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Farming of extractive species such as filter feeding bivalves has been proposed as a potential method to mitigate impacts of eutrophication in marine environments. For such efforts to be sustainable, potential negative effects from mussel farms, such as accumulation of biodeposits in sediment below them, need to be considered and addressed. Benthic burrowing macrofauna strongly influence biogeochemical processes in soft bottom marine habitats by sediment reworking and irrigation and, thus, have the potential to mitigate some of the negative impacts. However, not all biodeposits are organic matter; shells that accumulate on and in the sediment below mussel farms also have the potential to influence processes in the sediment, the activity of bioturbators and the fluxes across the sediment-water interface. In this study, we evaluated the mitigation potential of the bioturbating polychaeteHediste diversicolorin sediments enriched with mussel waste material and the relative impact of mussel shells within the sediment matrix. The polychaetes generally increased fluxes and sediment oxygen uptake. With an observed tendency of increased fluxes of nutrients in sediments containing shells compared to sediments without, the results indicate that the accumulation of shell has a potential to further increase the mitigative effect of the polychaetes by influencing the solute fluxes across the sediment-water interface.

Mussel farming has been proposed as a mechanism to mitigate eutrophication in coastal waters. However, localizing the intensive filtration of organic matter by mussels can cause a concomitant enrichment of organic matter in sediments below farms, which may influence biogeochemical processes and fates of nutrients in the system. In the context of mitigating eutrophication, it is important to quantify sedimentary changes induced at early life stages of mussel farms. Accordingly, this study investigated how a newly re-established mussel farm affected sedimentation rates, sediment characteristics, sediment-water solute fluxes and nitrate (NO3−) reduction rates (measured in situ) during the first year of production. Sedimentation rates were enhanced at the farm relative to a reference station, and both organic and inorganic carbon accumulated in the sediment with time. Increased organic matter input likely drove the slightly elevated sedimentary effluxes of ammonium (NH4+) and dissolved inorganic phosphorus (DIP) in the farm. Denitrification was the main NO3− reduction process, however, there was a relative increase in the remobilization of bioavailable nitrogen underneath the farm as dissimilatory nitrate reduction to ammonium (DNRA) rates were enhanced by >200% and the denitrification efficiency was 49% lower compared to the reference station. The sedimentary methane (CH4) release tended to be higher at the farm, but fluxes were not significantly different from reference conditions. Low sedimentary pigment concentrations indicated a reduced presence of benthic microalgae at the farm, which likely influenced sediment-water solute fluxes. Over the production cycle, the release of dissolved inorganic nitrogen (DIN) and DIP underneath the farm were respectively 426% and 510% relative to reference conditions. Impacts of the mussel farm were thus measurable already during the first year of establishment. These immediate changes to the sediment biogeochemistry, as well as long-term effects, should be considered when estimating the environmental impact of mussel aquaculture.

Marine coastal areas are increasingly affected by human activities resulting in changes in species and habitat distributions. Understanding these patterns and its causes and consequences is important for conservation and restoration of such changing habitats. One habitat that has been heavily affected by human use are the North Sea oyster beds which once were abundant but have lost large parts of its coastal distribution due to overexploitation. Based on data of living and dead assemblages of

Aim Understanding spatial patterns of the distribution of adult native oyster, Ostrea edulis, and the invasive Magallana (Crassostrea) gigas is important for management of these populations. The aim of this study was to use ensemble SDM’s to (a) identify and predict conservation hotspots, (b) assess the current level of protection for O. edulis, and (c) quantify the amount of overlap between the two species where interactions with M. gigas are most likely. Location Skagerrak, Sweden. Methods We used data collected by video at depths from 0.5 to 10 m in 436 sites. Models of occurrence and densities >1 m−2 were fitted and assessed using ensemble methods (“biomod2” package). Models of high‐density hotspots were used to predict, map, and quantify areal extent of the species in order to assess the degree of overlap with protected areas and the potential for interactions between the two species. Results Both species were widely distributed in the region. Observations of high‐density habitats, mainly occurring at depths of ≈3 and 0.5 m for O. edulis and M. gigas, respectively, were found in 4% and 2% of the sites. Models provided useful predictions for both species (AUC = 0.85–0.99; sensitivity = 0.74–1.0; specificity = 0.72–0.97). High‐density areas occupy roughly 15 km2 each with substantial overlap between species. 50% of these are protected only by fisheries regulations, 44% are found in Natura 2000 reserves and 6% of the predicted O. edulis enjoys protection in a national park. Main conclusions Data collection by video in combination with SDM’s provides a realistic approach for large‐scale quantification of spatial patterns of marine population and habitats. O. edulis and M. gigas are common in the area, but a large proportion of the most valuable O. edulis habitats are not found in protected areas. The overlap between species suggests that efforts to manage the invasive M. gigas need to be integrated with management actions to conserve the native O. edulis., Understanding spatial patterns of the native oyster, Ostrea edulis, and the invasive Magallana gigas is important for management of these populations. We used data collected by video at depths from 0.5 to 10 m in 436 sites. Models of occurrence and densities > 1 m−2 were fitted and assessed using ensemble methods. Data collection by video in combination with SDM’s provides a realistic approach for large‐scale quantification of spatial patterns of marine population and habitats.

