Linnaeus' Neptunea (Mollusca: Gastropoda)

Three species of the arcto-boreal, large gastropod Neptunea , described by Linnaeus in 1758 and 1771, occur in large numbers over wide areas of the inshore North Atlantic and adjacent Arctic seas and are conspicuous among Pliocene and Pleistocene molluscs in the Icelandic, North Sea, and western Mediterranean basins. Selections of lectotypes for these species from shells in the collection of the Linnean Society of London, and designations of their type localities, establish the identity of Linnaeus' neptunes and more accurately determine their geographic and geologic distribution. The geographic range of Neptunea (Neptunea) antiqua (L.), the type species, now extends from southern Norway to the northern Biscay coast of France and from the westernmost Baltic Sea to southwestern Ireland; this species also occurs in Pliocene-Holocene marine deposits in West and East Germany, Sweden, the Netherlands, England and France. Its type locality is determined to be the North Sea. N. (Neptunea) despecta (L.) lives in the eastern Canadian Arctic, off southern Greenland, the Barents Sea, and North Atlantic as far south as Massachusetts and Portugal; it also occurs in Pliocene-Holocene strata of eastern Canada, east-central Greenland, Norway (including Svalbard), the Soviet Union, Sweden and England. Its type locality is determined to be the postglacial deposits at Uddevalla in southwestern Sweden. N. (Sulcosipho) contraria (L.) now extends from the southern Biscay coast of France to Cape Spartel, Morocco; this species also occurs in Pleistocene and lower Holocene sequences of the western Mediterranean. Its type locality is determined to be Vigo Bay, Spain. A closely related fossil species, N. (S.) angulata (S. V. Wood), occurs in Pliocene and Pleistocene deposits of the North Sea basin.     

Depth distributions of Fucus vesiculosus L. and Zostera marina L. as classification parameters for implementing the European Water Framework Directive on the German Baltic coast

A classification approach was developed within the European Water Framework Directive for the outer coastal waters of the German Baltic Sea. We concentrated on the known recent presence and depth distribution of Zostera marina and Fucus vesiculosus along the German coast. According to the European Water Framework Directive the reference conditions were reconstructed based on historical data. The available databases indicate that both species formerly occurred down to 10 m depth along the whole German Baltic Sea coastline, independent on the salinity gradient. The recent depth distribution of Z. marina varied between 2.5 and 7.9 m along the German Baltic coast. Dense F. vesiculosus stands were observed only along the western part of this coast at a maximum depth of 4.7 m. Comparing the historical data sets with recent findings reveals a strong decline of depth limits for both species during the last century. Therefore, we used both species to describe the degradation of the Baltic Sea coastal waters using change in the depth distribution. The boundaries of the ecological status according to the Water Framework Directive were calculated based on modelling. Ecophysiological light demands of species and decrease of water transparency (light reduction in percent) were used to describe the degradations. This approach is robust against variation of macrophyte light requirements and is straightforward to classify recent long-term macrophyte monitoring. However, it is very sensitive against changes in the depth distribution and may result in erroneous estimations of ecological class boundaries when insufficient historical data are used as reference. This model allows the adaption of the boundaries calculations to new knowledge about historical data and ecophysiological light demand of plants. Actually, the boundaries of the classification were defined as follows: 1% light reduction represents the transition from high/pristine to good ecological status, and 5% indicates the transition from good to moderate status. At least 25% reduction corresponds to a poor status, more than 75% to a bad status.     

Habitats and Distribution Patterns of Marine Luminous Bacteria in the Western Baltic Sea

Numbers of luminous bacteria were counted at three stations of the brackish water ecosystem of the western Baltic Sea from July 1985 to July 1986. Additional samples were taken during three cruises from stations at the North Atlantic Ocean, the Norwegian Sea and adjacent marine areas. — In Kiel Bight (western Baltic) values varied between 0 and 68,000 luminous cfu 1⁻¹. With exception of the coastal station a distinct seasonal distribution pattern was shown in a water depth of 20 m: high numbers found in summer were opposed to low numbers in winter, the peaks being rather high in comparison to those of other areas. Statistical analysis showed that the results of 20 m were significantly different from those of 0 and 10 m depth; however, there was no correlation with temperature and salinity. Taxonomic studies revealed that the population consisted primarily of the genus Photobacterium. — The optimum of salinity was not a brackish but a marine one and was about 30% for the majority of the strains tested. A smaller number of strains grew best at a salinity between 10 and 15%. Optima of temperature ranged from 15 to 20 °C for most of the test strains. — Taxonomic analysis was also performed with luminous strains from marine areas adjacent to the western Baltic Sea, Photobacterium being the dominant genus here, too. Luminous bacteria were also enriched from the external surface and the gut contents of whitings (Merlangius merlangus) and cods (Gadus morhua). A model is proposed which explains the distribution pattern found. According to this, the gut-dwelling luminous bacteria are transported by their hosts from the North Sea into the western Baltic Sea. Here they are released into the environment, thus inhabiting another niche.     

