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Benthic macrofauna are important and widely used biological indicators of marine ecosystems as they have limited mobility and therefore integrate the effects of local environmental stressors over time. Recently, environmental DNA (eDNA) analysis has provided a potentially more resource‐efficient approach for benthic biomonitoring than traditional morphology‐based methods. Several studies have compared eDNA with morphology‐based monitoring, but few have compared the two approaches using the exact same sediment cores. In addition, the meiofauna and pelagic organisms obtained as 'bycatch' using eDNA have largely been disregarded from comparisons. Here, we address these shortcomings through comparative invertebrate analyses of six sediment sample replicates from each of four stations in Denmark, using eDNA metabarcoding and morphological identification. Our results revealed large variation between the six replicates for both methods and little overlap in taxon compositions between methods. While the morphological dataset was dominated by molluscs and annelids, the eDNA dataset was dominated by arthropods and annelids. Using community composition data, we found that sampling stations could be distinguished both with eDNA and morphology. Finally, we inferred expected total richness from extrapolated accumulation curves of detected taxa from each method. This indicated that eDNA metabarcoding requires less replication than morphology for maximum coverage of diversity to be reached. However, both methods required high levels of replication, and our results on taxonomic composition add to the evidence that morphological and eDNA‐based methods should preferably be used as complimentary tools for marine bioassessment. [ABSTRACT FROM AUTHOR]

Grey seals from both the Atlantic and Baltic Sea subspecies are recovering from dramatic declines and recolonising former ranges, potentially leading to overlapping distributions and an emerging subspecies transition zone in Kattegat between Denmark and Sweden. The two subspecies have asynchronous moulting and pupping seasons. We present aerial survey data from 2011 to 2023 in Danish Kattegat during the Atlantic subspecies' moulting (March–April) and pupping (December–January) seasons, as well as the Baltic subspecies' moulting season (May–June). During the Atlantic subspecies' peak moulting season, 82% of the grey seals were recorded north of the island of Læsø (N57°18′, E11°00′). In contrast, during the Baltic moulting season in those years, only 9% of the grey seals were recorded here. This indicates a predominance of Atlantic grey seals in the north and Baltic grey seals in central and southern Kattegat. In 2022 and 2023, three pups were recorded around Læsø during early January, which coincides with the pupping season of northern Wadden Sea grey seals. Previously, pups have been recorded in the same locations during the Baltic pupping season, which demonstrates overlapping breeding ranges. Grey seals are known to have plasticity in the timing of pupping indicated by a west to east cline of progressively later pupping in the eastern North Atlantic. Historical sources document that the Baltic pupping season in Kattegat was earlier than it has been in recent years. Thus, the expanding ranges may be associated with convergence of Atlantic and Baltic subspecies' pupping seasons and potential hybridisation in this emerging transition zone. [ABSTRACT FROM AUTHOR]

The barnacle Austrominius modestus, native of New Zealand and Australia was introduced to the South of England around 1943 and has since spread to most coastal waters in Western Europe, including the southern North Sea. Apart from an ephemeral incursion into the Danish Wadden Sea in 1978, since 2010 it has established permanent populations capable of reproduction along the North Sea coast of the Jutland peninsula, the Limfjord, the north-western Kattegat, and the Skagerrak. It has probably invaded Danish waters by pelagic larvae originating in the German Wadden Sea. The species has since spread to other Danish localities, likely following the prevailing currents, but other means, as for instance transport by vessels, are possible. The barnacle inhabits stones, stone-reefs, mollusk shells, and live shore crabs in shallow waters. Based on hydrographical data from its native and recently invaded areas, we predict its future distribution to extend to most coasts of continental Europe except for brackish waters (< 20 PSU), and the Arctic seas. The northernmost distribution limit may include the Lofoten Islands of Norway. [ABSTRACT FROM AUTHOR]

The Nekselø Wickerwork provides an unusually solid estimate on the marine reservoir age in the Holocene. The basis for this result is a 5200-year-old fish weir, built of hazel wood with a brief biological age of its own. Oysters settled on this construction. They had lived only for a short number of years when the fence capsized and was covered in mud and the mollusks suffocated. Based on the difference in radiocarbon (14C) age between accelerator mass spectrometry (AMS) samples of oyster shells and wood, respectively, the marine reservoir age for this site is estimated to 273 ± 18 14C years. Re-evaluations of previously produced data from geological and archaeological sites of Holocene date in the Danish archipelago indicate marine reservoir ages in the same order as that of the Wickerwork. Consequently, we recommend the use of the new value, rather than the ca. 400 14C years hitherto favored, when correcting for the dietary induced reservoir effect in radiocarbon dates of humans and animals from the Late Mesolithic and Early Neolithic periods of this region. [ABSTRACT FROM AUTHOR]

