The Pacific planktonic diatom Neodenticula seminae re-entered the North Atlantic in 1998-1999 after an absence of 800,000 years, carried by anomalously strong Pacific-water flow through the Arctic Ocean under reduced sea-ice cover. It has since been recorded in water-column and sediment samples from the Labrador Sea to the northern Nordic Seas (up to 79 degrees N), including six May 2002 samples from the Greenland Sea between 65 and 68 degrees N. Because this species can account for over 40% of diatom assemblages in its native subarctic Pacific and routinely dominates blooms in the Gulf of St. Lawrence, its continued northward spread raises the question, posed explicitly by Olofsson and Wulff (2021), of what effect it may have on the northern ecosystem - a question the literature still cannot answer. The open problem is to determine the ecological consequences of N. seminae for the northern Nordic Seas and Greenland Sea pelagic ecosystem: whether it reaches bloom-forming abundances at Nordic Seas latitudes, and what its establishment would mean for the native plankton community, the grazing food web, and biogenic silica cycling. Existing work to date documents occurrence, spread, or physical dispersal connectivity, while the ecological-effect question remains open.

Background

Diatoms are single-celled algae with silica shells that form a major part of the phytoplankton - the photosynthetic plankton base of marine food webs. Neodenticula seminae is an open-ocean (oceanic) diatom whose native range is the subarctic Pacific Ocean and Bering Sea, where it is a dominant member of the spring and summer diatom assemblages and a key driver of biogenic silica export (the sinking of silica shells that transports silicon and carbon to the deep ocean). The Nordic Seas - the Greenland, Icelandic, and Norwegian Seas between Greenland and Scandinavia - are the Atlantic-sector gateway of the Arctic; the Greenland Sea lies on its western, ice-influenced side and is warming and losing ice faster than almost any other marine region.

In 1998-1999, Continuous Plankton Recorder surveys (an instrument towed behind merchant ships that filters and records plankton along ship tracks) detected N. seminae in the Labrador Sea, its first record in the North Atlantic in 800,000 years, as documented by Reid et al. (2007). Its reappearance was attributed to a period of anomalously strong near-surface flow of Pacific water through the Arctic Ocean into the Atlantic, made possible by reduced Arctic sea-ice cover; it is widely cited as the first observed biological consequence of an opening trans-Arctic dispersal corridor between the Pacific and Atlantic oceans. Poulin et al. (2010) confirmed by morphology and molecular phylogeny that the Atlantic population is the same species as the Pacific one. Miettinen et al. (2013) then found N. seminae in northern Nordic Seas sediment cores in layers deposited after about 1998, up to 79 degrees N, evidence of an ongoing northward spread; Matul and Kazarina (2020) showed from surface sediments that it is now a routine element of the modern diatom flora of the Nordic, Labrador, and Irminger Seas. Kelly et al. (2020) used a high-resolution ocean model with Lagrangian particle tracking (numerically following passive drifters in simulated ocean currents) to map the trans-Arctic pathways and timescales over which such Pacific-to-Atlantic dispersal can continue, framing N. seminae's arrival as possible early evidence of a looming ecological regime shift in the Atlantic.

Within this lineage, Olofsson and Wulff (2021) re-examined a light-microscopy plankton survey of the Greenland Sea from May 2002 and recorded N. seminae in six samples between 65 and 68 degrees N, alongside 195 other micro- and nanoplankton taxa (plankton roughly between about 2 and 200 micrometers in size). Their concern is quantitative and comparative: in its native range N. seminae can account for more than 40% of diatom assemblages (Shimada et al. 2006) and it usually dominates blooms in the Gulf of St. Lawrence, so if it behaves similarly at higher latitudes it could substantially alter the species composition, biomass, and silica flux of Nordic Seas plankton communities. Their paper states the open issue directly: "The potential effect on the northern ecosystem is, however, still unknown but should be under observation." No dedicated ecological study of this species in the Nordic Seas has followed.

Problem Statement

Determine the ecological consequences of the non-native Pacific diatom Neodenticula seminae for the pelagic ecosystem of the northern Nordic Seas, including the Greenland Sea, into which it has been spreading since its 1999 reintroduction to the North Atlantic and where it was recorded in the water column at 65-68 degrees N in 2002. Concretely, the problem - whose ecosystem-effect aspect Olofsson and Wulff (2021) state is 'still unknown but should be under observation' - comprises two linked questions: (i) Abundance and bloom potential: does the species reach abundances at which it contributes substantially to phytoplankton biomass or forms blooms at Nordic Seas latitudes, as it does in the subarctic Pacific (more than 40% of diatom assemblages) and the Gulf of St. Lawrence, or does it remain a minor, advected component of the flora? (ii) Ecosystem effect: if it establishes at meaningful abundance, what are the consequences for the native micro- and nanoplankton community and the food web - competition with native diatoms, edibility to and grazing by local zooplankton, contribution to primary production, and alteration of biogenic silica export? The species' direct and indirect ecological effects in the region are to be quantified or bounded.