Previous studies have shown clearly that the deposit feeding polychaete, Hediste diversicolor, can promote oxygenation of sediments exposed to excess loads of mussel faeces. In this experimental study, we explicitly test their utility as food for H. diversicolor to survive and grow on. Furthermore, in order to understand the consequences of experimental manipulations, we also evaluated effects on chemical fluxes in and out of the sediment. The results show strong differences in growth but no difference in short-term survival. Fed only on mussel faeces, the polychaetes grew on average 17% in wet weight after a period of 10 days, compared to 3% when given equivalent amounts of organic matter from the natural sediments. Addition of faeces to natural sediments resulted in 19–20% growth, thus suggesting an approximate additive effect of the two food sources. Chemical analyses showed that, oxygen consumption increased with load of organic material irrespective of origin, faecal material caused higher fluxes of ammonia compared to natural organic material, but neither oxygen consumption nor nutrient fluxes were affected by the ashing of sediments. In contrast, fluxes of silicate increased as a consequence of ashing but were not affected by the addition of mussel faeces. Thus, despite risks of experimental artefacts due to ashing of sediments, the results show that oxygen and nutrient dynamics responded to manipulations of organic material and not to the potential modification of sediment structure. Therefore, the observed effects on growth of H. diversicolor can be safely interpreted as caused by differences in amount and quality of organic material. Mussel faeces is a high-quality food source for this species of polychaete and, in combination with ample evidence from previous studies that bioturbation, we conclude that H. diversicolor is a suitable candidate in further efforts to develop technical solutions based on bioturbation for mitigation of adverse effects on benthic environments in connection with mussel-farming.

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.

Benthic habitats and communities are key components of the marine ecosystem. Securing their functioning is a central aim in marine environmental management, where monitoring data provide the base for assessing the state of marine ecosystems. In the Baltic Sea, a > 50-year-long tradition of zoobenthic monitoring exists. However, the monitoring programmes were designed prior to the current policies, primarily to detect long-term trends at basin-scale and are thus not optimal to fulfil recent requirements such as area-based periodic status assessments. Here, we review the current monitoring programmes and assess the precision and representativity of the monitoring data in status assessments to identify routes for improvement. At present, the monitoring is focused on soft-bottoms, not accounting for all habitat types occurring in the Baltic Sea. Evaluating the sources of variance in the assessment data revealed that the component accounting for variability among stations forms the largest proportion of the uncertainty. Furthermore, it is shown that the precision of the status estimates can be improved, with the current number of samples. Reducing sampling effort per station, but sampling more stations, is the best option to improve precision in status assessments. Furthermore, by allocating the sampling stations more evenly in the sub-basins, a better representativity of the area can be achieved. However, emphasis on securing the long-term data series is needed if changes to the monitoring programmes are planned.

The value of an ecological indicator is no better than the uncertainty associated with its estimate. Nevertheless, indicator uncertainty is seldom estimated, even though legislative frameworks such as the European Water Framework Directive stress that the confidence of an assessment should be quantified. We introduce a general framework for quantifying uncertainties associated with indicators employed to assess ecological status in waterbodies. The framework is illustrated with two examples: eelgrass shoot density and chlorophyll a in coastal ecosystems. Aquatic monitoring data vary over time and space; variations that can only partially be described using fixed parameters, and remaining variations are deemed random. These spatial and temporal variations can be partitioned into uncertainty components operating at different scales. Furthermore, different methods of sampling and analysis as well as people involved in the monitoring introduce additional uncertainty. We have outlined 18 different sources of variation that affect monitoring data to a varying degree and are relevant to consider when quantifying the uncertainty of an indicator calculated from monitoring data. However, in most cases it is not possible to estimate all relevant sources of uncertainty from monitoring data from a single ecosystem, and those uncertainty components that can be quantified will not be well determined due to the lack of replication at different levels of the random variations (e.g. number of stations, number of years, and number of people). For example, spatial variations cannot be determined from datasets with just one station. Therefore, we recommend that random variations are estimated from a larger dataset, by pooling observations from multiple ecosystems with similar characteristics. We also recommend accounting for predictable patterns in time and space using parametric approaches in order to reduce the magnitude of the unpredictable random components and reduce potential bias introduced by heterogeneous monitoring across time. We propose to use robust parameter estimates for both fixed and random variations, determined from a large pooled dataset and assumed common across the range of ecosystems, and estimate a limited subset of parameters from ecosystem-specific data. Partitioning the random variation onto multiple uncertainty components is important to obtain correct estimates of the ecological indicator variance, and the magnitude of the different components provide useful information for improving methods applied and design of monitoring programs. The proposed framework allows comparing different indicators based on their precision relative to the cost of monitoring.

The need for methods for sustainable management and use of coastal ecosystems has increased in the last century. A key aspect for obtaining ecologically and economically sustainable aquaculture in threatened coastal areas is the requirement of geographic information of growth and potential production capacity. Growth varies over time and space and depends on a complex pattern of interactions between the bivalve and a diverse range of environmental factors (e.g. temperature, salinity, food availability). Understanding these processes and modelling the environmental control of bivalve growth has been central in aquaculture. In contrast to the most conventional modelling techniques, quantile regression can handle cases where not all factors are measured and provide the possibility to estimate the effect at different levels of the response distribution and give therefore a more complete picture of the relationship between environmental factors and biological response. Observation of the relationships between environmental factors and growth of the bivalve Mytilus edulis revealed relationships that varied both among level of growth rate and within the range of environmental variables along the Swedish west coast. The strongest patterns were found for water oxygen concentration level which had a negative effect on growth for all oxygen levels and growth levels. However, these patterns coincided with differences in growth among periods and very little of the remaining variability within periods could be explained indicating that interactive processes masked the importance of the individual variables. By using quantile regression and local regression (LOESS) this study was able to provide valuable information on environmental factors influencing the growth of M. edulis and important insight for the development of ecosystem based management tools of aquaculture activities, its use in mitigation efforts and successful management of human use of coastal areas.

Cultivation of extractive species, such as bivalves and seaweeds, provides opportunities for food production while removing excess nutrients in eutrophic coastal waters. However, to optimize these ecosystem services, selecting aquaculture sites that affect growth and nutrient uptake is important. In a transplant experiment we assessed spatial growth patterns of the blue mussel Mytilus edulis and the kelp Saccharina latissima, which were used to estimate nutrient removal. Optimal locations for growth and nutrient extraction differed, mussels grew better in relatively sheltered inner coastal areas, whereas seaweed growth increased in outer more exposed coastal areas. Estimates of mitigatory capacity indicated that under the best available conditions, mussels remove approximately 700 kg N and 6600 kg C ha−1yr−1, whereas seaweed removes approximately 100 kg N and 1000 kg C ha−1yr−1. We identified the importance of site selection for the overall capacity of two extractive species (bivalves and seaweeds) in order to synergistically maximise their growth and nutrient mitigation.

