Marine protected areas (MPAs) are designated parts of the ocean that restrict human activities to a certain degree. MPAs are established around the world using a wide range of legislative instruments and thus come in a variety of forms and shapes. Despite being regarded as the “cornerstone” of global marine conservation efforts, they currently cover less than 10% of the ocean surface. Individual MPAs aim to achieve goals ranging from the protection of specific habitats or species to sustaining certain commercial activities, such as fishing. By default, the establishment of MPAs intertwines social, ecological and economic considerations. Yet, the emphasis put on each of these domains can vary substantially when setting on-the-ground objectives, frequently creating conflict among stakeholders. In this manuscript, we first discuss current international conservation targets as well as potential future goals and delve into the question of how to assess the effectiveness of MPAs. Subsequently, we discuss the ambivalent role of this widely applied management tool at the crossroads between biodiversity conservation and fisheries management. Placing MPAs in a social-ecological framework, we call for clear and measurable goals to evaluate MPAs from an interdisciplinary perspective. Finally, we present the Baltic Sea, with its high degree of anthropogenic impact, long fishing history and comparatively extensive MPA coverage, as an interesting case study to investigate the role of MPAs in promoting a sustainable management of the ocean.

Non-compliance with fishing regulations is a widespread phenomenon in fisheries worldwide, jeopardizing the recovery of stocks and ecosystem services. There is an urgent need to fill the gaps in our understanding of the scale and nature of illegal fishing in artisanal fisheries, balancing the advances made in industrial fisheries. We explored patterns of fisher compliance with the existing minimum legal size (MLS) regulation in the small-scale benthic fisheries of central Chile. We focus on two of the most conspicuous species (loco Concholepas concholepas and keyhole limpets Fissurella spp.) and comparing two management regimes: management areas (MAs; local name for territorial use rights for fisheries) and open access areas (OAAs; no spatial entry restrictions). We also evaluated the effect of the spatial distribution of MAs, which determines the availability of OAAs on compliance. For both species, we measured the size of individuals in the catch in two consecutive years. We developed an index that accounts for the availability of open access areas per fisher. We found that a) the number of undersized individuals in the catch in OAAs is enormous, b) management regime influences both the median size and fraction of the undersized catch, and c) as the availability of OAAs per fisher decreases, illegal fishing increases, demonstrating the need to manage the levels of effort displacement in designing area-based instruments for management and conservation. Our findings also highlight the need to a) analyze the benefits of area-based instruments at the seascape scale, and b) develop and adapt instruments to prevent illegal fishing.

Knowledge co-production involving researchers and non-academic actors is becoming increasingly important for tackling sustainability issues. Coastal and marine social-ecological systems are one example where knowledge co-production is important, yet also particularly challenging due to their unique characteristics. Early-Career Researchers (ECRs) often face specific obstacles when engaging in the process of knowledge co-production. In this perspective paper, we shed light on the particular characteristics of knowledge co-production in marine social-ecological systems and the obstacles ECRs in the marine sciences face. Based on these obstacles, we discuss actions that can be taken at various organizational levels (institutional, community, supervisor, and individual) in order to leverage change towards a more inclusive environment for ECRs engaging in knowledge co-production. We conclude that both bottom-up (individual to institutions) and top-down (institutions to individual) actions are required. However, we emphasize the responsibilities of institutions to create conditions in which the needs of ECRs are met. This will be necessary to adequately support ECRs engaging in knowledge co-production and thus contribute to tackling sustainability challenges in coastal and marine social-ecological systems.

Bottom trawling is one of the main pressures on benthic ecosystems, directly impacting the targeted species and physically disturbing the seabed and the benthic invertebrate communities, in turn indirectly impacting benthivorous fish and the entire benthic food web structure and functioning. To predict the cascading effect of bottom trawling on benthic and demersal fish communities, it is crucial to understand the trophic interactions between benthic and demersal fish and benthic invertebrates. Here, we assessed the diet of benthic and demersal fish and the structure and functioning of the benthic food web in two areas in the German Baltic Sea, the Fehmarnbelt and the Odra Bank. The Fehmarnbelt benthic invertebrate community is characterized by a high number of species and biomass, contrary to the one on the Odra Bank which is species poor with high individual abundance but low biomass. We used mixing models based on stable isotopes of carbon and nitrogen combined with stomach content analyses to estimate the fish diet at both sites, and we used community-wide trophic indices, derived from stable isotopes to compare the structure and functioning of the fish benthic food webs. We show that fish in the Fehmarnbelt can chose preferential prey items, resulting in higher trophic diversity, contrary to fish on the Odra Bank, which feed on all available prey species, resulting in higher trophic redundancy. We found that the generalist behavior of fish on the Odra Bank is likely the result of scarcity in prey items, the benthic invertebrate community being species poor with high abundance of small individuals. We demonstrate that the differences in structure and functioning of the benthic fish food web between the two sites was mainly driven by differences in the characteristics of the benthic prey communities.