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Mussel populations (Mytilus edulis) around the coasts of Europe and the North Atlantic are often ephemeral and have notably experienced a large decline in abundance. Since 1993, annual blue mussel stock surveys have been carried out in the Limfjorden, Denmark. We used the stock survey data combined with electronic monitoring fishing data and Mechanistic Models for the Limfjorden, providing environmental data to investigate the impact of various stressors. Multiple factors were found to affect the longevity of subtidal mussel beds in Limfjorden. Predation by starfish, fishing activities, shell length of the mussels, amplitude in summer temperature and consecutive days of oxygen depletion decreased the longevity of the beds. Conversely, increased biomass, multiple cohorts and increasing water depth demonstrate stabilizing effects. Water column stratification had both a negative and positive impact on bed longevity depending on the duration. These analyses can help inform environmental, conservation, and fisheries managers on the long-term trends of population dynamics and gain a deeper understanding of what factors can affect mussel bed longevity in the context of declining stocks.

Rapporten giver en kortfattet gennemgang af og et overblik over vigtige kriterier af både praktisk, fysisk og biologisk karakter, der har betydning for valg af passende lokaliteter til etablering af blåmuslingebanker. Kriterierne er udvalgt på baggrund af generelle forhold i danske fjorde og kystområder og vejledningen er tiltænkt som en hjælp til at planlægge arbejdet.

Formålet med denne rapport er at kortlægge den aktuelle klimabelastning fra de forskellige dele af den danske fiskeflåde og udarbejde et katalog over tekniske virkemidler til reduktion af påvirkningen. Den overordnede danske målsætning på tværs af sektorer og udledningstyper er at reducere CO2-udledningen med 70% i 2030 og opnå klimaneutralitet i 2050. Resultater og konklusioner i rapporten baserer sig på en litteraturgennemgang af studier omhandlende CO2-reduktion (primært brændstof-relateret) i kommercielt fiskeri og i skibsfart generelt. Energiforbruget før og efter fangstprocessen, til f.eks. fremstilling af fartøjer og redskaber og til transport og processering af fangsten, er ikke medtaget i litteraturgennemgangen, ligesom potentiel frigivelse eller binding af CO2 i sedimentet ved fiskeri med bundslæbende redskaber ikke er adresseret. I det følgende er analyser af klimapåvirkningen fra fiskeriet således næsten udelukkende baseret på fartøjernes brændstofforbrug (energiforbrug) under sejlads og fiskeri. Rapporten er målrettet Fiskeristyrelsen til brug ved udmøntningen af kommende ordninger under EHFAF. DTU Aquas arbejde med rapporten er finansieret af ydelsesaftalen om fiskeri og akvakultur mellem Fødevareministeriet og DTU Aqua.

Denne rapport består af en række uafhængige kapitler vedrørende klapning og klapningspraksis samt anbefalinger til Best Practice ved større klapninger typisk i forbindelse med anlægsarbejder. Den aktuelle forvaltningspraksis i en række europæiske lande er gennemgået med udgangspunkt i anbefalinger vedrørende praksis for klapning udarbejdet af HELCOM og OSPAR. Anbefalingerne fra HELCOM/OSPAR omfattes i rapporten af følgende emner: a) Hierarki for placering af opgravet marint materiale; b) Krav til ansøgninger om klapning; c) Plan for prøvetagning i forbindelse med klapninger både før og under klapningen; d) Krav til karakterisering af det opgravede materiale i relation til fysiske, biologiske og miljøkemiske parametre; e) Procedurer for udstedelse af klaptilladelse; f) Håndtering af klapningen herunder angivelse af ”Best Practice”; g) Iværksættelse af overvågning/monitering af klapningen; h) Krav til afrapportering til HELCOM og OSPAR. De enkelte landes praksis er vurderet i forhold til HELCOM/OSPARs anbefalinger med særligt fokus på den danske forvaltning, som den er beskrevet i Klapbekendtgørelsen. I tilhørende bilag til rapporten er angivet diverse krav til tilladelser til klapning i danske farvande samt internationale kriterier for tålegrænser for miljøfremmede stoffer. I Danmark er den foretrukne metode til dumpning af opgravet sedimentært materiale klapning. Det opgravede materiale placeres i en splitpram, og frigives ved åbning af klapperne i bunden af splitprammen, deraf navnet. Materialet synker straks efter klapning mod bunden forårsaget af materialets højere densitet. Der findes en række alternative metoder til klapning fra splitpram, som i dag anvendes forskellige steder i verden. Pumpning af det opgravede materiale til bunden evt. i kombination med en diffusor ved overgangen fra pumperør til bund er et alternativ, der vil fjerne spredning af finkornet materiale og frigivelse af næringsstoffer m.m. under transporten fra splitprammen til