The diet of whiting Merlangius merlangus in the western Baltic Sea

The diet of whiting Merlangius merlangus in the western Baltic Sea was investigated and compared to the diet in the southern North Sea. Clupeids were important prey in both areas, but especially in the western Baltic Sea where they constituted up to 90% of the diet of larger individuals. Gobies, brown shrimps and polychaetes were the main prey of juveniles in the western Baltic Sea, while a wider range of species were consumed in the North Sea. The shift to piscivory occurred at smaller sizes in the western Baltic Sea and the fish prey consumed was proportionately larger than in the southern North Sea. Estimates of prey abundance and food intake of M. merlangus are required to evaluate its predatory significance in the western Baltic Sea, but its diet suggests that it could be just as significant a fish predator here as in the southern North Sea.     

Zoobenthic diversity-gradients in the Baltic Sea: Continuous post-glacial succession in a stressed ecosystem

The Baltic Sea, formed after the latest glaciation, is an enclosed, low-saline, non-tidal ecosystem and has steep latitudinal and vertical gradients from sub-arctic conditions in the north to temperate in the south. The sea has undergone rapid changes since the glaciation, and the “ecological age” of the present ecosystem is only about 8000 years. Primary successional processes are still ongoing, and numerous ecological niches (e.g. large-bodied sediment bioturbators) remain available for immigration. The system is species-poor and vulnerable to the threat of exotic invasive species, and to date about 50 zoobenthic species have established populations in the Baltic Sea. The present biota is a mixture of species of different ecological and zoogeographical origin (marine to limnic; northern Arctic marine and limnic, to North Sea and Atlantic marine). The current distribution patterns of zoobenthos are illustrated, using marine, limnic and non-indigenous examples of structure and ecosystem functions. The species richness decreases from over 1600 marine benthic species in the open Skagerrak to about 500 in the western parts of the Baltic Sea, approximately 80 in the southern regions, to less than 20 in the northern regions. On the other hand, limnic species increase diversity in the inner reaches of the Gulf of Finland and the Gulf of Bothnia. Polychaetes, molluscs and echinoderms are dramatically reduced in numbers from the south to the north.     

Phylogeographical structure, distribution and genetic variation of the green algae Ulva intestinalis and U. compressa (Chlorophyta) in the Baltic Sea area

The marine algae Ulva intestinalis and U. compressa are morphologically plastic with many overlapping characters and are therefore difficult to distinguish from each other. The present distribution of U. intestinalis and U. compressa is investigated along the salinity gradient in the Baltic Sea area through analyses of internal transcribed spacer (ITS) sequence data. Also, the amount and distribution of intraspecific genetic polymorphism in the ITS region is studied allowing inferences on the phylogeographical pattern and postglacial recolonization of the Baltic Sea area. The data show that of the two species only U. intestinalis occurs in the Baltic Sea. The distribution of U. compressa is more restricted than previously reported, and it was not found in salinities lower than 15 ppt. All of Scandinavia and the Baltic Sea were covered with ice during the last ice age and the organisms in the Baltic Sea must have colonized the area after the ice had started to melt. The genetic diversity of U. intestinalis and U. compressa in the Baltic Sea and the neighbouring area was found to be reduced compared to that in the British Isles. This reduction may be the result of either a historical reduction of diversity or an adaptation of specific clones to the northern environmental conditions.     

Ceramium gobii n. sp. (Rhodophyta, Ceramiales), a brackish-water red alga in the Baltic Sea

A geographical survey was made of the distribution of diaphanoid Ceramia in the Baltic Sea and adjacent waters west of the Baltic. It was found that Ceramium plants with so-called 'Gobi's' parasporangia (monosporangia) have a wide distribution in the Baltic Sea at salinities of ca (3) 5–8%. This brackish-water Ceramium is here described as a new species, Ceramium gobii. At higher salinities in the south of the Baltic Sea and on the Swedish west coast, round parasporangia (polysporangia) indicate the occurrence of other Ceramium species. The new species is very similar to the brackish-water species Ceramium radiculosum , which was described from river-mouths to the Gulf of Trieste (Italy). A comparison was made of several diaphanoid Ceramium species, C. diaphanum, C. tenuicorne, C. gobii , and C. radiculosum , including (1) size of male plants, (2) type of paraspores, (3) vegetative characters.     

