The vertical distribution of Radiolaria in the waters surrounding Japan Yoshiyuki Ishitani ⁎ , Kozo Takahashi Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University, Fukuoka 812-8581, Japan Received 1 March 2007; received in revised form 6 June 2007; accepted 6 June 2007 Abstract Geographic and vertical distribution patterns of living Radiolaria are closely related to the characters of the water column. We studied living Radiolaria in samples collected at closely spaced depth intervals in the waters surrounding Japan in order to understand their vertical distribution and its controlling factors. Such information is needed to reconstruct past vertical water mass structure. The Japanese Islands are surrounded by the marginal Japan Sea and the North Pacific Ocean, and from approximately 46° N to 26° N. They thus extend across a large latitudinal range and are exposed to a similarly wide range of environmental conditions, inducing the warm Kuroshio, Tsushima, and Tsugaru Currents and the cold Oyashio Current. We performed plankton tows (mesh size 63 mm) from late May to early June 2002 at eight sites, sampling the upper 200 m of the water column, at seven depth intervals. We recognized five radiolarian assemblages: the Upper Surface Assemblage (0–40 m), the Lower Surface Assemblage (40–80 m), the Surface Assemblage (0–80 m), the Subsurface Assemblage (80–200 m), and the Lower Surface–Subsurface Assemblage (40–200 m) groups. Pseudodictyophimus gracilipes and Tetrapyle octacantha (juvenile) show “tropical submergence”, i.e. they live at the surface in high latitudes and at greater depth in low latitudes. Four taxa live at specific temperature and salinity: Acrosphaera spinosa, Larcopyle butschlii, Challengeron diodon, and Stichocorys seriata. Four taxa are associated with characteristic temperatures: Neosemantis distephanus, Arachnocorys umbellifura, Antarctissa sp. 1, and Saccospyris conithorax. © 2007 Elsevier B.V. All rights reserved. Keywords: Radiolaria; Tropical submergence; Vertical geographic; Around Japan 1. Introduction Radiolaria are protozoan microzooplankton with siliceous shells, some of which harbor symbionts. They live at various depths in the epipelagic to bathypelagic ocean, and show characteristic vertical distributions (e.g., Renz, 1976; Kling, 1979; Reshet- nyak, 1955). These distributions are related to physical (e.g., temperature, salinity and density), chemical (e.g., oxygen and nutrients), and biological (e.g., food availability and symbionts) conditions. Knowledge of the ecology of living radiolarians will improve our understanding of the water mass structure of the past. Information on the relation between the occurrence and abundance of specific radiolarian taxa and environ- mental factors can be obtained by studying living plank- ton assemblages. Most previous studies primarily used data from sediments and sediment traps. Usually, data from sediments cannot be used to decipher radiolarian vertical distributions in details. Data from sediment traps Available online at www.sciencedirect.com Marine Micropaleontology 65 (2007) 113 – 136 www.elsevier.com/locate/marmicro ⁎ Corresponding author. Tel.: +81 92 642 2657; fax: +81 92 642 2686. E-mail address: shitani@geo.kyushu-u.ac.jp (Y. Ishitani). 0377-8398/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.marmicro.2007.06.002