Bottom trawling (hereafter trawling) is the dominant human pressure impacting continental shelves globally. However, due to ongoing data deficiencies for smaller coastal vessels, the effects of trawling on nearshore seabed ecosystems are poorly understood. In Europe, the Water Framework Directive (WFD) provides a framework for the protection and improvement of coastal water bodies. It requires member states to track the status of ‘biological quality elements’ (including benthic macrofauna) using WFD-specific ecological indicators. While many of these metrics are sensitive to coastal pressures such as nutrient enrichment, little is known about their ability to detect trawling impacts. Here, we analysed a comprehensive data set of 5885 nearshore benthic samples – spatiotemporally matched to high-resolution trawling and environmental data – to examine how these pressures affect coastal benthos. In addition, we investigated the ability of 8 widely-used benthic monitoring metrics to detect impacts on benthic biological quality. We found that abundance (N) and species richness (S) were strongly impacted by bottom trawling. A clear response to trawling was also observed for the WFD-specific Benthic Quality Index (BQI). Relationships between N and S, and trawling were particularly consistent across the study area, indicating sensitivity across varying environmental conditions. In contrast, WFD indices such as AZTIs Marine Biotic Index (AMBI), multivariate AMBI (M-AMBI), and the Danish Quality Index (DKI), were unresponsive to trawling. In fact, some of the most heavily trawled areas examined were classified as being of ‘high/good ecological status’ by these indices. A likely explanation for this is that the indices are calculated using species sensitivity scores, based on expected species response to eutrophication and chemical pollution. While the BQI also uses species sensitivity scores, these are based on obs

Denne rapport beskriver status for viden om ni potentielle marine virkemidler og tiltag, der kan anvendes til at forbedre miljø- og naturforholdene i Lillebælt. De ni potentielle virkemidler inkluderer: Etablering af ålegræs, etablering af stenrev, etablering af biogene rev, anvendelse af biohuts, dyrkning af muslinger og tang i vandsøjlen, opfiskning af krabber og søstjerner, områder beskyttet mod trawlfiskeri (MPAs) og anvendelse af naturbaserede løsninger til klima-sikring af kysterne. Virkemiddelbeskrivelserne har fokus på de forventede økosystemtjenester relateret til biodiversitet, natur og miljø, men andre økosystemtjenester associeret med virkemidlerne beskrives også. Anvendeligheden og effekterne af de forskellige virkemidler og tiltag til miljø- og naturgenopretning afhænger i høj grad af lokale fysiske og miljømæssige forhold, og derfor vil der være stor forskel på, hvor virkemidlerne kan placeres. Såfremt der findes viden om kriterierne for anvendelse, så indgår det i virkemiddelbeskrivelsen. Vidensgrundlaget for de beskrevne virkemidler er meget varierende og status for eksisterende vidensgrundlag er, ligesom områder hvor der mangler viden, inkluderet i beskrivelserne.

Dredging for wild mussels Mytilus edulis Linnaeus, 1758 takes place in the marine protected areas (Natura 2000 sites) in Denmark. The fishery is strictly regulated to limit the impact of dredging to the benthic environment, and requires the use of modified lightweight mussel dredges. Nevertheless, the depletion of the benthic macrofauna associated with M. edulis beds after impact from such dredges is yet to be quantified. Here, dredging is shown to result in a significant decline in the density, species richness, and biological traits directly in the dredge track but no significant impact on the community composition. Species richness remained significantly affected 4 mo post dredging, although the positive trend after 4 mo may signal recovery. An effect of dredging was also detected in areas adjacent (approximately 5 m) to the dredge tracks, but needs further investigation to understand this impact. The results provide an estimate of benthic macrofaunal depletion in the dredge track as well as of the short-term recovery, which may be of use in the management of the fishery. Finally, it is suggested that species richness may be a more sensitive indicator than density in a eutrophic and species-poor system.

Aquaculture is one of the world’s fastest-growing industries, with 6 % annual growth since 2010, and is becoming an increasingly important component of the world’s food production. European aquaculture has not kept up with the pace of change in other parts of the world, growing only 24 % since 1990, and only 6 % since 2007. As with all food production industries, aquaculture has a range of positive and negative impacts for the environment and the socio-economic system, which varies across production type, species, geography and biophysical context. The overall purpose of this study is to present the scientific basis of the positive and negative impacts of European aquaculture from an economic, environmental and social point of view, in order to facilitate a well-informed debate. However, the study does not seek to assess the magnitude or likelihood of impacts, compare magnitude or likelihood of impacts among different types of aquaculture nor compare the impacts identified to those of alternative food production systems. In order to achieve this aim, the project first undertook an extensive literature review to collate state-of-the-art scientific information on the positive and negative impacts of aquaculture. The study examined scientific peer-reviewed literature, supplemented by the Scientific, Technical and Economic Committee for Fisheries and European Data Collection Framework for aquaculture and focused on finfish culture (sea cages; ponds, tanks, and raceways; and recirculating aquaculture systems), shellfish culture (suspended, trays, and bottom culture), macroalgae and microalgae. To complement the impacts derived from the scientific literature a deeper analysis of impacts was conducted via 18 case studies across Denmark, Germany, France, Poland, Netherlands, Croatia, Greece, Ireland, Italy, Portugal and Spain. The case studies covered a range of production technologies and species types. The case studies were used to verify impacts identified in the scienti

Marine protected areas are often designated in areas which represent important or historic fishing grounds. Within the European Union, the Natura 2000 (N2000) network of nature protection areas consists of Special Areas of Conservation and Special Protection Areas designated under the Habitats Directive and Birds Directive, respectively. In Denmark, an ecosystem-based approach to the management of bivalve fisheries has been implemented in a number of these N2000 areas, ensuring the sustainability of these fisheries and the conservation status of the designated areas. Here, we outline the key management strategies which have been implemented in the N2000 areas under the Danish Mussel Policy. These include the mandatory enforcement of monitoring systems on fishing vessels, acceptance of a maximum 15% cumulative fishery impact to specific ecosystem components, and a remarkable research effort to provide high resolution spatial habitat mapping. Additional strategies such as depth-based spatial restrictions, regulation enforcements, detailed assessments of fisheries impact, and documentation of positive effects of the ecosystem-based approach are also outlined. The results and lessons learnt outlined here are expected to be relevant to those concerned with the management and sustainability of fisheries activities in marine protected areas.