Genetic relatedness of a new Japanese isolates of Alexandrium ostenfeldii bloom population with global isolates

In recent years, blooms of toxic Alexandrium ostenfeldii strains have been reported from around the world. In 2013, the species formed a red tide in a shallow lagoon in western Japan, which was the first report of the species in the area. To investigate the genetic relatedness of Japanese A. ostenfeldii and global isolates, the full-length SSU, ITS and LSU sequences were determined, and phylogenetic analyses were conducted for isolates from western and northern Japan and from the Baltic Sea. Genotyping and microsatellite sequence comparison were performed to estimate the divergence and connectivity between the populations from western Japan and the Baltic Sea. In all phylogenetic analyses, the isolates from western Japan grouped together with global isolates from shallow and low saline areas, such as the Baltic Sea, estuaries on the east coast of U.S.A. and from the Bohai Sea, China. In contrast, the isolates from northern Japan formed a well-supported separate group in the ITS and LSU phylogenies, indicating differentiation between the Japanese populations. This was further supported by the notable differentiation between the sequences of western and northern Japanese isolates, whereas the lowest differentiation was found between the western Japanese and Chinese isolates. Microsatellite genotyping revealed low genetic diversity in the western Japanese population, possibly explained by a recent introduction to the lagoon from where it was detected. The red tide recorded in the shallow lagoon followed notable changes in the salinity of the waterbody and phytoplankton composition, potentially facilitating the bloom of A. ostenfeldii.     

Range-edge genetic diversity: locally poor extant southern patches maintain a regionally diverse hotspot in the seagrass Zostera marina

Refugial populations at the rear edge are predicted to contain higher genetic diversity than those resulting from expansion, such as in post-glacial recolonizations. However, peripheral populations are also predicted to have decreased diversity compared to the centre of a species' distribution. We aim to test these predictions by comparing genetic diversity in populations at the limits of distribution of the seagrass Zostera marina, with populations in the species' previously described central diversity 'hotspot'. Zostera marina populations show decreased allelic richness, heterozygosity and genotypic richness in both the 'rear' edge and the 'leading' edge compared to the diversity 'hotspot' in the North Sea/Baltic region. However, when populations are pooled, genetic diversity at the southern range is as high as in the North Sea/Baltic region while the 'leading edge' remains low in genetic diversity. The decreased genetic diversity in these southern Iberian populations compared to more central populations is possibly the effect of drift because of small effective population size, as a result of reduced habitat, low sexual reproduction and low gene flow. However, when considering the whole southern edge of distribution rather than per population, diversity is as high as in the central 'hotspot' in the North Sea/Baltic region. We conclude that diversity patterns assessed per population can mask the real regional richness that is typical of rear edge populations, which have played a key role in the species biogeographical history and as marginal diversity hotspots have very high conservation value.     

Zonation of ground beetles (Coleoptera: Carabidae) and spiders (Araneida) in salt marshes at the North and the Baltic Sea and the impact of the predicted sea level increase

The ground beetles and spiders of two salt marshes at the German Northand Baltic Sea coast were investigated by pitfall traps in 1997 and 1998. Whilethe sites at the North Sea coast are tidal salt marshes, the salt marshes at theBaltic Sea are not influenced by tides. Pitfall traps were installed in agradient from 20 to 150 cm above MHT (mean high tide: 157cm + NN, NN: 500 cm above 0 at Amsterdam gauge) atthe North Sea coast or NN at the Baltic Sea coast at six or sevensampling elevations, each with five replicates. Conductivity, water content, organic substance,frequency or duration of floodings, sand content and pH of the soil weredetermined. The flooding regime is the major factor controlling the zonation ofinvertebrates. Two and three invertebrate assemblages at the North and BalticSea, respectively, were distinguished. These corresponded well with thevegetational zones. The border between the two zones was at 60–80cm above MHT at the North Sea. The three zones at the Baltic Seaextended between 20 and 30 cm, 40 to 80 cm and 100 to150 cm above NN. The elevation of the mean abundance of speciesabove MHT or NN was calculated. A tide simulation experiment resulted in ashifting population and in an increasing activity under a tidal regime aspredicted for the global climate change conditions in 2050. From the actualelevation of the mean abundance, the habitat size of salt marsh species wascalculated for a moderate and worse scenario of global climate change. Habitatreduction becomes highest for species of the lower salt marsh zone. Under worseconditions the gradiental length of habitat will only amount to a maximum of 20m at the slopes of the dikes.     

