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.     

The Dogger Bank: A special ecological region in the central North Sea

This paper is a review of the present state of knowledge about the ecology of the Dogger Bank, a shallow area in the central southern North Sea. The biological situation in this region is different from other regions in the North Sea; phytoplankton production occurs throughout the year, connected with low periodicity in macrofaunal abundance and condition of fish. Against prevailing opinions, the Dogger Bank, an offshore region, seems to be affected by eutrophication and pollution.     

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.     

Thermal affinity as the dominant factor changing Mediterranean fish abundances

Recent decades have seen profound changes in species abundance and community composition. In the marine environment, the major anthropogenic drivers of change comprise exploitation, invasion by nonindigenous species, and climate change. However, the magnitude of these stressors has been widely debated and we lack empirical estimates of their relative importance. In this study, we focused on Eastern Mediterranean, a region exposed to an invasion of species of Red Sea origin, extreme climate change, and high fishing pressure. We estimated changes in fish abundance using two fish trawl surveys spanning a 20‐year period, and correlated these changes with estimated sensitivity of species to the different stressors. We estimated sensitivity to invasion using the trait similarity between indigenous and nonindigenous species; sensitivity to fishing using a published composite index based on the species’ life‐history; and sensitivity to climate change using species climatic affinity based on occurrence data. Using both a meta‐analytical method and random forest analysis, we found that for shallow‐water species the most important driver of population size changes is sensitivity to climate change. Species with an affinity to warm climates increased in relative abundance and species with an affinity to cold climates decreased suggesting a strong response to warming local sea temperatures over recent decades. This decrease in the abundance of cold‐water‐associated species at the trailing “warm” end of their distribution has been rarely documented. Despite the immense biomass of nonindigenous species and the presumed high fishing pressure, these two latter factors seem to have only a minor role in explaining abundance changes. The decline in abundance of indigenous species of cold‐water origin indicates a future major restructuring of fish communities in the Mediterranean in response to the ongoing warming, with unknown impacts on ecosystem function.     

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     

Cold winter effects on benthic macrofauna communities in near- and offshore regions of the North Sea

In order to investigate the effect of severe winters on the long-term variability of benthic macrofauna communities four stations from the inner German Bight towards the Dogger Bank (North Sea) were sampled in March 1990 and from May 1995 to 2002. The stations were chosen to reflect a gradient in the hydrographic regime, temperature and organic matter supply. We initially hypothesized that the effect of severe winters on benthic communities will be more pronounced in the offshore more stable environment than in the nearshore regions. Our results clearly showed the opposite pattern. The benthic communities at the nearshore stations in the German Bight changed dramatically in species abundance and community structure after the severe winter 1995/1996. But the community structure in the German Bight returned to the previous stage within 2 years. In contrast, the offshore stations in the Oyster Ground and at the Dogger Bank remained rather unaffected by the severe winter and changed gradually during the study period. The results are discussed concerning the ecological importance of severe winters for benthic communities and the utility of our results for interpreting long-term changes.     

Climate and cyclic hydrobiological changes of the Barents Sea from the twentieth to twenty-first centuries

The Barents Sea is a transition zone between North Atlantic and Arctic waters, so its marine ecosystem is highly sensitive to climate dynamics. Understanding of marine biota response to climate changes is necessary to assess the environmental stability and the state of marketable biological resources. These processes are analyzed using a database from the Murmansk Marine Biological Institute which holds oceanographic and hydrobiological data sets collected for more than 100?years along the meridional Kola Transect in the Barents Sea. The data demonstrate high variability in thermal state of the upper layer of the Barents Sea, which is regulated by varying the inflow of Atlantic water and by regional climate. At irregular intervals, cold periods with extended seasonal ice cover are followed by warm periods. The most recent warm period started in the late 1980s and reached its maximum from 2001 to 2006. These cyclic changes in hydrologic regime across the twentieth century and first decade of the twenty-first century are reflected (with a specific lag of 1–5?years) by changes in species composition, as well as abundance and distribution of boreal and arctic groups of macrozoobenthos and fish fauna. For instance, cod and cod fisheries in the Barents Sea are closely linked to the marine climate. Furthermore, Kamchatka crab stock recruitment benefited from the warm climate of 1989 and 1990. In general, studies in this region have shown that climatic dynamics may be assessed using biological indices of abundance, biomass, and migration of marine organisms, including commercial species.     

