The usability of eDNA to identify and quantify zooplankton communities

Our ocean is in the middle of a triple planetary crisis. Climate change, pollution, and biodiversity loss impacts its habitats and inhabitants. Ocean monitoring programs are valuable as they provide data which can help predict the impacts of both climate change and human activity. Yet, biodiversity monitoring has traditionally relied on morphological species identification, which is both time-consuming and costly. Molecular methods have, on the other hand, shown promising results in detecting the hidden species diversity. However, many studies emphasize that morphology is the only reliable method for quantification, and DNA-based methods cannot give reliable abundance data, but currently there is no consensus. Thus, the aim of this study was to test the applicability of DNA-based methods compared to traditional morphological species identification in biodiversity assessment for future monitoring programs, and test if molecular methods can be used in a quantitative matter. Zooplankton species are good indicators for changes in the environment, but species diversity assessments present challenges and thus main focus of this study. Water samples for environmental DNA (eDNA) and zooplankton net samples were collected at surface, 10-, 25- and 50-meters depth both night and day in spring 2022 from the Mausund Bank (63.8° – 64.2°N, 8.2° − 9.0° E), which is an area of significant importance for both biological diversity and production. QPCR of mock community of cultured Calanus finmarchicus and experimental water was used. In the samples collected at the Mausund Bank, a total of 180 taxa were detected using eDNA and only 29 taxa using morphological species identification, showing how DNA based methods are suitable for improving species identification and exposing the hidden diversity. On the other hand, quantification of mock communities showed no correlation between C. finmarchicus counts and eDNA reads, hence, emphasizing the difficulty in species quantification using molecular methods. DNA-based methods have a great potential for species identification and detection, and it is perhaps the most likely source of a new and innovating marine monitoring technique.