The increased pressure on the marine ecosystems highlights the need for policies and integrated approaches for sustainable management of coastal areas. Spatial planning based on geographic information of human activities, ecological structures and functions, and their associated goods and services is a fundamental component in this context. Here, we evaluate the potential of predictive modeling to provide spatial data on one ecosystem function, mussel growth for use in such processes. We developed a methodology based on statistical modeling, spatial prediction, and mapping for the relative growth of the blue mussel, Mytilus edulis. We evaluated the performance of different modeling techniques and classification schemes using empirical measurements of growth from 144 sampling sites and data on biological, chemical, and physical predictors. Following comparisons of the different techniques and schemes, we developed random forest models to predict growth along the Swedish west coast. Implemented into GIS the best model produced in this study predicts that low, intermediate, and high growth rates can be expected in 53%, 32%, and 15% of modeled area, respectively. The results of this study also suggest that the nature and quality of predictor data hold the key to improving the predictive power of models. On a more general note, this study exemplifies a feasible approach based on measuring, modeling, and mapping for obtaining scientifically based spatial information on ecosystem functions and services affected by a complex set of factors. Such information is fundamental for maritime spatial planning and ecosystem‐based management and its importance is likely to increase in the future. Because of its close link to nutrient assimilation and production yield, site‐specific information of soft tissue growth such as the map of predicted growth rate developed in this study can be used as a tool for optimizing actions aimed at mitigating eutrophication and aquaculture operations and in maritime spatial planning processes of coastal areas.

Methods to increase the precision of spat collection and strategies to mitigate fouling are greatly needed in aquaculture production. As such, larval recruitment of mussels and a common tunicate species was investigated. Recruitment was measured in shallow (1–2 m) and deeper (4–5 m) water at three sites during the summer of 2012. In addition, to evaluate the importance of timing in deployment of mussel ropes, differences in mussel yield were examined. The settlement plates provided a good description of the settling community with high temporal resolution. Peaks in recruitment were observed for both mussels and tunicates but recruitment rates and the timing of peaks differed among sites. Although mussel larvae preferred shaded substrates at some sites and times, these substrates were consistently preferred by tunicates. Mussels preferred to settle at shallow depths, whereas tunicates were consistently more abundant deeper. In contrast to predictions, there was no positive relationship between the...

Blue mussels Mytilus edulis and the invasive Pacific oyster Crassostrea gigas are both ecosystem engineering species which modify the environment, thus having large effects on associated species. With the introduction of the Pacific oyster, a new biogenic structure has been added to subtidal sediment habitats in Scandinavia. By conducting a field experiment, the effects of live and post-mortem shell structures of C. gigas and M. edulis on associated infauna, epiben- thic fauna and fish on the Swedish west coast were evaluated. Plots with 5 different treatments (live Pacific oysters, oyster shells, live blue mussels, mussel shells and sand control) were con- structed on bare sandy sediment at 2 subtidal localities. Epibenthic macrofauna and fish were sampled with a drop trap, and sediment and infauna samples were collected with sediment cores. Live bivalve treatments had significant effects on organic content of the sediment; however, no treatment effects on infauna were found. In contrast, abundance and biomass of epibenthic fauna increased 4 to 8 times and species richness increased in the presence of the bivalves or their shells, compared to the sand control. Epibenthic fauna abundance and biomass was higher in the oyster shell treatment compared to the live bivalve treatments, which in turn had higher abundance and biomass than the mussel shell treatment. In general, the mussel shell treatment favoured small crustaceans, while the oyster shell and live bivalve treatments favoured fish and larger inverte- brate species. Based on these results, we conclude that further establishment of the Pacific oyster in Swedish waters will cause large changes to community structure of benthic macrofauna and fish.

Due to large-scale habitat losses and increasing pressures, benthic habitats in general, and perhaps oyster beds in particular, are commonly in decline and severely threatened on regional and global scales. Appropriate and cost-efficient methods for mapping and monitoring of the distribution, abundance and quality of remaining oyster populations are fundamental for sustainable management and conservation of these habitats and their associated values. Towed video has emerged as a promising method for surveying benthic communities in a both non-destructive and cost-efficient way. Here we examine its use as a tool for quantification and monitoring of oyster populations by (i) analysing how well abundances can be estimated and how living Ostrea edulis individuals can be distinguished from dead ones, (ii) estimating the variability within and among observers as well as the spatial variability at a number of scales, and finally (iii) evaluating the precision of estimated abundances under different scenarios for monitoring. Overall, the results show that the can be used to quantify abundance and occurrence of Ostrea edulis in heterogeneous environments. There was a strong correlation between abundances determined in the field and abundances estimated by video-analyses (r2 = 0.93), even though video analyses underestimated the total abundance of living oysters by 20%. Additionally, the method was largely repeatable within and among observers and revealed no evident bias in identification of living and dead oysters. We also concluded that the spatial variability was an order of magnitude larger than that due to observer errors. Subsequent modelling of precision showed that the total area sampled was the main determinant of precision and provided general method for determining precision. This study provides a thorough validation of the application of towed video on quantitative estimations of live oysters. The results suggest that the method can indeed be very useful for this purpose and we therefor recommend it for future monitoring of oysters and other threatened habitats and species.

