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Dive into the research topics where Jonas Thormar is active.

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Featured researches published by Jonas Thormar.


Ecology Letters | 2015

Biodiversity mediates top–down control in eelgrass ecosystems: a global comparative‐experimental approach

J. Emmett Duffy; Pamela L. Reynolds; Christoffer Boström; James A. Coyer; Mathieu Cusson; Serena Donadi; James G. Douglass; Johan S. Eklöf; Aschwin H. Engelen; Britas Klemens Eriksson; Stein Fredriksen; Lars Gamfeldt; Camilla Gustafsson; Galice Hoarau; Masakazu Hori; Kevin A. Hovel; Katrin Iken; Jonathan S. Lefcheck; Per-Olav Moksnes; Masahiro Nakaoka; Mary I. O'Connor; Jeanine L. Olsen; J. Paul Richardson; Jennifer L. Ruesink; Erik E. Sotka; Jonas Thormar; Matthew A. Whalen; John J. Stachowicz

Nutrient pollution and reduced grazing each can stimulate algal blooms as shown by numerous experiments. But because experiments rarely incorporate natural variation in environmental factors and biodiversity, conditions determining the relative strength of bottom-up and top-down forcing remain unresolved. We factorially added nutrients and reduced grazing at 15 sites across the range of the marine foundation species eelgrass (Zostera marina) to quantify how top-down and bottom-up control interact with natural gradients in biodiversity and environmental forcing. Experiments confirmed modest top-down control of algae, whereas fertilisation had no general effect. Unexpectedly, grazer and algal biomass were better predicted by cross-site variation in grazer and eelgrass diversity than by global environmental gradients. Moreover, these large-scale patterns corresponded strikingly with prior small-scale experiments. Our results link global and local evidence that biodiversity and top-down control strongly influence functioning of threatened seagrass ecosystems, and suggest that biodiversity is comparably important to global change stressors.


Marine Biodiversity | 2010

Wollunquaderes majkenae gen. et sp. nov.—a new cyclorhagid kinorhynch genus and species from the Coral Sea, Australia

Martin V. Sørensen; Jonas Thormar

A new kinorhynch genus and species, Wollunquaderes majkenae gen. et sp. nov., is described from a locality in the Coral Sea, southeast of the Great Barrier Reef, Australia. The new genus and species is recognized by the presence of outer oral styles with a conspicuous fishbone-like substructure and 16 placids that articulate with segment 1 through distinct joints. Segment 1 has a completely straight anterior margin, and is composed of a closed, cuticular ring, whereas segments 2–11 are composed of one tergal and two sternal plates. The posterior segment margins of segments 2–9 form conspicuous flare-like extensions in the lateral accessory positions. Sexually dimorphic characters include presence of paired papillae on the sternal plates of segments 8 and 9 in females, and acicular spines in middorsal and sublateral positions on segment 10 in females, opposed to middorsal and midlateral crenulated spines in males. The new genus displays several traits found in species of Antygomonas and/or Semnoderes, but also characters that otherwise are considered unique for taxa of Centroderidae. Hence, Wollunquaderes gen. nov. cannot be assigned to any known family.


Polar Biology | 2007

Sympagic amphipods in the Arctic pack ice: redescriptions of Eusirus holmii Hansen, 1887 and Pleusymtes karstensi (Barnard, 1959)

Martin O. Macnaughton; Jonas Thormar; Jørgen Berge

During an expedition into the Arctic Ocean, in September 2004, six different species of amphipods were collected in the ice above 82°N. All six species (Apherusa glacialis, Gammarus wilkitzkii, Onisimus nanseni, O. glacialis, Pleusymtes karstensi and Eusirus holmii) were observed to be living adjacent to the sea ice or partly within its brine channels. The nature of the association with the ice for the last two species is uncertain, but the finding raises important questions regarding our knowledge of the sympagic fauna. Based on the obtained material, the two species E. holmii and P. karstensi are redescribed, and their association with the sea ice is discussed.


PLOS ONE | 2016

Eelgrass (Zostera marina) Food Web Structure in Different Environmental Settings

Jonas Thormar; Harald Hasler-Sheetal; Susanne Baden; Christoffer Boström; Kevin Kuhlmann Clausen; Dorte Krause-Jensen; Birgit Olesen; Jonas Rasmussen; Carl Johan Svensson; Marianne Holmer

This study compares the structure of eelgrass (Zostera marina L.) meadows and associated food webs in two eelgrass habitats in Denmark, differing in exposure, connection to the open sea, nutrient enrichment and water transparency. Meadow structure strongly reflected the environmental conditions in each habitat. The eutrophicated, protected site had higher biomass of filamentous algae, lower eelgrass biomass and shoot density, longer and narrower leaves, and higher above to below ground biomass ratio compared to the less nutrient-enriched and more exposed site. The faunal community composition and food web structure also differed markedly between sites with the eutrophicated, enclosed site having higher biomass of consumers and less complex food web. These relationships resulted in a column shaped biomass distribution of the consumers at the eutrophicated site whereas the less nutrient-rich site showed a pyramidal biomass distribution of consumers coupled with a more diverse consumer community. The differences in meadow and food web structure of the two seagrass habitats, suggest how physical setting may shape ecosystem response and resilience to anthropogenic pressure. We encourage larger, replicated studies to further disentangle the effects of different environmental variables on seagrass food web structure.