Small usually beautifully coloured mussels from the Kattegat were to date identified as Modiolus adriaticus (Lamarck, 1819) since C.G.Johs. Petersen’s account of the shell-bearing molluscs was published in 1888. However, these mussels from Danish and Swedish waters represent a very distinct new species which also is endemic. The present paper serves to describe this new species, Modiolus cimbricus sp. nov., which belongs to the genus Modiolus Lamarck, 1799. The genus Gibbomodiola Sacco, 1898, to which Modiolus adriaticus has been moved, is here synonymized with Modiolus Lamarck, 1799.

During the British gunboat war against Denmark–Norway in the period 1808–13, the Danish island of Anholt posed a navigational hazard to Baltic convoys carrying strategic materials and manufactured goods through the Baltic. It also offered a secure supply of freshwater and an alternative anchorage to Wingo Sound. When the lighthouse marking the island and its reefs was extinguished, a Royal Navy invasion force of marines and seamen captured the island and, with the assistance of the inhabitants, subsequently fortified the structure and adjacent land. Thereafter light vessels operating from the island carried supplies from Sweden and conducted commerce raiding. On the subsequent attempt to recapture the island in March 1811, Danish forces, including oared gunboats, were repulsed by the Royal Marines using artillery in prepared positions, and warships that were sent following intelligence of the attack. [ABSTRACT FROM AUTHOR]

• Transport by surface currents of a toxic cyanobacteria (Nodularia spumigena) bloom, from the Baltic Sea, through the Öresund strait, into the Kattegat. • Satellite images confirms a dense bloom of Nodularia spumigena in the central and southern Baltic Sea during the study period, and surface current measurements in the Öresund strait supports the assumption of a transport of the bloom in the more saline waters. • Measurements of plankton at different depths in the water column in the northern part of the Öresund strait (on the border to the Kattegat area) shows that the concentration of Nodularia spumigena cells and the toxin nodularin first increase and then decrease during a one month period in connection to the bloom in the Baltic Sea. • Both Nodularia spumigena and nodularin is tracked well below the strong halocline, both in water samples and in sedimentation traps. • Nodularin is found both in pelagic (copepods, herring) and benthic (blue mussels, flounder) parts of the ecosystem. • A laboratory study shows a decreased buoyancy, and even sinking of Nodularia filaments when they are exposed to a gradually increasing salinity, simulating the transport of Nodularia, from the Baltic Sea into the Kattegat. • The manuscript conclude that Nodularia spumigena blooms and the toxin nodularin is sinking to the bottom, reaching the benthic food web, to a higher extent in more saline waters, than being the case within the brackish Baltic Sea, where the major part of the blooms are believed to decay in the surface waters. Nodularia spumigena is a toxic cyanobacteria that blooms in the Baltic Sea every year. In the brackish water of the Baltic Sea, its toxin, nodularin, mainly affects the biota in the surface water due to the natural buoyancy of this species. However, the fate of the toxin is unknown, once the cyanobacteria bloom enters the more saline waters of the Kattegat. In order to investigate this knowledge gap, a bloom of N. spumigena was followed during its passage, carried by surface currents, from the Baltic Sea into the Kattegat area, through the Öresund strait. N. spumigena cells showed an increased cell concentration through the water column during the passage of the bloom (up to 130 103 cells ml−1), and cells (4.2 103 cells ml−1) could be found down to 20 m depth, below a pycnocline. Sedimentation trap samples from below the pycnocline (10–12 m depth) also showed an increased sedimentation of N. spumigena filaments during the passage of the bloom. The toxin nodularin was detected both in water samples (0.3–6.0 μg l−1), samples of sedimenting material (a toxin accumulation rate of 20 μg m-2 day−1), zooplankton (up to 0.1 ng ind.−1 in copepods), blue mussels (70–230 μg kg−1 DW), pelagic and benthic fish (herring (1.0–3.4 μg kg−1 DW in herring muscle or liver) and flounder (1.3-6.2 μg kg−1 DW in muscle, and 11.7-26.3 μg kg−1 DW in liver). A laboratory experiment showed that N. spumigena filaments developed a decreased buoyancy at increased salinities and that they were even sinking with a rate of up to 1,7 m day−1 at the highest salinity (32 PSU). This has implications for the fate of brackish water cyanobacterial blooms, when these reach more saline waters. It can be speculated that a significant part of the blooms content of nodularin will reach benthic organisms in this situation, compared to blooms decaying in brackish water, where most of the bloom is considered to be decomposed in the surface waters. [ABSTRACT FROM AUTHOR]