The Danish Environmental Protection Agency has funded a project “Effects on the quality elements defined by the EU Water Framework Directive (WFD) of other pressure factors than excess nutrient load and climate change” with the aim to identify a number of environmental pressure factors other than excess nutrient loading and climate change that potentially can affect the quality elements of the WFD. The project has resulted in 8 independent reports that are summarized in this study: 1. Petersen et al. 2018: DTU Aqua rapport nr. 336-2018 (1), 2. Høgslund et al. 2019: Videnskabelig rapport fra DCE nr. 323 (2), 3. Stæhr et al. 2019: DTU Aqua rapport nr. 353-2019 (3), 4. Petersen et al. 2020: DTU Aqua rapport nr. 358-2020 (4), 5. Petersen et al. 2020: DTU Aqua r rapport nr. 361-2020 (5), 6. Petersen et al. 2020: DTU Aqua rapport nr. 359-2020 (6), 7. Helmig et al. 2020: DTU Aqua rapport nr. 360-2020 (7), 8. Petersen et al. 2020: DTU Aqua rapport nr. 365-2020 (8), where (1) is a review of potential effects of a number of pre-defined pressure factors - sand and gravel extraction, dredging of shipping lanes and harbours and clipping of the dredged material, physical constructions, fishery, shipping, plastic waste incl. micro plastics, hazardous substances and invasive species – was carried out. Based on the results of the review (1), more specific analyses were carried out for effects of fishery and other localized pressure factors (4, 5), sediment chemistry (2), 3 invasive species (3, 8) and exploitation of boulder reefs (7). All the specific analyses were carried out based on existing data sets primarily extracted from the Danish environmental monitoring programme NOVANA. Finally, methods of cumulation of effects of different types of pressure factors were assessed (6). Overall, the screening of the scientific research literature and the performed data analyses that have been possible show that primarily fishing

Through the mechanisms of particle immobilization and subsequent depletion of particles, mussel cultivation has a direct effect on chlorophyll-a concentrations and Secchi depth; both of which are primary indicators of marine ecological status and metrics for water quality management. As such, mussel cultivation has been proposed as a measure to mitigate the effects of coastal eutrophication. However, the extent to which this ecosystem service, and relatedly, biomass accumulation, are affected by ambient environmental conditions involves complex interactions. To explore the interacting mechanisms underpinning depletion dynamics under various biophysical conditions along the salinity gradient in the Baltic Sea, we used an updated Dynamic Energy Budget (DEB) model with field data from the western Baltic Sea, accommodating osmotic stress. We use the DEB model to drive a 3D farm-scale model within a novel precompiled hydrodynamic framework (FlexSem) to evaluate the effects of different environmental conditions and farm configuration on the intensity and extent of the chlorophyll-a depletion signal. We also report on extensive in situ monitoring of chlorophyll-a and Secchi depth within and around mussel farms, from several cultivation areas from around the western Baltic Sea to evaluate site-specific characteristics of depletion. Monitoring reflected the high degree of spatio-temporal variability in the quantification of this ecosystem service; with relative differences in chlorophyll-a from −14 to 69% and Secchi depth from 0 to 75%. We find that the extensive in situ measurements in different environmental conditions can be represented by the integrated farm model in terms of mussel biomass accumulation and depletion, providing insight on the interactions of current velocity, farm orientation to predominant current direction, ambient chlorophyll-a concentrations, and total biomass loads on the intensity and spatial extent of the depletion signal. Furthermore, the mode

Fremskrivning af menneskelige aktiviteter og presfaktorer er et notat beståen af tre trin, der iterativt fremskriver EU's havstrategiindikatorer frem mod 2030. Det betyder, at rapporten er opbygget over tre trin, som inkluderer kobling af menneskelige aktiviteter og presfaktorer, derefter fremskrivning af menneskelige aktiviteter frem mod 2030 og slutteligt en fremskrivning af indikatorer frem mod 2030. Fremskrivningerne i notatet er så vidt muligt en kort kvantitativ fremskrivning. Hvor det ikke er muligt at fremskrive kvantitativt, er fremskrivningen kvalitativ. Når det er muligt, inddrages betydningen af klimaforandringer. Miljøministeriet har ikke ønsket, at effekten af planlagte nationale og internationale indsatser til forbedring af havmiljøet er inddraget, da Miljøministeriet selv ønsker at stå for denne del. Hvis det alligevel ikke kan undgås at tage højde for visse indsatser, fx indsatser, som allerede er implementeret (men ikke har haft effekt endnu), skal dette noteres for hver deskriptor.