References

  1. Malin Olofsson and Angela Wulff (2021) Looking back to the future—micro- and nanoplankton diversity in the Greenland Sea. Marine Biodiversity 51(4):61. DOI: 10.1007/s12526-021-01204-w. https://doi.org/10.1007/s12526-021-01204-w
  2. Philip C. Reid, David G. Johns, Martin Edwards, Michel Starr, Michel Poulin, and Pauli Snoeijs (2007) A biological consequence of reducing Arctic ice cover: arrival of the Pacific diatom Neodenticula seminae in the North Atlantic for the first time in 800 000 years. Global Change Biology 13(9):1910–1921. DOI: 10.1111/j.1365-2486.2007.01413.x. https://doi.org/10.1111/j.1365-2486.2007.01413.x
  3. Arto Miettinen, Nalan Koç, and Katrine Husum (2013) Appearance of the Pacific diatom Neodenticula seminae in the northern Nordic Seas — An indication of changes in Arctic sea ice and ocean circulation. Marine Micropaleontology 99:2–7. DOI: 10.1016/j.marmicro.2012.06.002. https://doi.org/10.1016/j.marmicro.2012.06.002
  4. Michel Poulin, Nina Lundholm, Lyse Bérard-Therriault, Michel Starr, and Réal Gagnon (2010) Morphological and phylogenetic comparisons of Neodenticula seminae (Bacillariophyta) populations between the subarctic Pacific and the Gulf of St. Lawrence. European Journal of Phycology 45(2):127–142. DOI: 10.1080/09670260903509362. https://doi.org/10.1080/09670260903509362
  5. Alexander Matul and Galina Kh. Kazarina (2020) The North Pacific Diatom Species Neodenticula seminae in the Modern and Holocene Sediments of the North Atlantic and Arctic. Geosciences 10(5):173. DOI: 10.3390/geosciences10050173. https://doi.org/10.3390/geosciences10050173
  6. S. J. Kelly, E. Popova, Y. Aksenov, R. Marsh, and A. Yool (2020) They Came From the Pacific: How Changing Arctic Currents Could Contribute to an Ecological Regime Shift in the Atlantic Ocean. Earth's Future 8(4):e2019EF001394. DOI: 10.1029/2019EF001394. https://doi.org/10.1029/2019EF001394
  7. Chieko Shimada, Yuichiro Tanaka, and Yoshihiro Tanimura (2006) Seasonal variation in skeletal silicification of Neodenticula seminae, a marine planktonic diatom: Sediment trap experiments in the NW Pacific Ocean (1997–2001). Marine Micropaleontology 60(2):130–144. DOI: 10.1016/j.marmicro.2006.04.006. https://doi.org/10.1016/j.marmicro.2006.04.006
  8. E. A. Agafonova, A. A. Klyuvitkin, A. N. Novigatsky, E. A. Kudryavtseva, and M. D. Kravchishina (2025) Invasive Diatom Species in Sinking Material of the Lofoten Basin (the Norwegian Sea). Doklady Earth Sciences 524(1):3. DOI: 10.1134/S1028334X25606443. https://doi.org/10.1134/S1028334X25606443
  9. E. A. Novichkova, E. A. Agafonova, A. A. Klyuvitkin, T. S. Klyuvitkina, M. D. Kravchishina, A. N. Novigatsky, and A. V. Bulokhov (2025) Dynamics of the Sedimentary Matter Composition in the Lofoten Basin of the Norwegian Sea. Oceanology 65(5):741–757. DOI: 10.1134/S0001437025700407. https://doi.org/10.1134/S0001437025700407
  10. Bérengère Husson, Bodil A. Bluhm, Frédéric Cyr, Seth L. Danielson, Elena Eriksen, Maria Fossheim, Maxime Geoffroy, Russell R. Hopcroft, Randi B. Ingvaldsen, Lis L. Jørgensen, Connie Lovejoy, Lorenz Meire, Franz Mueter, Raul Primicerio, and Mie Winding (2024) Borealization impacts shelf ecosystems across the Arctic. Frontiers in Environmental Science 12:1481420. DOI: 10.3389/fenvs.2024.1481420. https://doi.org/10.3389/fenvs.2024.1481420
  11. Farrah T. Chan, Keara Stanislawczyk, Anna C. Sneekes, Alexander Dvoretsky, Stephan Gollasch, Dan Minchin, Matej David, Anders Jelmert, Jon Albretsen, and Sarah A. Bailey (2019) Climate change opens new frontiers for marine species in the Arctic: Current trends and future invasion risks. Global Change Biology 25(1):25–38. DOI: 10.1111/gcb.14469. https://doi.org/10.1111/gcb.14469