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IntroductionEcosystem engineers play a pivotal role in shaping habitats through their activities and presence. In shallow Baltic waters, seagrasses, patch-forming mussels, and infaunal clams modify soft bottom habitats, impacting benthic community structure. While the individual effects of these ecosystem engineers are well studied, interactions among co-occurring engineers are poorly understood. MethodsWe conducted a mesocosm experiment to assess the independent and combined impacts of seagrass (Zostera marina), epifaunal mussels (Mytilus spp.), and infaunal clams (Macoma balthica) on invertebrate colonization in soft sediments. ResultsOur findings reveal significant engineer-driven alterations in macrofaunal community structure. Combined engineer effects diverged from individual impacts, indicating potential synergies or antagonisms in sediment (re)colonization. Notably, a higher number of engineer species positively affected the diversity of settled macrofauna, with the lowest macrofaunal abundance and biomass but the highest Shannon diversity found in the presence of all three engineers. DiscussionResults suggest that seagrass, mussels, and clams influence benthos through larval settlement and sediment biogeochemistry, providing insights into the distinct roles of habitat-forming organisms in shaping the benthic communities in coastal ecosystems of the Baltic Sea.

Responses to potentially dangerous stimuli are among the most basic animal behaviors. While research has shown that threats automatically capture the attention of human participants, research has failed to demonstrate automatic behavioral responses to threats in humans. Using a novel naturalistic paradigm, we show that two species of animals humans often report fearing trigger rapid withdrawal responses: participants withdrew their arm from photos of snakes and spiders faster, and with higher acceleration when compared to bird and butterfly stimuli. The behavior was specific to withdrawal as approach movements or button-press/release tasks failed to detect a similar difference. Moreover, between-participant differences in how aversive they found the stimuli predicted the participant's withdrawal speed, indicating that the paradigm was also sensitive to trait-level differences between individuals. Using electroencephalography (EEG), we show that the fast withdrawal was mediated by two attentional processes. First, fast withdrawal responses were associated with early amplification of sensory signals (40–110 ms after stimulus). Second, a later correlate of feature-based attention (early posterior negativity, EPN, 200–240 ms after stimulus) revealed the opposite pattern: Stronger EPN was associated with slower behavioral responses, suggesting that the deployment of attention towards the threatening stimulus features, or failure to “disengage” attention from the stimulus, was detrimental for withdrawal speed. Altogether, the results suggest that rapid behavioral withdrawal from a threatening animal is mediated by reflex-like attentional processing, and later, conscious attention to stimulus features may hinder escaping the treat.

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.

Despite many theories, the recent evident decreases in blue mussel (Mytilus edulis) abundance in southern Norway and western Sweden (eastern North Sea) have not yet been explained. To test the possible role of increased predation, an ongoing mesocosm experiment exploring general effects of two mesopredators on the structure of littoral macroalgal and macrofaunal communities was used. These mesopredators were the green crab (Carcinus maenas) and the goldsinny wrasse (Ctenolabrus rupestris) which were distributed in a crossed manner to 12 large mesocosms containing diverse rocky shore communities. For the purposes of this study, boulders covered with recently recruited blue mussels and barnacles (Balanus improvisus) from a natural shore were brought in to the mesocosms during two seasons (August and October), and the coverage of the animals (just blue mussels in summer, both mussels and barnacles in autumn) was registered repeatedly over 24 h. The mussels were rapidly consumed by crabs and wrasses, whereas high survival was recorded on boulders in the controls without predators. The barnacles were only eaten by the crabs and not before most of the mussels had been consumed. As both the green crab and the goldsinny wrasse have been reported to increase in abundance, probably related to overfishing of top predators, the resulting higher predation pressure on especially small blue mussels (recruits) may contribute to the mussel decline along these temperate rocky shores.

Abstract In the course of the ongoing global intensification and diversification of human pressures, the study of variation patterns of biological traits along environmental gradients can provide relevant information on the performance of species under shifting conditions. The pronounced salinity gradient, co‐occurrence of multiple stressors, and accelerated rates of change make the Baltic Sea and its transition to North Sea a suitable region for this type of study. Focusing on the bladderwrack Fucus vesiculosus, one of the main foundation species on hard‐bottoms of the Baltic Sea, we analyzed the phenotypic variation among populations occurring along 2,000 km of coasts subjected to salinities from 4 to >30 and a variety of other stressors. Morphological and biochemical traits, including palatability for grazers, were recorded at 20 stations along the Baltic Sea and four stations in the North Sea. We evaluated in a common modeling framework the relative contribution of multiple environmental drivers to the observed trait patterns. Salinity was the main and, in some cases, the only environmental driver of the geographic trait variation in F. vesiculosus. The decrease in salinity from North Sea to Baltic Sea stations was accompanied by a decline in thallus size, photosynthetic pigments, and energy storage compounds, and affected the interaction of the alga with herbivores and epibiota. For some traits, drivers that vary locally such as wave exposure, light availability or nutrient enrichment were also important. The strong genetic population structure in this macroalgae might play a role in the generation and maintenance of phenotypic patterns across geographic scales. In light of our results, the desalination process projected for the Baltic Sea could have detrimental impacts on F. vesiculosus in areas close to its tolerance limit, affecting ecosystem functions such as habitat formation, primary production, and food supply.

