The megaepifauna of the Dogger Bank (North Sea): species composition and faunal characteristics 1991–2008

During a long-term study in the summer months of the years 1991–2008, 176 megaepifaunal species were recorded through a series of beam trawl surveys on a grid of fixed stations on the Dogger Bank (central North Sea). This paper gives a qualitative overview on species composition throughout the research period, determined from samples collected during 15 cruises. In recent years, a number of species with more oceanic distribution patterns (e.g. species from SW British coasts) has been collected. In spite of these newcomers, there was a slight decrease in total species numbers during the research period.     

Macrofauna communities of the Dogger Bank (central North Sea) in the late 1990s: spatial distribution,species composition and trophic structure

Macrofauna samples were taken in May 1996–1998 at 28 stations on the Dogger Bank (central North Sea) to describe species composition, spatial distribution and trophic structure of the macrofaunal communities. In general, five communities could be distinguished depending on the influence of different water masses, depth, type of sediment and food availability. Except for those species which feed in the sediment, macrofauna communities did not show any correlation to the measured sediment variables. In fact, macrofauna communities of the Dogger Bank were mainly structured by lateral food supply via frontal systems. This was indicated by the dominance of interface feeders foraging in the benthic boundary layer, which are able to switch from surface deposit to suspension feeding depending on flow conditions. The importance of sandlickers in the shallowest parts of the Dogger Bank hints at an important contribution of benthic primary production to the nutritional and energetic needs of the benthic community. Electronic Publication     

Lead and cadmium contents in selected macrofauna species from the Dogger Bank and the eastern north Sea

Lead and cadmium concentrations were measured in the polychaetesNephtys hombergi andN. caeca, in the sea-urchinEchinocardium cordatum, and in the bivalveVenus striatula obtained from the Dogger Bank and the eastern North Sea. The cadmium concentrations determined in all four species from these areas were relatively equal, except for an increase in concentration found in those species from the northeastern part of the Dogger Bank. A lower lead content was generally observed in the individuals taken from the German Bight than in those from the Dogger Bank, especially from its northeastern part. In the case of lead, it is possible to divide the southern North Sea into three regions according to the different concentration levels by statistical treatment: the less contaminated German Bight, the more contaminated central Dogger Bank and the highly affected northeastern Dogger Bank. The results obtained contradict the prevailing opinion that offshore invertebrate populations are, in comparison to individuals from coastal regions, less affected by contaminants such as heavy metals.     

Trophodynamics of the plankton community at Dogger Bank: predatory impact by larval fish

The trophodynamics of a coastal plankton community were studied,focusing on fish larvae and their copepod prey. The major objectiveswere to describe distributional overlap and evaluate the predatoryimpact by larval fish. The study was carried out across DoggerBank in the North Sea, August-September 1991. Sampling transectscrossed tidal fronts off the Bank and plankton at all trophiclevels showed peak abundance within frontal zones. Also Verticallythere was a significant overlap in distributional patterns ofthe plankton. Seven species of fish larvae were abundant, ofthese sprat (Sprattus sprattus) dominated. The abundance ofone group of fish larvae peaked in the shallow water close tothe Bank, whereas other species, including sprat, were foundin deeper water. Prey preference and predation pressure of fishlarvae were assessed using information on prey sizes and growthrates of larvae and the copepod prey. We estimated larval removalof preferred prey sizes to 3–4% day^–1, counterbalancedby a 3–7% day^–1' replenishment from copepod productionand growth. Additional predation pressure on copepods by aninvertebrate predator was estimated to 1–3%day^–1.In conclusion, the dynamics of fish larvae and other zooplankterswere closely linked. At peak abundances of fish larvae (>35mg dry weight m^–2), the accumulated predation on specificsize ranges of copepods, exerted by larvae and other predators,could exceed the ability of copepod replenishment and intra-/interspecificcompetition among predators might take place.     

Primary production in the deep chlorophyll maximum of the central North Sea

Deep chlorophyll maxima (CM) are commonly observed in the summerstratified North Sea. This feature was studied north of DoggerBank in August and showed high chlorophyll a (Chl a) concentration(     

The impact of subsidies on the ecological sustainability and future profits from North Sea fisheries

Background

This study examines the impact of subsidies on the profitability and ecological stability of the North Sea fisheries over the past 20 years. It shows the negative impact that subsidies can have on both the biomass of important fish species and the possible profit from fisheries. The study includes subsidies in an ecosystem model of the North Sea and examines the possible effects of eliminating fishery subsidies.

