Species assemblages of pelagic fish embryos in the southern North Sea between 1984 and 2000

The occurrence and abundance of the pelagic eggs of southern North Sea spring-spawning fish were analysed between 1984 and 2000. Species number varied between six (1986) and 14 (1999) and was positively correlated with sea surface temperature. With one exception, dab eggs were always the most abundant and usually highly dominant. Ranking of species depended on temperature, but no significant differences in ranking between years was discernible. Although with the increase in temperature in the 1990s a change in species assemblage was evident [species belonging to the boreal-Mediterranean (Lusitanian) group became more apparent in the species assemblage] this did not lead to an increased species diversity (Shannon Index) or a change in other community parameters. It appears that the recent developments regarding spawning stock biomass of commercial North Sea fish is reflected in the declining egg abundance of the respective commercial and larger species (i.e. cod, flounder, plaice) and an increase in abundance of the eggs of small species (i.e. long rough dab, rockling) over the years. Received in revised form: 5 November 2001 Electronic Publication     

Marine molluscs and fish as biomarkers of pollution stress in littoral regions of the Red Sea, Mediterranean Sea and North Sea

The intensive development of industry and urban structures along the seashores of the world, as well as the immense increase in marine transportation and other activities, has resulted in the deposition of thousands of new chemicals and organic compounds, endangering the existence of organisms and ecosystems. The conventional single biomarker methods used in ecological assessment studies cannot provide an adequate base for environmental health assessment, management and sustainability planning. The present study uses a set of novel biochemical, physiological, cytogenetic and morphological methods to characterize the state of health of selected molluscs and fish along the shores of the German North Sea, as well as the Israeli Mediterranean and Red Sea. The methods include measurement of activity of multixenobiotic resistance-mediated transporter (MXRtr) and the system of active transport of organic anions (SATOA) as indicators of antixenobiotic defence; glutathione S-transferase (GST) activity as an indicator of biotransformation of xenobiotics; DNA unwinding as a marker of genotoxicity; micronucleus test for clastogenicity; levels of phagocytosis for immunotoxicity; cholinesterase (ChE) activity and level of catecholamines as indicators of neurotoxicity; permeability of external epithelia to anionic hydrophilic probe, intralysosomal accumulation of cationic amphiphilic probe and activity of non-specific esterases as indicators of cell/tissue viability. Complete histopathological examination was used for diagnostics of environmental pathology. The obtained data show that the activity of the defensive pumps, MXRtr and SATOA in the studied organisms was significantly higher in the surface epithelia of molluscs from a polluted site than that of the same species from control, unpolluted stations, providing clear evidence of response to stress. Enhanced frequency of DNA lesions (alkaline and acidic DNA unwinding) and micronucleus-containing cells was significantly higher in samples from polluted sites in comparison to those from the clean sites that exhibited genotoxic and clastogenic activity of the pollutants. In all the studied molluscs a negative correlation was found between the MXRtr levels of activity and the frequency of micronucleus-containing hemocytes. The expression of this was in accordance with the level of pollution. The complete histopathological examination demonstrates significantly higher frequencies of pathological alterations in organs of animals from polluted sites. A strong negative correlation was found between the frequency of these alterations and MXRtr activity in the same specimens. In addition to these parameters, a decrease in the viability was noted in molluscs from the polluted sites, but ChE activities remained similar at most sites. The methods applied in our study unmasked numerous early cryptic responses and negative alterations of health in populations of marine biota sampled from the polluted sites. This demonstrates that genotoxic, clastogenic and pathogenic xenobiotics are present and act in the studied sites and this knowledge can provide a reliable base for consideration for sustainable development. Received: 2 March 1999 / Received in revised form: 2 August 1999 / Accepted: 3 August 1999     