This paper describes presently applied sailing rules and environmental conditions on Danish waters such as Kattegat and the Sund. Those rules were established in late 70’s of the twentieth century by Danish authorities as Denmark is a coastal country and has the legal right to do so. Presently International Maritime Organization – IMO is in the process of approving a new set of routeing measures and traffic separation schemes which should comply with resolution A.257(14) – General provisions on ships’ routeing, and will be introduced by Organization.

An extensive data series of salinity, nutrients and coloured dissolved organic material (CDOM) was collected in the Skagerrak, the northern part of the Kattegat and off the Jutland west coast in April each year during the period 1996–2000, by the Institute of Marine Research in Norway. In this month, after the spring bloom, German Bight Water differs from its surrounding waters by a higher nitrate content and higher nitrate/phosphate and nitrate/silicate ratios. The spreading of this water type into the Skagerrak is of special interest with regard to toxic algal blooms. The quantification of the spatial distributions of the different water types required the development of a new algorithm for the area containing the Norwegian Coastal Current, while an earlier Danish algorithm was applied for the rest of the area. From the upper 50 m a total of 2227 observations of salinity and CDOM content have been used to calculate the mean concentration of water from the German Bight, the North Sea (Atlantic water), the Baltic Sea and Norwegian rivers. The Atlantic Water was the dominant water type, with a mean concentration of 79%, German Bight Water constituted 11%, Baltic Water 8%, and Norwegian River Water 2%. At the surface the mean percentages of these water types were found to be 68%, 15%, 15%, and 3%, respectively. Within the northern part of the Skagerrak, closer to the Norwegian coast, the surface waters were estimated to consist of 74% Atlantic Water, 20% Baltic Water, and 7% Norwegian River Water. The analysis indicates that the content of German Bight Water in this part is less than 5%.

Lateglacial submarine lake sediments are reported for the first time from the Kattegat Sea in southern Scandinavia. The Lateglacial sediments were collected from a vibrocore that contained, from top to bottom, Holocene marine muddy sand, Holocene brackish‐water mud, Early Holocene peat with remains of Betula pubescens and telmatic plants, Lateglacial lake deposits that are the focus of this paper, and homogenous sand. Radiocarbon dating of terrestrial plant remains from the Lateglacial sediments gave ages between 12 400 and 12 800 cal a bp, corresponding to the Younger Dryas. The Lateglacial sediments contain remains of Betula nana and other plants indicating a tundra‐like open landscape with dwarf shrub heaths, which is typical for the region. Remains of macrolimnophytes indicate shallow carbonate‐rich, cool lake waters. Remains of larvae of Trichoptera and Chironomidae dominate the invertebrate fauna and indicate a fairly species‐rich fauna. Half of the trichopteran taxa today have their distribution north of Denmark or show a generally northern distribution in Europe. The lake sediments are found at ∼ 24 m below sea level, and the presence of lake sediments shows that this part of Kattegat had not been transgressed by the sea during the Younger Dryas. [ABSTRACT FROM AUTHOR]

Ocean acidification can impair an animal's physiological performance and energetically demanding activities such as swimming. Behavioural abnormalities and changed activity in response to ocean acidification are reported in fish and crustacean species. We studied swimming activity in the calanoid copepod Pseudocalanus acuspes in response to near-future ocean acidification. Water and copepods were sampled from ten mesocosms deployed on the Swedish west coast. The experiments were conducted on animals reared in the mesocosms for 2 months during spring. Copepods were filmed after long-term (chronic) high-CO, and after 20 h acute exposure to CO. There was no significant effect of CO on copepods in chronic high-CO, nor significant effect after the 20 h acute exposure. In addition, we measured prosome length from a large number of adult copepods, but no effect of acidification on body size was found. In this study, P. acuspes did not show sensitivity to near-future pCO levels. Even if a number of papers suggest that copepods seem robust to future ocean acidification, interaction between multiple stress factors, such as elevated temperature, hypoxia and salinity changes may impair a copepod's ability to resist lowered pH. [ABSTRACT FROM AUTHOR]

