Stæhr, P.A.U., Jakobsen, H.H. 2023. Testing the D2C1 GES indicator for marine non-indigenous species with long-term data from Danish Seas. Aarhus University, DCE – Danish Centre for Environment and Energy, 23 pp. Scientific Report No. 546 http://dce2.au.dk/pub/SR546.pdf
We investigated the usefulness of a proposed Good Ecological Status (GES) indicator for assessing the arrival rate of non-indigenous species (NIS), an assessment criterion applied under the Marine Strategy Framework Directive. Based on NIS records in Danish seas from 1850 to 2020, we applied a statistical baseline analysis to define a baseline level for annual NIS introductions (#NIS per year). We aggregated NIS observations into six-year assessment periods and investigated changes (#NIS per six years) compared to a GES threshold of a 50% reduction relative to the identified baseline introduction rate. We discuss the importance of human activities influencing the observed changes in NIS introductions. Finally, we highlight possible ways of accounting for uneven monitoring efforts and pressures associated with different pathways of introduction on setting a GES threshold.