Methodology/Principal Findings

Hindcast analysis between 1991 and 2003 indicates that subsidies reduced the profitability of the fishery even though gross revenue might have been high for specific fisheries sectors. Simulations seeking to maximise the total revenue between 2004 and 2010 suggest that this can be achieved by increasing the effort of Nephrops trawlers, beam trawlers, and the pelagic trawl-and-seine fleet, while reducing the effort of demersal trawlers. Simulations show that ecological stability can be realised by reducing the effort of the beam trawlers, Nephrops trawlers, pelagic- and demersal trawl-and-seine fleets. This analysis also shows that when subsidies are included, effort will always be higher for all fleets, because it effectively reduces the cost of fishing.

Conclusions/Significance

The study found that while removing subsidies might reduce the total catch and revenue, it increases the overall profitability of the fishery and the total biomass of commercially important species. For example, cod, haddock, herring and plaice biomass increased over the simulation when optimising for profit, and when optimising for ecological stability, the biomass for cod, plaice and sole also increased. When subsidies are eliminated, the study shows that rather than forcing those involved in the fishery into the red, fisheries become more profitable, despite a decrease in total revenue due to a loss of subsidies from the government.     

Environmental influence on the bottom and near-bottom megafauna communities of the Dogger Bank: a long-term survey

This paper deals with climate-driven changes of the species composition of the bottom and near-bottom megafauna of the Dogger Bank (central North Sea), which was sampled each summer with a 2-m beam trawl on a yearly basis since 1991. The station grid consists of 37 stations, covering an area of approximately 17.000?km2. A selection of commoner species is analysed and correlated with temperature data gained during the research period. Temperatures are derived from our own measurements, combined with CTD data from the International Council for the Exploration of the Sea. The results show a decrease in biodiversity and a clear regime shift around the beginning of the 21st century, combined with rising mean bottom temperatures. In addition, details are given about the Dogger Bank hydrography and the climate sensitivity and abundance of the main species caught with the beam trawl. Our long-term study reveals the changes in the community structure of the megafauna of the Dogger Bank over a period of almost two decades. It suggests a link between changes in species composition/abundance and changes in the environment, especially the marine climate.     

Benthic communities in the Southern Bight of the North Sea and their use in ecological monitoring

Macrobenthic and meiobenthic communities of an area off the Belgian coast of the North Sea were studied from 1970 until 1975 at 74 stations. On the basis of both macro- and meiobenthos, three zones can be distinguished in the area. The coastal zone is characterized by the macrobenthicAbra alba community, corresponding to the meiobenthicMicroarthridion littorale — Halectinosoma herdmani community, and the open sea zone by the macrobenthicVenus gallina community and the meiobenthicLeptastacus laticaudatus — Paramesochra helgolandica community. In between is a transient zone where elements of both other zones mix. The distribution of these zones is governed by the hydrodynamical regime of the region, especially by the residual and tidal current system of the Southern Bight. Within the coastal zone, the composition of the community is influenced by pollution which especially affects the epibenthic detritus-feeders of the meiobenthos. The spatial stability of parameters describing community structure can be used for monitoring changes. Temporal characteristics of these parameters could not be investigated properly, but diversity seems to be much stabler than biomass.     

Biological consequences of marine pollution with special reference to the North Sea fisheries

Summary 1. A case of copper pollution on the Dutch coast is used to demonstrate that waste disposal in inshore waters can easily lead to damage to the living resources of the sea, since dilution is under such conditions a much slower process than is usually assumed.2. Pollution by domestic sewage, its direct hazards for human health, and its contaminating effect on shellfish, is discussed. Next to these direct and indirect health hazards, discharge of domestic waste may lead to eutrophication, which in its turn can contribute to the development of plankton blooms producing truly poisonous metabolites. Some examples of eutrophication of the marine environment are given.3. Of the industrial waste, examples are given which clearly demonstrate how dangerous discharge of heavy metals and pesticides can be, also in the marine environment. Possible effects of petrochemical waste products and of synthetic detergents and soaps are discussed.4. Radio-active waste disposal in sea is more carefully studied and monitored than disposal of other types of waste.5. The increasing quantity and variety of industrial waste is a reason for serious concern. Careful discrimination between the many products is advocated and discharge far offshore is advised for certain categories of pollutants. Pesticides and other very dangerous products should never be admitted in the shallow sea areas, so important as nursery grounds for the fishery resources.

