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 Rasmus, Krabberød, Anders Kristian, Nishino, Shigeto, Wassmann, Paul
• Format: Article in Journal/Newspaper
• Language: English
• Published: Norwegian Polar Institute 2023
• Subjects: Arctic; Balsfjord; Malangen; Pacific; Climate change; Polar Research
• Online Access: https://hdl.handle.net/10037/31546; 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 –3 in the Sognefjord complex, which was the southern research site, and, in the north, 945 m –3 in Malangen and 89 m –3 in Balsfjord, both above the Arctic Circle. Sticholonche zanclea was 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 –3 in the Sognefjord complex, 51 m –3 in Malangen and 11 m –3 in Balsfjord. Medusetta arcifera was the most abundant phaeodaria in the Sognefjord complex, accounting for >99% of phaeodarian abundance, but was absent in Malangen and Balsfjord, where Protocystis tridens accounted for >96% of phaeodarian abundance. The carbon biomass of S. zanclea and M. arcifera was 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 that M. arcifera contributes 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.