Biogeography 22. 1–5. Sep. 20, 2020 Discovery of vestimentiferan tube worms from the Kikai Caldera off Satsuma Peninsula, Kagoshima, Japan Hiroshi Miyake 1* and Koji Kiyosugi 2 1 School of Marine Biosciences, Kitasato University, 1-15-1, Kitazato, Minami Ward, Sagamihara, Kanagawa 252–0373, Japan 2 Kobe Ocean-Bottom Exploration Center (KOBEC), Kobe University, 5-11, Fukae Minami, Higashi Nada, Kobe, Hyogo, 658-0022, Japan Abstract: Kikai Caldera formed during the latest supereruption in the Japanese Archipelago was surveyed (Tatsumi et al., 2018). Vestimentiferan tube worms were captured in the video images recorded by the Remotely Operated Vehicle (ROV) survey. However, no attention was paid to the tube worms. To confirm the existence of deep-sea chemosynthetic ecosystem communities in the Kikai Caldera, video footage reported by Tatsumi et al. (2018) was analysed. Many vestimentiferan tube worms, Lamellibrachia sp. were observed. Vestimentiferan tube worms attached to lava blocks where white bacterial mats and gas emission from the gaps of lava blocks were observed. The density of vestimentiferan tube worms was up to 29 individuals/frame. This is the first report of deep-sea chemosynthetic ecosystem in Kikai Caldera, a very important site for studying larval dispersion in hydrothermal vent animals. Key words: vestimentiferan tube worm, Kikai Caldera, Lamellibrachia, chemosynthetic ecosystem Introduction km off southern Kyushu Island, Japan. Except for two islands (Satsuma Iwo-jima Island and Take-Shima Island) on the Many hydrothermal vent sites have been found in Japanese northern part of the caldera rim, most of the caldera structure waters. There are two main areas of hydrothermal vents along is under the sea. Kikai Caldera was formed by the latest super- the Izu-Bonin-Mariana Arc and the Southwestern Japan Arc eruption in the Japanese Archipelago that occurred 7300 years (Fujikura et al., 2008; Kaneko et al., 2019). Although the ago (Tatsumi et al., 2018). Based on geophysical, geological, Southwestern Japan Arc is about 1500 km in a straight line and petrological investigations, Tatsumi et al. (2018) deter- away from the Izu-Bonin-Mariana Arc, the same species of mined that a giant rhyolite lava dome (~32 km3) was created hydrothermal vent animals are distributed in both areas (Mi- in the caldera after the caldera-forming eruption. In addition yake et al., 2010; Miyake et al., 2019; Tokuda et al., 2006). It to the giant post-caldera lava dome, there are several post-cal- is presumed that this distribution is owing to larval dispersion dera volcanoes. Two post-caldera volcanoes are located in by the Kuroshio Current and the Kuroshio Counter Current the middle and eastern sides of the Satsuma Iwo-jima Island, (Miyake et al., 2010). called Inamura-dake and Iwo-dake, respectively. Hydrother- As for hydrothermal vent areas on the Southwestern Japan mal activity is intense at Iwo-dake volcano and around the Arc, many vent biological studies have been conducted at Satsuma Iwo-jima Island (e.g. Kazahaya et al., 2002). The Wakamiko Proto-Caldera in Kagoshima Bay and between latest activity in this caldera volcano took place in 1934–1935 Minami-Ensei Knoll and Dai-yon Yonaguni Knoll. Although (Tanakadate, 1935), 2 km east of Satsuma Iwo-jima Island on there are many underwater hot springs and active volcanos in a 500-m-deep seafloor, and formed a rhyolitic post-caldera the Tokara Islands and Osumi Islands, little vent biological volcano called Showa Iwo-jima Island, around which hydro- research has been conducted. Therefore, there is no report on thermal activity is still observed. deep-sea chemosynthetic ecosystems in the area; however, hot Tatsumi et al. (2018) reported some images captured by the springs shallower than 10 m have been investigated with the ROV. There was fumarolic activity and vestimentiferan tube discovery of vent crabs, Xenograpsus testudinatus Ng, Huang worms, as seen at Wakamiko Proto-Caldera in Kagoshima & Ho, 2000 (Ng et al., 2014; Suzuki et al., 2015). Bay. However, no member among Tatsumi et al.’s (2018) team Kikai volcano (Kikai Caldera) is located approximately 45 paid attention to the vestimentiferan tube worm because no −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− biologist was present. This was a big discovery for the study *Corresponding author: [email protected] of deep-sea chemosynthetic ecosystem animals, especially for – 1 – Vestimentiferan tube worm from Kikai Caldera the study of their larval dispersion, because until now they houses of larvaceans, and comb jellies, such as Bolinopsis sp. have not been recorded in the Osumi Islands and the Tokara were observed. The seabed was visible at Point B in Fig.2 at a Islands. The purpose of this report is to confirm the existence depth of 332 m. There were