Epidemiology of pseudobranchial tumours in Atlantic cod(Gadus morhua) from the North Sea and the Baltic Sea

Investigations during several cruises (1979–1981) showed that Atlantic cod with pseudobranchial tumours occurred in all areas investigated. Statistical analysis of data revealed that there was a marked prevalence of the condition in the centre of the German Bight, whereas a lower incidence of the condition was observed on the Dogger Bank, off the Dutch coast and in the western Baltic Sea. The higher prevalence of pseudobranchial tumours in the German Bight coincides with a dense population of cod and impacts of pollution.     

On the formation of net phytoplankton patches in the southern Black Sea during the spring

Species composition, community structure and spatial distribution of net phytoplankton in the southern Black Sea have been studied. In the fraction over 55 m, diatoms were found to be predominant in cell abundance and followed by dinoflagellates. Net phytoplankters were found to be more abundant in the southwestern sector, especially near the Bosporus and near Sakarya River mouth. MDS (Multi-Dimensional Scaling) analysis has projected four distinct patches along the coast, two of which appear to occupy smaller regions compared to the main western and eastern patches which have lower species numbers and diversity. The diatom species Pseudo-nitzschia seriata and Cerataulina pelagica and the dinoflagellates Noctiluca scintillans and Scrippsiella trochoidea dominate the west, while diatom species Synedra acus and Asterionella formosa together with Microspora sp. and Ankistrodesmus falcatus from chlorophyceae dominate the east.     

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.     

南黄海、东海鲐鲹鱼索饵场浮游动物生态特征

本文采用比较的方法,研究了黄海南部东海北部和东海中南部两个鲐鲹鱼索饵场浮游动物生态特征。结果表明,南部渔场生物量的极差、变异系数小于北部渔场。若扣除个别站位的影响,则南部渔场的平均值高于北部渔场。北部渔场群落多样度、均匀度、丰富度、单纯度较高,南部渔场则相反。北部渔场浮游动物优势种较少,且大多数种具有较高的聚集强度;而南部渔场优势种较多,优势度低,聚集性差。     

Further expansion of the genus Cercopagis (Crustacea,Branchiopoda, Onychopoda) in the Baltic Sea,with notes on the taxa present and their ecology

The onychopod cladoceran Cercopagis that recently invaded the Baltic Sea is reported from new zones of the northern Baltic proper. Because of successful survival and an expanding distribution range, the addition of Cercopagis to the Baltic fauna is considered to be permanent. What has previously been cited as Cercopagis pengoi encompasses the morphology of several other species, subspecies and forms. Either a number of morphologically similar species is present, or there is a number of spurious species in Cercopagis. The last hypothesis is favoured. The spatial distribution pattern of Cercopagis, as well as that of total zooplankton, was correlated with depth. Deep (>100 m) and shallow (<10 m) stations had significantly lower abundance than stations of intermediate depth (<100 m). An overview of the distribution of C. pengoi group in fresh and brackish waters suggests a high tolerance to environmental factors, but with differences among taxa. Due to this ecological flexibility, the colonization of the Baltic is not unexpected. Increasing salinity may restrict dispersal of cercopagids to the southern areas of the Baltic and to the North Sea, but inland lakes (e.g. in Sweden) present an ecological profile suitable for colonization.     

Foraminiferal response to the Northeast Monsoon in the western and southern Arabian Sea

Sediments from the western and southern part of the Arabian Sea were collected periodically in the spring intermonsoon between March and May 1997 and additionally at the end of the Northeast Monsoon in February 1998. Assemblages of Rose Bengal stained, living deep-sea benthic foraminifera, their densities, vertical distribution pattern, and diversity were analysed after the Northeast Monsoon and short-time changes were recorded. In the western Arabian Sea, foraminiferal numbers increased steadily between March and the beginning of May, especially in the smaller size classes (30–63 μm, 63–125 μm). At the same time, the deepening of the foraminiferal living horizon, variable diversity and rapid variations between dominant foraminiferal communities were observed. We interpret these observations as the time-dependent response of benthic foraminifera to enhanced organic carbon fluxes during and after the Northeast Monsoon. In the southern Arabian Sea, constant low foraminiferal abundances during time, no distinctive change in the vertical distribution, reduced diversity, and more stable foraminiferal communities were noticed, which indicates no or little influence of the Northeast Monsoon to benthic foraminifera in this region.     