Recently, there have been reports of increased abundance and landings of European hake in the northern part of the species range. Biological studies are however scarce and information about finer scale population structure important for stock assessments and fishery management is largely lacking. Here, we report on a population genetic study using neutral and outlier SNP loci assessing population structure in hake in the north-eastern parts of its range in the Atlantic. Hake samples from localities along the west coast of Norway, the Kattegat, the northern North Sea, and one locality in the Bay of Biscay were analysed using 53 SNPs, six of which were outliers potentially influenced by natural selection. We detected small-scale structure among northern samples, all of which were also distinct from Bay of Biscay hake, with the exception of a few individuals from the North Sea and the coast of Norway who clustered genetically together with Bay of Biscay hake. Our findings suggest that the present management unit of a single northern stock of hake is not biologically correct, and that there is more detail in the fine-scale population structure indicating that independent population dynamics could be expected in response to fishing patterns or changing environmental conditions. [ABSTRACT FROM AUTHOR]

The aim of the study was to investigate the relative importance of bottom-up and top-down forcing on trophic cascades in the pelagic food-web and the implications for water quality indicators (summer phytoplankton biomass and winter nutrients) in relation to management. The 3D ecological model ERGOM was validated and applied in a local set-up of the Kattegat, Denmark, using the off-line Flexsem framework. The model scenarios were conducted by changing the forcing by ± 20% of nutrient inputs (bottom-up) and mesozooplankton mortality (top-down), and both types of forcing combined. The model results showed that cascading effects operated differently depending on the forcing type. In the single-forcing bottom-up scenarios, the cascade directions were in the same direction as the forcing. For scenarios involving top-down, there was a skipped-level-transmission in the trophic responses that was either attenuated or amplified at different trophic levels. On a seasonal scale, bottom-up forcing showed strongest response during winter-spring for DIN and Chl a concentrations, whereas top-down forcing had the highest cascade strength during summer for Chl a concentrations and microzooplankton biomass. On annual basis, the system was more bottom-up than top-down controlled. Microzooplankton was found to play an important role in the pelagic food web as mediator of nutrient and energy fluxes. This study demonstrated that the best scenario for improved water quality was a combined reduction in nutrient input and mesozooplankton mortality calling for the need of an integrated management of marine areas exploited by human activities. [ABSTRACT FROM AUTHOR]

Possible future changes in Baltic Sea acid–base (pH) and oxygen balances were studied using a catchment–sea coupled model system and numerical experiments based on meteorological and hydrological forcing datasets and scenarios. By using objective statistical methods, climate runs for present climate conditions were examined and evaluated using Baltic Sea modelling. The results indicate that increased nutrient loads will not inhibit future Baltic Sea acidification; instead, the seasonal pH cycle will be amplified by increased biological production and mineralization. All examined scenarios indicate future acidification of the whole Baltic Sea that is insensitive to the chosen global climate model. The main factor controlling the direction and magnitude of future pH changes is atmospheric CO2 concentration (i.e. emissions). Climate change and land-derived changes (e.g. nutrient loads) affect acidification mainly by altering the seasonal cycle and deep-water conditions. Apart from decreasing pH, we also project a decreased saturation state of calcium carbonate, decreased respiration index and increasing hypoxic area – all factors that will threaten the marine ecosystem. We demonstrate that substantial reductions in fossil-fuel burning are needed to minimise the coming pH decrease and that substantial reductions in nutrient loads are needed to reduce the coming increase in hypoxic and anoxic waters.

A multi-disciplinary study was conducted to clarify stock identity and connectivity patterns in the populations of European plaice ( Pleuronectes platessa ) in the Skagerrak-Kattegat transition area between the Eastern North Sea and the Baltic Sea. Five independent biological studies were carried out in parallel. Genetic markers suggested the existence of different genetic populations in the transition area. Growth backcalculation with otoliths resulted in significant although limited differences in growth rates between North Sea and Skagerrak, indicating weak differentiation or important mixing. Hydrogeographical drift modelling suggested that some North Sea juveniles could settle along the coast line of the Skagerrak and the Kattegat. Tagging data suggested that both juveniles and adult fish from the North Sea perform feeding migrations into Skagerrak in summer/autumn. Finally, survey data suggested that Skagerrak also belongs to the area distribution of North Sea plaice. The outcomes of the individual studies were then combined into an overall synthesis. The existence of some resident components was evidenced, but it was also demonstrated that North Sea plaice migrate for feeding into Skagerrak and might constitute a large share of the catches in this area. The mixing of different populations within a management area has implications for stock assessment and management. Choice must be made to either lump or split the populations, and the feasibility and constraints of both options are discussed. The outcomes of this work have directly influenced the management decisions in 2015. [ABSTRACT FROM AUTHOR]

