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Establishment of artificial reefs and no-take areas are management measures available for restoring deteriorated marine ecosystems, compensating for habitat loss and strengthening harvested populations. Following the establishment of no-take artificial reefs in western Sweden to compensate for hard bottoms lost to a shipping lane, we detected rapid positive effects on crustaceans and demersal fish compared to fished reference areas. The relative abundance and size structure of European lobster (Homarus gammarus) increased strongly in the no-take area indicating more than doubled and tripled egg production in 5 and 10 years, respectively. For benthic fish and crustacean communities, the abundances of gadoids and wrasses increased and the abundances of small decapod crustaceans decreased in the no-take area, likely indicating cascading effects of increased predation. The study demonstrates that relatively small no-take areas, enhanced by artificial reefs, can rapidly invigorate populations of lobster and fish that in turn may re-initiate local top-down control.

Marine protected areas (MPAs) are increasingly established worldwide to protect and restore degraded ecosystems. However, the level of protection varies among MPAs and has been found to affect the outcome of the closure. In no-take zones (NTZs), no fishing or extraction of marine organisms is allowed. The EU Commission recently committed to protect 30% of European waters by 2030 through the updated Biodiversity Strategy. Importantly, one third of these 30% should be of strict protection. Exactly what is meant by strict protection is not entirely clear, but fishing would likely have to be fully or largely prohibited in these areas. This new target for strictly protected areas highlights the need to evaluate the ecological effects of NTZs, particularly in regions like northern Europe where such evaluations are scarce. The Swedish NTZs made up approximately two thirds of the total areal extent of NTZs in Europe a decade ago. Given that these areas have been closed for at least 10 years and can provide insights into long-term effects of NTZs on fish and ecosystems, they are of broad interest in light of the new 10% strict protection by 2030 commitment by EU member states. In total, eight NTZs in Swedish coastal and offshore waters were evaluated in the current report, with respect to primarily the responses of focal species for the conservation measure, but in some of the areas also ecosystem responses. Five of the NTZs were established in 2009-2011, as part of a government commission, while the other three had been established earlier. The results of the evaluations are presented in a synthesis and also in separate, more detailed chapters for each of the eight NTZs. Overall, the results suggest that NTZs can increase abundances and biomasses of fish and decapod crustaceans, given that the closed areas are strategically placed and of an appropriate size in relation to the life cycle of the focal species. A meta-regression of the effects on focal species of the NTZs showed that CPUE was on average 2.6 times higher after three years of protection, and 3.8 times higher than in the fished reference areas after six years of protection. The proportion of old and large individuals increased in most NTZs, and thereby also the reproductive potential of populations. The increase in abundance of large predatory fish also likely contributed to restoring ecosystem functions, such as top-down control. These effects appeared after a 5-year period and in many cases remained and continued to increase in the longer term (>10 years). In the two areas where cod was the focal species of the NTZs, positive responses were weak, likely as an effect of long-term past, and in the Kattegat still present, recruitment overfishing. In the Baltic Sea, predation by grey seal and cormorant was in some cases so high that it likely counteracted the positive effects of removing fisheries and led to stock declines in the NTZs. In most cases, the introduction of the NTZs has likely decreased the total fishing effort rather than displacing it to adjacent areas. In the Kattegat NTZ, however, the purpose was explicitly to displace an unselective coastal mixed bottom-trawl fishery targeting Norway lobster and flatfish to areas where the bycatches of mature cod were smaller. In two areas that were reopened to fishing after 5 years, the positive effects of the NTZs on fish stocks eroded quickly to pre-closure levels despite that the areas remained closed during the spawning period, highlighting that permanent closures may be necessary to maintain positive effects. We conclude from the Swedish case studies that NTZs may well function as a complement to other fisheries management measures, such as catch, effort and gear regulations. The experiences from the current evaluation show that NTZs can be an important tool for fisheries management especially for local coastal fish populations and areas with mixed fisheries, as well as in cases where there is a need to counteract adverse ecosystem effects of fishing. NTZs are also needed as reference for marine environmental management, and for understanding the effects of fishing on fish populations and other ecosystem components in relation to other pressures. MPAs where the protection of both fish and their habitats is combined may be an important instrument for ecosystembased management, where the recovery of large predatory fish may lead to a restoration of important ecosystem functions and contribute to improving decayed habitats. With the new Biodiversity Strategy, EUs level of ambition for marine conservation increases significantly, with the goal of 30% of coastal and marine waters protected by 2030, and, importantly, one third of these areas being strictly protected. From a conservation perspective, rare, sensitive and/or charismatic species or habitats are often in focus when designating MPAs, and displacement of fisheries is then considered an unwanted side effect. However, if the establishment of strictly protected areas also aims to rebuild fish stocks, these MPAs should be placed in heavily fished areas and designed to protect depleted populations by accounting for their home ranges to generate positive outcomes. Thus, extensive displacement of fisheries is required to reach benefits for depleted populations, and need to be accounted for e.g. by specific regulations outside the strictly protected areas. These new extensive EU goals for MPA establishment pose a challenge for management, but at the same time offer an opportunity to bridge the current gap between conservation and fisheries management.

Marine eutrophication is a pervasive and growing threat to global sustainability. Macroalgal cultivation is a promising circular economy solution to achieve nutrient reduction and food security. However, the location of production hotspots is not well known. In this paper the production potential of macroalgae of high commercial value was predicted across the Baltic Sea region. In addition, the nutrient limitation within and adjacent to macroalgal farms was investigated to suggest optimal site-specific configuration of farms. The production potential of Saccharina latissima was largely driven by salinity and the highest production yields are expected in the westernmost Baltic Sea areas where salinity is >23. The direct and interactive effects of light availability, temperature, salinity and nutrient concentrations regulated the predicted changes in the production of Ulva intestinalis and Fucus vesiculosus. The western and southern Baltic Sea exhibited the highest farming potential for these species, with promising areas also in the eastern Baltic Sea. Macroalgal farming did not induce significant nutrient limitation. The expected spatial propagation of nutrient limitation caused by macroalgal farming was less than 100–250 m. Higher propagation distances were found in areas of low nutrient and low water exchange (e.g. offshore areas in the Baltic Proper) and smaller distances in areas of high nutrient and high water exchange (e.g. western Baltic Sea and Gulf of Riga). The generated maps provide the most sought-after input to support blue growth initiatives that foster the sustainable development of macroalgal cultivation and reduction of in situ nutrient loads in the Baltic Sea.