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Biologische Konsequenzen der Meerwasserverschmutzung unter besonderer Berücksichtigung der Nordseefischerei

Kurzfassung Obwohl das Gesamtvolumen der Ozeane erheblich größer ist als der Süßwasservorrat der Welt, so kann doch das hemmungslose Einbringen von Haus- und Industrieabwässern in das Meer zu schädlichen Folgen für den Bestand der Meeresflora und -fauna führen. Besonders anfällig sind die Küstengewässer, da diese oft die Ernährungsgrundlage für viele Nutzfische bieten und zudem dort Austern und Miesmuscheln gezüchtet werden. Aus wirtschaftlichen Gründen erfolgt andererseits das Verklappen von Abfall und Unrat vorzugsweise dicht unter der Küste. Schädliche Wirkungen können erfolgen durch Bakterien- und Virusinfektionen, durch biologische Akkumulation von Schwermetallen und von Schädlingsbekämpfungsmitteln (unter ihnen besonders chlorhaltige Kohlenwasserstoffe), durch petrochemische Produkte, wodurch übler Geschmack bei Fischen und Muscheln hervorgerufen wird, und durch eine allgemeine Eutrophierung, die zu einer Vermehrung von unerwünschtem Plankton führen kann.

     

Regional analysis of litter quality in the central grassland region of North America

Abstract. The central grassland region of North America is characterized by large gradients of temperature and precipitation. These climatic variables are important determinants of the distribution of plant species, and strongly influence plant morphology and tissue chemistry. We analysed regional patterns of plant litter quality as they vary with climate in grassland ecosystems throughout central North America including tall‐grass prairie, mixed grass prairie, shortgrass steppe, and hot desert grasslands. An extensive database from the International Biological Program and the Long‐Term Ecological Research Program allowed us to isolate the effects of climate from those of plant functional types on litter quality. Our analysis of grass species confirms a previously recognized positive correlation between C/N ratios and precipitation. Precipitation exhibited a similar positive relationship with lignin/N and percent lignin. Although there was no significant correlation between temperature and C/N, there was a significant positive relationship between temperature and both percent lignin and lignin/N. Among functional types, C₃ grasses had a slightly lower C/N ratio than C₄ grasses. Tall grass species exhibited higher C/N, lignin/N, and percent lignin than short grass species. This understanding of the regional patterns of litter quality and the factors controlling them provides us with a greater knowledge of the effect that global change and the accompanying feedbacks may have on ecosystem processes.     

The development of an assessment system to evaluate the ecological status of rivers in the Hindu Kush-Himalayan region: introduction to the special feature

Development of an Assessment System to Evaluate the Ecological Status of Rivers in the Hindu Kush-Himalayan Region (ASSESS-HKH) was a 3-year research project funded by the European Union (Contract number: INCO-CT-2005-003659). This article provides an overview of this research project by summarising the objectives, the approaches and the main achievements. The main objective was to develop and apply a biological assessment system to evaluate the river’s ecological quality and to provide a scientific basis for the identification of sustainable water policy options and management strategies. The assessment tools were jointly developed by European partners, who provided their experience from recent research activities (STAR, AQEM) and Asian partners, who provided the knowledge about Asian river catchments and management necessities. The project was organised into eight work packages defining the time line for all phases, such as establishment of a stream typology and definition of reference conditions and stages of impairment classes for the rivers in the Asian countries, including a review of existing policies for water management. A specific part of the project was dedicated to increasing the overall poor knowledge of benthic invertebrates in the region and their value to the classification of the river’s ecological quality. All activities were accompanied by information events for local residents, universities and water managers. A total of 396 multi-habitat samples, from 115 rivers in five different ecoregions, were taken in two different seasons and accompanied by information on 95 parameters describing river and catchment characteristics. The benthic invertebrates in the samples were taxonomically identified based on keys generated within the project. Taxalists, with abundances per site, and field protocol information were entered into a specifically developed software tool. This dataset was the basis for developing ecological river assessment methods, called HKHscreening (Rapid Field Assessment), HKHbios (HKH Biotic Score) and HKHindex (Multimetric Index). Furthermore, a software tool (ECODAT) for using these methods was developed. The monitoring tools will serve citizens and scientists of the Hindu Kush-Himalayan region and will provide a scientific basis for policy recommendations, mitigation strategies, transnational water resource planning and sustainable ecosystem management. Additional outputs, including all sampling and laboratory protocols and project deliverables, together with the freely downloadable software, are available at the following website: http://www.assess-hkh.at.     