The study was based on CTD-casts performed on 5 consecutive daysat 7 positions along a shallow- to deep-water transect duringthe spring bloom in the southwest Kattegat. The development,dynamics and fate of the sub-surface chlorophyll maximum (SCM)are described. The SCM developed at a constant rate of1.4 mg chl a m-3 d-1,which is equal to a carbon fixation rate of49.0 mg C m-3 d-1. The SCM developed at 6 m depth at low irradiancelevels (10-43.0 µE m-2 s-1). Chl a concentrations reachedup to 23 mg chl a m-3 in the centre of the SCM. Growth ratesin the SCM were estimated at 0.82 d-1. The water column wasonly weakly stratified, with nutrients in excess in the wholeof the water column. The SCM was relocated vertically to depthsbelow the photic zone by wind-induced advection between the bayand the outer Kattegat. There were indications of a horizontalrelocation of the SCM by an internal standing wave. Applicationof high spatial and temporal resolution made it possible to estimatekey SCM parameters, such as growth rates [mg chl a m-3 d-1]and carbon fixation rate [mg C m-3 d-1],on the basis of chl a variations in time and space.

Bottom-trawl fisheries are widespread and cause mortality of benthic invertebrates, which in turn may lead to a decrease in the availability of prey for target fish species. Exploitation also reduces the abundance of the fish species themselves. Modelling studies have shown that bottom trawling could lead to both increases and decreases in fish production, but so far empirical evidence to test these ideas has been very limited. We hypothesize that the effect of bottom trawling on the food intake and condition of fish depends on how the ratio of prey to consumers changes with increasing fishing pressure., We assessed the impact of bottom trawling on the food availability, condition and stomach contents of three flatfishes and the Norway lobster in an area in the Kattegat that is characterized by a steep commercial bottom-trawling gradient due to the establishment of an area closed to all fisheries, but otherwise has homogeneous environmental conditions., For plaice, prey biomass initially decreased at a slower rate with trawling than the biomass of fish, and as a result, the amount of food available per plaice increased before decreasing at trawling frequencies >5 times year−1. This pattern was mirrored in both the condition and stomach contents of plaice and for long-rough dab., No effect of trawling on dab prey and condition was found. Conversely, the condition of the main target species - Norway lobster - increased as its biomass decreased with increased trawling intensities., Together, these results support the idea that when the abundance of the prey declines in response to exploitation, the ratio of the prey to consumer biomass will determine whether exploitation will result in an increase or a decrease in the food intake and condition of the predator., Synthesis and applications. Our study indicates that fish production may be maximized by keeping bottom-trawling intensities relatively low, although this may negatively affect the economically more important Nephrops fishery. The effects of bottom trawls may be mitigated by switching to gears, which affect prey availability to a lesser extent, such as pots or creels. [ABSTRACT FROM AUTHOR]

Cod stocks in the North Sea, including the Kattegat and the Skagerrak, have declined dramatically since the 1970s. Occasionally there is a high recruitment of juveniles in Kattegat/Skagerrak, without leading to the rebuilding of adult cod stocks despite reduced fishing mortality. In a biophysical model of egg and larval drift, we examined the potential importance of extant and historical spawning grounds for recruitment of cod in the Kattegat/Skagerrak seas using data of spawning stock biomass from the 1970s and from today's reduced stocks. The results suggest that Kattegat in the 1970s relied on largely locally retained (83%) larvae with little annual variation in recruitment. Kattegat also provided a substantial proportion of larvae recruiting in Swedish Skagerrak (72%). This is in contrast to present conditions where the Kattegat spawning stock has been reduced by 94%, and Kattegat only provides 34% of locally retained larvae and 30% to Swedish Skagerrak. Instead, the protected area in the Öresund and the Belt Sea are expected today to provide most larvae recruiting in Kattegat. Also, the inflow of larvae from the North Sea to Skagerrak and Kattegat can be significant although highly variable between years, with a positive correlation to the North-Atlantic Oscillation index ( NAO). The rebuilding of healthy spawning areas in the Kattegat may be key for restoring local cod stocks in both Kattegat and along the Skagerrak coast. This poses a management challenge if cod with local 'Kattegat' adaptations, e.g., in terms of egg density and migration patterns, are lost or reduced to non-resilient densities. [ABSTRACT FROM AUTHOR]