Kustekosystemen är mycket viktiga för både biologisk mångfald och ekosystemtjänster, men påverkas samtidigt negativt av ett kontinuerligt ökat nyttjande av kustzonen för boende och olika verksamheter. Ekologisk kompensation är ett förvaltningsverktyg som syftar till att gottgöra oundviklig skada på naturmiljöer, exempelvis arter, naturtyper, ekosystemfunktioner och upplevelsevärden, i samband med mänsklig verksamhet. Verktyget har dock hittills använts i mycket begränsad omfattning i grunda kustmiljöer. Inom projektet ECOCOA, finansierat av Naturvårdsverket, har vi fokuserat på att utvärdera förutsättningarna för ökad användning av ekologisk kompensation i kustområden, som ett av flera verktyg som kan stöda miljövården. Projektets slutrapport (Bergström m.fl. 2021) ger en övergripande bild av samtliga resultat, medan vi i föreliggande rapport ger en fördjupning av de mer konkreta problem som kan uppstå vid handläggning av miljöärenden i förvaltningen, och möjliga lösningar på kort och lång sikt. Rapporten riktar sig i första hand till handläggare som vill utveckla tillämpningen av ekologisk kompensation vid vattenverksamhetsärenden, till tekniska råd vid markoch miljödomstolar, samt miljökonsulter och andra som kan behöva insyn i hur ekologisk kompensation kan användas och vidareutvecklas inom svensk kustmiljöförvaltning. I rapporten återger vi hur man hanterar ekologisk kompensation i svenska kustområden idag, till exempel hur handläggare arbetar med att mäta skada och bedöma omfattningen av kompensationsbehov. Vi beskriver även problematiken med småskaliga anmälningspliktiga ärenden, där den sammanlagda påverkan från många små exploateringar ger upphov till betydande förluster av biologisk mångfald och ekosystemtjänster. Slutligen beskriver vi hur den så kallade särskilda fiskeavgiften, som syftar till att tillvarata fiskeintresset i samband med vattenverksamhetsfrågor, tillämpas idag, samt analyserar hur beräkningsgrunderna skulle kunna utvecklas för att stärka användningen av ekologisk kompensationen som verktyg. Vår sammanställning och utvärdering utgår från ett generellt ramverk som utvecklats inom ECOCOA för att skatta skada och identifiera kompensationsbehov. Ramverket baseras på en kaskadmodell, som visar kopplingar mellan ekosystemets struktur, funktion, ekosystemtjänster och nyttigheter för människor. Modellen kan användas för att synliggöra hur verksamheter påverkar arter och livsmiljöer och vilka kostnader och förluster detta medför. Ramverket kan även användas för att bedöma i vilken omfattning en föreslagen åtgärd faktiskt kompenserar för de förluster som verksamheten innebär. Här följer en kort sammanfattning av resultaten som presenteras i rapporten: • En enkätundersökning riktad till aktörer inom kustförvaltningen visar att ekologisk kompensation i praktiken tillämpas mycket sällan inom kustmiljöförvaltningen idag, och att det finns ett stort behov av att ta fram riktlinjer för dess tillämpning, som stöd till handläggare, konsulter, domstolar och andra aktörer. På en mer generell nivå omfattar detta även ett behov av att förbättra kunskapen om restaureringsmetoder samt att ta fram metoder för värdering av skador på naturvärden. Det finns även ett behov av resurser för Sammanfattning 6 handläggare i form av tid och stöd för att tillämpa ekologisk kompensation i kustförvaltningen. • En utvärdering av befintliga domslut för ett antal tillståndspliktiga (dvs. storskaliga) vattenverksamhetsärenden visar att biologisk mångfald och ekosystemtjänster mycket sällan beaktas på ett sätt som är i linje med Sveriges åtaganden inom till exempel konventionen för biologisk mångfald och EU:s biodiversitetstrategi, där en bärande princip är att ingen nettoförlust ska ske. Det finns ett förbättringsutrymme som borde kunna mötas direkt genom en ökad kunskapsdelning mellan aktörer, och en förbättrad praxis gällande tillämpning av ekologisk kompensation. Samtidigt uppstår flera mer komplexa frågor som berör till exempel behovet av en gemensam fysisk planering och identifiering av lämpliga kompensationsåtgärder, där ett kunskapsbyggande behövs. • Småskalig kustexploatering, exempelvis bryggbyggen och små muddringar, är en särskilt utmanande fråga. Enskilda små ingrepp är anmälningspliktiga (dvs. sällan tillståndspliktiga), och trots att det vid handläggningen av dessa ärenden ställs krav på miljöhänsyn kan det ofta inte bedömas som skäligt att kräva att exploatören själv utför ekologisk kompensation. Den sammanlagda påverkan av dessa många små ingrepp är dock betydande, och det är angeläget att utforma ett system där även småskalig vattenverksamhet kompenserar för sina miljökostnader. Vi undersöker hur ett system för ekologisk kompensation som även omfattar småskalig exploatering skulle kunna se ut, i relation till konceptet habitatbanker eller kompensationspooler, där exploatören kan bidra ekonomiskt till habitatrestaureringar i stället för att själv utföra dem. • Den särskilda fiskeavgiften syftar till att kompensera för skador från vattenverksamheter på fisket och skulle kunna betraktas som ett förvaltningsverktyg för kompensation av en viss typ av förlust. I rapporten utvärderar vi hur det rådande fiskeavgiftssystemet fungerar och utforskar hur det kan fungera ur ett kompensationsperspektiv, samt ger förslag på hur beräkningsmodellen kan utvecklas. Sammantaget finns det ett stort behov av att utveckla ekologisk kompensation som ett av de verktyg som kan bidra till att motverka den allt snabbare förlusten av biologisk mångfald och ekosystemfunktioner. Parallellt behövs ytterligare åtgärder för att stärka skyddet av de känsligaste livsmiljöerna i kustzonen, eftersom bevarande av fungerande livsmiljöer är att föredra som ett mer kostnadseffektivt verktyg än restaurering av störda miljöer.

Understanding and communicating the links among human activities and marine ecosystem services are fundamental for ecosystem-based management, which aims at attaining ecological, economic and social sustainability in the use of our seas. Relationships are typically complex and may differ between geographic areas. Here, an assessment model that combines available quantitative, semi-quantitative and qualitative information, rooted in the DAPSIR (Driver—Activity—Pressure—State—Impact—Response) framework and assessment requirements of the EU Marine Strategy Framework Directive, is developed and applied. Focusing on Swedish marine waters, major human activities at sea are evaluated in relation to their dependencies and impacts on the status of marine ecosystem services. This case study is a consensus assessment based on evaluation of available literature and data. By relating degrees of dependencies and impacts to values of different economic sectors, discrepancies among sectors with respect to their impact versus their monetary value can be identified. In our case, commercial fishing depends on and influences a wide range of ecosystem services, while other sectors, such as shipping, depend little on marine ecosystem services. At the extreme end of the range, pressures from human activities in the past, such as historical nutrient emissions, still have prominent influence on ecosystem services today, entailing considerable losses. Marine tourism and commercial fishing show similar dependencies on ecosystem services, but tourism has a clearly lower impact on ecosystem services and a higher monetary value. The model may serve as a useful tool for communicating and guiding priorities in integrated environmental management and maritime spatial planning.

Advancing our understanding of how environmental variability affects the distribution of organisms is crucial for ecology and conservation. The exploration of changes in demographic patterns close to species distribution margins is important as populations here may provide a window into future population changes also elsewhere. However, the knowledge of factors causing recruitment variation is still inadequate in many systems and this deficiency is particularly evident close to species’ distribution borders. We studied the spatiotemporal variability in recruit-adult dynamics in a blue mussel, Mytilus trossulus, population to get insights into how environmental variables drive variation in recruitment and how this variability affects adult population growth. Thirty sites along a wave exposure gradient were monitored during four consecutive years. From each site, mussels were collected both from artificial recruitment units and from natural mussel beds. Our results showed high year-to-year variation in recruitment strength with high spatial variation. Mussel recruitment to artificial units and later recruitment to the benthos correlated highly. Juvenile abundances 1 year later paralleled prior recruitment strengths and caused synchronous but time-lagged changes in adult cohorts. Seawater salinity was the strongest predictor for recruitment variation, whereas sea temperature and wave exposure had low predictive power for this early life stage. For juveniles and for adults in the benthos, wave exposure explained the variation best, whereas temperature and especially salinity explained less. The results indicate that (a) the studied blue mussel population is strongly driven by variation in recruitment strength that (b) drives the size of the later cohorts, and the population is possibly even (c) recruitment limited in some years. Our study predicts a challenging future for this range population, resulting from a higher frequency of recruitment failure caused by a deteriorating sea climate. Knowledge about factors underlying variation in recruitment is thus essential for forecasting the future of this range population and for conserving its future state.

