Improved knowledge on the risk in ecologically important habitats on a regional scale from multiple stressors is critical for managing functioning and resilient ecosystems. This risk assessment aimed to identify seagrass ecosystems in southern Sweden that will be exposed to a high degree of change from multiple global change stressors in mid- and end-of-century climate change conditions. Risk scores were calculated from the expected overlap of three stressors: sea surface temperature increases, ocean acidification and wind driven turbid conditions. Three high-risk regions were identified as areas likely to be exposed to a particularly high level of pressure from the global stressors by the end of the century. In these areas it can be expected that there will be a large degree of stressor change from the current conditions. Given the ecological importance of seagrass meadows for maintaining high biodiversity and a range of other ecosystem services, these risk zones should be given high priority for incorporation into management strategies, which can attempt to reduce controllable stressors in order to mitigate the consequences of some of the impending pressures and manage for maintained ecosystem resilience.

While movements of organisms have been studied across a myriad of environments, information is often lacking regarding spatio-seasonal patterning in complex temperate coastal systems. Highly mobile fish form an integral part of marine food webs providing linkages within and among habitats, between patches of habitats, and at different life stages. We investigated how movement, activity, and connectivity patterns of Atlantic cod (Gadus morhua) are influenced by dynamic environmental conditions. Movement patterns of 39 juvenile and subadult Atlantic cod were assessed in two coastal sites in the Swedish Skagerrak for 5 months. We used passive acoustic telemetry and network analysis to assess seasonal and spatial movement patterns of cod and their relationships to different environmental factors, using statistical correlations, analysis of recurrent spatial motifs, and generalized linear mixed models. Temperature, in combination with physical barriers, precludes significant connectivity (complex motifs) within the system. Sea surface temperature had a strong influence on connectivity (node strength, degree, and motif frequency), where changes from warmer summer waters to colder winter waters significantly reduced movement activity of fish. As the seasons changed, movement of fish gradually decreased from large-scale (km) linkages in the summer to more localized movement patterns in the winter (limited to 100s m). Certain localized areas, however, were identified as important for connectivity throughout the whole study period, likely due to these multiple-habitat areas fulfilling functions required for foraging and shelter. This study provides new knowledge regarding inshore movement dynamics of juvenile and subadult Atlantic cod that use complex, coastal fjord systems. The findings show that connectivity, seasonal patterns in particular, should be carefully considered when selecting conservation areas to promote marine stewardship.

Movements of organisms comprise a fundamental aspect of coastal habitat connectivity. Determining the distribution and co-existence of habitat specialists and generalists in shallow-water seascapes leads to a better understanding of the strength of connectivity-driven community patterns in coastal areas. In this study, unbaited Remote Underwater Video (RUV) systems were used to examine habitat usage and connectivity of fish within six shallow-water coastal seascapes on the Swedish west coast. Within each seascape, video sampling was conducted at three different shallow-water habitats: seagrass meadows, rock-macroalgae and unvegetated areas, in June 2014. Comparative analyses showed that the shallow-water fish community was similar in adjacent habitats within a seascape, though abundances of fish were higher within the structurally complex habitats. All habitats were dominated by juveniles, highlighting the importance of the coastal seascape for early fish life stages. The findings demonstrate that adjacent shallow-water habitats in temperate coastal waters are linked through similar species utilization and that the coastal matrix could be regarded in terms of a seascape nursery for fish. The study highlights the importance of considering shallow-water seascape connectivity in coastal conservation planning and management.

Coastal shallow-water ecosystems are essential for providing several goods and services globally, with seagrasses as an important contributor for maintaining high biodiversity and productivity within the nearshore seascape. The temperate species Zostera marina serves as a vital habitat for many species, including ecologically and economically important juvenile fish. Ecological patterns and processes within the shallow-water seascape are driven by a multitude of factors, for instance food-web dynamics, species interactions, habitat configuration, oceanographic hydrodynamics, and influenced by human impacts, all occurring at different spatial and temporal scales. A complex interworking of abiotic and biotic processes takes place within the coastal environment with the system expected to be impacted by future climate changes. This scientific work contributes to the ecological understanding of coastal marine ecosystems by examining connectivity and disturbance effects on multiple spatiotemporal scales. 

