Environmental DNA from seawater samples correlate with trawl catches of subarctic, deepwater fishes

Remote polar and deepwater fish faunas are under pressure from ongoing climate change and increasing fishing effort. However, these fish communities are difficult to monitor for logistic and financial reasons. Currently, monitoring of marine fishes largely relies on invasive techniques such as bottom trawling, and on official reporting of global catches, which can be unreliable. Thus, there is need for alternative and non-invasive techniques for qualitative and quantitative oceanic fish surveys. Here we report environmental DNA (eDNA) metabarcoding of seawater samples from continental slope depths in Southwest Greenland. We collected seawater samples at depths of 188-918 m and compared seawater eDNA to catch data from trawling. We used Illumina sequencing of PCR products to demonstrate that eDNA reads show equivalence to fishing catch data obtained from trawling. Twenty-six families were found with both trawling and eDNA, while three families were found only with eDNA and two families were found only with trawling. Key commercial fish species for Greenland were the most abundant species in both eDNA reads and biomass catch, and interpolation of eDNA abundances between sampling sites showed good correspondence with catch sizes. Environmental DNA sequence reads from the fish assemblages correlated with biomass and abundance data obtained from trawling. Interestingly, the Greenland shark (Somniosus microcephalus) showed high abundance of eDNA reads despite only a single specimen being caught, demonstrating the relevance of the eDNA approach for large species that can probably avoid bottom trawls in most cases. Quantitative detection of marine fish using eDNA remains to be tested further to ascertain whether this technique is able to yield credible results for routine application in fisheries. Nevertheless, our study demonstrates that eDNA reads can be used as a qualitative and quantitative proxy for marine fish assemblages in deepwater oceanic habitats. This relates directly to applied fisheries as well as to monitoring effects of ongoing climate change on marine biodiversity-especially in polar ecosystems

Short-term temporal variation of coastal marine eDNA

Temporal variation in eDNA signals is increasingly explored for understanding community ecology in aquatic habitats. Seasonal changes have been addressed using eDNA sampling, but very little is known regarding short-term temporal variation that spans hours to days. To address this, we filtered marine water samples from a single coastal site in Denmark every hour for 32 h. We used metabarcoding to target both fish and broader eukaryote diversity and evaluated temporal changes in this marine community. Results revealed variation in fish species richness (15–27) and eukaryote class richness (35–64) across the 32 h of sampling, and we further evaluated sampling efforts needed to reach different levels of diversity saturation. Relative read frequency data for both fish and eukaryotes indicated a clear diel change in community composition, with different communities detected during daylight versus dark hours. The abundance signals in our data reflected biological variation rather than stochastic variation, since replicates taken at the same hour were more similar to each other than those taken at different hours. Our compositional results indicated a dynamic community, rather than a static pool of eDNA—even across a few hours. The fish data showed a daily pattern of relative species abundances, and the uncoupling of fish and broader eukaryote data suggest that variation in eDNA profiles across a single day can provide valuable information reflecting diel changes, at least for highly mobile organism groups. However, our results also point to several pitfalls in current eDNA experimental design, in which samples are taken over large areas without relative time-consistency or short-term replication. Our findings shed new light on short-term variation in coastal eDNA and have wide implications for experimental study design and for incorporating temporality into project conceptualization for future aquatic biodiversity monitoring.publishedVersio

A National Scale “BioBlitz” Using Citizen Science and eDNA Metabarcoding for Monitoring Coastal Marine Fish

Marine biodiversity is threatened by human activities. To understand the changes happening in aquatic ecosystems and to inform management, detailed, synoptic monitoring of biodiversity across large spatial extents is needed. Such monitoring is challenging due to the time, cost, and specialized skills that this typically requires. In an unprecedented study, we combined citizen science with eDNA metabarcoding to map coastal fish biodiversity at a national scale. We engaged 360 citizen scientists to collect filtered seawater samples from 100 sites across Denmark over two seasons (1 p.m. on September 29th 2019 and May 10th 2020), and by sampling at nearly the exact same time across all 100 sites, we obtained an overview of fish biodiversity largely unaffected by temporal variation. This would have been logistically impossible for the involved scientists without the help of volunteers. We obtained a high return rate of 94% of the samples, and a total richness of 52 fish species, representing approximately 80% of coastal Danish fish species and approximately 25% of all Danish marine fish species. We retrieved distribution patterns matching known occurrence for both invasive, endangered, and cryptic species, and detected seasonal variation in accordance with known phenology. Dissimilarity of eDNA community compositions increased with distance between sites. Importantly, comparing our eDNA data with National Fish Atlas data (the latter compiled from a century of observations) we found positive correlation between species richness values and a congruent pattern of community compositions. These findings support the use of eDNA-based citizen science to detect patterns in biodiversity, and our approach is readily scalable to other countries, or even regional and global scales. We argue that future large-scale biomonitoring will benefit from using citizen science combined with emerging eDNA technology, and that such an approach will be important for data-driven biodiversity management and conservation

Holistic monitoring of freshwater and terrestrial vertebrates by camera trapping and environmental DNA

The anthropogenic impact on the world's ecosystems is severe and the need for non-invasive, cost-effective tools for monitoring and understanding those impacts are therefore urgent. Here, we combine two such methods in a comprehensive multi-year study; camera trapping (CT) and analysis of environmental DNA (eDNA), in river marginal zones of a temperate, wetland Nature Park in Denmark. CT was performed from 2015 to 2019 for a total of 8778 camera trap days and yielded 24,376 animal observations. The CT observations covered 87 taxa, of which 78 were identified to species level, and 73 were wild native species. For eDNA metabarcoding, a total of 114 freshwater samples were collected from eight sites in all four seasons from 2017 to 2018. The eDNA results yielded a total detection of 80 taxa, of which 74 were identified to species level, and 65 were wild native species. While the number of taxa detected with the two methods were comparable, the species overlap was only 20%. In combination, CT and eDNA monitoring thus yielded a total of 115 wild species (20 fishes, 4 amphibians, one snake, 23 mammals, and 67 birds), representing half of the species found via conventional surveys over the last ca. 20 years (83% of fishes, 68% of mammals, 67% of amphibians, 41% of birds, and 20% of reptiles). Our study demonstrates that a holistic approach combining two non-invasive methods, CT, and eDNA metabarcoding, has great potential as a cost-effective biomonitoring tool for vertebrates

On Reading Grace\u27s Potiki

In her article On Reading Grace\u27s Potiki Eva Rask Knudsen takes as her point of departure the critical impasse of postcolonial analyses of Indigenous literatures and the claim made by some (Indigenous) commentators that non-Indigenous scholars and critics often re-colonize the texts they deem to be postcolonial because — in their theoretical concern with issues of marginalization and resistance — they overlook (and so overwrite) the specific indigenous knowledges and ontologies that the literatures draw on. Through an analysis of the 1986 novel Potiki by Māori writer Patricia Grace, Rsak Knudsen looks in other directions than those catalogued by postcolonial convention. With attention to Māori storytelling procedures and Māori notions of textuality, Rask Knudsen postulates that the non-Indigenous scholar/critic may venture legitimately and purposefully into indigenous territory if the cultural signposts of that territory are acknowledged. As Potiki is structured as a narrative told within the context of a Māori meeting house (whare nui), a ceremonial site that encourages dialogue and public debate, the novel offers, by extension, a venue also for the scholar\u27s/critic\u27s encounter with indigenous difference