It is unclear whether transport by human vectors can increase the robustness of translocated populations and thereby enhance their invasiveness. To test this concept, we investigated the effect of heat stress on the tolerance of mussel populations towards a second stress event of the same kind. The heat challenges we mimicked can be faced by marine invertebrates that are transported through regions with high sea surface temperatures on ship hulls or in ballast water tanks. The study included 5 mussel species that were collected at sites in Brazil, Chile, Finland, Germany (Baltic Sea) and Portugal. In parallel laboratory experiments, monospecific groups of individuals were exposed to heat challenges that caused 60–83% mortality in the experimental groups within 15–28 days. The surviving individuals were exposed to a second stress event of the same kind, while their survival was then compared to the robustness of conspecifics that had not been exposed to elevated temperatures before. We observed that thermal tolerance was significantly enhanced by previous heat stress experience in case of Semimytilus algosus from Chile and in case of Mytilus edulis from Germany. Our results suggest that heat challenges, which marine invertebrates experience during transport, can enhance stress tolerance in founder populations of these species in their non-native range by potentially increasing the frequency of genetically adapted genotypes. This points at the necessity to learn more about selection acting on organisms during human-mediated transport—in the aquatic but also in the terrestrial environment.

Ecological impacts of top-down trophic cascades in combination with bottom-up nutrient enrichment are increasingly being reported. Such effects may be triggered by decline in the abundance and size of piscivore fish leading to a release of smaller-sized mesopredatory fish that are capable of reducing mesograzers and their buffering herbivorous effects, thus intensifying eutrophication symptoms. Hitherto, such mesopredator release has not been studied in controlled manner in macroalgal-dominated rocky shore communities. This study utilised twelve littoral mesocosms in southeastern Norway to investigate the impact of increased nutrient levels and increased abundance of the mesopredatory goldsinny wrasse (Ctenolabrus rupestris) over 6 months, from spring (April) to autumn (October). The study mainly revealed typical eutrophication responses in both July and in October with nutrient enrichment leading to more ephemeral algae and less perennial Fucacean and red macroalgae. Significant responses to the addition of mesopredatory fish alone or with nutrients in combination were clearly fewer in July and almost non-existent in October. Mesopredatory fish reduced the number of some mesograzers, but not others, and some herbivores even benefitted. Few joint effects occurred between fish and nutrients and the anticipated negative consequences for perennial macrophytes were largely absent; the possible reasons for these observations are discussed in depth. Curiously, the presence of mesopredatory fish seems to favour some canopy-forming macrophytes. This last finding warrants further investigation as the labrid fishery in coastal waters of southern Norway and western Sweden is increasing and a too heavy reduction of mesopredators may have its own unforeseen ecosystem implications.

Eutrophication is a serious threat to aquatic ecosystems globally with pronounced negative effects in the Baltic and other semi-enclosed estuaries and regional seas, where algal growth associated with excess nutrients causes widespread oxygen free “dead zones” and other threats to sustainability. Decades of policy initiatives to reduce external (land-based and atmospheric) nutrient loads have so far failed to control Baltic Sea eutrophication, which is compounded by significant internal release of legacy phosphorus (P) and biological nitrogen (N) fixation. Farming and harvesting of the native mussel species (Mytilus edulis/trossulus) is a promising internal measure for eutrophication control in the brackish Baltic Sea. Mussels from the more saline outer Baltic had higher N and P content than those from either the inner or central Baltic. Despite their relatively low nutrient content, harvesting farmed mussels from the central Baltic can be a cost-effective complement to land-based measures needed to reach eutrophication status targets and is an important contributor to circularity. Cost effectiveness of nutrient removal is more dependent on farm type than mussel nutrient content, suggesting the need for additional development of farm technology. Furthermore, current regulations are not sufficiently conducive to implementation of internal measures, and may constitute a bottleneck for reaching eutrophication status targets in the Baltic Sea and elsewhere. Highlights • Mussel farming is a viable internal measure to address Baltic Sea eutrophication. • Rates of nutrient removal depend on salinity at the regional scale and food availability at the local scale. • Cost effectiveness of nutrient removal by mussel farming depends also on farm type. • Total farm area needed for achieving HELCOM nutrient reduction targets is realistic.

Ecological patterns are inherently scale-dependent and driven by the interplay of abiotic gradients and biotic processes. Despite the fundamental importance of such gradients, there are many gaps in our understanding of how abiotic stress gradients interplay with biotic processes and how these collectively affect species distributions. Using a hierarchical design, we sampled two communities separated by depth along wave exposure and salinity gradients to elucidate how these two gradients affect species composition in habitats formed by the foundation species Mytilus trossulus and Fucus vesiculosus. Specifically, we looked at the impacts of regional salinity and temperature, local wave exposure, and site-dependent facilitation effects on the associated community composition. Wave exposure was the best predictor for species assembly structure, which was also affected by Mytilus biomass and by salinity and water temperature. While the tested variables provided robust explanations for community structure and density, they did not provide conclusive explanations for variation in species richness or evenness. Mytilus biomass had a stronger effect on the associated community with increasing wave exposure at the deeper depth, but the patterns were less obvious at the shallower depth. The latter was also the case for Fucus. These findings comply partly with theoretical predictions suggesting stronger facilitation effects in physically harsh environments. Our results indicate that environmental drivers are the main structuring forces that affect species assembly structure, but also foundation species are important. Thus, predicting changes in species distributions and biodiversity requires the simultaneous consideration of environmental gradients, as well as the structure and composition of foundation species and the interplay between these factors. This work advances our understanding of the processes that modulate species distributions in a marginal marine area and broadens the knowledge of how biological and environmental factors interplay and have an influence on hard-bottom community structure in brackish water seas. peerReviewed

Environmental compensation should address negative impacts from human activities on nature, including loss of biodiversity and ecosystem services. However, successful compensation, achieving no net loss, requires broad quantitative information on different types of losses and gains. We find that the scope of compensatory schemes varies in what is considered compensable, which makes it challenging to apply a conceptual approach consistently across schemes with different needs. We propose a flexible yet structured framework for determining which values should be compensated and how. Our framework focuses specifically on habitat deterioration and is illustrated with a case study involving loss of eelgrass habitat. The framework helps identify compensation needs and selects among suitable compensation options, merging science-based information with normative issues and local concerns. By integrating the ecosystem services cascade model, it encompasses aspects from biodiversity structure to human wellbeing. The framework prefers in-kind compensation because this targets the structure level and thus meets compensation needs in all subsequent levels of the cascade model; further, it is more likely to capture non-instrumental values (i.e. in nature) and reduce exposure to uncertainty. We highlight the importance of spatial aspects of ecosystem functions, services and their subsequent impacts on wellbeing. Although our selection hierarchy assumes a “similar and nearby” principle for habitat restoration (preference for in-kind/on-site), this criterion is not universal. We underscore the hierarchy’s implicit normative assumptions and suggest that apparent disagreement about who should benefit may be traced to an unresolved conflict between egalitarianism and utilitarianism.

Understanding the relative impacts of pressures on coastal ecosystems is central for implementing relevant measures to reach environmental management objectives. Here, survey data on the species and size composition of coastal fish are evaluated in relation to fishing and eutrophication, by comparing a long-standing no-take area to an environmental gradient in the Baltic Sea. The no-take area represents an intermediate eutrophication level, but the species composition resembles that seen at low eutrophication in areas with fishing. The catch biomass of piscivores is 2–3 times higher in the no-take area than in the other areas, while the biomass of Cyprinids, generally benefitted by eutrophication, corresponds to that of areas with low eutrophication. The results support that fishing may generate eutrophication-like effects, and, conversely, that no-take areas may contribute to improving environmental status in impacted areas by enhancing piscivores, which in turn may contribute to further improvement in the food web. Electronic supplementary material The online version of this article (10.1007/s13280-018-1133-9) contains supplementary material, which is available to authorized users.