We evaluated performance of species distribution models for predictive mapping, and how models can be used to integrate human pressures into ecological and economic assessments. A selection of 77 biological variables (species, groups of species, and measures of biodiversity) across the Baltic Sea were modeled. Differences among methods, areas, predictor, and response variables were evaluated. Several methods successfully predicted abundance and occurrence of vegetation, invertebrates, fish, and functional aspects of biodiversity. Depth and substrate were among the most important predictors. Models incorporating water clarity were used to predict increasing cover of the brown alga bladderwrack Fucus vesiculosus and increasing reproduction area of perch Perca fluviatilis, but decreasing reproduction areas for pikeperch Sander lucioperca following successful implementation of the Baltic Sea Action Plan. Despite variability in estimated non-market benefits among countries, such changes were highly valued by citizens in the three Baltic countries investigated. We conclude that predictive models are powerful and useful tools for science-based management of the Baltic Sea.

Due to increasing pressure on the marine environment there is a growing need to understand species–environment relationships. To provide background for prioritising among variables (predictors) for use in distribution models, the relevance of predictors for benthic species was reviewed using the coastal Baltic Sea as a case-study area. Significant relationships for three response groups (fish, macroinvertebrates, macrovegetation) and six predictor categories (bottom topography, biotic features, hydrography, wave exposure, substrate and spatiotemporal variability) were extracted from 145 queried peer-reviewed field-studies covering three decades and six subregions. In addition, the occurrence of interaction among predictors was analysed. Hydrography was most often found in significant relationships, had low level of interaction with other predictors, but also had the most non-significant relationships. Depth and wave exposure were important in all subregions and are readily available, increasing their applicability for cross-regional modelling efforts. Otherwise, effort to model species distributions may prove challenging at larger scale as the relevance of predictors differed among both response groups and regions. Fish and hard bottom macrovegetation have the largest modelling potential, as they are structured by a set of predictors that at the same time are accurately mapped. A general importance of biotic features implies that these need to be accounted for in distribution modelling, but the mapping of most biotic features is challenging, which currently lowers the applicability. The presence of interactions suggests that predictive methods allowing for interactive effects are preferable. Detailing these complexities is important for future distribution modelling.

Increased focus on predictive aspects of ecology has recently been urged by scien- tists and policy makers to provide solutions to pressing societal needs. Current challenges include the large knowledge gap on the spatial distribution of marine biodiversity, and its associated goods and services, and the dependence of model performance on spatial resolution. We eva - luated the importance of resolution on the predictive power and precision of empirical models of distributions of marine sessile invertebrates and macroalgae along the Swedish west coast. This was done by simulating the limits to prediction, based on 2 independent simulated proportions of biological variables, and comparing these limits to observed models at different resolutions. Simulations showed the highest achievable predictive power (r 2 ) and precision (RMSE) of models at fine resolutions (~1 m). In contrast to the simulations, the performance of quantitative models was better at relatively coarse resolutions (~100 m). Increased model performance at coarse resolutions could not be explained by differences in sampling or spatial variability. Instead, the improvement is likely caused by the mechanistic coupling (direct or indirect) between predictor variables, depth and hard substratum cover and patterns at coarser scales, whereas complex processes, e.g. biological interactions, shape patterns at finer scales. This match between resolu- tion and the scale at which environmental variables operate may differ among systems, which could explain the discrepancy in outcomes between our study and previous studies. Furthermore, we provide an approach for error analysis that identifies contributions of different model compo- nents to the total uncertainty, thus facilitating model optimization.

When spatial fishing data is fed into systematic conservation planning processes the cost to a fishery could be ensured to be minimal in the zoning of marine protected areas. We used vessel monitoring system (VMS) data to map the distribution of prawn trawling and calculate fishing intensity for 1-ha grid cells, in the Kosterhavet National Park (Sweden). We then used the software Marxan to generate cost-efficient reserve networks that represented every biotope in the Park. We asked what were the potential gains and losses in terms of fishing effort and species conservation of different planning scenarios. Given a conservation target of 10 % representation of each biotope, the fishery need not lose more than 20 % of its fishing grounds to give way to cost-efficient conservation of benthic diversity. No additional reserved area was needed to achieve conservation targets while minimizing fishing costs. We discuss the benefits of using VMS data for conservation planning.

Bučas, M., Bergström, U., Downie, A-L., Sundblad, G., Gullström, M., von Numers, M., Šiaulys, A., and Lindegarth, M. 2013. Empirical modelling of benthic species distribution, abundance, and diversity in the Baltic Sea: evaluating the scope for predictive mapping using different modelling approaches. – ICES Journal of Marine Science, 70: 1233–1243. The predictive performance of distribution models of common benthic species in the Baltic Sea was compared using four non-linear methods: generalized additive models (GAMs), multivariate adaptive regression splines, random forest (RF), and maximum entropy modelling (MAXENT). The effects of data traits were also tested. In total, 292 occurrence models and 204 quantitative (abundance and diversity) models were assessed. The main conclusions are that (i) the spatial distribution, abundance, and diversity of benthic species in the Baltic Sea can be successfully predicted using several non-linear predictive modelling techniques; (ii) RF was the most accurate method for both models, closely followed by GAM and MAXENT; (iii) correlation coefficients of predictive performance among the modelling techniques were relatively low, suggesting that the performance of methods is related to specific responses; (iv) the differences in predictive performance among the modelling methods could only partly be explained by data traits; (v) the response prevalence was the most important explanatory variable for predictive accuracy of GAM and MAXENT on occurrence data; (vi) RF on the occurrence data was the only method sensitive to sampling density; (vii) a higher predictive accuracy of abundance models could be achieved by reducing variance in the response data and increasing the sample size.

