In many areas of the Baltic Sea, three-spined stickleback (Gasterosteus aculeatus) has increased several fold since the early 2000s. Two major planktivores of the Baltic Sea, Atlantic herring (Clupea harengus) and European sprat (Sprattus sprattus), may interact with stickleback via competition for food and predation, but the potential implications at the population level are still unknown. Here, we explored interactions between stickleback, herring, and sprat using (i) herring diet analyses and (ii) fish biomass estimates from hydroacoustics for 2001–2019 covering the largest Baltic Sea basins—the Central Baltic and the Bothnian Sea. The diet analyses revealed that stickleback is an important prey for large herring along the Swedish Baltic Sea coast, comprising up to 64% of the diet of individuals >22 cm. We found a negative influence of large herring (>18 cm) on stickleback in the Central Baltic, and a negative relationship between sprat and small herring (<18 cm) (pooled) and stickleback in the Bothnian Sea. The decline in herring and sprat population after the mid-1990s could have contributed to the increase in stickleback population via reduced predation and competition. Overall, herring may be an underappreciated piscivore, and high fishing pressure on herring could generate cascading effects on lower trophic levels.

Submersed aquatic vegetation (SAV) provides essential habitat and food to numerous coastal invertebrate species. In the eutrophic Baltic Sea, fast-growing drifting algae form extensive mats that can negatively impact SAV. However, these mats also offer additional habitat and food to epifauna. The aim of this study was to assess the effects of SAV and filamentous mats on epifaunal communities in shallow soft-bottom habitats around Gotland, Sweden, in the central Baltic Sea. We used generalised linear models (GLMs) to evaluate the influence of SAV vertical structure, biomass and macrophyte species richness (including macroalgae) and filamentous mat biomass on epifaunal community properties as well as on those of key grazer species. Diversity, vertical structure and biomass of SAV were positively associated with higher total epifaunal abundance and greater abundance gastropod grazers. In contrast, filamentous mats only increased gastropod abundance and biomass. In addition to introducing a rapid tool for quantifying vegetation structural complexity, this study highlights the selective effects of different habitat types on invertebrate communities in a relatively understudied region of the Baltic Sea. As warming temperatures and eutrophication promote filamentous mat growth, reducing nutrient pollution and protecting SAV will be crucial for sustaining abundant and diverse epifaunal communities.

Human society relies on, and interacts with, a diverse assortment of organisms and ecological systems, from the local to the global level. Research and management of these coupled social-ecological systems requires data that speaks to the variety of processes, statuses, and situations defined by them. Effective stewardship is enhanced by interdisciplinary thinking and, critically, access to interoperable data describing human society and governance and ecological and environmental conditions. Such approaches are inherently challenging, especially for those without broad training. In this paper, we propose a workflow harnessing the Social-Ecological System Framework to identify, access, and utilize geospatial data from across a spectrum of social and ecological indicators. We demonstrate the application of this workflow using Tropical Indo-Pacific seagrasses as an example system and in doing so, demonstrate the wealth of available open-data which can support an enhanced understanding of social-ecological system dynamics. With this workflow, we provide a readily applicable tool for use by coastal researchers and managers to support more inclusive social-ecological decision making.

Intraspecific variation modifies ecological processes and ecosystem functioning. Still, we know relatively little of how the nature and strength of ecosystem effects caused by intraspecific variation may interact with climate change. We conducted a mesocosm experiment to test if, and to what extent, ocean warming modifies the ecological impacts of intraspecific variation in a predatory fish. The mesocosms consisted of a simplified coastal food web with threespine stickleback (Gasterosteus aculeatus) as the top predator, from a population where two stickleback phenotypes with either complete or incomplete lateral armour plating coexist and display differentiated predation behaviour: The completely plated phenotype often feeds more on invertebrate herbivores compared with the incompletely plated phenotype. Presence of stickleback reduced biomass of arthropod shredders (crustaceans, insect larvae). Warming (+4°C) strengthened this predation, releasing benthic primary producers (diatoms) from top-down control, causing a trophic cascade. This trophic cascade was attributed to one of the plate phenotypes: the completely plated stickleback increased their predation on shredders under warming, while the incompletely plated stickleback instead decreased their predation. Diatom biomass responded accordingly: warming increased diatom biomass in the presence of completely plated stickleback but not when incompletely plated stickleback was present. Our results suggest that different plate phenotypes of threespine stickleback differentially affect lower trophic levels and that warming may exacerbate these cascading effects. These trait-dependent effects on trophic cascades highlight the consequences of intraspecific variation on ecosystem functioning. Read the free Plain Language Summary for this article on the Journal blog.