The thesis consists of two main themes: 1) evaluation of the influence of seascape structure on seagrass fish communities at different scales, and 2) understanding species’ physiological responses to multiple global change stressors in Z. marina meadows, and the regional implications of these results. The work focused on temperate Swedish coastal waters. To address these themes a variety of methods were performed including a seascape ecology field approach, experimental laboratory work and spatial modeling. The results contribute to the understanding of seascape connectivity and the impact of disturbance from climate-related stressors on the shallow-water ecosystem and associated fish communities. 

The results highlight the importance of evaluating fish assemblages at multiple spatial scales, from within-meadow characteristics to region-wide geographical features. Generally, fish with higher site fidelity were found to be influenced by smaller scale (meters) habitat characteristics, while broader ranging, more migratory species showed impacts on a larger scale (kilometers). It was also shown that the shallow-water environment has a fish assemblage overlap, with the same species found within multiple coastal habitats, dominated by juvenile fish (in summer), thus constituting a shallow-water seascape nursery. Regarding the consequences of global change the thesis showed that, while individual global change stressors can have either positive, negative or neutral affects depending on the species in question, all trophic levels of the mesocosm study showed a deleterious stress response to multiple stressors combined. With the significance of these laboratory results in mind, the final risk assessment identified three high-risk regions for seagrass meadows along parts of the Swedish coast that are expected to be exposed to a high degree of change from multiple coinciding global stressors by the end of the century.

In shallow-water marine environments, ecosystem functioning is a complex interworking of fine-scale characteristics and region-wide factors, and the importance of these variables can vary on multiple temporal and spatial scales. This underwater video study targeted seasonal changes in the fish community of seagrass habitats along the Swedish west coast and the influence of offshore seascape variables (latitudinal position, wave exposure, open ocean, and deep water). Results showed that fish assemblage structure exhibited seasonal changes between summer and autumn and strong spatiotemporal variations in the importance of offshore factors affecting shallow-water fish communities. In summer, abundance from the Gobiidae family responded to wave exposure, whereas the Gadidae family and juvenile migrant habitat preference guild responded to latitudinal position and proximity to deep water. In autumn, deep water was related to abundance of Gadidae and juvenile migrants, whereas latitudinal position influenced Gasterosteidae. These findings underscore the importance of understanding the influence of offshore factors on facets of coastal fish assemblages to address large-scale geographic connectivity along nearshore–offshore gradients.

Understanding how spatial patterning relates to ecological processes is fundamental to define important species-environment associations at broader scales. Analyses targeting habitat structure (i.e. composition and configuration) in terrestrial landscapes are increasing, but similar studies in marine landscapes are still relatively uncommon. In this study, we explored how seascape structure and complexity (determined from significant spatial pattern metrics) influenced summer and autumn fish assemblage composition in 30 seagrass (Zostera marina) meadows along the west coast of Sweden. Species density was not influenced by seascape structure in any season. In contrast, the majority of significant fish assemblage variables were influenced by seascape structure during the summer (i.e. abundance and proportion of juveniles, abundance of Labridae and abundance of occasional shallow-water visitors) whilst fewer in the autumn (i.e. abundance of occasional shallow-water visitors and Synganthidae). For instance, less complex seascapes were more suitable for juvenile assemblages in summer, as these seascapes exhibit larger patch sizes of appropriate habitat (e.g. Z. marina) and less edge boundaries providing refuges from predators and food resources. Abundances of migrating fish, such as the sea trout Salmo trutta, also responded positively to a less complex seascape in the summer though perhaps ecological processes, such as prey availability, were additional contributing factors driving this relationship. High complexity seascapes only had a positive influence on the abundance of taxa using multiple habitats (Labridae during the summer). Our study shows that fish assemblages in temperate marine environments are significantly linked to spatial habitat patterning and seascape complexity. This offers valuable insights into species-habitat-seascape linkages, information important for coastal conservation and marine spatial planning.