In the Kattegat area, Denmark, the Sorgenfrei–Tornquist Zone, an old crustal weakness zone, was repeatedly reactivated during Triassic, Jurassic and Early Cretaceous times with dextral transtensional movements along the major boundary faults. These tectonic events were minor compared to the tectonic events of the Late Carboniferous – Early Permian and the Late Cretaceous – Early Tertiary, although a dynamic structural and stratigraphic analysis indicates that the Sorgenfrei–Tornquist Zone was active compared to the surrounding areas.At the end of the Palaeozoic, the area was a peneplain. Regional Triassic subsidence caused onlap towards the north-east, where the youngest Triassic sediments overlie Precambrian crystallinebasement. During the Early Triassic, several of the major Early Permian faults were reactivated, probably with dextral strike-slip along the Børglum Fault. Jurassic – Early Cretaceous subsidence was restricted primarily to the area between the two main faults in theSorgenfrei–Tornquist Zone, the Grenå–Helsingborg Fault and the Børglum Fault. This restriction of basin development indicates a change in the regional stress field at the Triassic–Jurassic transition. Middle Jurassic and Late Jurassic – Early Cretaceous subsidence followed the Early Jurassic pattern with local subsidence in the Sorgenfrei–Tornquist Zone, but now even more restrictedto within the zone. The subsidence showed a decrease in the Middle Jurassic, and increased again during Late Jurassic – Early Cretaceous times. Small faults were generated internally in theSorgenfrei–Tornquist Zone during the Mesozoic with a pattern that indicates a broad transfer of strike-slip/oblique-slip motion from the Grenå–Helsingborg Fault to the Børglum Fault.

This paper presents the results of a Secchi depth data mining study for the North Sea - Baltic Sea region. 40,829 measurements of Secchi depth were compiled from the area as a result of this study. 4.3% of the observations were found in the international data centers [ICES Oceanographic Data Center in Denmark and the World Ocean Data Center A (WDC-A) in the USA], while 95.7% of the data was provided by individuals and ocean research institutions from the surrounding North Sea and Baltic Sea countries. Inquiries made at the World Ocean Data Center B (WDC-B) in Russia suggested that there could be significant additional holdings in that archive but, unfortunately, no data could be made available. The earliest Secchi depth measurement retrieved in this study dates back to 1902 for the Baltic Sea, while the bulk of the measurements were gathered after 1970. The spatial distribution of Secchi depth measurements in the North Sea is very uneven with surprisingly large sampling gaps in the Western North Sea. Quarterly and annual Secchi depth maps with a 0.5o × 0.5o spatial resolution are provided for the transition area between the North Sea and the Baltic Sea (4oE-16oE, 53oN-60oN).

Research into the influence of environmental variables on the behaviour of Norway lobster ( Nephrops norvegicus), and hence catch rates, dates back to the 1960s (e.g., Höglund and Dybern, Diurnal and seasonal variations in the catch-composition of Nephrops norvegicus (L.) at the Swedish west coast. ICES CM 1965/I46; Simpson, Variations in the catches of Nephrops norvegicus at different times of day and night. Rapport et Proés-verbaux des Réunions Conseil permanent international pour 1'Exploration de la Mer 156:186). However, the use of fishery-dependent data in identifying influential factors is relatively limited and only includes a number of papers on a limited dataset (e.g., Redant and De Clark, Diurnal variations in CPUE and length composition of the catches in a Nephrops directed fishery in the Central North Sea. ICES CM 1984/K:3; Maynou and Sardà, Influence of environmental factors on commercial trawl catches of Nephrops norvegicus (L.). ICES J. Mar. Sci. 58:1318). Here, we aimed to dissociate environmental variability in Norway lobster catches to improve resource exploitation efficiency within the Skagerrak and Kattegat trawl fisheries by utilising data collected as part of an extensive at-sea-sampling programme spanning 16 years. Catch rates were modelled using Generalized Additive Mixed Models ( GAMMs) and considered a range of response variables, including depth, temperature, current speed, season, moon phase and time of day. The results obtained herein showed that time of day, season, depth, temperature, year, trawl type and location all significantly affect catch rates of Nephrops. [ABSTRACT FROM AUTHOR]

Oersted in 1843 gave a brief description of Dodecaceria concharum collected from the Kattegat. This was inadequate for identifying the species. Caullery and Mesnil in 1898 described three forms of Dodecaceria (A, B and C) but they were uncertain which form Oersted described. Dehorne in 1933 described D caulleryi (now D. fimbriata), which reproduce asexually, and Form B of Caullery and Mesnil. By default Form B became D. concharum the parthenogenetic species Form A of Caullery and Mesnil. Gibson and Heppell in 1995 in an attempt to consolidate these names deposited new types for the two species at the Cambers Street Museum in Edinburgh. [ABSTRACT FROM PUBLISHER]