many huge lava rocks at the bot- of deep-sea chemosynthetic ecosystem communities in Kikai tom. White actiniarians, white sponges and gorgonians were Caldera using video footage recorded by the ROV reported in observed (324–334 m depth) at the beginning of the bottom Tatsumi et al. (2018). observation toward the area with green spots in Fig. 2 for 6 min (Fig. 3, Zone A). When moving to the area with green Materials and Methods spots in Fig. 2 for about 12 min, 20 individuals of Bolinopsis sp. and many euphausiids were observed in the water column Video footage was recorded at Kikai Caldera (Fig. 1) by (308–382 m depth) in Zone B in Fig. 3. There were sponges a 2K video camera equipped on the ROV ‘SHINDAI-2K’ at depths of 371–388 m, mainly Hexactinellid species in the (Kowa Corporation, Osaka, Japan) mounted on the T/S “Fukae area marked with green points in Fig. 2 and Zone C in Fig. 3 Maru” of Kobe University on 5 March 2017. In this system, (Fig. 4A). Vestimentiferan tube worms were found at depths the live video displayed on a monitor of the ship was saved of 379–382 m in areas marked with yellow and red points on an SD card in QuickTime format (.mov). During the dive, (30° 47.3, 130° 22.3E) in Fig. 2 and Zone D in Fig. 3 (Fig. real-time latitude, longitude, depth, and heading direction of 4B). The area with red points was a highly-density area of the ROV were also recorded every 0.1 seconds. The latitude vestimentiferan tube worms with up to 29 individuals/frame. and longitude of the position of the ROV were determined by White bacterial mats and gas emission from the gaps of lava the ultra-short baseline (USBL) navigation system (EvoLogics blocks were observed in Zone D in Fig. 3. Vestimentiferan USBL S2C R 12/24) and the global positioning system of the tube worms were attached to the lava blocks near the bacterial ship. mat and gas emission (Fig. 4C). There was a field of glass IINA (https://iina.io/), a free media player software for sponge, Hyalonematid species, on the volcanic rocks at depths macOS, was used for video analysis. The occurrence of or- of 377–380 m in Zone E in Fig. 3 (Fig. 4D). ganisms in the video was recorded in an Excel spread sheet including the number of organisms, its habitat characteristics, Discussion the local time of occurrence, depth, and heading direction of the ROV. Vestimentiferan tube worms could not be collected in this study. According to Karaseva et al. (2016), the shape of the Results tube from the video image indicated that this tube worm was Lamellibrachia sp. There are three species of Lamellibrachia The ROV ‘SHINDAI-2K’ started the dive at 09:07, reached in Japanese waters, Lamellibrachia satsuma Miura, Tsukaha- a bottom depth of 334m at 09:31 and left the bottom at 10:57 ra & Hashimoto, 1997; Lamellibrachia columna Southward, on 5 March 2017. The dive track is shown in Fig. 2. The dive 1991; and Lamellibrachia sp. L5 (Kobayashi et al., 2015; Mc- track of the ROV was smoothed using the positioning data. Cowin & Rouse, 2018; McCowin et al., 2019; Miura & Fuji- The position of the colored point deviates from the ROV kura, 2008; Miura et al., 1997). Lamellibrachia columna was track, because of variations in acoustic positioning. During the reported from depths of 270–1500 m and 3270 m at cold seep descent to the bottom (Points A to B in Fig. 2), euphausiids, and hydrothermal vent areas in Sagami Bay (off Hatsushima Fig. 1. Map of survey point A: Location of Kikai Caldera, B: Dive point of the ROV in Kikai Caldera – 2 – Hiroshi Miyake and Koji Kiyosugi Fig. 2. Dive track chart of ROV and distribution of animals Fig. 3. Depth of ROV and the number of tube worms observed with time scale The green point shows sponges, mainly Hexac- tinellid species. The blue point shows the glass sponge, Hyalonematid species. Yellow and red points indicate the vestimentiferan tube worm. A: the ROV landing point on the sea surface, B: the visual confirmation point of the bottom Fig. 4. Video frame of animals observed in the ROV dive A: Sponges, B: Lamellibrachia sp., C: Lamelli- brachia sp., sponges, and white bacterial mats, D: Hyalonematid glass sponge field. – 3 – Vestimentiferan tube worm from Kikai Caldera Caldera is likely to be one of both species. This tube worm resembles L. columna. The situation where the tube worm was attached to the lava block and the habitat of the tube worm was similar to that of L. columna in the cold seep area off Hatsushima, Sagami Bay. However, species identification is impossible from video images in this study, and identification is left to future research. Lamellibrachia satsuma and hydrothermal vent crabs, Xen- ograpsus testudinatus as Xenograpsus novaeinsularis Takeda & Kurata, 1977 were reported from Omuro-dashi at a depth of 200 m (Tsuchida et al., 2014; personal observations).