Summary 1. Eutrophication is severely affecting species distributions and ecosystem functioning in coastal areas. Targets for eutrophication reduction have been set in the Baltic Sea Action Plan (BSAP) using Secchi depth, a measure of water transparency, as the main status indicator. Despite the high economic costs involved, the potential effects of this political decision on key species and habitats have not been assessed. 2. In a case study including species central to coastal ecosystem functioning, we modelled the effects of changing Secchi depth on the distribution of bladderwrack Fucus vesiculosus and eelgrass Zostera marina vegetation as well as recruitment areas of the main predatory fish species, perch Perca fluviatilis and pikeperch Sander lucioperca. Specifically, we explored the effects of changing Secchi depth on species distributions under a set of scenarios based on the BSAP, using three fundamentally different modelling techniques: maximum entropy, generalized additive and random forest modelling. 3. Improved Secchi depth (reduced eutrophication) was predicted to cause a substantial increase in the distribution of bladderwrack, while the distribution of eelgrass remained largely unaffected. For the fish, a large increase in perch recruitment areas was predicted and a concurrent decrease in recruitment areas of pikeperch. These changes are likely to have effects on biodiversity and ecosystem services. 4. The three modelling methods exposed differences in the quantitative predictions for species with a weaker coupling to Secchi depth. Qualitatively, however, the results were consistent for all species. 5. Synthesis and applications. We show how ecological effects of environmental policies can be evaluated in an explicit spatial context using species distribution modelling. The modelspecific responses to changes in eutrophication status emphasize the importance of using ensemble modelling for exploring how species distributions may respond to alternative management regimes. A pronounced difference in response between species suggests that eutrophication mitigation will have consequences for ecosystem functioning, and thus ecosystem goods and services, by inducing changes in the simple food webs of the Baltic Sea. These model predictions form a basis for spatially explicit cost-benefit estimates under different scenarios, providing valuable information for both decision-makers and the wider society.

Biodeposits from farmed mussels severely influencethe biogeochemistry of sediments by increasing thelevels of organic matter (OM). Mitigation of suchnegative impacts is important for the developmentof sustainable aquaculture operations. As a steptowards developing methods for remediation ofcoastal sediments affected by mussel farming, theeffects of the polychaete, Hediste diversicolor wasevaluated experimentally. In a series of field- andlaboratory experiments we tested hypotheses aboutthe effects of polychaetes on sediment oxygen con-sumption, nutrient fluxes and sulphide pools underdifferent polychaete densities and sedimentationregimes. The experimental results support the ideathat polychaetes can mitigate negative effects onthe benthic environment beneath mussel farms.H. diversicolor oxidized the sediment and generallyenhanced the oxygen consumption, and thus thedecomposition of OM. The accumulation of porewater sulphides were reduced and fluxes of nutri-ents across the sediment-water interface increased.Additional calculations suggest that the effects ofpolychaetes were mainly indirect and driven byincreased microbial activity due to the borrowingactivity of the polychaetes. Trends of increasingdecomposition with increasing polychaete densitysuggest that the decomposition could be furtherenhanced by higher densities. Overall, we con-cluded that H. diversicolor is a potentially strongcandidate for remediation of mussel farm sedi-ments. The results show that sediments inhabitedby H. diversicolor have high assimilative capacityof OM and oxygen conditions are significantlyimproved following the addition of polychaetes atnaturally occurring densities. However, technologi-cal developments are needed in order to allow theapproach to be used in practice.Keywords: sediment remediation, oxygenconsumption, biogeochemistry, Hediste diversi-color, mussel faecesIntroductionAquaculture is well known to cause environmen-tal impacts due to increased sedimentation andaltered nutrient cycling (Holmer, Duarte, Heilskov,Olesen & Terrados 2003; Giles, Pilditch & Bell2006; Nizzoli, Welsh, Fano & Viaroli 2006;Richard, Archambault, Thouzeau, McKindsey D Robert, McKindsey, Chaillou A Callier, Richard, McKindsey, Archam-bault & Desrosiers 2009; Carlsson, Glud P Robert et al. 2013), which stimu-late O

We estimated and tested variability of seagrass leaf-associated epifaunal assemblages at a range of scales. Sampling was performed in 36 seagrass (Zostera marina) meadows within three regions along the Swedish west coast following a hierarchical design (samples separated by 10 s m, km or 100 km). Results showed strongest variability (43–81%) at the intermediate amongst-meadow (km) scale using biomass of functional categories, while considering taxa composition the within-meadow (10 s m) scale contributed most to variability (60%). Using functional categories, we found that embayment exposure and seagrass shoot density were the most important predictor variables explaining part of the variability in biomass of suspension feeders (bivalves and barnacles) and grazers. In contrast, variability in epifaunal taxa composition was predicted mainly by sediment chemistry, substratum coverage and geographical positioning. Our findings suggest that models to develop predictive power and mechanistic understanding should focus on variables and processes varying at small and intermediate scales rather than those varying at larger scales.

Although the comparison of relevant scales of variation is a prerequisite for understanding processes structuring benthic communities, deep-sea studies have traditionally examined spatial patterns of distribution of assemblages along a single scale or environmental gradient. A multiple-scale approach identifying which spatial-scale and associated environmental gradient is the most important in structuring the deep-sea benthos has never been attempted. To answer this question this study merged three independent data sets of nematodes from the Arctic deep seas. The data set included 300 samples and covered both margins of the Arctic Seas (Greenland and Norway–Spitsbergen, ca. 10 3 km distant apart), seven degrees of latitude (72–79°N), 2700 m depth differences (656–3350 m), horizontal distances between cores (20 cm) and vertical distances within the uppermost sediment layers (1–5 cm). Results showed that for abundance (N) and generic composition, differences between margins (M) and between cores (C) were the most important sources of variability, followed by water depth (D), vertical distribution within the sediment (VD) and latitude ( L ). For species and genera diversity, measured as ES(50) and EG(50), the order was slightly different. For species, C was the most important source of variability, followed by D , M and L , while for genera VD was the most important. Relationships between environmental variables and the fauna were highly dependent on scale indicating that, at least for the deep-sea environment, we cannot predict the structure of nematode assemblages by scaling up or down results obtained on one or another scale. The only consistent pattern across different spatial scales was that higher abundances were associated with higher number and lower turnover of species. This raises the hypothesis that the most abundant species are also the most widespread and that abundance is the best predictor of nematode diversity patterns in deep-sea ecosystems.

