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Anthropogenic impacts on marine habitats are a global problem, particularly in coastal areas. While boulder reefs in temperate waters hold high biomass and biodiversity, and may be unable to recover from anthropogenic stressors without restoration efforts, little is known about how to restore and conserve this important marine habitat. Limited knowledge is a serious impediment to projects aimed at restoring boulder reefs that have been degraded or removed by substrate extraction. In 2008, a boulder reef was restored in Kattegat, the transitional waters between the North Sea and the Baltic Sea, using differently sized boulders. The restored reef covered approximately 27,600 m 2 seafloor and included 100,712 tons of boulders added at depths ranging between 4 and 11 m. This paper describes methodology and lessons learned during the restoration project. Before the restoration, geological and geotechnical surveys confirmed that the sea bed could support added boulders, and high resolution bathymetric surveys provided input for the design of the reef, particularly for numerical modelling of the hydrographic and sediment transport conditions. Numerical modelling was used to derive hydrographic design conditions for boulder placements and further, to ensure that the restored reef would not affect the sea bed morphology and hydrographic conditions at a local harbour and at a protected habitat, both situated in the vicinity of the restoration area. Data on the physical structure of the restored boulder reef, collected in 2009, demonstrated that cavernous structures and shallow reef areas were restored. Moreover, data collected in 2012 confirmed the stability of the restored reef. Finally, results highlighted the importance of stakeholder mapping at the outset, appropriate timing of stakeholder involvement and ongoing consideration of stakeholder perceptions. Charting strategy and introducing a checklist for marine restoration projects, this paper outlines important considerations and methodology needed to ensure that restoration of temperate reef structures meet the objectives, without having undesirable effects on existing hydrographic and morphological conditions, including nearby coastal areas and protected marine habitats.

During the last century, eutrophication significantly reduced the depth distribution and density of the habitat forming eelgrass meadows (Zostera marina) in Danish coastal waters. Despite large reductions in nutrient loadings and improved water quality, Danish eelgrass meadows are currently not as widely distributed as expected from improvements in water clarity alone. This point to the importance of other environmental conditions such as sediment quality, wave exposure, oxygen conditions and water temperature that may limit eelgrass growth and contribute to constraining current distributions. Recently, detailed local models have been set up to evaluate the importance of such regulating factors in selected Danish coastal areas, but nationwide maps of eelgrass distribution and large-scale evaluations of regulating factors are still lacking. To provide such nationwide information, we applied a spatial habitat GIS modeling approach, which combines information on six key eelgrass habitat requirements (light availability, water temperature, salinity, frequency of low oxygen concentration, wave exposure, and sediment type) for which we were able to obtain national coverage. The modeled potential current distribution area of Danish eelgrass meadows was 2204 km 2 compared to historical estimates of around 7000 km 2 , indicating a great potential for further distribution. While validating the modeled eelgrass distribution area in three areas (83-111 km 2 ) that hold large eelgrass meadows, we found an agreement of 67% with in situ monitoring data and 77% for eelgrass areas as identified from summer orthophotos. The GIS model predicted higher coverage especially in shallow waters and near the depth limits. Areas of disagreement between GIS-modeled and observed coverage generally exhibited higher exposure level, mean summer temperature and salinity compared to areas of agreement. A sensitivity analysis showed that the modeled area distribution of eelgrass was highly sensitive to light conditions, with 18-38% increase in coverage following an increase in light availability of 20%. Modeled coverage of eelgrass was also sensitive to wave exposure and temperature conditions while less sensitive to changes in oxygen and salinity conditions. Large regional differences in habitat conditions suggest spatial variation in the factors currently limiting the recovery of eelgrass and, hence, variations in actions required for sustainable management.

Modern ecosystem-based forms of marine management such as Marine Spatial Planning (MSP) deal with various complex systems and often with huge amounts of data. Software-based simulative and analytical tools are therefore frequently mentioned in the scientific literature on marine management approaches. But in addition to the evolution of management approaches, the requirements for more integrated tools are also progressing. MSP, for instance, comes with different spatial resolutions, an increased need to consider multiple interdepencies, and increased requirements for validity than most of the previous marine management questions. We reviewed seven well-known Decision Support Tools (DSTs) by asking 59 MSP practitioners from at least 25 countries worldwide about their experience with these tools. The results revealed that, while respondents were mostly positive about the use of DSTs in MSP processes, DSTs are still mainly used in the academic realm and have not yet found their way into everyday MSP practice. There is a broad range of reasons for not using DSTs, including the complexity of these tools, the resources required to operate them, low stakeholder confidence in DST outcomes, and the lack of additional value in using DSTs.

The role of tools and approaches is currently much debated in maritime spatial planning (MSP). Past evaluation has mainly concentrated on decision support tools and the tangible outputs these can provide for MSP, but little attention has so far been been given to the soft or indirect benefits tool use can have in MSP. This paper assesses the potential benefits of tool use in the context of four common integration challenges in MSP. Drawing on case study material from the Baltic Sea region, the paper reviews the potential contribution of five selected tools and approaches to multi-level and transboundary, policy and sector, stakeholder and knowledge integration. Specific end points are defined for each integration challenge, including general desired outcomes of integrated MSP processes as a template for assessment. Our review shows that the selected tools play different roles in moving towards the various end points of MSP integration. There is an important difference between the potential of each tool, or its inherent capacity, and how it is applied, e.g. in a participative or non-participative setting. Another lesson is that some integration benefits can be achieved by the tools alone, while others – often secondary benefits - depend on how the outcomes of tool use are taken up by the subsequent MSP process. Although the nature of a tool does restrict its potential contribution to MSP integration challenges, the secondary “soft” benefits that can be achieved through certain styles of application and good links to the MSP process can add important integration benefits up and beyond the tool itself. The results presented here may also be relevant to other types of spatial planning and conservation management.

Integrated assessment of the status of marine biodiversity is and has been problematic compared to, for example, assessments of eutrophication and contamination status, mostly as a consequence of the fact that monitoring of marine habitats, communities and species is expensive, often collected at an incorrect spatial scale and/or poorly integrated with existing marine environmental monitoring efforts. The objective of this Method Paper is to introduce and describe a simple tool for integrated assessment of biodiversity status based on the HELCOM Biodiversity Assessment Tool (BEAT), where interim biodiversity indicators are grouped by themes: broad-scale habitats, communities, and species as well as supporting non-biodiversity indicators. Further, we report the application of an initial indicator-based assessment of biodiversity status of Danish marine waters where we have tentatively classified the biodiversity status of Danish marine waters. The biodiversity status was in no areas classified as “unaffected by human activities.” In all the 22 assessment areas, the status was classified as either “moderately affected by human activities” or “significantly affected by human activities.” Spatial variations in the biodiversity status were in general related to the eutrophication status as well as fishing pressure. &nbsp