The conservation of British North Sea estuaries

Estuaries are amongst the most productive, but scarce, ecosystems in the world. Britain and the southern North Sea have many and extensive estuaries. Many British North Sea coast estuaries are nationally and internationally important for nature conservation for their variety of sand-dune, saltmarsh, sandflat and mudflat habitats, and the plants and animals that they support. The wildlife of estuaries are currently being affected by a great many of man's activities. Many, particularly land-claim, pollution and recreational activities cause loss and damage to this scarce wildlife habitat. Conservation of British estuaries is achieved mainly through site safeguard — the notification of Sites of Special Scientific Interest (SSSIs) and declaration of National Nature Reserves (NNRs) by the Nature Conservancy Council (NCC), and the designation of sites of international importance under the Ramsar Convention and the EC Directive on Wild Birds — and the amelioration of existing damage by sensitive management and pollution control. Several nationwide surveys, particularly NCC's Estuaries Review, are underway in Britain. These will provide sound comparable information on all estuarine sites, and will form the basis for developing an overall estuarine conservation strategy.     

Introduction into the ecosystem of the North Sea: Hydrography,biota, and food web relationships

The North Sea, one of the most productive of the earth's seas and oceans, is also surrounded by some of earth's most densely populated and heavily industrialized regions. A growing number of signals are being received which indicate that this valuable ecosystem is increasingly under stress. This has generated a corresponding increase in concern over the steps to be taken to protect the North Sea. While there are divergent views on what constitutes an ‘ideal’ North Sea, there is a general recognition that any decisions that are made should be based on a good understanding of this ecosystem. The intention of this paper is to give an overview of what is presently known, and to identify areas where more studies are needed. A brief summary of the hydrography and the biota of the North Sea is given. Biotic and abiotic structure justify partitioning the North Sea into three ecologically different regions: southern, central, and northern. For the most part, neither the top predators,e.g. marine birds and mammals, nor the macroalgae and sea grasses are included in this overview.     

The houting Coregonus oxyrinchus(L.)(Salmoniformes: Coregonidae), a globally extinct species from the North Sea basin

Coregonus oxyrinchus is redescribed and a neotype is designated (BMNH 1862.11.20.1.). It was restricted to south England and the lower parts of the Rivers Rhine, Meuse and Schelde. It is now globally extinct; the last individual was caught in 1940. Coregonus oxyrinchus is distinguished from other coregonids by having 38–46 gill rakers and a long, pointed snout.     

Influence of pollution on the harpacticoid copepods of two North Sea estuaries

Seasonal monitoring of the meiobenthos in the Dutch estuaries revealed an anomaly in density and diversity of harpacticoid copepods in the Westerschelde.Another Dutch estuary, the Eems Dollard, has comparable hydrodynamical, physical and sedimentological, characteristics and a similar fauna, but even in the severely organically polluted oligohaline mudflats of this estuary, annual average density and diversity of endo-epibenthic harpacticoid communities are higher than at similar less enriched meso- to polyhaline biotopes of the Westerschelde.Besides the concentrations of inorganic pollutants, such as phosphates and nitrates, the concentrations of pesticides, cyanide, detergents, phenoles, oils, polychlorobenzenes, polycyclic aromatic hydrocarbons and heavy metals were compared in both estuaries and compared to suggested permissive levels when available. From this it appears that these pollutants are present in the Westerschelde either in too low concentrations to be considered dangerous or at concentrations comparable to those occurring in the Eems Dollard, except for heavy metals.The load of a.o. Zn, Cu and Pb is distinctly and persistently higher in sediments and suspensions of the Westerschelde than in the Eems Dollard and copper is continuously present in a concentration at which, according to bioassays, egg production and larval development of planktonic copepods are severely affected. The remarkable scarcity of harpacticoid life on nutrient rich mudflats of the Westerschelde is thus probably due to heavy metal pollution.Since no other hardbodied meio- and macrobenthic taxa nor the plankton of this estuary show such a marked impoverishment, benthic harpacticoids prove to be suitable as indicators for the first stages of ecosystem-breakdown in estuarine and coastal zones polluted by trace-metals.     