Long-term changes in distribution and demographic composition of thornback ray, Raja clavata, in the northern and central Adriatic Sea

Population structure and distribution of the thornback ray, Raja clavata , L. 1758, in the northern and central Adriatic Sea were described based on data from bottom trawl surveys conducted in the area between 1996 and 2006 within the scope of the 'MEDITS' project. R. clavata was caught at depths between 23 and 270 m; highest abundance and density indices were recorded at a depth stratum 50–100 m. The sex ratio was close to 1 : 1. Length at first sexual maturity for both sexes was calculated. Length–weight relationships were obtained for males, females and the whole sample. Calculated parameters of the length–weight ratio showed a positive allometry for both sexes. The recent state of the population was compared with data from the 1948–49 'Hvar' expedition. The comparison revealed that significant changes have occurred in distribution and abundance of R. clavata in the Adriatic Sea since the time of the 'Hvar' expedition. During the 1948–49 'Hvar' expedition R. clavata was distributed throughout the entire continental shelf; during the 1996–2006 MEDITS expedition the species was found only in restricted areas and with much lower abundances. Significant changes also occurred in the demographic composition of the population. All described changes indicate an over-fishing of the thornback ray in the Adriatic Sea, a result of the high fishing intensity to which the species has been exposed for the past 60 years.     

Bioavailability of lead in North Sea sediments

As part of an interdisciplinary research programme, lead contents were measured in the polychaeteNephtys spp. and in the sea-urchinEchinocardium cordatum as well as in the respective sediment fractions <20 μm taken from the Dogger Bank proper and the eastern coastal North Sea. A lower lead content was generally observed in the organisms taken from the German Bight than in those from the Dogger Bank, especially from its northeastern part. It is possible to divide both areas according to the slope found in the linear regression of lead versus total organic carbon contents in sediments, which is twice as steep for the Dogger Bank as for the eastern North Sea. This criterium points to a difference in sediment quality with regard to toxic metal contamination. The sediment quality of the Dogger Bank seems to be twice as bad compared with that of the eastern North Sea. This is in good agreement with the differences found in lead contamination of the sediment-dwelling polychaetes from both areas. The results indicate that lead is primarily accumulated by food ingestion.     

Species and length composition of fish in the south-western Baltic Sea

Length distributions of fish were analysed based on data from the German annual (November/December) bottom trawl surveys in the Mecklenburg Bight and Arkona Basin [ICES Subdivisions (SD) 22 and 24, respectively] of the southwest Baltic Sea, covering the period from 1991 to 2000. The length spectra for all fish species, and those for demersal and pelagic species separately, all showed a consistent pattern of declining logarithmic numbers with increasing length over the fully selected size range. Such consistency allowed the shape of the spectra to be used as a community property that could be tracked in space and time. There was a rapid reduction in the number of specimens in the larger size classes, resulting in steep slopes of the spectra, which may be due to intensive fishing pressure in the Baltic. The species composition of fish communities in the southwest Baltic Sea was stable during the period considered. No consistent species replacement was found, although the clupeid group dropped sharply in the catch during the 1996 survey, which might have been due to sudden environmental changes in that year.     

Oceanographic characteristics of the habitat of benthic fish and invertebrates in the Beaufort Sea

We relate the spatial variability in the distribution of benthic taxa of the Beaufort Sea to oceanographic characteristics of their habitat with the goal of illustrating potential mechanisms linking climate change to Arctic marine communities. Offshore fish of the Beaufort Sea have not been surveyed since 1977 and no synchronous measures of fish distribution and the oceanographic characteristics of their habitat have been made previously. A survey was conducted during August 2008 in the western Beaufort Sea, Alaska. The distribution and abundance of benthic fish and invertebrates were assessed with standard bottom trawl survey methods. Oceanographic data were collected at each trawl station and at several locations between stations. The dominant benthic taxa, Polar cod (Boreogadus saida), eelpouts (Lycodes sp.), and snow crab (Chionoecetes opilio) were associated with cold (<?1.5°C), high salinity (>33) water found offshore of the shelf break, derived from the Chukchi Sea. These waters are expected to be high in secondary productivity, such that we hypothesize that the distribution of fish and crab was driven by conditions favorable for successful foraging. Predictions of the impacts of climate change require an understanding of the mechanisms linking the distribution and abundance of marine organisms to their oceanographic habitat. Our study documents the association of dominant benthic fish and invertebrates of the Beaufort Sea with specific water mass types and is thus a step toward this understanding.     

