Mapping fish diversity in the Oslo fjord by combining eDNA and citizen science
There is a great need to track biodiversity if we want to counteract biodiversity decline caused by anthropogenic impacts including global warming and pollution. Novel, innovative methods have been proposed to improve biodiversity monitoring such as environmental DNA (eDNA) approaches. In this study, the eDNA metabarcoding method was combined with citizen science with the aim of gaining novel insight into marine biodiversity. The Oslo fjord was surveyed by 32 volunteers collecting 96 samples over the summer of 2022. The eDNA detections were compared to the combined efforts of traditionally sampled registrations in the national species registration bank, Artsdatabanken, and the beach sein survey by Havforskningsinstituttet, limited to within 1 km radius of the sampling locations and a time period of the last five years, which resulted in 55 observed species. This can be compared with the eDNA approach which detected 66 species across the sampling locations in the fjord. As such this provided novel insight into the species diversity in the Oslo fjord by the rediscovery of seven species that had not been registered the last five years and the detection of two novel species.  Furthermore the data revealed lower diversity in the inner when compared to the outer fjord with the physical differentiation potential caused by the Drøbak sill, and 5 species were only detected in the inner while 15 species were only detected in the outer part of the fjord. Still, there is no distinct community divided by the sill which was discovered in this study. This study concludes that locals are willing to aid in research toward conservation of the fjord, resulting in a successfully implemented citizen science project in the area. The combination of eDNA metabarcoding and citizen science can provide novel insight and aid in tracking biodiversity changes in vast areas in a successful way.