Eivind Stensrud

• Kvalheim, Lone; Stensrud, Eivind; Knutsen, Halvor; Hyvärinen, Olli Petteri & Eiler, Alexander (2024). Integration of citizen science and eDNA reveals novel ecological insights for marine fish conservation. Environmental DNA. 6(4). doi: 10.1002/edn3.584. Full text in Research Archive Show summary

  In the face of climate change, the accelerating nature crisis, and other anthropogenic impacts, conserving biodiversity demands effective monitoring. While innovative approaches have emerged to enhance biodiversity assessment, significant data gaps persist, particularly within marine ecosystems. In this study, we assess the utility of combining citizen (community) science with environmental DNA (eDNA) metabarcoding for characterizing and quantifying marine fish biodiversity. Over the summer of 2022, 32 volunteers conducted extensive water sampling in a large Norwegian fjord, yielding 96 samples. Contrasting eDNA findings with conventional observational surveys (such as a national species registration database and beach seine surveys) unveiled a substantial overlap in recorded species inventories. The eDNA citizen science initiative identified previously undocumented species and rediscovered others emphasizing an increase in warm-water species within the study area. Additionally, eDNA data unveiled reduced diversity within the inner fjord relative to the outer fjord. To conclude, our study demonstrates the successful integration of eDNA within a citizen science framework, facilitating comprehensive biodiversity tracking across coastal marine regions. These findings hold promise for advancing marine conservation efforts by providing valuable data to inform critical decision-making processes.

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• Stensrud, Eivind; Hyvärinen, Olli Petteri; Rostum, Tarjei; Angell, Thorvald; Knutsen, Halvor & Lundström, Karl [Show all 8 contributors for this article] (2026). PREDATORS AS SENTINELS: UNRAVELING TROPHIC SHIFTS IN A DARKENING FJORD USING dDNA AND STABLE ISOTOPES OVER THE LAST 20 YEARS. Full text in Research Archive Show summary

  The Greater Oslofjord, like many other coastal systems, is undergoing rapid ecological shifts driven by climate change, coastal freshening and darkening. To understand how these bottom-up stressors restructure food webs, we utilized a multi-trophic approach analyzing three sympatric predators (approx. 500 individuals): Harbour seals (Phoca vitulina), Great Cormorants (Phalacrocorax carbo), and Atlantic Cod (Gadus morhua). We combined dietary DNA (dDNA) metabarcoding with stable isotope analysis (δ13C, δ15N) to trace temporal and spatial dietary changes over 20 years. Traditional morphological methods often fail to capture soft-bodied prey and secondary consumption; thus, we used dDNA combined with novel reference databases to maximize taxonomic resolution. Our dDNA results revealed high-resolution predation data, including the detection of secondary consumption (zoo- and phytoplankton) alongside primary prey, effectively mapping the food web from top predators down to primary producers. Isotope data complemented this by delineating trophic niche widths and source of primary production (land vs. sea). We observed distinct dietary variations linking predator foraging behavior to environmental gradients. This included observable changes over the last 20 years, such as an increase in invasive species in their diet and a shift in zoo- and phytoplankton composition. These findings demonstrate that combining molecular and isotopic analysis of top predators provides a powerful tool for monitoring the cascading effects of anthropogenic changes on marine food webs.

• Angell, Thorvald; Eiler, Alexander & Stensrud, Eivind (2026). Changes at the Base of the Food Web in the Oslofjord and Skagerrak. Top predators as food web sentinels using DNA metabarcoding and stable isotope analysis. Universitetet i Oslo. Full text in Research Archive Show summary

  The coastal food webs of the Oslofjord and Skagerrak are undergoing alterations in structure, energy transfer, and basal organic matter (OM) sources due to multiple anthropogenic drivers, including eutrophication, increased terrestrial runoff, and climate change. These interacting pressures elevate the influx of terrestrial OM (tOM) and are associated with an increase in chromophoric dissolved OM (cDOM) to the coastal areas. As these allochthonous inputs increasingly exceed the autochthonous OM production, the resulting brownification alters the light attenuation regimes and thus drives the base of coastal ecosystems towards heterotrophic processes. Despite these documented biogeochemical shifts, the extent to which they disrupt the base of the food web and propagate upward through trophic interactions to the top predators remains poorly understood. Resolving how anthropogenic stressors restructure trophic pathways is also essential for predicting ecosystem responses to conservation and restoration strategies. To investigate how anthropogenic pressures have altered the coastal food web over the last two decades, dietary DNA metabarcoding was conducted on gut content from harbour seal (Phoca vitulina) and great cormorant (Phalacrocorax carbo), targeting secondary consumption with emphasis on the base of the food web. Two complementary gene markers were used: 18s rRNA V4 (Pirreda) to characterize the eukaryotic protist communities and COI (Leray-XT) to identify metazoan prey, including fish and invertebrates. To assess temporal shift in basal energy and organic matter sources, stable isotope analysis of top predator tissue was complemented with longterm monitoring data of Atlantic cod (Gadus morhua) and blue mussel (Mytilus edulis). These multiple approaches successfully characterized the food web from top predators down to the base of the food web. Although the findings revealed diet partitioning in the top predators primary consumption, reflecting different foraging strategies, they exhibit a strong overlap in the lower trophic levels and at the base of the food web. This suggests that the top predators are affected by the same bottom-up regime, rendering them mutually susceptible to the cascading effects of anthropogenic pressures, particularly increased terrestrial organic matter inputs. Finally, complementary isotopic data revealed a significant decrease in d 13C over the past 20 years, signaling a systemic shift in the coastal food web’s primary energy base toward allochthonous carbon sources.

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