The blue mussel Mytilus edulis is a foundation species with ecosystem engineering functions in the brackish, non-tidal Baltic Sea. In this study from the western Gulf of Finland, the relationship between the spatial patchiness of blue mussels and the diversity of associated macrofauna was examined across small scales (centimeters to meters) for the first time in subtidal habitats. It was demonstrated using geostatistical tools that blue mussel abundance and the diversity of associated macrofauna varied and interacted at 2 depths. Classic analyses (ANOVAs, correlations and multivariate techniques) detected no relationships between the abundance of blue mussels and their associated macrofaunal diversity, or differences in the abundance of mussels or the diversity of associated macrofauna between depths. Using semivariograms, differences in spatial heterogeneity between depths emerged: i.e. patchiness at 5 m and random patterns at 8 m depth. Cross-semivariograms detected negative spatial co-variation between blue mussel abundance and diversity of macrofauna at 5 m, but positive and neutral spatial relationships at 8 m depth. Combining the approaches suggested that high dislodgment of mussels in shallow environments causes this pattern. Dislodgement effects may be compensated for by increased turnover of small mussels in patches within mussel beds, which would result in reduced habitat space for associated macrofauna. On the basis of our results, it is suggested that patchiness of a foundation species is an ecological response, or result of a disturbance, that reduces the diversity of the associated macrofaunal community.

Many coastal and offshore fish species are highly dependent on specific habitat types for population maintenance. In the Baltic Sea, shallow productive habitats in the coastal zone such as wetlands, vegetated flads/lagoons and sheltered bays as well as more exposed rocky and sandy areas are utilized by fish across many life history stages including spawning, juvenile development, feeding and migration. Although there is general consensus about the critical importance of these essential fish habitats (EFH) for fish production along the coast, direct quantitative evidence for their specific roles in population growth and maintenance is still scarce. Nevertheless, for some coastal species, indirect evidence exists, and in many cases, sufficient data are also available to carry out further quantitative analyses. As coastal EFH in the Baltic Sea are often found in areas that are highly utilized and valued by humans, they are subjected to many different pressures. While cumulative pressures, such as eutrophication, coastal construction and development, climate change, invasive species and fisheries, impact fish in coastal areas, the conservation coverage for EFH in these areas remains poor. This is mainly due to the fact that historically, fisheries management and nature conservation are not integrated neither in research nor in management in Baltic Sea countries. Setting joint objectives for fisheries management and nature conservation would hence be pivotal for improved protection of EFH in the Baltic Sea. To properly inform management, improvements in the development of monitoring strategies and mapping methodology for EFH are also needed. Stronger international cooperation between Baltic Sea states will facilitate improved management outcomes across ecologically arbitrary boundaries. This is especially important for successful implementation of international agreements and legislative directives such as the Baltic Sea Action Plan, the Marine Strategy Framework Directive, the Habitats Directive, and the Maritime Spatial Planning Directive, but also for improving the communication of information related to coastal EFH among researchers, stakeholders, managers and decision makers. In this paper, efforts are made to characterize coastal EFH in the Baltic Sea, their importance and the threats/pressures they face, as well as their current conservation status, while highlighting knowledge gaps and outlining perspectives for future work in an ecosystem-based management framework.

Shallow nearshore habitats are highly valued for supporting marine ecosystems, but are subject to intense human-induced pressures. Mesopredatory fish are key components in coastal food webs, and alterations in their abundance may have evident effects also on other parts of the ecosystem. The aim of this study was to clarify the relationship between the abundance of coastal mesopredatory fish, defined as mid-trophic level demersal and benthic species with a diet consisting predominantly of invertebrates, and ambient environmental variables in a fjord system influenced by both eutrophication and overfishing. A field survey was conducted over a coastal gradient comprising 300 data points sampled consistently for fish community and environmental data. Results from multivariate and univariate analyses supported each other, demonstrating that mesopredatory fish abundance at species and functional group level was positively related to the cover of structurally complex vegetation and negatively related to eutrophication, as measured by water transparency. Contrary to other studies showing an inverse relationship to piscivore abundance over time, the spatial distribution of mesopredatory fish was not locally regulated by the abundance of piscivorous fish, probably attributed to piscivores being at historically low levels due to previous overfishing. Mesopredatory fish abundance was highest in areas with high habitat quality and positively related to the abundance of piscivores, suggesting a predominance of bottom-up processes. We conclude that, in parallel with ongoing regulations of fishing pressure, measures to restore habitat function and food web productivity are important for the recovery of coastal fish communities in the area. Electronic supplementary material The online version of this article (doi:10.1007/s00227-016-2977-9) contains supplementary material, which is available to authorized users.

Many fish species in the Baltic Sea are dependent on shallow and sheltered near-shore habitats for their spawning, nursery, feeding and migration. Still, the role of these essential fish habitats, ...

In many temperate estuarine areas, ongoing climatic changes are expected to lead to higher seawater temperatures, to increased inflow of freshwater and nutrients (due to increased rainfall) and to altered light conditions. During the last two decades, several winters have been unusually mild in southern Finland, and the subsequent springs have been early. This may have consequences for the seasonality of many species, including the bladder-wrack, Fucus vesiculosus, whose reproductive cycle may be especially sensitive. In the present study, F. vesiculosus receptacles from the field were weighed regularly during three warm (early) springs and compared with receptacles from three cold (late) springs. On average, the first sign of receptacle growth in the field occurred 5–6 weeks earlier and receptacles probably matured 2–3 weeks earlier during the warm springs than during the cold springs. This may be due to differences in seawater temperatures among years, but significantly heavier receptacles at 0.8 m compared to at 3.1 m further suggests the importance of light for receptacle growth as a measure of maturation, since there were no depth-related differences in seawater temperatures. Also, when plotting receptacle wet weights against seawater temperatures, the importance of light can be seen as different regression relationships (slopes and intercepts). In an outdoor aquarium experiment, the effects of temperature and light on receptacle growth were also tested, and there were significant differences between shallow and deep specimens, but temperature and light had no effects, except on initial receptacle growth. Since oogonian development, and thereby the time for zygote release, followed the receptacle growth curve, this could mean a mismatch between the timing of F. vesiculosus zygote settlement and the cover of competing filamentous algae, but such species interactions require further investigations in order to better understand their possible consequences.

Spatiotemporal distribution patterns in relation to feeding behavior of herbivorous gastropods have been studied extensively, but still knowledge about small-scale patterns is limited in relation to eutrophication. This experimental study aimed to describe the small-scale distribution of Littorina littorea in nutrient-enriched and nutrient-unenriched mesocosms in a merely atidal region and relate the distribution to food abundance and possible competing organisms, while checking simultaneously for feeding activities. The latter part was accomplished through the “gut fluorescence technique” GFT (which, to our knowledge, has not previously been used for benthic grazers) to estimate per capita grazing rates and the former part through monitoring of spatial heterogeneity of L. littorea and co-variation with sessile organisms (using semivariograms and cross-semivariograms, respectively). After 5 months of nutrient addition, the abundance and biomass of L. littorea had increased in enriched systems, which also had significantly higher total biomass of green algae. Gut pigment content was higher in L. littorea from enriched mesocosms, and gut depletion rate was higher in L. littorea from unenriched mesocosms. Spatial analysis showed that L. littorea exhibited generally random patterns (suggesting feeding activities) but sometimes (often in the morning) spatial patchiness (clumped distribution) in both enriched and unenriched conditions. There was mainly positive co-variation between L. littorea and biofilm, while different nutrient conditions exhibited contrasting co-variation between L. littorea and barnacles (positive co-variation in enriched and negative co-variation in unenriched mesocosms). The study offered insights into how feeding behavior and spatial distribution of a species may interact with community components differently under different nutrient regimes. The applied methodology can be useful for purposes of faster examination of grazing effects among different regions and also to compare grazing intensities and interactions between grazers and the benthic communities in disturbed (including pollution and nutrient enrichment) and non-disturbed systems, as well as in up-welling versus non-upwelling areas.