Ecological research on algal-derived metabolites with antimicrobial activity has recently received increased attention and is no longer only aimed at identifying novel natural compounds with potential use in applied perspectives. Despite this progress, few studies have so far demonstrated ecologically relevant antimicrobial roles of algal metabolites, and even fewer have utilized molecular tools to investigate the effects of these metabolites on the natural community composition of bacteria. In this study, we investigated whether the red alga Bonnemaisonia asparagoides is chemically defended against bacterial colonization of its surface by extracting surface-associated secondary metabolites and testing their antibacterial effects. Furthermore, we compared the associated bacterial abundance and community composition between B. asparagoides and two coexisting macroalgae. Surface extracts tested at natural concentrations had broad-spectrum effects on the growth of ecologically relevant bacteria, and consistent with this antibacterial activity, natural populations of B. asparagoides had significantly lower densities of epibacteria compared with the coexisting algae. Terminal restriction fragment length polymorphism analysis further showed that B. asparagoides harboured surface-associated bacteria with a community composition that was significantly different from those on coexisting macroalgae. Altogether, these findings demonstrate that B. asparagoides produces surface-bound antibacterial compounds with a significant impact on the abundance and composition of the associated bacterial community.

It is widely acknowledged that mapping of benthic diversity is needed to aid in the management and conservation of marine ecosystems, but the choice of scale is contingent upon the patterns of spatial structure inherent to the benthos, which are often unknown. In this paper, spatial autocorrelation analysis is used to detect and describe fine-scale patterns of spatial structure in assemblages of epibenthic megafauna of the seabed below 20 m depth at the Koster fjord/archipelago area (Sweden). Presence/absence of benthic organisms was obtained from video images, which had been collected by means of a remotely operated vehicle. For sample sizes (grain) of

A field experiment was conducted to examine the short- and long-term effects of ottertrawling on a macrobenthic infaunal community in shallow subtidal waters of Faxafloi Bay (SW Ice-land) that had never been trawled before. The experimental design consisted of 4 sites trawled 10times and 4 areas left undisturbed (controls). Sampling of fauna and sediments was carried out inJune 1997, immediately after trawling, and subsequently 2 and 7 mo later, in order to investigatelonger term impacts of trawling. No significant treatment effects could be detected on total abun-dance or on multivariate structure, and tests for individual species revealed only a single short-termeffect (for the bivalve Thyasira flexuosa) . However, trawling affected several aspects of diversity withsignificant short-term reduction in species richness and persistent effects on the Shannon-Wienerindex. Power analysis revealed that larger changes were needed to detect changes in abundancecompared to measures of diversity. Analyses of qualitative changes revealed a decreasing trend inabundance of the majority of taxa (especially the rarer ones) immediately after trawling. This was themost likely cause for the reduced diversity and the augmented small-scale variability in species rich-ness. The size of initial impacts and the persistence of effects were largely consistent with those ofprevious studies in similar environments. Similar to other types of environmental impacts in aquaticenvironments, our analyses reveal that impacts of trawling on measures of diversity can be detectedat a high statistical power and that larger effects are necessary to detect impacts on abundances.KEY WORDS: Otter trawl · Experimental fishing · Infauna · Variability · Analysis of variance ·Iceland · Diversity · Power analysis

Recent research has shown the potential for nonallopatric speciation, but we lack an adequate understanding of the mechanisms of prezygotic barriers and how these evolve in the presence of gene flow. The marine snail Littorina saxatilis has distinct ecotypes in different shore microhabitats. Ecotypes hybridize in contact zones, but gene flow is impeded by assortative mating. Earlier studies have shown that males and females of the same ecotype copulate for longer than mates of different ecotype. Here we report a new mechanism that further contributes to reproductive isolation between ecotypes in the presence of gene flow. This mechanism is linked to the ability of males to track potential partners by following their mucous trail. We show that cliff ecotype males follow the trails of females of the same ecotype for longer than females of the alternate (boulder) ecotype. In addition, cliff males are more likely to follow the mucous trail in the correct direction if the trail is laid by a cliff-female. The capacity to discriminate the ecotype of female mucous trails combined with differential copulation times creates a strong prezygotic reproductive barrier between ecotypes of L. saxatilis that reduces gene flow from cliff to boulder ecotypes by/=80%.

We review approaches and tools currently usedin Nordic countries (Denmark, Finland, Norway andSweden) for integrated assessment of ‘ecological status’sensu the EU Water Framework Directive as well asassessment of ‘eutrophication status’ in coastal and marinewaters. Integration principles for combining indicatorswithin biological quality elements (BQEs) and combiningBQEs into a final-integrated assessment are discussed.Specific focus has been put on combining different types ofinformation into indices, since several methods arecurrently employed. As a consequence of the variety ofmethods used, comparisons across both BQEs and watercategories (river, lakes and coastal waters) can be difficult.Based on our analyses, we conclude that some principlesand methods for integration can be critical and that aharmonised approach should be developed. Further, weconclude that the integration principles applied withinBQEs are critical and in need of harmonisation if we want abetter understanding of potential transition in ecologicalstatus between surface water types, e.g. when riverinewater enters a downstream lake or coastal water body.