Habitat selection and temporal abundance fluctuations of demersal cartilaginous species in the Aegean Sea (eastern Mediterranean)

Predicting the occurrence of keystone top predators in a multispecies marine environment, such as the Mediterranean Sea, can be of considerable value to the long-term sustainable development of the fishing industry and to the protection of biodiversity. We analysed fisheries independent scientific bottom trawl survey data of two of the most abundant cartilaginous fish species (Scyliorhinus canicula, Raja clavata) in the Aegean Sea covering an 11-year sampling period. The current findings revealed a declining trend in R. clavata and S. canicula abundance from the late '90 s until 2004. Habitats with the higher probability of finding cartilaginous fish present were those located in intermediate waters (depth: 200-400 m). The present results also indicated a preferential species' clustering in specific geographic and bathymetric regions of the Aegean Sea. Depth appeared to be one of the key determining factors for the selection of habitats for all species examined. With cartilaginous fish species being among the more biologically sensitive fish species taken in European marine fisheries, our findings, which are based on a standardized scientific survey, can contribute to the rational exploitation and management of their stocks by providing important information on temporal abundance trends and habitat preferences.     

Demersal fish assemblages associated with hard bottom habitat in the South Atlantic Bight of the U.S.A.

Synopsis Demersal fish communities associated with hard bottom habitats in the South Atlantic Bight were investigated in three depth zones (inner, middle and outer shelf) between 30° and 33°N latitudes. Fishes were sampled with trawls and baited fishing gear, and were observed by remotely operated underwater television. Most demersal hard bottom fishes demonstrated seasonal differences in abundance in each depth zone, especially at the inner and outer shelf stations. Diversity values from trawl catches were higher in winter than summer at inner and outer shelf stations, but lower in winter at middle shelf stations. Species richness was higher in summer than in winter at most stations, but H' diversity patterns were more influenced by community evenness. Diversity values were higher than those reported for similar depths in the Middle Atlantic Bight. Mean biomass of demersal teleosts for all stations combined was slightly greater in winter than in summer. There was no significant difference in biomass between stations in summer, however, middle shelf stations had significantly greater biomass than inner or outer shelf stations in winter. Biomass estimates from the hard bottom areas studied were considerably higher than those reported in the literature for sand bottom areas in the South Atlantic Bight, but less than those reported for tropical reefs. Cluster analysis revealed differences in community composition between day and night trawl tows at all stations, and greater seasonal differences in species composition at inner and outer shelf stations than at middle shelf depths. Underwater television provided useful complementary data to trawl catches, documented the presence of large fishes which avoided the trawl, and provided information on the community composition at high relief stations which could not be trawled.     

气候变化对冬季东海外海中下层游泳动物群落结构及重要经济种类的影响

以全球气候变暖为主要特征的全球气候变化对海洋生物和海洋生态系统造成的影响已引起国际学者的高度关注。根据中国14家国营渔业公司底拖网渔业生产和渔业资源大面定点调查获得的17种中下层渔业数据,结合1960—2011年东海北部水域海表温度的变化情况,利用Fox模型移除捕捞效应产生的趋势变化后,分析了气候变化对中、下层游泳动物群落结构及几种重要经济种类的影响。通过气候跃变检验分析发现,海表温度在整体变暖的趋势上叠加有年代际波动,研究水域分别在1982/1983年发生了从寒冷期(1960—1982年)向升温期(1983—1998)、经由1998/1999年再到温暖期(1999—2011年)的跃变。群落结构变化特征显示:相比于寒冷期,温暖期间底层类和大型捕食类资源指数降低,中层类和无脊椎类升高;暖水种资源指数升高,暖温种降低;生物多样性指数略有增加。移除捕捞效应后,对不同生态属性种类CPUE与海表温度距平进行相关分析显示:底层类、中层类和无脊椎类残差与海表温度距平均呈正相关关系,其中中层类与海表温度距平显著正相关,而大型捕食类则呈负相关关系;暖水种残差与海表温度距平呈正相关,而暖温种则呈负相关关系。中层类中的黄鲫(Setipinna taty)、银鲳(Pampus argenteus)的CPUE残差均与海表温度距平呈显著正相关关系,近底层类中的带鱼(Trichiurus japonicus)和头足类(Squid)的CPUE残差均与海表温度距平呈正相关关系,而底层类小黄鱼(Larimichthys polyactis)和对虾(Shrimp)则呈负相关关系。在气候变化的大背景下,需加强其对海洋生态系统结构和功能影响的研究,查明渔业资源对气候变化的响应机制和机理,制定科学有效的渔业管理制度,实现渔业资源的可持续发展。     

Estimating the Abundance of Bottom Fish at the Shelf and Continental Slope in Northern Primorye

Journal of Ichthyology - Based on materials from bottom trawl surveys of 2009–2015, biomass and abundance of bottom fish of the Sea of ​​Japan between the Povorotny and Zolotoy...     