In order to improve the scientific basis for public management of mussel and oyster fisheries, it is the purpose of this investigation to develop new knowledge about the indirect effects on the marine environment of mussel and oyster dredging activities, and in particular to develop new tools and methods to assess the indirect fishery effects at the level of entire basins. Three main topics are studied: The extension and duration of sediment plumes caused by resuspension of sediments due to mussel dredging, the effects of transplantation of mussels from areas frequently exposed to oxygen depletion and links between fishery and recruitment of new spat to mussel beds. Sediment plumes created by dredging was studied as a combination of in situ experiments in Lovns Bredning and Løgstør Bredning in the Limfjorden, Denmark. In the field experiments, mussel fishermen dredged along specified tracks or in predefined areas, and water properties like light extinction, oxygen consumption, hydrodynamic conditions and turbidity were measured in relation to fishing intensity. Further, sediment characteristics of the test area were determined. Data from the field experiments were fed into a new sediment resuspension and plume dispersion model included in a newly established FlexSem framework model of the Limfjorden with a spatial resolution of 10 m in the studied areas. The FlexSem framework was coupled to a new hydrodynamic version of DMI’s ocean model HBM that had been expanded with a Limfjorden domain, and new modules were added. This new hydrodynamic setup enhances the forecasting capabilities from sea level predictions to forecasts of all physical ocean parameters with reasonably good quality predictions of temperatures, salinity and currents in high temporal and spatial resolution. Results showed that the plume has an extension of 260-540 m from the dredge track and with a duration of approximately one h. Results showed that the plume has an extension of 260-540 m fr

Losses due to predation are recognized as an important factor affecting shellfish stocks, restoration efforts and aquaculture production. Managing and mitigating the impact of predators require information on the population dynamics and functional responses to prey availability under varying environmental conditions. Asterias spp. are well-known keystone predators with the capacity to exert a top down control on shellfish populations. Asterias spp. populations are extremely plastic, booming fast when prey is abundant and exhibiting a remarkable individual resilience to starvation and adverse environmental conditions. These aspects have led Asterias spp. to be considered pests by shellfish producers and fishers and to be catalogued among the most devastating invasive species. Assessment and mitigation of the impact of Asterias rubens in northern Europe have been the objective of several projects. However, there is still a limited understanding of the processes behind A. rubens population plasticity and how environmental conditions affect individual growth and predation. Under these circumstances a comprehensive eco-physiological model becomes necessary. These models can integrate available information on biology and eco-physiology to gain understanding of the effect of the environmental conditions on the impact of A. rubens. In this work, we performed a number of eco-physiological experiments and combined them with field data from a Danish estuary to estimate and validate the parameters of a dynamic energy budget (DEB) model for the whole life cycle of A. rubens. DEB models can be used to assess the effects of environmental variability on the life cycle and key population traits allowing the prediction of the performance, abundance, resource requirements and potential distribution of individuals and populations under dynamic environments. As such the DEB model presented in this study aims to become a tool to be used to assess

Marine virkemidler er løsninger som bl.a. kan nedbringe mængden af næringsstoffer i kystnære marine områder og derved forbedre havmiljøet. I EU’s vandrammedirektiv er samtlige lande forpligtet til at opnå god tilstand i de marine områder inden 2027. Marine virkemidler kan implementeres i de nye vandområdeplaner, og bidrage til at opfylde miljømålene – og samtidig gavne klima og biodiversitet.

Mussel dredging causes resuspension of sediment particles that reduce water clarity and potentially leads to reduced eelgrass growth. In order to study the impact of resuspension from mussel dredging on light conditions in the water column, field experiments were conducted at two sites in the Limfjorden. Light loggers were placed in two circular arrays around the dredge area. Vertical profiles of current velocity were measured by an ADCP and the sediment particle size composition was obtained from sediment core samples. The field data was used to force, calibrate and validate a sediment transport model developed in the RexSem model system. Changes in sediment concentrations during and after mussel dredging were modeled for the two sites and for seven scenarios. We found that the distance and direction of the plume in the model was in good agreement with light logger data. The plume duration was less than 1 h, and the impact range was between 260-540 m. The scenarios showed that fishing intensity and current speeds were most important for shaping the sediment plumes. Changes in suspended sediment concentrations were 0.62-1.79 mg l-1 on median average and 1.22-11.61 mg l-1 for the upper quantile of the plume, which were on the same order of magnitude as background values in the Limfjorden. The amount of fishing days during the eelgrass growth season was 6-8% in Lovns Bredning and 16-35% in Legstor Bredning and less than 1-2% of the total area was dredged per season. Even though there are substantial changes in the light conditions from the sediment plumes, the overall spatio-temporal impact in the study area is considered low. We recommend that management plans in other areas could sustain a shellfish fishery by limiting fishing intensity and frequency near eelgrass beds. The presented approach combines observational data, sediment transport modeling and reported fishing activity. It is a step forward within sediment transport modeling and could

This study aims to understand the economic and bio-physical conditions under which mussel farming is a cost-effective mitigation measure to improve water quality related to excess nitrogen in fjords and coastal areas. We set-up a mixed-integer optimization model including every farm in three agricultural catchments surrounding Limfjorden, the largest fjord in Denmark. We include a number of relevant nitrogen abatement measures, including agricultural land-use measures and mussel farming in the sea. The aim is to model the least costly combination of mitigation measures to improve water quality when agricultural, environmental and market conditions vary. We run three scenarios varying environmental conditions for mussel productivity and market opportunities for mussel-based products as organic animal feed. We analyze the resulting marginal abatement costs and draw insights about the potential scale of mussel farming for the different catchments. We show that mussel farming is a cost-effective option for 2 of the 3 catchments, but that decreasing mussel productivity over time may make the measure ineffective for one of the catchments, if a market for feed is not available. The possibility of a market for mussel-based organic feed significantly increases the share of nitrogen reduction done by mussels and decreases overall costs by up to 65%. Ultimately, the results indicate that, for catchments where environmental conditions are adequate, mussel farming can be a cost-effective nutrient reduction measure. Therefore, mussel farming can potentially increase the cost-effectiveness of incentive schemes aimed at reducing eutrophication in fjords and coastal waters.

