Ecological restoration measures for shallow coastal habitats of the Baltic Sea and the Skagerrak – effectiveness, costs and knowledge gaps

Abstract

Human-induced pressures are interfering with the environmental status of marine and coastal areas impacting their ability to maintain ecosystem functions and services. In combination with planning and conservation measures to halt ongoing biodiversity loss, there is a need for developing and adapting toolboxes for active and passive restoration. Such habitat-specific restoration measures need to be tailor-made to strengthen the ecosystem services we depend on and to increase the resilience to climate change and other pressures. Today, there is a knowledge gap both regarding potential restoration measures and in the follow-up and evaluation of the effectiveness of existing measures. There is also a lack of general guidance about which measures are the most functional ones. Such knowledge is of utmost importance for implementation of the EU nature restoration law.

Here, we provide an overview of eight marine/coastal active and passive restoration measures relevant and applicable for the Northeast Atlantic, focusing on the Baltic Sea and the Skagerrak region. The measures reviewed foremostly aim at reversing negative impacts from physical disturbance on coastal habitats, focusing on active restoration of eelgrass beds, macrophyte beds on soft sediment, rocky-shore macroalgal beds, blue mussel reefs, stony reefs, as well as coastal wetlands and flads/lagoons. Two passive restoration methods are also reviewed, including strengthening populations of predatory fish and undertaking habitat protection. When relevant, these measures are reviewed with regard to type of restoration target, threats, benefits from restoration, restoration measures/methodologies and documented effects, pertinent geographical areas, approximate costs and possible additional information/key knowledge gaps. Among the measures reviewed, three stand out as having especially low costs per area/effort, i.e., 1) restoration of coastal wetlands and flads/lagoons, 2) strengthening populations of predatory fish and 3) habitat protection. We further conclude that there is a general lack of evidence for the cost-effectiveness of measures and that even the more costly measures may still bring more benefits than costs. Nevertheless, many measures are still understudied, provide limited positive effects in relation to their costs, are hard to upscale, have geographical limitations for a broader use or are sensitive to poor environmental status and continued environmental degradation. Additionally, all measures continuously need various degrees of development and fine tuning in order to improve success rates and value for money. The results are intended to support management in this maritime region and they are also applicable to other areas where the studied or similar habitat types exist.