Out of the North Sea: the Zeeland Ridges Neandertal

In 2001, a portion of human frontal bone was discovered in sediments extracted from the bottom of the North Sea, 15 km off the coast of the Netherlands. The extraction zone is located in the so-called Zeeland Ridges area located at 51°40′ northern latitude and 3°20′ eastern longitude. The specimen was dredged up from sediments containing Late Pleistocene faunal remains and Middle Palaeolithic artefacts, including well-finished small handaxes and Levallois flakes. The details of the supraorbital morphology, as well as the quantitative assessment of the shape of the external surface of the squama using traditional and 3D geometric morphometrics, unambiguously assign the Zeeland Ridges frontal bone to Homo neanderthalensis. Carbon and nitrogen isotopic analysis indicate that the Zeeland Ridges hominin, like other Neandertals, was highly carnivorous and does not show evidence for the consumption of aquatic foods. A lesion on the outer table and diploic layer of the bone in the area of the supratoral sulcus can be interpreted as the result of an intradiploic epidermoid cyst, a type of neoplasm diagnosed for the first time in Neandertal remains. So far, the Zeeland Ridges Neandertal is the first Pleistocene fossil hominin found under seawater and the first recorded in the Netherlands.     

Effects of the large-scale uncontrolled fertilisation process along the continental coastal North Sea

In this paper, effects of eutrophication in selected compartments of the North Sea ecosystem are discussed, encompassing the possibly positive effects of nutrient enrichment. Based on a variety of studies, impacts on biomass of phytoplankton, macrozoobenthos, microzooplankton, shrimps and fishes and productivity are presented. Enhanced nutrient concentrations and loadings can be observed in several coastal areas of the North Sea. As a result, increases in the concentration, production and changes in the species composition was observed in the phytoplankton. In addition, there are some indications for an increased biomass of macrozoobenthos, whereas an increase in microzooplankton can only be assumed from mesocosm experiments. A concomitant increase of higher trophic levels such as shrimps and fishes, as observed in some coastal regions of the North Sea, is difficult to link directly to eutrophication due to a lack of conclusive field observations showing the causality of the changes. That the large fertilisation process in the North Sea has led to a series of changes is, however, without doubt. The answer, to what extent these can be claimed as being harmless, positive or negative from the anthropogenic point of view, is hampered by the lack of good assessment criteria for marine ecosystems and requires a thorough analysis of all compartments involved by means of long-term-series long enough to discriminate between man-made and natural variability.     

Seasonal variability of inorganic and organic nitrogen in the North Sea

This study considers the cycling of nitrogen in the waters of the North Sea, particularly focussing on organic nitrogen. Dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON) and particulate organic nitrogen (PON) were measured in the North Sea over a one-year period (autumn 2004–summer 2005). The surface water concentrations of nitrate, ammonium, DON and PON during the present study ranged from <0.1–7.2 μM, <0.1–2.0 μM, 1.9–11.2 μM and 0.3–5.6 μM, respectively, with DON the dominant fraction of total nitrogen at all times. These nutrients concentrations were significantly lower compared to previous studies in the southern North Sea. The seasonal variations showed high mean surface concentrations of nitrate (4.7 ± 0.6 μM) and DON (8.9 ± 0.9 μM), low ammonium (<0.1 μM) and PON (0.8 ± 0.1 μM) in winter, shifting to low nitrate (0.3 ± 0.3 μM) and DON (4.2 ± 1.2 μM) in summer, with high ammonium (0.8 ± 0.4 μM) in autumn and PON (2.5 ± 1.2 μM) in spring. Highest mean surface DON concentration was measured in winter and may be due to resuspension of the organic matter from the bottom sediments. For autumn and spring, phytoplankton DON release was likely to be the most significant source of DON as shown by high concentrations of low molecular weight (LMW) DON and its positive correlation to chlorophyll a. Low total and LMW DON concentrations during summer were likely to be due to the uptake of the LMW DON fraction by phytoplankton and bacteria and the stratification of the water column. DON is therefore shown to be a potentially important source of nitrogen in shelf seas especially after the spring bloom has depleted nitrate to limiting concentrations. Handling editor: L. Naselli-Flores     