To predict the risk associated with future introductions, ecologists seek to identify traits that determine the invasiveness of species. Among numerous designated characteristics, tolerance towards environmental stress is one of the most favored. However, there is little empirical support for the assumption that non-native species generally cope better with temporarily unfavorable conditions than native species. To test this concept, we ran five pairwise comparisons between native and non-native marine invertebrates at temperate, subtropical, and tropical sites. We included (natives named first) six bivalves: Brachidontes exustus and Perna viridis, P. perna and Isognomon bicolor, Saccostrea glomerata and Crassostrea gigas, two ascidians: Diplosoma listerianum and Didemnum vexillum as well as two crustaceans: Gammarus zaddachi and G. tigrinus. We simulated acute fluctuations in salinity, oxygen concentration, and temperature, while we measured respiration and survival rates. Under stressful conditions, non-native species consistently showed less pronounced deviations from their normal respiratory performance than their native counterparts. We suggest that this indicates that they have a wider tolerance range. Furthermore, they also revealed higher survival rates under stress. Thus, stress tolerance seems to be a property of successful invaders and could therefore be a useful criterion for screening profiles and risk assessment protocols.

Despite their central roles in ecology, patterns and scales of variation in the distribution of species and their densities are seldom satisfactorily described for most ecosystems. This is mainly due to spatial structures being scale-dependent across broad ranges of scales with partly different processes operating at different scales. In this study, scale-dependent distributional patterns in soft- sediment macrofaunal communities of naturally low species richness were studied on the Aland Islands, northern Baltic Sea, in 3 model areas (I, II and III) representing different environmental regimes with regard to openness (water renewal rate), depth, and organic and nutrient content as well as an increasing intrasite variability. A systematic grid design comprising 64 biotic and 16 abi- otic sampling points, hierarchically arranged at 3 (at distances 10, 100 and 1000 m) and 2 spatial scales (100 and 1000 m), respectively, was used in each area. The intrasite distribution of macrofauna was predictably the most uniform in Area I, the least variable environmentally, followed by Area II, which was intermediate with respect to both abiotic and biotic variability, and then Area III, which was always the most variable area. This was true when analysed by both univariate and multivariate statistical means. When examining the contribution of each spatial scale to the total variance, most variability was observed at the smallest sampled level (10 m) for the majority of the studied variables. Despite a high overlap in species composition, the areas differed significantly in animal community structure. This was driven by both (1) the top-dominant species (Macoma, Mytilus, Monoporeia, Oligochaeta, Marenzelleria) and (2) the proportion and distribution of rare species. These systems with low diversity showed clear species distribution patterns driven by local environmental condi- tions, but also showed a substantial biotic component seen as the proportion and role of rare species and the high spatial variability observed at the smallest scale. Our understanding of spatial variabil- ity (or 'stability') is thus influenced by both the habitat and the species composition. The results are valuable for the refinement of sampling design, improved interpretation of monitoring programs (including detection of anthropogenic impact) and incorporation of scaling issues into questions of marine biodiversity and conservation.

The littoral zone of temperate rocky shores is normally dominated by perennial macroalgae (e.g. Fucus, Ascophyllum, Laminaria), but nutrient enrichment and/or permanently decreased wave action may lead to structural community changes from dominance of perennials to increased amounts of annual opportunistic species (mainly green algae). Macroalgal biomass, diversity and production as well as relationships between the two latter were studied using Solbergstrand’s rocky shore mesocosms in SE Norway in connection with a long-term experimental manipulation of nutrient addition and wave action (high and low levels of both factors applied in a crossed way to eight outdoor basins). After more than 2 years of experimental treatment, the total standing stock of macroalgae was larger in low nutrient than in high nutrient treatments as well as in high wave compared to low wave treatments (in autumn only). For macroalgal functional groups, bushy and filamentous brown and filamentous red algae were generally favoured by low nutrient concentrations, while annual filamentous and sheet-like green algae were stimulated by the nutrient enrichment. There was only one significant interaction between nutrient enrichment and wave action (for brown filamentous algae in autumn) and also only one significant main effect of the wave treatment (for bushy brown algae in autumn). Surprisingly, the high nutrient treatments supported a higher diversity of macroalgae, whereas the low nutrient treatments generally showed higher production rates. Moreover, significantly negative correlations were found between macroalgal diversity and primary productivity in both summer and autumn. This study shows that it is the biological components of the communities subjected to external forcing (nutrient addition or decreased wave action) that regulate production and this contradicts the common misperception that resource production in natural systems simply can be fast-forwarded by fertilization. The negative relationships between diversity and productivity, although a consequence of unexpected results for diversity and production, are also novel and hint towards species identities having more important functional consequences than general species dominance patterns and the amount of species per se. These results also emphasise the context dependency of findings within the field of biodiversity and ecosystem functioning.

A high degree of resistance against nutrient enrichment has previously been demonstrated for macroalgal-dominated rocky shore communities in the presence of moderate to large amounts of macroinvertebrate grazers. To experimentally examine, under controlled conditions, the possible roles for this resistance of two other factors, i.e. disturbance (presence/absence of the macroalgal canopy itself) and wave action, the canopy algae and associated algal and animal assemblages were removed by scraping from approximately one third of the area of eight littoral mesocosms, subjected to two different wave action regimes. After this, excessive nutrients were added to four mesocosms with the factor nutrients fully crossed with the factor wave action with two replicate mesocosm basins of each nutrient/wave treatment combination. Disturbance was added to the design as a within-basin factor thus making up a split-plot experiment. The abundance of grazers was allowed to vary freely and under the influence of the treatments. After 11 summer weeks, there were significant differences in community structure between nutrient enrichment levels for both algal and animal assemblages when examined by multivariate statistical techniques. Univariate analyses confirmed a significantly stimulated colonisation by green algae, mainly Ulva lactuca , in both disturbed (scraped) and undisturbed areas of nutrient-enriched mesocosms. In un-enriched mesocosms, the green algae were absent from undisturbed areas and rare in disturbed areas, where mainly brown Ectocarpus spp. and red algae had settled. Among the macrofauna, the total abundance of grazers was stimulated in nutrient-enriched mesocosms with individuals of the amphipod genus Gammarus and the isopod genus Jaera being especially numerous. With regard to wave action, no significant differences occurred in community structure, although there were indications of significant nutrient × wave effects for both the amount of exported red algae and the amount of accumulated brown algae. The study shows that eutrophication-related community shifts on rocky shores may occur very rapidly, regardless of the level of wave-energetic stress and the abundance of grazers, if the nutrient concentrations are high and the colonisation and growth of opportunistic algae are facilitated by disturbance such as (naturally or anthropogenically driven) canopy gap forming processes.

During the reproduction period of Fucus vesiculosus, which occurs only once a year (in May–June) along the Finnish coast of the northern Baltic Sea, a thick carpet of filamentous algae often covers hard substrates suitable for zygote settlement. By placing out artificial substrates into the field, monthly over a period of eight months prior to F. vesiculosus settlement (October 2001–June 2002), we investigated the autumn/winter/spring colonisation and succession of filamentous algae and their possible relationships with the settlement success of F. vesiculosus under naturally variable field conditions. The substrates exposed in October 2001 became covered by filamentous brown algal Pilayella littoralis mats, which persisted over the settlement period of F. vesiculosus, but now also were accompanied by large amounts of the filamentous green alga Cladophora glomerata. The substrates exposed from November 2001 onwards hosted smaller amounts of P. littoralis during the winter and different filamentous algal communities at the time of F. vesiculosus settlement, i.e. less P. littoralis and C. glomerata, but Dictyosiphon foeniculaceus, Ceramium tenuicorne and Ulva intestinalis instead. We observed recruits of F. vesiculosus on all substrates, except on the ones placed out in October 2001. Significantly more P. littoralis and C. glomerata on the October substrates may explain the failed F. vesiculosus recruitment, although we could not establish direct causal or correlational relationships between filamentous algae and F. vesiculosus settlement. We compared the results with a previous un-replicated pilot study in the same area demonstrating similar response patterns.