Commercial dredging for blue mussels (Mytilus edulis) and oysters (Ostrea edulis, Crassostrea gigas) constitute the main bivalve fisheries in Denmark. These activities predominantly take place in Limfjorden, a large microtidal sound, and in the Inner Danish waters. Both areas are shallow, estuarine, receive high nutrient inputs from agriculture, and are of nature conservation interest (Natura 2000 sites), thus presenting challenges for an ecosystem approach to fisheries management. Using high-resolution fisheries data (~10 m), we investigated the effects of bivalve dredging on benthic communities at both local (Natura 2000 site) and regional (fishery-wide) scales. Regionally, our results showed that dredging intensity correlated with shifts in species composition and reduced community biomass. We were, however, unable to detect an effect of dredging on community density, trait richness, and trait composition. These metrics were significantly related to other environmental drivers, such as sediment organic content (negative) and mussel bed biomass (positive). At the local scale, the observed relationships between dredging, biomass, and species composition varied significantly. This occurred as dredging impacts were greater in areas that contained suitable reference conditions and experienced relatively low levels of eutrophication and natural disturbance. By contrast, communities which experienced high nutrient loading, regular anoxic events, and high natural variability were relatively unaffected by dredging. Our results therefore highlight the importance of spatial scales in fishing impact estimations. Furthermore, we demonstrate how targeted sampling, high-resolution fisheries data, and suitable reference areas can be used to detect fishery effects in coastal areas that are highly stressed by eutrophication.

As part of a larger project funded by the Danish Environmental Protection Agency (“Effects on the quality elements defined by the EU Water Framework Directive (WFD) of other pressure factors than excess nutrient load and climate change”) a number of environmental pressure factors other than excess nutrient loading and climate change have been identified as potential risks to all of the quality elements of the WFD (Petersen et al. 2018). In a larger review, a number of invasive species were identified as potential pressure factors on the quality elements of the WFD. In the review, it was estimated that the invasive species Mnemiopsis leidyi and Neogobius melanostomus may have potential significant effects on the quality elements phytoplankton and benthic fauna, respectively (Petersen et al. 2018). Both species are known to be aggressive invaders and in international per-reviewed studies, effects on the ecosystem have been documented but for none of the species, sufficient data were available to perform a scientific analysis at the level of water bodies as defined in the WFD (Petersen et al. 2018). However, the Danish Environmental Protection Agency wanted an expert assessment of potential effects of the two invasive species based on the data available at present. Mnemiopsis leidyi possess many characteristics of invasive species such as rapid growth, high dispersal potential, high fertility, short generation time, high competitiveness and high tolerance to environmental conditions. Mnemiopsis leidyi was first observed in northern European waters in 2005 and major occurrences were observed in Limfjorden in 2007. Since then, it has been observed in most Danish waters. The expected effect of Mnemiopsis leidyi in the ecosystem is that it eats zooplankton, thereby reducing grazing pressure on phytoplankton, which can then grow uncontrolled and thereby lead to a number of biological cascade effects. As data on occurrenc

As part of a larger project funded by the Danish Environmental Protection Agency (“Effects on the quality elements defined by the EU Water Framework Directive (WFD) of other pressure factors than excess nutrient load and climate change”) a number of environmental pressure factors other than excess nutrient loading and climate change have been identified as potential risks to all of the quality elements of the WFD (Petersen et al. 2018). In Denmark, boulder reefs in shallow waters have been extensively exploited habitats targeted for their high concentration of easy-to-collect large boulders for constructing sea defences and harbour jetties. This has destroyed important habitats for the EU WFD quality element macroalgae. Extraction of boulders has for all practical matters been prohibited since 1999 but there is no record of the extent of the volume of stones extracted. However, in order to assess how the historical extraction may potentially have affected attached macroalgae vegetation, an analysis based on historical records have been carried out. For the assessment of the amounts of boulders that have been removed, we have partly assessed the few available direct sources of boulder extraction from recordings from the extraction vessels as well as estimated consumption of the boulders for major construction work, primarily in relation to the construction of harbour jetties. We have then applied these amounts to the total number of boats that have been recorded performing boulder extraction in the period 1900-1999. There are no complete inventory of all boats extracting boulders and we have only had access to a few logbooks of the ships. Based on these data, it was estimated that 8.3 million m3 m of boulders (corresponding to 83 million stones) have been extracted from coastal Danish waters (<10 m water depth, predominantly 4-7 m). In the analysis, only stone fractions from 150-600 mm in diameter (type 5) and 340-2000 mm in diameter (type 6) have

In this document, we present a synthesis of updated documented experience in the implementation of mussel cultivation for mitigating effects of eutrophication and parameter estimates to facilitate potential application in coastal water management plans. Included are descriptions of potential for nutrient extraction, ecological effects, and economics of mussel cultivation. The documentation presented is primarily gathered in the BONUS OPTIMUS project as well as in some nationally funded projects on mussel farming or mussel mitigation farming including project participants, while data from other projects is only included to a lesser degree.