Community structure and functional roles of meiofauna in the North Sea

Knowiedge on community structure of North Sea meiofauna has greatly increased recently. A quasisynoptic picture of meiofauna densities and copepod community structure from 171 stations of the southern North Sea, sampled in April–May 1986, has been obtained during the North Sea Benthos Survey. Latitudinal patterns in meiofauna abundance and copepod weight, abundance and diversity exist in an area between 51°30′N and 58°30′N. Using TWINSPAN-classification five major groups of copepod species can be recognized which are related to sediment type, latitude and depth. The part of the meiofauna in total benthic energy flow, their role in the benthic food web and in biogeochemical cycles is discussed based on existing literature. There are still considerable gaps in knowledge and the field is not progressing rapidly. Publication no. 599 Netherlands Institute of Ecology, Centre for Estuarine and Coastal Ecology, Yerseke, The Netherlands.     

Candidatus Abditibacter,a novel genus within the Cryomorphaceae,thriving in the North Sea

Coastal phytoplankton blooms are frequently followed by successive blooms of heterotrophic bacterial clades. The class Flavobacteriia within the Bacteroidetes has been shown to play an important role in the degradation of high molecular weight substrates that become available in the later stages of such blooms. One of the flavobacterial clades repeatedly observed over the course of several years during phytoplankton blooms off the coast of Helgoland, North Sea, is Vis6. This genus-level clade belongs to the family Cryomorphaceae and has been resistant to cultivation to date. Based on metagenome assembled genomes, comparative 16S rRNA gene sequence analyses and fluorescence in situ hybridization, we here propose a novel candidate genus Abditibacter, comprising three novel species Candidatus Abditibacter vernus, Candidatus Abditibacter forsetii and Candidatus Abditibacter autumni. While the small genomes of the three novel photoheterotrophic species encode highly similar gene repertoires, including genes for degradation of proteins and algal storage polysaccharides such as laminarin, two of them – Ca. A. vernus and Ca. A. forsetii – seem to have a preference for spring blooms, while Ca. A. autumni almost exclusively occurs in late summer and autumn.     

Variations in spatial and temporal distribution of Archaea in the North Sea in relation to environmental variables

The spatial and temporal distribution of pelagic Archaea was studied in the southern North Sea by rRNA hybridization, sequencing and quantification of 16S rRNA gene and membrane lipid analyses and related to physical, chemical and biological parameters to determine the factors influencing archaeal biogeography. A clear temporal variability was observed, with marine Crenarchaeota (Group I.1a) being relatively more abundant in winter and Euryarchaeota dominating the archaeal assemblage in spring and summer. Spatial differences in the lateral distribution of Crenarchaeota were also evident. In fact, their abundance was positively correlated with the copy number of the gene encoding the alpha subunit of crenarchaeotal ammonia monooxygenase (amoA) and with concentrations of ammonia, nitrate, nitrite and phosphorus. This suggests that most Crenarchaeota in the North Sea are nitrifiers and that their distribution is determined by nutrient concentrations. However, Crenarchaeota were not abundant when larger phytoplankton (>3 microm) dominated the algal population. It is hypothesized that together with nutrient concentration, phytoplankton biomass and community structure can predict crenarchaeotal abundance in the southern North Sea. Euryarchaeotal abundance was positively correlated with chlorophyll a concentrations, but not with phytoplankton community structure. Whether this is related to the potential of Euryarchaeota to perform aerobic anoxygenic phototrophy remains to be shown, but the conspicuous seasonal distribution pattern of Crenarchaeota and Euryarchaeota suggests that they occupy a different ecological niche.     