Since her shipwreck in 1771, the wooden vessel Vrouw Maria has been lying on the seabed at 41. m depth on the border between the Archipelago Sea and the northern Baltic proper, off the southern coast of Finland. The wreck lies in an upward position in a right angle to the dominating bottom current, which is potentially affecting seabed topography, sediment characteristics and zoobenthic communities both upstream (NE) and downstream (SW) of the wreck. This multidisciplinary study attempts to clarify abiotic and biotic patterns and processes in the vicinity of the wreck by combining field investigations with physical simulation studies in the field and in the laboratory. Multibeam echo-sounder techniques were utilised to generate a map of the wreck area and sediment grab samples were taken to characterize the sediment type and its zoobenthic community. A medium-sized field experiment generated data on the accumulation of sediment organic matter in the presence and absence of a current and/or a barrier on the seafloor and a small-scaled laboratory study was conducted to simulate scour forming processes. The results showed that a deeper basin, scour area, with the dimensions 150×300m, was present downstream of the wreck and there was also a smaller scour area upstream of the wreck. Similar traces on the bottom were simulated in the laboratory. The organic content (recent mud) and the proportion of finer sediment were more pronounced in areas closer to both sides of the wreck. These results were in turn imitated in a field experiment, where the accumulation of organic matter in the sediment increased significantly downstream, when a current was interrupted by a barrier. Regarding zoobenthos in the wreck area, 11 taxa and a mean total abundance of 773 individuals per m2 were registered. The dominant species were Macoma balthica and Marenzelleria sp., which together made up >80% of the total number of individuals. Multivariate data analyses showed significant differences in community structure between upstream and downstream sides of the wreck and these differences were basically expressed as more individuals upstream of the wreck of the seven most common species. Univariate data analyses also showed significantly more species and higher total abundance in the scour area upstream of the wreck compared to the downstream scour area. The weakened communities downstream of the wreck were possibly due to accumulation of organic matter and more frequent occurrence of hypoxia. The results are useful for describing bottom areas around long-term physical barriers/artificial reefs, as background measurements ahead of possibly increased archaeological diving activities, sediment excavations or measures taken to raise the wreck to the surface, as well as for any attempts to preserve the wreck in situ.

Coastal eutrophication may alter the dominance patterns of marine macroalgae, with potential consequences for the associated fauna and the entire ecosystem. Benthic macroalgae and animals in control and nutrient-enriched mesocosms were monitored to investigate eutrophication-induced changes in rocky shore communities. During a 3-year project, nutrient addition had only minor effects on the community structure, such as increased cover and biomass of green Ulva spp. and increased abundance of certain animal species at high nutrient levels. This study is a 4-year extension of a previously reported project, with 2 extra years of effect studies (altogether 5 years) and a subsequent 2 years for recovery. During the 4th year of nutrient enrichment, the cover of Fucus vesiculosus and Fucus serratus started to decline. In the 5th year, these canopy species crashed and there was an evident take-over by green algae at high nutrient addition levels. The previously observed abundance stimulation for fauna disappeared later in the time series, probably due to the loss of the macroalgal canopy. After less than 2 years on regular seawater, the algal and animal communities had returned to within the range of normal variability. The results indicate that established rocky shore communities of perennial algae with associated fauna are able to persist for several years, even at very high nutrient levels, but that community shifts may suddenly occur if eutrophication continues. They also indicate that rocky shore communities have the ability to return rapidly to natural undisturbed conditions after the termination of nutrient enhancement.

This study, conducted in mesocosms, natural field sites, and in laboratory aquaria, showed that eutrophication altered the nutrient status and dominance patterns among marine macroalgae, which in turn, stimulated gammaridean density. Gammaridean abundance correlated positively with both nutrient addition and the amount of green algae (also stimulated by nutrient enrichment). Path analysis indicated that the direct effect of nutrients on gammaridean density was of less importance than the indirect effect through increased production of green algae. In cage colonisation experiments, either in the field or in a control mesocosm kept under ambient nutrient conditions, more gammarids colonised nutrient enriched algae (E-algae) than algae with ambient nutrient levels (A-algae). Gammarus locusta generally grew faster on nutrient enriched algal specimens and when reared on green rather than on brown algae (fucoids). The nutrient status of periphytic algae did not affect gammaridean growth significantly, but the number of egg-carrying females (and thus egg production) was significantly higher among gammarids reared on E-periphyton. The gammaridean habitat preference order (red > green > brown > periphyton) was almost the reverse of their growth rate in feeding assays (periphyton > green > brown). This implies that macroalgae may be more important as a habitat than as a food source for these animals, which then have to become mobile in search of optimal food items. In this process, algal nutrient content was important as the gammarids in our study actively chose high quality nutrient-rich food, which, in addition, increased their fitness. Stimulated growth rates and egg production may ultimately lead to population increase, which, combined with the preference for high nutrient food items may dampen the initial effect of nutrient enrichment (i.e. blooms of green macroalgae) in shallow coastal waters.

The number of human-mediated marine introductions is constantly growing globally, and whenever a non-indigenous species survives the most critical filters it encounters, such as tolerance to conditions during transport and survival in the new habitat with novel species interactions (Elton 1958; Mack et al. 2000; Lenz et al. 2011; Sareyka et al. 2011), it may become permanently established and in the worst case proceed to impose clearly negative impacts on its new surroundings. One such introduction may be exemplified by the common periwinkle, Littorina littorea, which supposedly was introduced to the NW Atlantic from Europe in the 1840s as a food source or in rock ballast (Chapman et al. 2007). Now, L. littorea constitutes one of the most abundant mollusks in its invaded NE American range with extensive ecological effects such as reduced recruitment of algae and invertebrates as well as generally altered rocky shore community structure and diversity (see Harley et al. 2013 for references, and Diaz et al. 2012 for more on its effects in its native European range). During the past few decades, L. littorea has also appeared in several locations on the North American Pacific coast (see Harley et al. 2013 for references), although it does not yet seem to be self-recruiting (Chang et al. 2011). This time, the main vector is probably the export of live seafood followed by people’s diverse reasons (ethical and religious considerations or a personal desire to establish a harvestable resource) for releasing living snails (Harley et al. 2013). Why are then some introductions immediately successful, while others are not? Understanding the factors restricting the establishment of a species is arguable one of the holy grails of invasion biology, and the unique opportunity to focus on a species that seems likely to establish, but has not yet done so, is very exciting from an strictly ecological point of view (e.g. Stachowicz et al. 2002), despite all the possible downsides associated with a permanent establishment. In their original article, Harley et al. (2013) provides a comprehensive case study of the current status for L. littorea in Vancouver, where L. littorea has been found only at a couple of sites, without detectable community impact, this far. Whenever encountered, the species has been eradicated by the authors and co-workers, and to date, L. littorea has not been found again during repeated revisits over the past 1.5 years. Regarding the collected individuals, their morphology and the presence of possible hitchhikers were examined and compared to market snails. The laboratory examination indicated that the field specimens likely originated from the live seafood trade and that cooccurring organisms, living on the gastropod shells and as gut parasites, could still be introduced even if a L. littorea introduction would fail. A set of experiments, focusing on potential future success and impact of L. littorea, like comparing its grazing effects with those of a native gastropod, determining its survival under low salinity and its susceptibility to native predators, rendered significant and interesting results. L. littorea had a similar dietary preference as the native gastropod Chlorostoma funebralis suggesting possible competition. L. littorea was also capable of surviving at seasonal low salinity in the area. Most Communicated by U. Sommer.

