Ecological Representativity of Marine Protected Areas along the Swedish West Coast : evaluating the effectiveness of the existing network and identifying expansion opportunities in the Skagerrak

Abstract: Marine protected areas (MPAs) are recognised worldwide as an important tool to combat biodiversity loss. The European union (EU) has recently adopted a new strategy aiming at protecting at least 30% of Europe’s marine environment and inferring strict protection for one third of the protected area. Examples of strict protection are no-take zones, a complete ban on commercial fishing. This study aimed to evaluate the efficiency of the current MPA network along the Swedish west coast and expansion opportunities were identified in the coastal zone of the Skagerrak in Västra Götaland county. By using monitoring data from samples of juveniles, habitat distribution for 21 species of fish and crustaceans were mapped using Esri ArcGIS Pro. The ecological representativity, i.e., the proportion of protected habitat (%) for each species, was calculated and compared against the goals set by the EU. Anthropogenic disturbances were also mapped to identify overlap of areas with high species richness and high anthropogenic pressure, focussing on endangered and commercially important species. The pressure data was further used as a cost-matrix to prioritise protection of habitats under high pressure, when analysing expansion opportunities using the conservation planning tool Marxan. Two target levels (40% and 50% habitat protection, based on results from the calculated ecological representativity) and two different scenarios were tested with Marxan; one unbiased solution with no spatial constraints, and one biased solution forcing already protected habitats to be included and thus focusing on expanding from existing MPAs. Results show that the ecological representativity provided by the current MPA network is sufficient in protecting ≥30% of the species habitat on the west coast, but in the Skagerrak, it fails to provide protection for the two-spotted goby (9%). The Marxan-analysis showed that it is possible to enhance protected habitat to >50% for all species in the Skagerrak. A best conservation solution was obtained when endangered and commercially important species were ranked as more important to protect than other species. Additionally, using the biased solution and instructing Marxan to emphasise MPA compactness yielded the most cost-efficient conservation solution with 39% less total reserve area required compared to 49% for the unbiased solution. Expansion opportunities should focus on the coastal area from Gothenburg northward to Orust where a large part of unprotected habitats are situated. Even though the ecological representativity is good for most of the species, many are endangered and a small frequency of occurrence in the fishing samples, suggests that merely establishing MPAs might not be enough. Inferring stricter protection such as no-take zones may be required, both from a species-perspective and as a measure to achieve the goal set by the EU. Thus, future work should focus on amending regulations in existing MPAs as well as expanding the current MPA network and include no-take zones.