Monitoring marine alien and invasive species. A comparison between the traditional method (eRAS) and DNA-based identification of species.

Abstract: There is a major concern with the uncontrolled spreading of alien and invasive species, caused by an increase in travelling by boat globally. These are dispersed via ballast water, by fouling on ships and in fishing gear. If an alien or invasive species is introduced into a foreign environment, it can have negative effects on the native species composition on the site. The aim of this study was to investigate which method, DNA-based or traditional, that is more suitable when tracking and identifying alien and invasive species in harbours. Detecting alien or invasive species in an early stage is crucial to prevent spreading, and for this, sensitive methods that can detect species in all their life stages are needed. The research question was “Which method is best to track and determine potentially alien – or invasive species in harbours?”. The DNA-based method, water samples, plankton samples and arms settling panels (Autonomous Reef Monitoring Structures), collected genetic material and metabarcoding was used to identify and species determine any findings. For the traditional methods; panels, scrapings and artificial habitats, only visual morphological identification was used for identification and determination of the findings. The results showed that the DNA-based method found ten alien and invasive species in their samples, were two, round goby and the red algae Bonnemaisonia hamifera, are classified as invasive. The traditional method recovered zero alien or invasive species in their samples. The traditional method are today included in the Swedish monitoring program and with the results of this study, it is proposed that these are replaced by the DNA-based method for future enhanced monitoring of alien and invasive species.