The substitution of canopy-forming perennial algae by annual filamentous algae is a common phenomenon on eutrophicated rocky shores with potential consequences for marine biodiversity. In the upper littoral of the northern Baltic Sea, this process is exemplified by decreased occurrence of the brown alga Fucus vesiculosus and increased amounts of filamentous algae (e.g. Cladophora glomerata and Pilayella littoralis). In this study, macrofauna communities of F. vesiculosus and C. glomerata during summer have been compared and the effects on littoral macroinvertebrates of a total or partial replacement of F. vesiculosus by C. glomerata have been estimated. The animal abundance and biomass were higher in C. glomerata than in corresponding amounts of F. vesiculosus (g dwt). Similar results were also obtained when animal abundance and biomass were extrapolated to algal cover per m 2 rocky substrate in the study area. Margalef’s species richness was, on the other hand, higher in F. vesiculosus, whereas the Shannon–Wiener diversity was the same. The results indicate that C. glomerata maintains a high diversity of macroinvertebrates in the upper littoral zone of the northern Baltic Sea during summer. A possible substitution of F. vesiculosus by C. glomerata does not immediately affect macroinvertebrate diversity negatively in the littoral zone, although, it is difficult to assess the full consequences due to lack of comparable algal data at wider temporal and spatial scales. 2004 Elsevier Ltd. All rights reserved.

Opportunistic filamentous algae are known to increase due to elevated nutrient levels (eutrophication) and to outcompete slow-growing perennial macroalgae in shallow coastal areas causing severe shifts in algal communities and habitat changes for the associated fauna. When the algae detach from the primary substrate and form sublittoral drifting mats, oxygen deficiency occurs frequently. We investigated the temporal succession of macrofauna in attached and loose-lying Cladophora glom-erata to establish the role of this transient substrate. We also conducted a series of aquarium experiments using clean sea-water and water from fresh and decaying C. glomerata to study preferences among juvenile and adult crustaceans (Gammarus spp. and Idotea baltica). Both attached and loose-lying littoral Cladophora glomerata hosted rich macrofauna assemblages with significantly higher faunal abundance and biomass among the attached algae and clear temporal trends. The dominant taxa were the gastropods Hydrobia sp...

Most conceptual marine eutrophication models predict that ephemeral and epiphytic macroalgae will become substantially more abundant with increasing nutrient richness. This expectation is based on the fact that most of these fast-growing algae possess high requirements for inorganic N and P and, therefore, suffer from nutrient limitation under nutrient poor conditions. We tested the hypothesis that nutrient enrichment will stimulate the abundance of ephemeral macroalgae by studying the abundance and species composition of these algae on several types of substrata along an artificial nutrient gradient. The total biomass of ephemeral macroalgae differed considerably among different types of substrata. The total ephemeral load was significantly higher on consolidated substrata than on large perennial algae, but we were unable to detect any systematic increase in the abundance of these ephemerals with increasing nutrient richness. We found, however, indications that the composition of the ephemeral assemblage changed with nutrient richness. Hence, corticated filamentous algae (mostly red algae) were more abundant at low nutrient richness while thin foliose algae (mainly green species) tended to become more abundant with increasing nutrient richness in most of the surveyed assemblages.

The relationship between biodiversity and stability of marine benthic assemblages was investigated through meta-analyses using existing data sets (n = 28) covering various spatial (m-km) and temporal (1973-2006; ranging from 5 to >250 months) scales in different benthic habitats (emergent rock, rock pools and sedimentary habitats) over different European marine systems (North Atlantic and western Mediterranean). Stability was measured by a lower variability in time, and variability was estimated as temporal variance of species richness, total abundance (density or % cover) and community structure (using Bray-Curtis dissimilarities on species composition and abundance). Stability generally decreased with species richness. Temporal variability in species richness increased with the number of species at both quadrat (

The general utility of large-scale artificial ecosystems for ecological and ecotoxicological research is evaluated by a case study of the replicability, repeatability and ecological realism of a Baltic Sea hard bottom littoral mesocosm (called BHB-mesocosm). The structure (species abundance and biomass listings) of the macrofauna community associated with bladder-wrack, Fucus vesiculosus L., in nine control mesocosms run during 4 separate years, is investigated by descriptive and analytical multivariate statistical techniques. Non-metric multidimensional scaling (NMDS) is used to visualise differences in community structure between mesocosm controls run during the same year (replicability), differences among mesocosms run during different years (repeatability) and differences between mesocosms and the field mother system (ecological realism). Analytically the community structure of parallel mesocosms is shown to differ significantly by use of one-way analysis of similarities (ANOSIM) tests, which demonstrates a poor replicability. Despite this high degree of variability between parallel mesocosms, the null hypothesis of no differences among years can in turn be rejected by a two-way nested ANOSIM for both abundance and biomass data, which is evidence of a poor repeatability. If it is assumed that the field samples taken in connection with the transplantation are representative of the initial situation in the mesocosms, the divergence of the mesocosms from the mother systems was considerable in all years. When all 4 years are used as replicates, i.e. independent observations on dissimilarities between the mother system and the mesocosms after 5 months of enclosure, in a two-way crossed ANOSIM, significant differences for both macrofauna abundance and biomass data are revealed, which is evidence of a poor ecological realism. The similarity percentage breakdown procedure (SIMPER) establishes the species principally responsible for these differences. Considering abundance data Theodoxus fluviatilis is always an important discriminator between groups, mostly accompanied by Mytilus edulis and either Idotea spp. (replicability) or Gammarus spp. (realism). For biomass data Mytilus and Idotea are the most important overall discriminators, followed by Lymnaea spp. (repeatability and realism) and Cerastoderma glaucum (realism). Finally the factors and processes restricting mesocosm performance are outlined and their consequences are briefly discussed. It is concluded that the degrees of replicability, repeatability and ecological realism are too low for straightforward use of these and probably most other mesocosms in predictive risk assessment or in extrapolation of results to natural ecosystems.

The concept of model ecosystem replicability is challenged by a case study of a land-based brackish-water mesocosm. Coefficients of variation (CVs) are calculated for a total of 50 population and community variables between unpolluted control systems, during five separate test years. These CVs are used for calculations of minimum detectable differences (MDDs) for a given number of treatments and replicates at specific levels of statistical significance and power, when analysis of variance (ANOVA) techniques are used. The CVs are also used for calculation of the minimum number of replicates (MNRs) theoretically needed to confirm that a specific deviation from the control is statistically significant. While variables with CVs lower than 20–30% have been regarded both as normal and manageable in mesocosm studies (in economic and practical terms), the mean CV values calculated in this study are generally higher. Exactly half of the studied variables have CVs higher than 60%. Therefore, there will be obvious difficulties in finding statistically significant deviations from the controls even if the test systems are rigorously replicated, the investigated effect sizes are large and the postulated acceptable magnitudes of statistical error are high.