Development of general theories and subsequent empirical testing are fun- damental ingredients in ecological science. The progress of such efforts is determined by the logical coherence among central concepts, theories, and predictions on one hand, and experimental design, statistical analyses, and interpretation of results on the other. Here, we specifically explore an example of how differences in the way ecological concepts are defined lead to differences in the formulation and statistical testing of hypotheses and ultimately to differences in conclusions about the relative importance of ecological pro- cesses. In marine intertidal habitats, the notion that wave exposure has an important structuring role is widely agreed upon. Nevertheless, generalizations about its effects and use for accurate prediction of assemblages are often limited. This may partly be explained by the frequent use of categorical rather than quantitative definitions of wave exposure. We com- pared the conclusions about the importance of wave exposure from (1) analyses of variance based on relative classification of wave exposure and geographic location to those of (2) regression analyses based on continuous measures from 16 locations on the Swedish west coast. Variability in richness was substantially better explained by the regression analyses, while for the cover of individual taxa there was no consistent difference between the two analytical approaches in terms of explained variability. The two approaches detected sig- nificant spatial patterns for the same taxa, but conclusions about the nature of these patterns were often divergent. Categorical analyses of relative measures of wave exposure and geographic location indicated that interactive effects and differences between geographic areas were predominant. Regression analyses of absolute, continuous measures suggested that mean significant wave height was a better predictor than geographic location and interactive terms. Thus, the choice of definition of wave exposure has important conse- quences for how causes of spatial patterns of intertidal assemblages are perceived. Cate- gorical analyses appear to provide clearer indications as to which factors are important while the use of continuous predictors sometimes provides a better fit to the data. The consequences of these findings are discussed in the context of rocky shore ecology as well as in a general perspective of ecological models, hypotheses, experimentation, and analysis.

The relative sizes and importance of spatial, temporal and interactive variability of soft-sediment assemblages in Swedish coastal waters were estimated using a hierarchical sampling programme. Spatial scales ranged between 10 0–1 and 10 3 m and samples were collected at three times within 1 year. Variability in diversity of assemblages, as well as abundances of the 15 most common taxa, were estimated and tested using ANOVA. Nonparametric multivariate analyses of variance (NPMANOVA) were used to test and estimate the variability of whole assemblages. Univariate analyses revealed that all variables showed significant spatial and temporal patterns but that these differed among individual taxa. A general finding was that there was much interactive variability between times of sampling and the two spatial scales tested. This means that abundance and diversity of infauna changed differently among bays located a few kilometers apart and among locations within bays located hundreds of meters apart. Thus, spatial patterns of assemblages changed among times of sampling. Conclusions were similar for univariate as well as multivariate analyses, although multivariate patterns appeared slightly more persistent. Furthermore, estimation of variance components showed a substantial variability among cores within locations. The results provide the first coherent analysis of interactive scale-dependent variability in these geographic areas and one of few in soft sediments. Results are discussed in relation to previously observed patterns of spatio-temporal variability in soft sediments and in a context of potential processes responsible for creating patterns at particular spatial scales. Results were also used for cost– benefit analyses in order to compare precision of optimal solutions to what was observed and to optimise future sampling of these assemblages. D 2004 Elsevier B.V. All rights reserved.

The effects of small-scale disturbances (80×30-cm plots) of canopy and grazers on intertidal assemblages were investigated in this 4-year experiment on sheltered rocky shores on the Swedish west coast. Canopy disturbances due to ice scouring were mimicked by removal of adult plants of the seaweed Ascophyllum nodosum (L.) Le Joli. Density of the main epilithic grazing gastropods, Littorina spp., was lowered by exclosure and handpicking. Based on earlier experiments in other areas, the general hypothesis was that canopy removal and grazer exclosure, alone or in combination, should increase the recruitment of A. nodosum or other fucoid juveniles, and change the structure of the understorey assemblage. There was an effect of canopy removal on the development of this assemblage, lasting for more than 31 months. Both increased and decreased abundances of species were found as short-term effects, but there was also a longer-term effect with increased abundance. Grazer exclosure was only effective in combination with canopy removal, causing a short-term increase in ephemeral green algae. Short-term effects of canopy removal were also the increase in recruitment of Semibalanus balanoides (Linnaeus) and the decrease of the red alga Hildenbrandia rubra (Sommerfelt) Meneghini. Fast recruitment and growth of fucoid species (Fucus serratus L. and F. vesiculosus L.) restored the canopy and conditions of the understorey within 18 months. Thus, the canopy removal changed the physical conditions for the understorey, making it possible for other species to coexist in this community. Surprisingly, no effect of canopy removal or grazer exclusion was found on the recruitment of juvenile A. nodosum, neither by canopy removal nor grazer exclosure. The lack of such effects might be due to the early mortality caused by other grazers (small, mobile crustaceans), or to the low density of periwinkles on these shores. However, despite the patchy and generally low recruitment of A. nodosum juveniles, observations suggested that the cover of A. nodosum in manipulated patches would return to initial levels, either by recruitment or regrowth of small holdfasts and from growth of edge plants.

Concentrations of heavy metals (zinc, copper and lead) were manipulated experimentally to test the hypotheses about effects on intertidal, soft-sediment assemblages of animals in two sand-flats in Port Hacking, Australia. Hypotheses about changes in the structure and composition of whole assemblages and changes in mean abundance and variability of individual taxa were tested. Specific hypotheses were derived a priori from repeated observations of assemblages in urban and non-urban areas of Port Hacking. After manipulation. concentrations of metals were similar to those in sediments near urban areas, Nevertheless, responses of assemblages to the increased concentrations of metals were weak. Polychaetes, spionids and amphipods responded to experimental treatments. Changes were, however, not consistent among times and places and generally not in agreement with what had been predicted. Significant spatial and temporal variability were detected for all variables investigated. Increased concentrations of metals did not affect variability or overall structure of assemblages. Thus, there was little evidence that increased concentrations of metals caused benthic assemblages in pristine areas to become more similar to those in areas contaminated by human activities, Several potential explanations for the discrepancy between previously observed correlative patterns and the results presented here arc discussed. These include a critical assessment of different aspects of the experimental study, such as lack of statistical power, insufficient basis for prediction, artefacts due to experimental procedures and issues to do with the difference between evidence based on correlation and manipulation. Explicit comparisons showed that there were significant effects of physical disturbance due to repeated sampling and that assemblages of animals at the start of the experiment were different from those previously observed in uncontaminated areas. These observations were surprising and made interpretation more difficult, Nevertheless, it is possible that the metals investigated really contribute only marginally to previously observed differences between urban and non-urban areas, Repeated comparisons between observations of patterns and manipulative experiments like these can only improve the basis for prediction and the power of current mechanistic models. (C) 2002 Elsevier Science B.V. All rights reserved.