Marine virkemidler har til formål at bidrage til opnåelse af god økologisk tilstand i de marine vandområder. Marine virkemidler er placeret i – og virker i – de marine vandområder, hvor de fjerner og/eller binder næringsstoffer (kvælstof (N) og fosfor (P)) og/eller har en direkte effekt på andre biologiske kvalitetselementer og støtteparametre. Denne rapport beskriver status for viden om syv potentielle marine virkemidler med fokus på N- og P-effekt, øvrige effekter på miljø og klima, samt økonomi for de virkemidler, hvor tilgængelig viden findes. Det eksisterende vidensgrundlag, og dermed datasikkerheden, for de beskrevne virkemidler er forskellig. Virkemidlerne er på basis af eksisterende viden inddelt i fire kategorier: ‘Operationelt’, ‘Potentielt lovende’, ‘Teoretisk lovende’ og ‘Ikke egnet til danske farvande’. De beskrevne virkemidler er af forskellig karakter, og de er ikke nødvendigvis virksomme eller effektive i alle marine områder. Der er ingen marine virkemidler, der bør anvendes uden en forudgående faglig vurdering af placering.

As part of a larger project funded by the Danish Environmental Protection Agency (“Effects on the quality elements defined by the EU Water Framework Directive (WFD) of other pressure factors than excess nutrient load and climate change”), fishery with trawl, dredge or other mobile bottom-contacting gear (MBCG) has been identified as a potential risk to all of the quality elements of the WFD (Petersen et al. 2018). In this report, we have analysed effects of fisheries on i) benthic fauna using statistical methods to correlate data on fishing pressure with data on fauna composition and ii) phytoplankton using a 3D dynamic model to show effects of mussel fishery on Chlorophyll a concentration (Chl.a) and iii) cascade effects on phytoplankton and nutrient concentrations in a review study of the literature. For impact on benthic fauna, we have mapped fishing pressure in Danish water bodies using information of vessel activity from VMS (Vessel Monitoring System), AIS (Automatic Identification System) and the BB (Black Box) system. The BB system is used only in the mussel and oyster fishery and monitors vessel position and activity every 10th second, allowing for fishing pressure to be mapped very precisely. The AIS and VMS systems are much less precise as they only record vessel activity once an hour (VMS) or at irregular intervals and vessel coverage (AIS). Slightly less than 50% of the 119 Danish water bodies had fishery with MBCGs in the period 2014-18. Based on data from all three monitoring systems, a map of fishing intensities (Swept Area Ratios [SARs]) in quadrats of 100 x 100 m was produced for all water bodies. In terms of spatial extent (proportion of water body seabed area impacted) fishing pressure was highest along the west coast of Jutland, in Ålbæk Bight, and south of Fyn (Figure 2.1). In the same areas, fishing intensity was also highest, with substantial parts of the seabed in the water bodies being impacted between 1 and 5 ti

As part of a larger project funded by the Danish Environmental Protection Agency (“Effects on the quality elements defined by the EU Water Framework Directive (WFD) of other pressure factors than excess nutrient load and climate change”) a number of environmental pressure factors other than excess nutrient loading and climate change have been identified as potential risks to all of the quality elements of the WFD (Petersen et al. 2018). When multiple pressure factors have been identified as being of importance to one or more of the WFD quality elements, the next task for environmental managers and their scientific support should be to cumulate their effects. This is easily done when the different anthropogenic pressures induce similar effects on the environment and can be cumulated by addition, e.g. resuspension of sediment by gravel extraction can be anticipated to have similar effects on water transparency as resuspension caused by deepening of shipping lanes or bottom trawling and can thus be added. However, pressures generated by e.g. invasive species and excess loading of nutrients have completely different effects on the marine environment and the WFD quality elements. Cumulating these pressures to calculate their overall impact is therefore not straight forward. In this report, we critically review the methods that have been proposed for cumulating anthropogenic pressures. These include the Delphi method, mechanistic models, univariate and multivariate statistical methods, Bayesian models and machine learning. As the need for cumulating effects is primarily related to pressures whose effects are non-additive i.e. are synergistic, antagonistic or dominant, we have focussed on methods that are able to quantify such interactions. We use a number of criteria to assess the applicability of each method based on 1) the requirements of the method in terms of input data and process knowledge. Very data-intensive methods will have limited utility because, for a num