Temporal and spatial changes in benthic invertebrate trophic networks along a taxonomic richness gradient

Species interactions underlie most ecosystem functions and are important for understanding ecosystem changes. Representing one type of species interaction, trophic networks were constructed from biodiversity monitoring data and known trophic links to assess how ecosystems have changed over time. The Baltic Sea is subject to many anthropogenic pressures, and low species diversity makes it an ideal candidate for determining how pressures change food webs. In this study, we used benthic monitoring data for 20 years (1980–1989 and 2010–2019) from the Swedish coast of the Baltic Sea and Skagerrak to investigate changes in benthic invertebrate trophic interactions. We constructed food webs and calculated fundamental food web metrics evaluating network horizontal and vertical diversity, as well as stability that were compared over space and time. Our results show that the west coast of Sweden (Skagerrak) suffered a reduction in benthic invertebrate biodiversity by 32% between the 1980s and 2010s, and that the number of links, generality of predators, and vulnerability of prey have been significantly reduced. The other basins (Bothnian Sea, Baltic Proper, and Bornholm Basin) do not show any significant changes in species richness or consistent significant trends in any food web metrics investigated, demonstrating resilience at a lower species diversity. The decreased complexity of the Skagerrak food webs indicates vulnerability to further perturbations and pressures should be limited as much as possible to ensure continued ecosystem functions.     

Abundance, depth distribution, and composition of aerobic bacteriochlorophyll a-producing bacteria in four basins of the central Baltic Sea

The abundance, vertical distribution, and diversity of aerobic anoxygenic phototrophic bacteria (AAP) were studied at four basins of the Baltic Sea. AAP were enumerated by infrared epifluorescence microscopy, and their diversity was analyzed by using pufM gene clone libraries. In addition, numbers of CFU containing the pufM gene were determined, and representative strains were isolated. Both approaches indicated that AAP reached maximal abundance in the euphotic zone. Maximal AAP abundance was 2.5 x 10(5) cells ml(-1) (11% of total prokaryotes) or 1.0 x 10(3) CFU ml(-1) (9 to 10% of total CFU). Environmental pufM clone sequences were grouped into 11 operational taxonomic units phylogenetically related to cultivated members of the Alpha-, Beta-, and Gammaproteobacteria. In spite of varying pufM compositions, five clones were present in all libraries. Of these, Jannaschia-related clones were always found in relative abundances representing 25 to 30% of the total AAP clones. The abundances of the other clones varied. Clones potentially affiliated with typical freshwater Betaproteobacteria sequences were present at three Baltic Sea stations, whereas clones grouping with Loktanella represented 40% of the total cell numbers in the Gotland Basin. For three alphaproteobacterial clones, probable pufM phylogenetic relationships were supported by 16S rRNA gene analyses of Baltic AAP isolates, which showed nearly identical pufM sequences. Our data indicate that the studied AAP assemblages represented a mixture of marine and freshwater taxa, thus characterizing the Baltic Sea as a "melting pot" of abundant, polyphyletic aerobic photoheterotrophic bacteria.     

Colour polymorphism and genetic variation in Idotea baltica populations from the Adriatic Sea and Baltic Sea

Phenotypic and genetic variation was studied in two of the four European subspecies of the marine isopod Idotea baltica; the Mediterranean I. b. basteri and the Baltic I. b. baltica. Spatial and temporal patterns of colour polymorphism were analysed in northern Adriatic and western Baltic Sea populations. Pronounced differences in phenotype composition were observed between populations of both subspecies as seen in the distribution of various colour variants bilineata, lineata, flavafusca and several combined forms). Compared with Adriatic samples, western Baltic Sea populations show higher phenotypic diversity. To obtain an estimate of the degree of genetic divergence between the subspecies, 12 gene-enzyme systems were investigated electrophoretically. The results obtained indicate a relatively high level of genetic variation; I. b. basteri from the nothern Adriatic tends to be more polymorphic and more heterozygous than I. b. baltica from the western Baltic. Both subspecies share identical electrophoretic mobilities of the homologous enzyme proteins examined; however, in allelic composition they exhibit significant differences at approximately half the number of loci scored. The genetic distance (Nei's D) measured at the subspecific level was 0.04. Amounts and geographical patterns of variation, observed both in colour phenotype and electrophoretic variation, are considered.