In eight mesocosms (land based basins) macroalgae communities with associated fauna were transplanted from the sea and established during two years. Then, different doses of nutrients (N and P) were added to the basins throughout the following three years. During the period of nutrient addition, macroinvertebrate grazers showed seasonal fluctuations with densities usually between 500,000 and 1 million individuals per mesocosm during summer and to a level of about 100,000 during winter. The macroinvertebrate grazers mainly consisted of about 10 species of amphipods and isopods, among which the amphipod Gammarus locusta dominated strongly by biomass. Although the number of predators was very low, the grazer populations never reached a density where considerable grazing impact could be found on the macroalgae. No increase in grazer density was found in the basins with improved nutrient conditions. Thus food quality may be insufficient for further population growth, or density dependant regulation mechanisms may have prevented the grazers from flourishing and overgrazing the system. In aquarium experiments we showed that G. locusta could grow and reproduce on Fucus serratus, Ulva lactuca, periphyton and detritus, and that cannibalism by adult G. locusta on juveniles may have great impact on the population growth. The basins were run with a water flow through system. Nets were placed in front of the inflow and outflow tubes to measure immigration and emigration. Only few individuals (and no Gammarus sp.) were recorded in the inflowing water, while high numbers of both amphipods and isopods were found in the outflowing water. Emigration reached peak values during night-time, and it was then two to three times as high as during day-time. Emigration of mobile grazers from the basins amounted to 1-2% of the standing stock daily. These mechanisms that regulate grazers do contribute to maintenance of the seaweed dominance and thus the stability of the seaweed community.

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.

The use of blue mussel farming in the Baltic Sea for mitigating eutrophication through nutrient bioextraction has recently been under debate, with emphasis on potential local negative effects induced by farmed mussels, based on theoretical scenarios. Here, we broaden the discussion by presenting an assessment of the faunal community around a noncommercial mussel farm, after two years of operation in a relatively well-oxygenated water area. It is the first large-sized farm (25 tonnes) in the northern Baltic proper. The biotic conditions at this mussel farm did not deviate negatively from the surrounding reference areas. The total abundance and species richness of sediment-dwelling fauna were higher at the farm site, which also showed a distinct zoobenthic species composition including many bioturbators which may provide extra protection against hypoxia. A snapshot view of water quality indicated relatively low P and chlorophyll-a concentrations at the farm. We caution against drawing conclusions from our study that are too far-reaching primarily because the mussel farm in question being smaller than those referred to in the debate. However, the study presents an important initial assessment of the functioning of a pilot mussel farm in the Baltic proper and provides baselines for future investigations and guidelines for improved sampling design. [ABSTRACT FROM AUTHOR]

Many studies worldwide have emphasized the need to mop the potential of commercial ports to function as receiver and donor areas for nonindigenous species (NIS). In this study, the macroinvertebrate composition of hard and soft sea bottoms, hydrographical conditions, and traffic connections of fonr Finnish coastal harbours (Naantali, Koverhar, Porvoo, Hamina) were investigated and compared with 'natural' reference areas lacking anthropogenic constructions. The harbours hosted macroinvertebrate communities fairly similar to those found in adjacent reference areas, but sediment community diversity was slightly higher in harbour basins relative to in surrounding areas. A total of eight NIS were registered in the study. With regard to hydrography, NIS that tolerate low salinities, low temperatures and eutrophic conditions are most likely to survive local conditions and hence pose a potential risk for larger areas of the Baltic Sea. A ship traffic analysis revealed that the most important donor and recipient areas of ballast water to and from the study harbours are coastal harbours of other parts of the Baltic Sea and of the North Sea. Some suggestions are made for future harbour surveys along the Finnish coast. [ABSTRACT FROM AUTHOR]

Plants are referred to as calciphilic (calcicole) or acidophilic depending on their relation to lime. We censused the vascular plant flora on seven shell gravel deposits from the Littorina Age and in two reference areas with naturally high species richness on the Åland Islands, assuming that a higher proportion of calciphilic plants would be found on the shell gravel deposits than elsewhere. Both the total number of plants and the number of calciphiles showed a significant positive correlation with the calcium (Ca) concentrations of the soils, but the highest number of species and proportions of calciphilic species were not found on shell gravel, but at intermediate to high Ca-levels in areas affected by man and domestic animals. We did not observe a strong influence of Ca on the species distribution patterns, otherwise than possibly indirectly via a raised pH-value. On the contrary, the strongest explanatory environmental variable seemed to be phosphorus, P. This in turn raises further questions: Should we rather use the world alkaphilic? Are plants Ca-dependent or Ca-tolerant? Could the whole story be about P and not Ca? When switching the analytical focus sites to species, Ca-neutral species were on average found at more sites than moderately or strongly calciphilic species. In a species-based ordination, the calciphiles also clustered significantly differently from the Ca-neutral species, both when analysing all species simlutaneously and when analysing a subset of the most widely distributed species. The exact meaning of this is hard to evaluate, but it may give a hint that many calciphiles could be poor generalists and that the Ca concentration not always was sufficiently high at all shell-gravel sites. It also demonstrates the functionality of dividing species into these four groups with regard to Ca dependency, especially if the Ca-neutral group solely consists of acidophilic species. This is also in support for a continuing use of calciphilic plants as indicators for rough assessments or initial screenings of plant diversity in applied conservation. [ABSTRACT FROM AUTHOR]

• Presents a flexible ecosystem-based framework for compensating habitat deterioration. • Integration with cascade model allows a structured selection of compensation options. • In-kind compensation on-site is the preferred option. • Compensating ecosystem structure has best potential to capture non-instrumental values. • Considering the spatial extent of benefits may increase flexibility in compensation schemes. 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. [ABSTRACT FROM AUTHOR]

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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier B.V.)

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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2019 The Authors. Published by Elsevier B.V. All rights reserved.)

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., (Copyright © 2011 Elsevier Inc. All rights reserved.)

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.