Peter A.U. Stæhr, Nikolaj R. Andersen, Karolina R. Andersen, Helle Buur, Hans H. Jakobsen, Janus Larsen, Marie Maar, Rumakanta Sapkota, Vibe Schourup-Kristensen, Kathrina Zimmer, Anne Winding 2023. Identification, dispersal, and possible mitigation responses for non-indigenous species in the Danish Wadden Sea area. Aarhus University, DCE – Danish Centre for Environment and Energy, 72 pp. Scientific Report No. 547 http://dce2.au.dk/pub/SR547.pdf
Summary
This report provides data and knowledge about non-indigenous species (NIS) established in the Danish part of the Wadden Sea. Through novel intensive monitoring and review of available data sources, comprehensive updated lists of NIS were obtained, along with information on pathways of introduction and assessments of various types of impacts. Dispersal routes of NIS into the Wadden Sea were quantified with a 3D hydrodynamic model. The combination of updated NIS lists, knowledge of pathways of introduction and modelling of dispersal routes were used to identify possible mitigation measures against NIS, including invasive species, in the Danish part of the Wadden Sea. As such, the project provides important information to the Danish Marine Strategy’s program of measures related to MSFD Descriptor 2. The project collaborated with an advisory board with representatives from Germany and the Netherlands to ensure compatibility with monitoring methods used in the other parts of the Wadden Sea and facilitate the exchange of knowledge on suitable mitigation measures.
A total of 50 NIS was detected using conventional and molecular techniques applied for four different sampling approaches in both selected harbours and tidal flats and tidal channels. Most NIS occurred in the two largest harbors, followed by water areas with intensive shipping, and with least NIS in the more disconnected water areas. Most NIS were observed within invertebrates (54%), phytoplankton (21%), macroalgae (14%), zooplankton (7%) and fish (4%). Interestingly, 14 NIS appear to be new for Danish marine waters compared to the most recent version of the Danish gross NIS list. Only two of these were detected with conventional techniques, one with qPCR and metabarcoding and the remaining 11 only by metabarcoding. We consider the latter group as potential NIS until validated against conventional sampling techniques.
Combining NIS detected with the novel sampling approaches with historical data from the Danish national monitoring program (NOVANA), previous research projects and records validated by taxonomic experts, a total list of 82 NIS were established in the Wadden Sea area. Of the 50 NIS detected through monitoring in this project, 26 were new to the region and the remaining NIS were primarily detected through the national monitoring program, from which it was possible to describe their annual presence since 1990. Of 82 NIS observed in the Wadden Sea, 41 appear to have been introduced via shipping (mostly ballast water and hull fouling), followed by 39 introduced through secondary spread (unaided), a few via aquaculture and 11 with unknown pathways. More than half of the NIS was assessed to have two or more pathways of introduction. While these numbers are associated with considerable uncertainty, our model-based NIS dispersal assessment supports shipping as a key introduction pathway. In addition, our model suggests that the secondary spread of NIS from populations in more southernly parts of the Wadden sea is of relevance.
Relevant mitigation measures to reduce NIS introductions and impact include enforcement of international agreements related to ballast water, biofouling and biosecurity guidelines, increased public awareness, considerations of improved protection and active restoration of selected sites. Continued monitoring is finally critical for assessments of NIS impact.