Ecosystem services provided by marine bivalves in relation to nutrient extraction from the coastal environment have gained increased attention to mitigate adverse effects of excess nutrient loading from human activities, such as agriculture and sewage discharge. These activities damage coastal ecosystems and require action from local, regional, and national environmental management. Marine bivalves filter particles like phytoplankton, thereby transforming particulate organic matter into bivalve tissue or larger faecal pellets that are transferred to the benthos. Nutrient extraction from the coastal environment takes place through two different pathways: (i) harvest/removal of the bivalves – thereby returning nutrients back to land; or (ii) through increased denitrification in proximity to dense bivalve aggregations, leading to loss of nitrogen to the atmosphere. Active use of marine bivalves for nutrient extraction may include a number of secondary effects on the ecosystem, such as filtration of particulate material. This leads to partial transformation of particulate-bound nutrients into dissolved nutrients via bivalve excretion or enhanced mineralization of faecal material. In this chapter, concepts in relation to nutrient extraction by bivalves are presented and discussed in relation to nutrient cycling and additional effects of enhancing bivalve communities. In addition, methods to valorise nutrient extraction by bivalves are evaluated. Examples of calculations of the value of nutrient extraction by bivalves are presented., Ecosystem services provided by marine bivalves in relation to nutrient extraction from the coastal environment have gained increased attention to mitigate adverse effects of excess nutrient loading from human activities, such as agriculture and sewage discharge. These activities damage coastal ecosystems and require action from local, regional, and national environmental management. Marine bivalves filter particles like phytoplankton, thereby transforming particulate organic matter into bivalve tissue or larger faecal pellets that are transferred to the benthos. Nutrient extraction from the coastal environment takes place through two different pathways: (i) harvest/removal of the bivalves – thereby returning nutrients back to land; or (ii) through increased denitrification in proximity to dense bivalve aggregations, leading to loss of nitrogen to the atmosphere. Active use of marine bivalves for nutrient extraction may include a number of secondary effects on the ecosystem, such as filtration of particulate material. This leads to partial transformation of particulate-bound nutrients into dissolved nutrients via bivalve excretion or enhanced mineralization of faecal material. In this chapter, concepts in relation to nutrient extraction by bivalves are presented and discussed in relation to nutrient cycling and additional effects of enhancing bivalve communities. In addition, methods to valorise nutrient extraction by bivalves are evaluated. Examples of calculations of the value of nutrient extraction by bivalves are presented.

I muslingepolitikken er der opstillet målsætninger og forvaltningsprincipper for muslingeskrab og øvrig muslingeproduktion i Danmark, der bl.a. omhandler særlige beskyttelsesbehov i forhold til udpegede arter – heraf økosystemkomponenterne ålegræs og makroalger. For ålegræs er der nul-tolerance, mens acceptabel påvirkning af makroalger vil kunne tillades. Imidlertid bygger mål-sætningerne ikke på et solidt fagligt grundlag forstået som viden om økosystemkomponenterne i de konkrete fiskeriområder, og derved havner forvaltningen i et dilemma mellem forsigtigheds-princippet i forhold til økosystemkomponenterne og udnyttelse af muslingeressourcerne til fiskeri. I habitatområderne Horsens Fjord og Lillebælt mangler der basal kendskab til beskyttelseskrav i områderne og der er bl.a. behov for tilvejebringelse af viden om de økosystemkomponenter, der indgår i muslingepolitikken. Dette projekt har således haft til formål, at tilvejebringe viden om øko-systemkomponenterne makroalger og ålegræs i Natura 2000-områderne Horsens Fjord og Lille-bælt til brug i forvaltningen af muslingefiskeriet i områderne. Områderne blev moniteret via videoundersøgelser i begyndelsen af sommeren 2016 og 2017. I alt 637 video-transekter blev udført i de to områder svarende til ca. 60 km havbund og 65 timers videooptagelser. Videoerne blev analyseret for tilstedeværelsen af ålegræs og 9 forskellige grup-per af makroalger samt dækning af sten, grus og skaller og sedimentkarakteristik. Desuden blev sedimentprøver taget på 50 stationer for at kalibrere de visuelle inspektioner fra videoerne. De indsamlede oplysninger blev omdannet til detaljerede kort over makroalge- og ålegræsforekom-sterne i områderne. Data fra kortlægningen blev desuden indarbejdet i en model for hvert af de to områder, der blev udviklet inden for projektet for at beskrive ålegræssets potentielle forekomst og spredningspotentiale. Endelig blev der udført et konceptstudie af droneteknologi til kortlægning af ålegræs for at udvikle

Ecosystem services provided by marine bivalves in relation to nutrient extraction from the coastal environment have gained increased attention to mitigate adverse effects of excess nutrient loading from human activities, such as agriculture and sewage discharge. These activities damage coastal ecosystems and require action from local, regional, and national environmental management. Marine bivalves filter particles like phytoplankton, thereby transforming particulate organic matter into bivalve tissue or larger faecal pellets that are transferred to the benthos. Nutrient extraction from the coastal environment takes place through two different pathways: (i) harvest/removal of the bivalves – thereby returning nutrients back to land; or (ii) through increased denitrification in proximity to dense bivalve aggregations, leading to loss of nitrogen to the atmosphere. Active use of marine bivalves for nutrient extraction may include a number of secondary effects on the ecosystem, such as filtration of particulate material. This leads to partial transformation of particulate-bound nutrients into dissolved nutrients via bivalve excretion or enhanced mineralization of faecal material. In this chapter, concepts in relation to nutrient extraction by bivalves are presented and discussed in relation to nutrient cycling and additional effects of enhancing bivalve communities. In addition, methods to valorise nutrient extraction by bivalves are evaluated. Examples of calculations of the value of nutrient extraction by bivalves are presented., Ecosystem services provided by marine bivalves in relation to nutrient extraction from the coastal environment have gained increased attention to mitigate adverse effects of excess nutrient loading from human activities, such as agriculture and sewage discharge. These activities damage coastal ecosystems and require action from local, regional, and national environmental management. Marine bivalves filter particles like phytoplankton, thereby transforming particulate organic matter into bivalve tissue or larger faecal pellets that are transferred to the benthos. Nutrient extraction from the coastal environment takes place through two different pathways: (i) harvest/removal of the bivalves – thereby returning nutrients back to land; or (ii) through increased denitrification in proximity to dense bivalve aggregations, leading to loss of nitrogen to the atmosphere. Active use of marine bivalves for nutrient extraction may include a number of secondary effects on the ecosystem, such as filtration of particulate material. This leads to partial transformation of particulate-bound nutrients into dissolved nutrients via bivalve excretion or enhanced mineralization of faecal material. In this chapter, concepts in relation to nutrient extraction by bivalves are presented and discussed in relation to nutrient cycling and additional effects of enhancing bivalve communities. In addition, methods to valorise nutrient extraction by bivalves are evaluated. Examples of calculations of the value of nutrient extraction by bivalves are presented.

