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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.

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%.

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.

Methods for preparing fluorescently labeled microparticles and bivalve larvae (Cerastoderma edule) are presented. The labeling is cheap, easy, and allows production of great quantities of fluorescent microparticles and larvae. Fluorescent visualization can be used as a tool to analyze hydrodynamical processes in the benthic boundary layer and to directly observe behavioral patterns in settling larvae.