Predictions that there should be more benthic invertebrates and greater diversity in deeper areas and differences in the spatial structure of assemblages on different types of beaches were tested on two Reflective and two Intermediate (Transverse Bar and Rip) sandy beaches around Sydney, New South Wales, Australia. The macrofaunal assemblages of surf zones were more diverse and there were more invertebrates on Reflective than TBR beaches, and there was an increase in number of invertebrates and, significantly, in diversity from 1·5 to 2·5 m depths. There was significant variation in the structure of assemblages among beaches of the same type. Spatial variability in the structure of assemblages on Intermediate beaches was greater than on Reflective beaches. Macrofaunal assemblages varied significantly at a scale of tens of metres across shore, particularly on Reflective beaches.

Influences of rocky reefs on composition and abundances of species in assemblages of macrofauna in nearby subtidal, soft-sediments were examined by sampling at three distances from four rocky reefs, three natural and one man-made, in Botany Bay, NSW, Australia. There was significant spatial variation in structure of assemblages between transects and among reefs. The proportion of coarse material in sediments was generally larger close to, than far from, reefs. Assemblages sampled close to reefs were generally different in structure from those sampled away from rocky reefs. In multivariate analyses, assemblages close to reefs were spatially more variable than were those far from reefs. Analyses demonstrated that there were more species close to, than far from, the reefs; polychaetes of the family Syllidae were more abundant far from, than near to, rocky reefs. Artificial and natural rocky reefs influenced nearby benthic assemblages in sediments and various models are discussed to explain the patterns detected, especially those concerning predation and characteristics of the sediments.

A manipulative experiment was done on the Swedish west coast to test hypotheses about effects of grazing on assemblages of algae and sessile animals on moderately exposed shores. The experiments, which lasted for 15 mo, involved a total of 144 experimental units at 16 sites in 2 areas 3 km apart. Experimental treatments involved fences to exclude grazing snails, open fences to control for effects of fences, and control areas, which were not manipulated in any way. In contrast to results from moderately exposed shores in other parts of the world and in contrast to sheltered areas in the region, grazers did not appear to significantly influence the structure and composition of these assemblages. Fences and manual removal of snails were only partly successful in removing grazers. Additional observational evidence, however, supports the conclusion that grazers have a limited impact on structure and abundance of these intertidal assemblages.

Hypotheses on the effects of shrimp trawling on large benthic macrofauna in a previously protected Swedish fjord were tested in a manipulative experiment. Three trawled sites and three untrawled (control) sites were sampled 1-4 months before, and 8-12 months after, experimental trawling on a weekly basis. Multivariate analyses indicate large temporal changes in assemblages of benthic fauna at both types of sites. The Bray-Curtis dissimilarity measure was used to test the hypothesis that changes in assemblages through time at trawled sites were different from those at untrawled sites. Although changes in average assemblages (centroids) from the start to the end of the experiment were larger at trawled sites, Ihc re were marked differences among sites, and differences between trawled and untrawled sites were not significant. There were, however, differences in temporal and spatial variability in structure of benthic assemblages. Variability at untrawled sires tended to be smaller. Thus, spatial and temporal variability in the structure of assemblages after one year of trawling was larger at the trawled sites than at the untrawled sites. Trawling with this particular type of gear at the experimental frequency for approximately one year appears to cause relatively subtle changes in the overall structure of assemblages of large macrofauna compared with changes caused by other factors. Furthermore, the results suggest that tests of hypotheses of changed patterns of variability may be sensitive to detecting effects of impacts of disturbance from trawling. (C) 2000 International Council for the Exploration of the Sea.

Disturbances due to trawling and dredging is a serious threat to assemblages of benthic marine animals. We tested hypotheses about effects of trawling on benthic assemblages in a manipulative field experiment, using gear and intensities relevant to future management of trawling in a Swedish fjord. Three trawled and three control sites were sampled at several times before and after trawling was initiated. This paper describes how conclusions about effects of trawling might differ between experiments involving replicate sites and experiments using only one trawled and one control site, as in several recent studies. Analyses of selected taxa showed that abundances of many species changed differently among control sites. Differences in temporal change between pairs of single trawled and control sites were also frequent. Neither the quantitative nor the qualitative nature of differences between treatments could, however, be coherently interpreted among the different combinations of trawled and control sites. This is consistent with results obtained from analyses using all sites, which showed no consistent effects of trawling on any of these taxa. These results provide empirical evidence that spatial confounding may cause serious problems to formal interpretation of experiments, which use only one control and one trawled area. Such potential problems can best be solved by ensuring that the study incorporates more than one control site.

Hypotheses about effects of shrimp-trawling on large benthic macrofauna were tested in a manipulative experiment in Gullmarsfjorden, Sweden. The experiment lasted 1.5 yr and included 3 trawl sites and 3 control sites, each of which was sampled at 4 times before and 4 times after trawling was commenced (a total of 480 samples). Gear and intensities were chosen to approximate those before trawling was prohibited 6 yr before the experiment. The overall trend was that biomass and abundances of animals decreased as a consequence of trawling but few taxa differed significantly among treatments. The mean abundance of echinoderms, in particular the brittlestars Amphiura sp., decreased significantly and substantially after 7 to 12 mo of trawling. In general, however, changes in abundances of animals from one time of sampling to another, and from before to after trawling started, differed among sites. General models based on size and feeding strategy did not accurately predict differences among taxa in sensitivity to disturbances. Differences in overall impacts between this and previous experiments are discussed in terms of fishing intensity, natural variability and experimental design.