Radiolaria and Phaeodaria (siliceous Rhizaria) in south-western and northern Norwegian fjords during late summer 2016: dominant species and biomass in shallow-water assemblages

• Published in: Polar Research
• Main Authors: Ikenoue, Takahito, Bjørklund, Kjell, Krabberød, Anders K., Nishino, Shigeto, Wassmann, Paul
• Format: Article in Journal/Newspaper
• Language: English
• Published: Norwegian Polar Institute 2023
• Subjects: zooplankton; biogeochemical cycle; climate change; biodiversity; Amphimelissa setosa; local extinction; Arctic; Pacific; Balsfjord; Malangen; Climate change; Polar Research; Zooplankton
• Online Access: https://polarresearch.net/index.php/polar/article/view/9584; https://doi.org/10.33265/polar.v42.9584

To determine the present-day community composition of siliceous Rhizaria (Radiolaria and Phaeodaria) in Norwegian fjords, plankton tows were conducted in south-western and northern Norwegian fjords in September 2016. The mean total abundance of radiolarians was 306 m–3in the Sognefjord complex, which was the southern research site, and, in the north, 945 m–3in Malangen and 89 m–3in Balsfjord, both above the Arctic Circle.Sticholonche zancleawas the most abundant radiolarian in the Sognefjord complex and Malangen, accounting for 78–100% (mean 89%) of radiolarian abundance. The mean total abundance of phaeodarians was 1554 m–3in the Sognefjord complex, 51 m–3in Malangen and 11 m–3in Balsfjord.Medusetta arciferawas the most abundant phaeodaria in the Sognefjord complex, accounting for >99% of phaeodarian abundance, but was absent in Malangen and Balsfjord, whereProtocystis tridensaccounted for >96% of phaeodarian abundance. The carbon biomass ofS. zancleaandM. arciferawas 188 and 438 µg C m–3, respectively, which is similar to and 8.6 times higher than, respectively, that of phaeodarians >1 mm in the western North Pacific, suggesting thatM. arciferacontributes to organic carbon transport in the Sognefjord complex.Amphimelissa setosa(Nassellaria, Radiolaria), which was a dominant species in the study area in 1982–83, was absent in the present study in all sampled fjords. This could have been caused by the approximately 2 °C increase in water temperature that has occurred since 1990 and can be taken as evidence of a climate-change-associated local temperature rise linked to the warming of advected Atlantic Water.