Benthic macrofauna communities of the submersed Pleistocene Elbe valley in the southern North Sea

Macrozoobenthic community structure was studied in two surveys along a transect of 13 stations following the submersed Pleistocene Elbe valley in the south-eastern North Sea during May to June 2000 and March 2001. Two replicates of bottom samples were taken with a van Veen grab of 0.1 m² sampling size. In order to analyse the benthic macrofauna communities, the animals obtained were identified and counted, and MDS and cluster analysis were performed. Out of 200 taxa identified, 84 were polychaetes, 46 molluscs, 40 crustaceans, 15 echinoderms, and 15 belonged to other groups. Mean abundance was 4,860 individuals per m², mean biomass 32.9 g ash free dry mass per m². Mean diversity was 1.76 and mean evenness 0.54. The macrofauna of the Pleistocene Elbe valley is composed of three associations according to the cluster analysis. Each association is described by a combination of characterizing and discriminating species. An Amphiura-brachiata―Tellimya-ferruginosa-association was found in the south-eastern part of the depression, whereas a transitional association with elements of both assemblages lead to an Amphiura-filiformis―Galathowenia-oculata―Nuculoma-tenuis-association in the north-western part of the valley. In the context of the entire southern North Sea, both associations are small-scale substructures, and as such are contained in the Nucula-nitidosa-community and the Amphiura-filiformis-community, respectively. A north-westward shift of the community of the southern Elbe valley was found and discussed as a possible consequence of warm winters of the last decades.     

Native Parasites Adopt Introduced Bivalves of the North Sea

Introduced species may have a competitive advantage over native species due to a lack of predators or pathogens. In the North Sea region, it has been assumed that no metazoan parasites are to be found in marine introduced species. In an attempt to test this assumption, we found native parasites in the introduced bivalves Crassostrea gigas and Ensis americanus with a prevalence of 35% and 80%, respectively, dominated by the trematode Renicola roscovita. When comparing these introduced species with native bivalves from the same localities, Mytilus edulis and Cerastoderma edule, trematode intensity was always lower in the introduced species. These findings have three major implications: (1) introduced bivalves are not free of detrimental parasites which raises the question whether introduced species have an advantage over native species after invasion, (2) introduced bivalves may divert parasite burdens providing a relief for native species and (3) they may affect parasite populations by influencing the fate of infectious stages, ending either in dead end hosts, not being consumed by potential final hosts or by adding new hosts. Future studies should consider these implications to arrive at a better understanding of the interplay between native parasites and introduced hosts.     

Year-to-year variation in larval fish assemblages of the Southern North Sea

In order to test the temporal stability within and the reproducibility of larval fish assemblages between years, the larval fish assemblage at Helgoland Roads, North Sea (NE Atlantic) was quantitatively sampled almost daily from January 2003 to December 2005. The survey resulted in a total of 462 samples containing 50,632 larval fish of at least 42 taxa. In winter the larval fish assemblage was mainly dominated by larvae emerging from demersal eggs. This changed gradually to larvae hatching from pelagic eggs. Larvae from pelagic eggs dominated the ichthyoplankton assemblage in summer. A remarkably stable seasonality in terms of dominance patterns with recurring, season-specific fish assemblages was observed over the 3 years, despite substantial variation in environmental conditions such as a temperature difference of almost 20°C between summer and winter. The lesser sandeel (Ammodytes marinus), was the only species which showed significant fluctuations in abundance between the years. After removal of this species from the analysis, the dominance patterns of the remaining fish species were almost identical between years.     

Phaeocystis colony distribution in the North Atlantic Ocean since 1948, and interpretation of long-term changes in the Phaeocystis hotspot in the North Sea

Monitoring of Phaeocystis since 1948 during the Continuous Plankton Recorder survey indicates that over the last 5.5 decades the distribution of its colonies in the North Atlantic Ocean was not restricted to neritic waters: occurrence was also recorded in the open Atlantic regions sampled, most frequently in the spring. Apparently, environmental conditions in open ocean waters, also those far offshore, are suitable for complete lifecycle development of colonies (the only stage recorded in the survey). In the North Sea the frequency of occurrence was also highest in spring. Its southeastern part was the Phaeocystis abundance hotspot of the whole area covered by the survey. Frequency was especially high before the 1960s and after the 1980s, i.e., in the periods when anthropogenic nutrient enrichment was relatively low. Changes in eutrophication have obviously not been a major cause of long-term Phaeocystis variation in the southeastern North Sea, where total phytoplankton biomass was related significantly to river discharge. Evidence is presented for the suggestion that Phaeocystis abundance in the southern North Sea is to a large extent determined by the amount of Atlantic Ocean water flushed in through the Dover Strait. Since Phaeocystis plays a key role in element fluxes relevant to climate the results presented here have implications for biogeochemical models of cycling of carbon and sulphur. Sea-to-air exchange of CO₂ and dimethyl sulphide (DMS) has been calculated on the basis of measurements during single-year cruises. The considerable annual variation in phytoplankton and in its Phaeocystis component reported here does not warrant extrapolation of such figures.     