A challenging aspect of benthic quality indices used for assessing the marine environment has been to compile reliable measures of the species’ sensitivity to disturbances. Sensitivity values and their uncertainties can be calculated, but a problem to cope with is that the results may depend on the actual proportion of samples from disturbed and undisturbed environments. Here we calculated sensitivity values for each species along an artificial disturbance gradient created by bootstrapping varying numbers of samples from disturbed and undisturbed environments. The values were increasing, decreasing, or more or less constant along this gradient. The lowest value with the lowest uncertainty was adopted as the species sensitivity value. Analyses of the uncertainties indicated that the accuracy rather than the precision might be a concern. We suggest a method to exclude species for which the uncertainty is outside predefined limits as a precaution to reduce bias in the environmental status classification. [ABSTRACT FROM AUTHOR]

The dispersal and retention of early life stages are essential factors for the recruitment of fish stocks, and often depend on local meteorological and hydrographical conditions. A BAltic sea Long-Term large Scale Eutrophication Model (BALTSEM) was used to examine interannual variation in the retention and dispersal of fish eggs, Atlantic cod (Gadus morhua) at spawning areas in the Kattegat and Öresund and to investigate the mechanisms responsible for this variation. Model simulations over period 1971–2006 showed that years with high retention were related to variable weak winds and a strong outflow of water from the Baltic Sea, while years with low retention were related to strong westerly winds. Low egg retention was associated with enhanced southward transport from the Kattegat towards the Great Belt and from the Öresund towards the Baltic Sea. This southward transport of eggs was highly correlated with the local westerly wind component. The southbound egg transport and the westerly wind component both increased after 1989, and were connected with a change in the large-scale atmospheric circulation pattern, as represented by the NAO index. Results of this study provide information about the connectivity between neighboring areas and suggest that sedimentation is an important mortality factor. [ABSTRACT FROM PUBLISHER]

Past, present, and possible future changes in the Baltic Sea acid-base and oxygen balances were studied using different numerical experiments and a catchment-sea model system in several scenarios including business as usual, medium scenario, and the Baltic Sea Action Plan. New CO partial pressure data provided guidance for improving the marine biogeochemical model. Continuous CO and nutrient measurements with high temporal resolution helped disentangle the biogeochemical processes. These data and modeling indicate that traditional understandings of the nutrient availability-organic matter production relationship do not necessarily apply to the Baltic Sea. Modeling indicates that increased nutrient loads will not inhibit future Baltic Sea acidification; instead, increased mineralization and biological production will amplify the seasonal surface pH cycle. The direction and magnitude of future pH changes are mainly controlled by atmospheric CO concentration. Apart from decreasing pH, we project a decreasing calcium carbonate saturation state and increasing hypoxic area. [ABSTRACT FROM AUTHOR]

Abstract: An essential prerequisite of sustainable fisheries is the match between biologically relevant processes and management action. Various populations may however co-occur on fishing grounds, although they might not belong to the same stock, leading to poor performance of stock assessment and management. Plaice in Kattegat and Skagerrak have traditionally been considered as one stock unit. Current understanding indicates that several plaice components may exist in the transition area between the North Sea and the Baltic Sea. A comprehensive review of all available biological knowledge on plaice in this area is performed, including published and unpublished literature together with the analyses of commercial and survey data and historical tagging data. The results suggest that plaice in Skagerrak is closely associated with plaice in the North Sea, although local populations are present in the area. Plaice in Kattegat, the Belts Sea and the Sound can be considered a stock unit, as is plaice in the Baltic Sea. The analyses revealed great heterogeneity in the dynamics and productivity of the various local components, and suggested for specific action to maintain biodiversity. [Copyright &y& Elsevier]

