By Anna Vader (UNIS) and main photo by Christian Morel/ christianmorel.net
Dr. Snorre Flo’s thesis investigated trophic species interactions of small Arctic marine copepods and nematodes using a novel molecular approach. Small invertebrates (≤ 2 mm) are key members of the Arctic marine ecosystem, yet their trophic interactions have rarely been researched due to methodological challenges. In this thesis, a novel brute force approach to prey metabarcoding was developed and applied to characterize the trophic interactions of small pelagic copepods and benthic nematodes over four seasons in the Barents Sea and Nansen Basin.
From left: Committee leader Associate Professor Christian Selbach (UiT), supervisor Anna Vader, Dr. Snorre, second opponent Dr. Jens C. Nejstgaard (Leibniz Institute of Freshwater Ecology and Inland Fisheries, Germany), first opponent Professor Monika Quinoes Winder (Stockholm University, Sweden)
The key findings of the thesis were: 1) the brute force approach provided plentiful of ecologically meaningful data, and offered a simple and less biased method of studying the prey of small, but important invertebrates; 2) small pelagic copepods and benthic nematodes consumed a broad variety of eukaryotes, and dietary compositions varied primarily along seasonal factors, rather than the specific feeding strategy or morphology of the consumers, respectively; and 3) significant portions of the diets were likely obtained from sinking particulate materials, including chaetognath fecal pellets, discarded larvacean houses, diatoms and metazoan bodies.
Nematode diets indicated that these particles had become colonized and reworked by marine fungi on their transit towards the seafloor, suggesting that marine fungi played important roles as prey and by modifying vertical export in the Arctic. To conclude, in this thesis we applied a novel molecular method to illuminate and expand on the trophic roles of the small but important invertebrates of the marine Arctic. We identified several novel interactions and highlighted hypotheses that require further testing. There are thousands of invertebrates in the Arctic and beyond, whose interactions remain unknown, and a brute force methodology may facilitate such ambitious but important work.
From left: Supervisors Tove M. Gabrielsen (UiA, UNIS) and Anna Vader (UNIS), Dr. Cheshtaa, committee leader professor Ane Timenes Laugen (UiA), first opponent professor Daniel Vaulot (UiO). Second opponent Dr. Matthias Wietz (AWI, Germany) participated digitally.
Dr. Cheshtaa Chitkara’s thesis investigated how communities of microbial eukaryotes are changing over time and space in a warming Arctic. Using over a decade of data from different Arctic fjords in Svalbard, Greenland and northern Norway, two main questions were addressed: (1) how communities shift with the seasons (Seasonality), and (2) how communities and species respond to warming events linked to Atlantification.
Microbial eukaryotes perform many important functions in the marine ecosystem – acting as primary producers, consumers and parasites. However, it is not known how their communities will be affected by increasing and shallower inflow of warm Atlantic water into the European Arctic (Atlantification).
Cheshtaas thesis investigated the community dynamics and resilience of microbial eukaryotes in the Isfjorden-Adventfjorden (IsA) time-series from 2011 to 2019. It also compared IsA with other Arctic time-series across a latitudinal gradient. Communities in water and net samples from four sites, Ramfjorden (RAM) in northern Norway, Nuup Kangerlua (NK) in western Greenland, and Isfjorden-Adventfjorden (IsA) and Billefjorden-Adolfbukta (BAB) in Svalbard, were determined by DNA metabarcoding and microscopy, and compared to chlorophyll-a biomass, primary production, grazer abundances, flow cytometry counts, nutrients, temperature and salinity.
Results indicate that seasonal changes in light availability is the primary driver of community dynamics across latitudinal gradients, with the influence of water masses (temperature and salinity) acting as a significant secondary factor. All fjords exhibited similar spring bloom species. However, bloom timing varied independent of latitude, showing that local fjord morphology, such as the presence of glaciers and sills, is also influential. While no significant trend in Atlantification or community dynamics was evident at IsA within the studied timeframe, warming pulses correlated with alterations in microbial eukaryotic communities, especially apparent during the productive period of the year. Indicator species for Atlantic water inflow were particularly abundant during the warm years 2014 and 2019.
The thesis highlights microbial responses to environmental change in the Arctic and the necessity for continued long-term monitoring to decipher shifts due to Atlantification from “normal” seasonality and interannual variation. While the overall eukaryotic microbial community demonstrated resilience, the potential for critical shifts in species richness, diversity and community composition could be a concern for ecosystem stability in the future due to prolonged Atlantification.
Dr. Cheshtaa Chitkara’s thesis was entitled “Arctic marine microbial eukaryotes – Spatiotemporal drivers of community structure and ecological impacts of Atlantification” and was supervised by Associate Professor Anna Vader (UNIS) and Professor Tove M. Gabrielsen (UiA/UNIS).
Dr. Snorre Flo’s thesis was entitled “On the appetites of small copepods and nematodes in the Arctic Barents Sea and Nansen Basin: In situ trophic interactions revealed by brute force prey metabarcoding” and was supervised by Associate Professor Anna Vader (UNIS) and Professors Camilla Svendsen, Bodil A. Bluhm and Kim Præbel (all UiT).
We congratulate Dr. Snorre Flo and Dr. Cheshtaa Chitkara on their excellent work and well-earned degrees and wish them all the best in their future careers!
All photos: Ingrid Ballari Nilsen/UNIS