International audience; Compensatory dynamics, overyielding and statistical averaging are mechanisms promoting the temporal stability of natural communities. Using the model of European intertidal rocky shore assemblages and collating 17 datasets, we investigated how the strength of these stability-enhancing mechanisms varies with latitude and how it can be altered by the loss of habitat-formers (e.g. canopy-forming macroalgae). Community stability decreased with increasing latitude, mostly as a consequence of a greater synchronization of species fluctuations. Statistical averaging and overyielding (i.e. richness effect) promoted stability, but their strength did not vary with latitude. An experimental removal of macroalgal canopies caused a strengthening of the statistical averaging effect that was consistent across the latitudinal gradient investigated. Nonetheless, the loss of canopies depressed stability by enhancing the synchronization of species fluctuations on southernmost shores, while it had weak effects on shores at higher latitudes. Variation in life-history traits among canopy-forming species and/or in prevailing environmental conditions across a gradient of latitude could underlie variable effects of habitat-formers on species fluctuations. Our study shows 1) that the stability of intertidal assemblages and strength of compensatory dynamics varies with latitude, 2) that canopy-forming macroalgae, exerting a strong control on understorey species, can influence the strength of compensatory dynamics and 3) that biological forcing (i.e. facilitation) can be as important as environmental forcing in enhancing the synchronization of species fluctuations.

Differences in stress tolerance and reproductive traits may drive the competitive hierarchy between non-indigenous and indigenous species and turn the former ones into successful invaders. In the northern Baltic Sea, the non-indigenous Gammarus tigrinus is a recent invader of littoral ecosystems and now occupies comparable ecological niches as the indigenous G. zaddachi. In laboratory experiments on specimens collected between June and August 2009 around Tvarminne in southern Finland (59°50′N/23°15′E), the tolerances towards heat stress and hypoxia were determined for the two species using lethal time, LT50, as response variable. The brood size of the two species was also studied and some observations were made on maturation of juveniles. Gammarus tigrinus was more resistant to hypoxia and survived at higher temperatures than G. zaddachi. Brood size was also greater in G. tigrinus than in G. zaddachi and G. tigrinus matured at a smaller size and earlier than G. zaddachi. Hence, there are clear competitive advantages for the non-indigenous G. tigrinus compared to the indigenous G. zaddachi, and these may be further strengthened through ongoing environmental changes related to increased eutrophication and a warming climate in the Baltic Sea region.

Species richness is the most commonly used but controversial biodiversity metric in studies on aspects of community stability such as structural composition or productivity. The apparent ambiguity of theoretical and experimental findings may in part be due to experimental shortcomings and/or heterogeneity of scales and methods in earlier studies. This has led to an urgent call for improved and more realistic experiments. In a series of experiments replicated at a global scale we translocated several hundred marine hard bottom communities to new environments simulating a rapid but moderate environmental change. Subsequently, we measured their rate of compositional change (re-structuring) which in the great majority of cases represented a compositional convergence towards local communities. Re-structuring is driven by mortality of community components (original species) and establishment of new species in the changed environmental context. The rate of this re-structuring was then related to various system properties. We show that availability of free substratum relates negatively while taxon richness relates positively to structural persistence (i.e., no or slow re-structuring). Thus, when faced with environmental change, taxon-rich communities retain their original composition longer than taxon-poor communities. The effect of taxon richness, however, interacts with another aspect of diversity, functional richness. Indeed, taxon richness relates positively to persistence in functionally depauperate communities, but not in functionally diverse communities. The interaction between taxonomic and functional diversity with regard to the behaviour of communities exposed to environmental stress may help understand some of the seemingly contrasting findings of past research., JRC.G.4-Maritime affairs

Bokn, Tor L. et al., The aim of this study was to determine whether the experimental nutrient enrichment of littoral rocky shore communities would be followed by a predicted accumulation of fast-growing opportunistic algae and a subsequent loss of perennial benthic vegetation. Inorganic nitrogen (N) and potassium (P) was added to eight concrete mesocosms inhabited by established littoral communities dominated by fucoids. The response to nutrient enrichment was followed for almost 2 1/2 years. Fast-growing opportunistic algae (periphyton and ephemeral green algae) grew significantly faster in response to nutrient enrichment, but the growth of red filamentous algae and large perennial brown algae was unaffected. However, these changes were not followed by comparable changes in the biomass and composition of the macroalgae. The biomass of opportunistic algae was stimulated only marginally by the nutrient enrichment, and perennial brown algae (fucoids) remained dominant in the mesocosm regardless of nutrient treatment level. Established rocky shore communities thus seem able to resist the effects of heavy nutrient loading. We found that the combined effects of the heavy competition for space and light imposed by canopy-forming algae, preferential grazing on opportunistic algae by herbivores, and physical disturbance, succeeded by a marked export of detached opportunistic algae, prevented the fast-growing algae from becoming dominant. However, recruitment studies showed that the opportunistic algae would become dominant when free space was available under conditions of high nutrient loading and low grazing pressure. These results show that established communities of perennial algae and associated fauna in rocky shore environments can prevent or delay the accumulation of bloom-forming opportunistic algae and that the replacement of long-lived macroalgae by opportunistic species at high nutrient loading may be a slow process. Nutrient enrichment may not, in itself, be enough to stimulate structural changes in rocky shore communities.

Macrofauna secondary responses to controlled eutrophication within two MARICULT/MAST-III projects, EULIT and COMWEB, are compared. EULIT utilises a nutrient gradient established in eight hard bottom mesocosms, whereas the data from COMWEB originate from a whole-ecosystem study – the case of experimental nutrient addition to Hopavagen lagoon. In both systems, nutrient addition started in May 1998, after initial studies of the background macrofauna communities, thus allowing application of Before-After-Control-Impact-Pairs techniques (BACIP). The main objectives have been to investigate the macrofauna responses to eutrophication in littoral rocky shore ecosystems and to evaluate if similar responses could occur in mesocosm and `field' systems, despite their inherent differences. Apart from a distinct increase in numbers of Littorina littorea L. and some indications of increased abundance of the genus Jaera, no significant changes, caused by 2.5 years of nutrient addition, could be detected in the mesocosm fauna. It is interesting, however, that these two possibly stimulated animal groups have two things in common: (1) both belong to the rather few mobile taxa, which are not flushed out of the system through the mesocosm outlets, (2) both feed on microalgae and green algae in the upper littoral zone, i.e., algal groups that have shown the clearest response to the nutrient addition. In Hopavagen, 1.5 years of nutrient addition only caused modest plant and animal responses in the rocky shore ecosystem, although there was a markedly increased settlement of Mytilus edulis L. at one lagoon site. This increase was probably due to elevated levels of digestible particles (increased phytoplankton production) caused by the nutrient addition. There were also some indications of increased production of filamentous algae at this same lagoon site. All in all, both studies demonstrate only minor responses to increased nutrient levels within the littoral community (both plants and animals). One explanation to this may be that longer time-scales are needed in order for clear-cut changes to occur. Several observations also indicate that wave exposure (significant in both systems) may largely modulate the impact of increased nutrient load on the structure of littoral communities. Another explanation is the high degree of stability among littoral macroalgae-dominated communities with internal biological regulation factors (like grazing) possibly being able to counteract effects.

Long-term changes in sediment macrofauna communities at two sites affected by fish farming in the Archipelago Sea, south-west Finland have been investigated. Sampling stations in the Sarkansalmi Strait and Kaukolanlahti Bay, previously investigated 1982-1991, were revisited in 1994, 1995 and 1998 to detect signs of recovery following a decrease in organic load since 1990 and 1991, respectively. The results indicate a partial recovery in Sarkansalmi during post-pollution years, whereas no improvement has taken place in Kaukolanlahti. The improvement in Sarkansalmi is shown by a significant increase in the number of species and total abundance, and by the community structures becoming more similar over time. On the other hand, a significantly decreased number of species, abundance and biomass values over time as well as the occurrence of defaunated anoxic sediments, are clear signs of continued deterioration in Kaukolanlahti. Differences in the recovery potential of the two water areas are interpreted as consequences of topography and water exchange patterns causing differences in oxygen saturation.