Historic mussel beds (Mytilus edulis) in the sedimentary record of a back-barrier tidal flat near Spiekeroog Island, southern North Sea

Mussel beds show irregular cycles of appearance, disappearance and reappearance at preferred distinct locations on intertidal flats. These cycles are documented in the depth profile by the presence of shell-rich sediments intercalated with sandy layers. Such mussel bed layers were regularly found over the past 12 years on the Swinnplate, a back-barrier tidal flat south of Spiekeroog Island, southern North Sea. They are characterised by the occurrence of sub-articulated pairs of Mytilus shells. Based on life span considerations, a period of at least 35–40 years over which mussel beds may have repeatedly established themselves is suggested. A survey in spring 2000 revealed a reduced occurrence of old, embedded beds on the Swinnplate. The present results, based on core profiles from 1992 to 2000 and amino acid age determination, show that alternations of shell layers indicative of former Mytilus beds and sediment layers provide insight into the historic development of tidal flat environments. The frequent occurrence of sub-articulated valve pairs in the shell layers documents that the embedding of the mussel beds took place soon after the death of the organisms without prior physical disturbance. Successions of historic Mytilus beds provide evidence that mussel beds are a regular, but not necessarily permanent, faunal feature of back-barrier tidal flats of the North Sea. Electronic Publication     

Comparative taphonomy of three bivalve species from a mass shell accumulation in the intertidal regime of North Sea tidal flats

This study comprises a comparative taphonomic analysis of three endobenthic bivalves (Mya arenaria, Cerastoderma edule, and Macoma balthica) derived from a mass accumulation of mainly vertically packed shells from the “Wurster Watt” in Lower Saxony’s Wadden Sea, German Bight. Bulk samples from two transects were analyzed with respect to taxonomic composition, left/right valve presence, counts and weight percentages of taxa, and size-frequency distributions. Taphonomic features including abrasion, fragmentation, encrustation and bioerosion were subjected to a semi-quantitative analysis. Taphonomic results show significant differences with respect to bivalve taxa as well as between transects. Mya arenaria, a large endobenthic bivalve, shows the greatest amount of fragmentation and is often encrusted by balanids and bryozoans. The smaller and more robust Cerastoderma edule has the greatest values for bioerosion especially by the polychaete Polydora ciliata. Macoma balthica, which has the thinnest valves, shows the highest values for abrasion, but low values for the rest of the measured taphonomic features. Taphonomic differences between the taxa, samples and transects are related to (1) the origin of the bivalves (from living populations or exposed colonization horizons), (2) the different size and morphology of the valves (themselves related to mode of life), (3) the taphonomic trajectories of the different bivalves, as well as (4) the varying depositional environment of the two transects.     

北海区海洋生态灾害的主要类型及分布现状研究

本文将海洋生态灾害定义为局部海域一种或少数几种海洋生物数量过度增多引起的海洋生态异常现象,包括赤潮、绿潮、水母旺发和外来种入侵等,根据相关研究及调查资料,探讨了北海区赤潮、绿潮、水母、外来生物入侵等生态灾害发生特点及趋势。结果表明,北海区赤潮和绿潮灾害频发,影响面积较大,渤海北部秦皇岛附近海域赤潮灾害严重,黄海西部山东半岛近岸海域浒苔绿潮灾害严重;水母灾害呈上升趋势,对人体健康威胁较大,北海区滨海城市都曾发生过水母蛰伤致死案例;黄河三角洲区域米草和泥螺入侵扩展速度较快。面对这些海洋生态灾害巨大威胁,北海区亟需加强海洋生态灾害防控研究。