Aim: Biogenic structural complexity increases mobile animal richness and abundance at local, regional and global scales, yet animal taxa vary in their response to complexity. When these taxa also vary functionally, habitat structures favouring certain taxa may have consequences for ecosystem function. We characterised global patterns of epifaunal invertebrates in eelgrass (Zostera marina) beds that varied in structural and genetic composition. Location: North America, Europe and Asia. Time Period: 2014. Major Taxa Studied: Peracarid crustaceans and gastropod molluscs. Methods: We sampled epifaunal invertebrate communities in 49 eelgrass beds across 37° latitude in two ocean basins concurrently with measurements of eelgrass genetic diversity, structural complexity and other abiotic and biotic environmental variables. We examined how species richness, abundance and community composition varied with latitude and environmental predictors using a random forest approach. We also examined how functional trait composition varied along with community structure. Results: Total species richness decreased with latitude, but this was accompanied by a taxonomic shift in dominance from peracarid crustaceans to gastropods, which exhibited different sets of functional traits. Greater eelgrass genetic diversity was strongly correlated with both richness and abundance of peracarids, but less so for gastropods. Main Conclusions: Our results add to a growing body of literature that suggests genetic variation in plant traits influences their associated faunal assemblages via habitat structure. Because peracarids and gastropods exhibited distinct functional traits, our results suggest a tentative indirect link between broad-scale variation in plant genetic diversity and ecosystem function.

In December 2022, representatives adopted the Kunming-Montreal Global Biodiversity Framework (GBF). The overarching goal of the agreement is to halt biodiversity loss and restore natural ecosystems – and a much-cited target is the “30x30” target of protecting and restoring 30% of Earth by 2030. Salt marshes are highly productive coastal ecosystems relevant for both biodiversity and climate change mitigation but have experienced historical major losses and are among the habitats in need of protection and restoration. Currently, there is little knowledge about how salt marshes are valued from a societal perspective, which has important management implications. This is particularly the case in the Nordic region where awareness of these habitats is low. Using survey data from Norway, Sweden, Finland, Denmark, and Germany, this study contributes understanding how citizens value salt marshes by examining support for different management initiatives framed as contributing to the goal of either biodiversity protection or climate change mitigation. Generally, both respondents primed with information about the importance of salt marshes for biodiversity and for climate change mitigation were supportive of the management initiatives despite having little previous knowledge of salt marshes. For one initiative, respondents who were informed of the importance of salt marshes for biodiversity were slightly more likely to support the management initiative than those informed about the importance of salt marshes for climate change mitigation. Our study provides guidance for assessment of trade-offs from a human valuation perspective, thus supporting policy makers when considering arguments for salt marsh management within the context of the 30x30 targets for protected areas.

Coastal marshes are productive and diverse habitats that act as essential linkages between marine and terrestrial ecosystems. Although the Nordic region comprises diverse, unique marsh habitats along the Baltic coast and the Atlantic coast of Norway, they are not widely recognized as coastal marshes, e.g., salt marshes in other parts of the world. This may be partly due to inconsistency in habitat classification, use of terminology, and the heterogeneity of these habitats across the region, which limit overviews of their ecology, distribution, and management. Here, we aim to improve the basis for assessments of Nordic coastal marshes by providing an overview of terminology, distribution, area, and management practices of these habitats across the region. We use the general term coastal marsh to cover the variety of habitat types in the study area, which are covered mainly by the European Union's (EU's) Habitats Directive Annex I habitat classes 1310 Salicornia and other annuals colonizing mud and sand, 1320 Spartina swards (Spartinion maritimae), 1330 Atlantic salt meadows (Glauco-Puccinellietalia maritimae), and 1630 Boreal Baltic coastal meadows. Based on input from national environmental officers, an expert survey, a workshop, and reviewing environmental databases, we compiled a comprehensive database on coastal marsh habitats regarding their distribution, classification, conservation status, management, and monitoring practices in four Nordic countries (Denmark, Finland, Norway, Sweden) and Germany, covering wide environmental gradients in, e.g., salinity and tidal range. Overall, we found that the four Annex I classes cover an area of ∼900 km² in the study region, one-fourth of the total area of these habitats in the EU, with an additional ∼450 km² of other potential coastal marsh areas and 500 km² of coastal reed beds. Beyond the variable terminology across the region, our study revealed a gap in the European habitat classification systems concerning the diversity of the Baltic Sea coastal marshes. Creating subtype(s) for the Annex I class 1630 would help to improve the conservation of the most threatened habitat types within the class. In addition, we found pronounced differences in monitoring and managing coastal marshes among countries, indicating that these important and diverse habitats between land and sea might receive insufficient attention and protection despite the multiple ecosystem services they provide. Coordinated harmonization of habitat classifications and monitoring across the Nordic countries could increase regional-scale coordination of the management of coastal marshes and facilitate comparative studies.

No-take zones can be an effective tool for protecting fish and crustacean stocks as well as marine ecosystems. However, it is important that these closed areas are properly designed and large enough. Seasonal spawning closures may be easier to enforce, but do not have as strong positive effects as no-take zones.

Fiskefria områden kan vara ett effektivt verktyg för att skydda både fisk- och kräftdjursbestånd och marina ekosystem. Men det är viktigt att områdena utformas på rätt sätt och är tillräckligt stora. Lektidsfredade områden kan vara enklare att driva igenom, men ger inte lika goda effekter.