned species were developed. Based on the frequency of isolating different fission yeast species in various substrates and on extensive literature survey, conclusions are drawn on their ecology. The results suggest that the primary habitat of S. pombe and S. octosporus is honeybee honey. Both species were also frequently detected on certain dried fruit like raisins, mango or pineapple to which they could be brought by the honey bees during ripening or during drying. While S. pombe was regularly isolated from grape mash and from fermented raw cacao beans S. octosporus was never isolated from fresh fruit. The main habitat of S. osmophilus seems to be solitary bee beebread. It was rarely isolated from raisins. S. japonicus was mainly found in forest substrates although it occurs on fruit and in fruit fermentations, too.

     

Community composition of the rocky intertidal at Helgoland (German Bight,North Sea)

At the rocky island of Helgoland (North Sea), the distribution and abundances of intertidal communities were assessed and the effects of wave exposure and tidal height on the spatial distribution patterns of the communities were evaluated. Macroalgae and invertebrates were sampled quantitatively along line transects in three intertidal locations, a semi-exposed, an exposed and a sheltered one. The semi-exposed location was characterised by (1) Ulva spp. at the high intertidal (Ulva-community), (2) mussels and periwinkles at the mid intertidal (Mytilus-community) and (3) Corallina officinalis and mainly the large brown alga Fucus serratus at the low intertidal (Fucus-community). The exposed location encompassed the mid and low intertidal; at both zones the Fucus-community occurred. The sheltered location was characterised by (1) barnacles (Balanus-community) and (2) bryozoans, hydrozoans and mainly the large brown alga Ascophyllum nodosum (Ascophyllum-community). At the semi-exposed, but not at the exposed location the communities changed with the intertidal position. A relationship between wave exposure and the occurrence of specific communities was shown for the sheltered location; in contrast, communities of the semi-exposed and the exposed location appear to be little influenced by wave exposure directly. The community concept and the potential causes of distribution patterns of the defined communities are discussed and suggestions for a future monitoring are given. Variations in the communities at different spatial scales speak in favour of a multiple scale sampling design to monitor changes in the intertidal communities at Helgoland. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Differences in trait compositions between rocky natural and artificial habitats

Question: What are the differences in trait compositions that enable native plants to colonise comparable natural and man‐made habitats? Are these traits independent of phylogenetic relationships between species? Location: Czech Republic. Methods: The relative importance of biological, ecological and distributional traits of native species was studied, using a dataset of 75 species growing in rock and wall habitats in the Czech Republic. Species preferences for individual habitats due to climatic conditions and proportions of different vegetation types in their surroundings were partialled out using partial canonical correspondence analysis. The pattern of plant traits along a gradient from natural rock habitats to secondary wall habitats was analysed using regression trees and generalized linear models with and without phylogenetic correction. Results: The most common native species colonising rock habitats are phanerophytes, mostly woody juveniles, with a CSR life strategy and most are adapted to epizoochory. Summer green leaves, annual life span, CR life strategy, reproduction mostly by seeds and dispersal by ants are all traits positively associated with the ability of species to colonise wall habitats. These species are also characterised by their high demand for nutrients, temperature, base‐rich substrates and light. Biological and ecological traits are more important for colonising new habitats than traits related to species dispersal ability or phylogenetic relationships between species. Biological and ecological traits alone explained 29.3% of variability in the species dataset, while dispersal characteristics and phylogeny alone explained 9.1% and 4.8%, respectively. Conclusions: We outline how the process of environmental filtering determines native species assemblages and identify a set of species traits that enable them to persist in particular habitats. We conclude that although urbanisation generally results in loss of natural habitats, there are new, man‐made habitats potentially suitable for native species.     

Five new species of the nanoflagellatePirsonia in the German Bight,North Sea,feeding on planktic diatoms

The structure, development, and host range of five newly detected species of the phagotrophic nanoflagellatePirsonia are described. They feed on planktic diatoms common in the North Sea:P. verrucosa sp. nov. (onRhizosolenia delicatula), P. formosa sp. nov. (onRhizosolenia setigera), P. diadema sp. nov. (onCoscinodiscus granii andC. wailesii), P. eucampiae (onEucampia zodiacus) andP. mucosa sp. nov. (onRhizosolenia shrubsolei). The occurrence of resting cysts inPirsonia guinardiae is reported. The impact ofPirsonia on phytoplankton communities is discussed.