Detection of fish species from marine protected areas of the North Sea using environmental DNA.

This report describe the first application of environmental DNA-metabarcoding approach for the assessment of fish species diversity in two marine protected areas of the North Sea: the Doggerbank and the Sylt Outer Reef. We collected 64 water samples and detected 24 fish species. We discuss qualitative differences between MPAs and compare the results with those obtained from bottom-trawl surveys in the same areas. We found three additional species to those documented in the same year with trawls, including the critically endangered European eel.

eDNA as a tool for non-invasive monitoring of the fauna of a turbid, well-mixed system, the Elbe estuary in Germany.

The Elbe is one of the longest European rivers and features a large, turbid and well-mixed estuary, which runs through the inner city of Hamburg. The Elbe has been closely monitored using classical catch techniques in the past. Here we tested a COI-based eDNA approach for assessing the biodiversity within the Elbe. We sampled three stations in the Elbe, included low and high tide events, as well as two adjoining lakes to compare the recovered faunas. To analyze the data, we employed two different pipelines: the automated mBRAVE pipeline utilizing the BOLD database and one including NCBI BLAST. The number of OTUs with species or higher-level identifications were similar between both approaches with 352 OTUs and 355 OTUs for BLAST and mBRAVE, respectively, however, BLAST searches recovered another 942 unidentified metazoan OTUs. Many taxa were well represented; however, fish species were poorly represented, especially in the Elbe estuary samples. This could be a result of the universal COI primers, which also yielded high read numbers for non-metazoan OTUs, and small-bodies taxa like Rotifera, which might have been sampled together with the eDNA. Our results show a strong tidal influence on the recovered taxa. During low tide, downstream stations resembled sites further upstream, but the former showed a very different OTU composition during high tide and early tide. Such differences might be due to varying impacts of upstream-originating eDNA during tide cycles. Such factors need to be considered when routinely employing eDNA for monitoring programs.

Evaluation of the bioaccumulation potential of alizarin red S in fish muscle tissue using the European eel as a model.

For fish stock management and large-scale stocking programs, the chemical substance alizarin red S (ARS) is an important tool to mark fish permanently. Equally, for the IUCN red list species European eel (Anguilla anguilla), ARS is proven to be the most promising option for mass marking. ARS binds to calcified structures (i.e., bones and otoliths) and can be detected using a fluorescence microscope. Despite the frequent application of ARS, not only for eels but also for fish in general, until today, no study has evaluated its bioaccumulation potential. Therefore, the German Federal Risk Assessment Authority was unable to classify ARS as harmless because of a potential risk to consumers' health. Using the technique of liquid chromatography mass spectrometry, an ARS detection protocol was developed and the bioaccumulation potential of ARS in European eel muscle tissue was estimated. A detection limit of 8.9 µg kg-1 could be reached by optimizing the detection method in fish muscle tissue. In the current study, 250 eels between 6 and 57 cm of total length have been analyzed for ARS between 0 day and 3 years after the marking process. The highest concentration of ARS (6056 µg kg-1) was observed immediately after marking in the smallest length class. Only 1 year after the marking procedure, the ARS concentration was below detection limit. A new method for ARS detection in fish muscle tissue, followed by utilization on marked eels, was able to show that the bioaccumulation of ARS in edible fish muscle was highly unlikely.