The fate of faecal pellets in the North Sea

During an intensive survey in May/June 1986, 129 stations in the North Sea were examined in different water depths with respect to several hydrographical parameters. The relations of planktonic faecal pellets to food (chl-a) and producers (zooplankton-wet weight) as well as to temperature, salinity and water depth were investigated. The amount of faecal pellets was positively correlated with chl-a and zooplankton. The length of the faecal pellets was negatively correlated with water depth indicating a degradation during sinking. Hardly any formed faecal material was detectable under 100 m water depth. The ratio of pellets to zooplankton was positively correlated to chlorophyll and influenced by daytime, indicating diel variations in pellet production. It is assumed that in summer most of the planktonic faecal material is disintegrated in the upper water layer and the role of faeces in sedimentation is minor.     

渤海浮游动物群落生态特点 Ⅱ.桡足类数量分布及变动

用1959年全国海洋普查浮游动物中网样品分析渤海浮游动物。尤其是中小型浮游动物的数量分布及变动特点。结果表明,渤海浮游动物全年平均丰度为3841ind／m^3,最大33756ind/m^3,最小6．5ind／m^3。其中桡足类年平均密度为3413ind／m^3,是数量的主要构成者。渤海浮游动物主要的高峰期出现在夏季,此外春、秋两季各自有一个小的高峰。春季峰主要是由双毛纺锤水蚤(Acartia bifilosa)的大量繁殖造成,秋季峰主要是由拟长腹剑水蚤(Oithona similis)构成。夏季峰是由于小拟哲水蚤(Paraclanus parvus)、强额拟哲水蚤(Paracalanus crassirostris)、拟长腹剑水蚤等多种桡足类和一些幼虫大量繁殖造成。渤海浮游动物季节演替比较明显。双毛纺锤水蚤、墨氏胸刺水蚤(Centropages mcmmurrichi)和中华哲水蚤(Calanus sinicus)是春季的优势种;小拟哲水蚤、拟长腹剑水蚤、近缘大眼剑水蚤(Corycaeus affinis)和太平洋纺锤水蚤（Acartia pacifica)是夏季的优势种;拟长腹剑水蚤、真刺唇角水蚤（Lubidocera euchaeta)等是秋季的优势种。数量的水平分布同温度的水平分布趋势基本一致。同盐度趋势相反。     

Decrease in water clarity of the southern and central North Sea during the 20th century

Light in the marine environment is a key environmental variable coupling physics to marine biogeochemistry and ecology. Weak light penetration reduces light available for photosynthesis, changing energy fluxes through the marine food web. Based on published and unpublished data, this study shows that the central and southern North Sea has become significantly less clear over the second half of the 20th century. In particular, in the different regions and seasons investigated, the average Secchi depth pre‐1950 decreased between 25% and 75% compared to the average Secchi depth post‐1950. Consequently, in summer pre‐1950, most (74%) of the sea floor in the permanently mixed area off East Anglia was within the photic zone. For the last 25+ years, changes in water clarity were more likely driven by an increase in the concentration of suspended sediments, rather than phytoplankton. We suggest that a combination of causes have contributed to this increase in suspended sediments such as changes in sea‐bed communities and in weather patterns, decreased sink of sediments in estuaries, and increased coastal erosion. A predicted future increase in storminess (Beniston et al., 2007; Kovats et al., 2014) could enhance the concentration of suspended sediments in the water column and consequently lead to a further decrease in clarity, with potential impacts on phytoplankton production, CO₂ fluxes, and fishery production.