Community dynamics of intertidal soft-bottom mussel beds over two decades

Macrozoobenthos communities in the North Sea showed pronounced changes over the past decade in relation to an increasing number of invasive species and climate change. We analysed data sets spanning 22 years on abundance, biomass and species composition of intertidal soft bottom mussel beds near the island of Sylt (German Bight) in the Northern Wadden Sea, based on surveys from 1983/1984, 1990, 1993 and from 1999 to 2005. Mussel bed area and blue mussel biomass decreased, and a change in the dominance structure in the associated community comparing 1984 to mid-1990s with the period from 1999 to 2005 was observed. Coverage of the mussel beds with the algae Fucus vesiculosus decreased since the end of the 1990s. Within the study period biomass and densities of the associated community increased significantly. Dominance structure changed mainly because of increasing abundances of associated epibenthic taxa. Apart from the Pacific oyster Crassostrea gigas all other alien species were already present in the area during the study period. Community changes already started before Pacific oysters became abundant. An attempt is made to evaluate effects on the observed changes of decreasing mussel biomass, ageing of mussel beds, decreasing fucoid coverage and increasing abundances of invader. All four factors are assumed to contribute to changing community structure of intertidal mussel beds.     

Macrofauna standing stock of the Dogger Bank. A comparison: III. 1950–54 versus 1985–87. A final summary

The macrofauna communities on the Dogger Bank in April/May 1985–87 were compared with those in April/May 1950–54 (Ursin, 1960). Unpublished data from Birkett on the central and western Dogger Bank from April/May 1952–54 were also used for the comparison. The changes in the communities from the fifties to the eighties were made clear by the increasing species numbers and in an increase or dominance of short-living opportunistic species. In contrast, a decrease in long-living bivalves was found. The total biomass in 1985–87 was 2.5 to 8 times higher than in 1950–54. Similarities between stations were below 20%. Some hypotheses concerning natural and anthropogenic impacts are given to interpret the observed changes.     

Mapping the spawning grounds of North Sea cod (Gadus morhua) by direct and indirect means

Despite recent evidence for sub-stock structuring, North Sea cod are assessed as a single unit. As a consequence, knowledge of sub-stock trends is poor. In particular, there are no recent evaluations of which spawning grounds are active. Here we report results from the first ichthyoplankton survey to cover the whole North Sea. Also, this survey, conducted in 2004, was the first to make extensive use of DNA-based molecular methods to unambiguously identify early developmental stage cod eggs. We compare the findings from the plankton survey with estimated egg production inferred from the distribution of mature cod in contemporaneous trawl surveys. Results from both approaches were in general agreement and showed hot spots of egg production around the southern and eastern edges of the Dogger Bank, in the German Bight, the Moray Firth and to the east of the Shetlands. These areas broadly coincide with known spawning locations from the period 1940 to 1970. We were, however, unable to directly detect significant numbers of cod eggs at the historic spawning ground off Flamborough (northeast coast of England). The results demonstrate that most of the major spawning grounds of cod in the North Sea are still active but that some localized populations may have been reduced to the point where it is now difficult to detect the presence of eggs in the plankton.     

Stability of spatial pattern of fish species diversity in the Strait of Sicily (central Mediterranean)

In this paper, species diversity of demersal fish communities was analysed over an area covering about 45,000 km² of the Italian side of the Strait of Sicily (central Mediterranean). Fish abundance data come from a 10-year series (1994–2003) of experimental bottom trawl surveys carried out within the framework of the international program MEDITS. A simple GIS-based method was proposed to identify areas supporting high or low values of diversity and evaluate their temporal stability. A well-defined spatio-temporal pattern in diversity emerged from the analysis, with some areas of great ecological relevance being identified. Importantly, the greatest diversity within the fish communities was consistently seen at the offshore bank on the western part of the south Sicilian shelf (Adventure Bank). The site also supports high total biomass of demersal resources and shows the presence of species of great concern to fisheries. Results suggest that Adventure Bank represents a priority site for investigating the possibility of innovative management of marine ecosystems and demersal fisheries in offshore zones.