The consequence of elevated ocean temperatures on commercial fish stocks is addressed using time series of commercial landings (1906-2004) and juvenile survey catch data (1904-2006) collected around Denmark. We analyze (i) whether warm-water sole ( Solea solea) has increased relative to Boreal plaice ( Pleuronectes platessa) and (ii) whether two related warm-water species (turbot, Psetta maxima and brill, Scophthalmus rhombus) show similar responses to increasing temperature or, alternatively, whether turbot (which has a broader juvenile diet) has been favored. Since the early 1980s, both sole and turbot have constituted an increasing part of the commercial landings and survey catches, as compared with plaice and brill, respectively. These changes in species composition were linked to sea surface temperatures, Northern Hemisphere temperature anomalies ( NHA) and the North Atlantic Oscillation. NHA was closely related and explained 43% of the observed variation in sole survey catches relative to the plaice catches and almost 38% of the observed variation in the sole landings relative to the plaice landings. For the less common species, turbot and brill, none of the global change indicators explained more than 15% of the variation, although all showed a positive relationship. Survey catch per unit effort increased significantly for both sole and turbot around the early 1980s, whereas catch per unit effort for plaice and brill remained constant. The results indicate that the abundance of warm-water species is likely to increase with increasing temperature but also that species with similar life histories might react differently according to degree of specialization. [ABSTRACT FROM AUTHOR]

Abstract: This paper gives an overview of results from a project which explored the feasibility of establishing a CO2 Capture and Storage infrastructure in the Skagerrak/Kattegat region of Southern Scandinavia. This involves assessment of the technical and economic parameters of the complete CCS chain and, in particular, identification of possible storage locations. The project ran from June 2009 to December 2011. Emissions from three major industrial clusters in the Skagerrak/Kattegat region – Gothenburg in Sweden, Grenland in Telemark County, southern Norway and Aalborg in Denmark - were targeted. Both emissions from process industries as well as power plants were included. [Copyright &y& Elsevier]

This study presents bioacoustic recordings in combination with movements and diving behavior of three free-ranging harbor porpoises (a female and two males) in Danish waters. Each porpoise was equipped with an acoustic data logger (A-tag), a time-depth-recorder, a VHF radio transmitter, and a satellite transmitter. The units were programmed to release after 24 or 72 h. Possible foraging occurred mostly near the surface or at the bottom of a dive. The porpoises showed individual diversity in biosonar activity (<100 to >50,000 clicks per hour) and in dive frequency (6-179 dives per hour). We confirm that wild harbor porpoises use more intense clicks than captive animals. A positive tendency between number of dives and clicks per hour was found for a subadult male, which stayed near shore. It showed a distinct day-night cycle with low echolocation rates during the day, but five times higher rates and higher dive activity at night. A female traveling in open waters showed no diel rhythm, but its sonar activity was three times higher compared to the males'. Considerable individual differences in dive and echolocation activity could have been influenced by biological and physical factors, but also show behavioral adaptability necessary for survival in a complex coastal environment. [ABSTRACT FROM AUTHOR]

The degree to which marine ecosystems may support the pelagic or benthic food chain has been shown to vary across natural and anthropogenic gradients for e.g., in temperature and nutrient availability. Moreover, such external forcing may not only affect the flux of organic matter but could trigger large and abrupt changes, i.e., trophic cascades and ecological regime shifts, which once having occurred may prove potentially irreversible. In this study, we investigate the state and regulatory pathways of the Kattegat; a eutrophied and heavily exploited marine ecosystem, specifically testing for the occurrence of regime shifts and the relative importance of multiple drivers, e.g., climate change, eutrophication and commercial fishing on ecosystem dynamics and trophic pathways. Using multivariate statistics and nonlinear regression on a comprehensive data set, covering abiotic factors and biotic variables across all trophic levels, we here propose a potential regime shift from pelagic to benthic regulatory pathways; a possible first sign of recovery from eutrophication likely triggered by drastic nutrient reductions (involving both nitrogen and phosphorus), in combination with climate-driven changes in local environmental conditions (e.g., temperature and oxygen concentrations). [ABSTRACT FROM AUTHOR]

Increasing partial pressure of atmospheric CO is causing ocean pH to fall-a process known as 'ocean acidification'. Scenario modeling suggests that ocean acidification in the Baltic Sea may cause a ≤3 times increase in acidity (reduction of 0.2-0.4 pH units) by the year 2100. The responses of most Baltic Sea organisms to ocean acidification are poorly understood. Available data suggest that most species and ecologically important groups in the Baltic Sea food web (phytoplankton, zooplankton, macrozoobenthos, cod and sprat) will be robust to the expected changes in pH. These conclusions come from (mostly) single-species and single-factor studies. Determining the emergent effects of ocean acidification on the ecosystem from such studies is problematic, yet very few studies have used multiple stressors and/or multiple trophic levels. There is an urgent need for more data from Baltic Sea populations, particularly from environmentally diverse regions and from controlled mesocosm experiments. In the absence of such information it is difficult to envision the likely effects of future ocean acidification on Baltic Sea species and ecosystems. [ABSTRACT FROM AUTHOR]