Marine Biology Research | 2016

Small-scale removal of seagrass (Zostera marina L.): effects on the infaunal community

Marc Jürgen Silberberger; Jonas Thormar; Stein Fredriksen

ABSTRACT Eelgrass meadows are a common feature in shallow waters along the Norwegian coast, where they provide a habitat for a diverse infaunal community. Recreational boat anchoring and moorings physically scour seagrass and may affect the ecosystem functioning and resilience of the system to natural and anthropogenic disturbances. A small-scale eelgrass (Zostera marina) removal experiment was conducted to study the effects on macro- and meiofauna. Entire plants, including the rhizomes, were removed from 4 m2 patches in three eelgrass meadows in the inner Oslofjord in October 2010. Core samples were taken after a recovery period of 10 months, from the removed patches as well as from the surrounding meadow. Macrofauna (>500 μm) and meiofauna (63–500 μm) in the sediment were investigated for possible effects of the eelgrass removal. Macrofauna and meiofauna composition were site specific and therefore location was identified as the main determinant for the infaunal community. The eelgrass did not regrow within the recovery period and bare sediment patches with only single eelgrass shoots were present during the sampling. Our analyses support an influence of the removal on individual species, but not the complete community. In particular one species, the gastropod Peringia ulvae, was encountered in higher numbers in samples from the removed patches than in control samples. From a management perspective, such minor removal of eelgrass, on the scale of square metres, appears to have no long-lasting detrimental effect to the infaunal community in sheltered meadows with muddy sediments.


Deep-sea Research Part Ii-topical Studies in Oceanography | 2008

Vertical migration in high Arctic waters during autumn 2004

Stig Falk-Petersen; Eva Leu; Jørgen Berge; Slawomir Kwasniewski; Henrik Nygård; Anders Røstad; Essi Keskinen; Jonas Thormar; Cecilie von Quillfeldt; Anette Wold; Bjørn Gulliksen


Zoologischer Anzeiger – A Journal of Comparative Zoology | 2012

Meristoderes gen. nov., a new kinorhynch genus, with the description of two new species and their implications for echinoderid phylogeny (Kinorhyncha: Cyclorhagida, Echinoderidae)

María Ángeles Herranz; Jonas Thormar; Jesús Benito; Nuria Sánchez; Fernando Pardos


Ecology | 2018

Latitude, temperature, and habitat complexity predict predation pressure in eelgrass beds across the Northern Hemisphere

Pamela L. Reynolds; John J. Stachowicz; Kevin A. Hovel; Christoffer Boström; Katharyn E. Boyer; Mathieu Cusson; Johan S. Eklöf; Friederike G. Engel; Aschwin H. Engelen; Britas Klemens Eriksson; F. Joel Fodrie; John N. Griffin; Clara M. Hereu; Masakazu Hori; Torrance C. Hanley; Mikhail Ivanov; Pablo Jorgensen; Kun-Seop Lee; Karen J. McGlathery; Per-Olav Moksnes; Masahiro Nakaoka; Mary I. O'Connor; Nessa E. O'Connor; Robert J. Orth; Francesca Rossi; Jennifer L. Ruesink; Erik E. Sotka; Jonas Thormar; Fiona Tomas; Richard K. F. Unsworth


25 | 2018

Pilotprosjekt - Kartlegging av marin natur i Møre og Romsdal. Årsrapport 2017

Trine Bekkby; Espeland Sigurd; Margaret F.J. Dolan; Eli Rinde; Frithjof E. Moy; Sigrid Elvenes; Hege Gundersen; Thijs Christiaan van Son; Guri Sogn Andersen; Jonas Thormar; Helene Frigstad; Siri Røang Moy; Bjørnar Beylich; Jon Albretsen; Lars Johan Naustvoll; Lise Ann Tveiten


Supplement to: Falk-Petersen, S et al. (2008): Vertical migration in high Arctic waters during autumn 2004. Deep Sea Research Part II: Topical Studies in Oceanography, 55(20-21), 2275-2284, https://doi.org/10.1016/j.dsr2.2008.05.010 | 2008

Zooplankton and phytoplankton abundance, and stomach content of polar cod in the southern Arctic Ocean and Rijpfjorden

Stig Falk-Petersen; Eva Leu; Jørgen Berge; Slawomir Kwasniewski; Henrik Nygård; Anders Røstad; Essi Keskinen; Jonas Thormar; Cecilie von Quillfeldt; Anette Wold

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Jørgen Berge

University Centre in Svalbard

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Anders Røstad

University Centre in Svalbard

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Anette Wold

Norwegian Polar Institute

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Essi Keskinen

University Centre in Svalbard

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Eva Leu

Norwegian Polar Institute

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Henrik Nygård

University Centre in Svalbard

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