Nærværende udredning er rekvireret af Fiskeristyrelsen og udarbejdet under Institut for Fødevare- og Ressourceøkonomis og DTU Aquas aftaler om myndighedsbetjening for 2018 med Miljø- og Fødevareministeriet/Udenrigsministeriet. Formålet med notatet er at vurdere effekterne ved fremover at anvende midlerne fra hav- og fiskeriudviklingsprogrammet ud fra de samme principper som i dag. Årsagen til, at effekterne vurderes ud fra uændrede principper, er, at der endnu ikke er fastlagt kriterier for midlernes anvendelse i Danmark i den kommende programperiode. For andre emner henvises til IFRO Udredning 2013/21 Vurdering af Fiskeriudviklingsprogrammets effekter, som yderligere oplister en række områder, som kunne være relevante at videreføre. I afsnit 1 gennemgås, med et økonomisk-teoretisk udgangspunkt og i hvilke situationer, det kan være hensigtsmæssigt at give støtte. I afsnit 2 præsenteres programmets målsætninger, i det der tages udgangspunkt i, at målsætningen fra programmet 2014-2020 opretholdes. Endelig vurderes i afsnit 3 effekter af mulige tiltag inden for programmets tre prioriteter om fiskeri, akvakultur og forarbejdning samt bæredygtig blå økonomi og velstående kystsamfund.

Sargassum muticum (herefter sargassotang) er en fastsiddende flerårig makroalge med flere invasive karaktertræk, bl.a. hurtig vækst, stort spredningspotentiale, høj konkurrenceevne og høj tolerance over for miljøforhold såsom temperatur, salinitet, lys og næring (Engelen et al. 2015). Siden sargassotang blev introduceret til Nissum Bredning i begyndelsen af 1980´erne, har den bredt sig til resten af Limfjorden, hvor den siden midten af 1990´erne har været den dominerende makroalge (Stæhr et al. 2000). Sargassotang har endvidere bredt sig til store dele af Kattegat, hvor den især trives i laveksponerede områder. På landsplan er sargassotang den hyppigst forekommende ikke-hjemmehørende makroalge (Stæhr et al. 2016). Algen er meget frugtbar og konkurrerer med andre alger foruden om lys også om plads til fasthæftning på faste substrater som fx sten og større skaller. Små flydeblærer på skuddene gør, at løvet står opret i vandsøjlen, hvorved lystilgængeligheden på bunden kan reduceres med op til 97% (Strong et al. 2006), og netop udskygning fremhæves i litteraturen som den væsentligste årsag til sargassotangs evne til at udkonkurrere andre makroalger (Ambrose & Nelsen 1982, Sánchez & Fernández 2005). Sargassotang medfører således strukturelle og funktionelle ændringer i dens nærmiljø. Som for makroalger, kan en potentiel effekt af sargassotang på ålegræs forventes at forekomme via udskygning i områder med blandet substrat (blød og hård bund), hvor arterne kan sameksistere. De få studier, der har belyst effekten af sargassotang på udbredelse og tæthed af ålegræs indikerer, at der kan være negative effekter, men der er ingen klar dokumentation herfor og ingen studier fra danske farvande. Nærværende analyse udspringer af en større undersøgelse af betydningen af andre presfaktorer end næringsstoffer og klimaændringer for den økologiske tilstand i vandområderne, som udover en identificering af potentielt betydende presfaktorer på vandområdeniveau (Pe

Bivalve environmental services have become a focal point for their inherent role in the management of eutrophication, while active cultivation has become increasingly acknowledged as a mechanism for integrated nutrient reduction. In recent years, cultivation practices designed specifically for nutrient extraction have emerged; “mitigation culture.” While modeling efforts have been able to describe expanded potential of these services, only a single commercial pilot scale, real-world demonstration, has been documented. Over two production seasons (2017–2018), the optimization of nutrient extractive potential of mussels (Mytilus edulis) at full commercial-scale was evaluated by first testing multiple density configurations of conventional longline-spat collector setups and potential harvest times, then by comparing different cultivation technologies at three farms. Potential biomass volumes of 770–1700 t with longlines and 2100–2600 t on nets was demonstrated in full-scale production (18.8 ha), yielding 0.6–1.27 t N ha–1 and 0.04–0.1 t P ha–1, and 1.63–2.0 t N ha–1 and 0.1–0.12 t P ha–1 respectively. In general, 1 t of harvested mitigation mussels will yield 13.7 kg N and 0.9 kg P. Winter harvests exhibited higher yields (103–124%) than early spring harvests on optimized configurations, favoring an abbreviated production season. Production potential was similar between sites, despite differing environmental conditions, indicating eutrophic waters are suitable for expanded mitigation production. This study presents for the first-time production data of mitigation mussels utilizing different configurations and technologies to maximize yield and nutrient extraction potential.