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Ecosystem studies in the Indian Ocean sector of the Southern Ocean undertaken by the training vessel Umitaka-maru
Polar Science 12 (2017) 1e4
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Polar Science j o u r n a l h o m e p a g e : h t t p s : / / w w w . e v i s e . c o m / p r o fi l e / # / J R N L _ P O L A R / l o g i n
Editorial
Ecosystem studies in the Indian Ocean sector of the Southern Ocean undertaken by the training vessel Umitaka-maru a b s t r a c t Keywords: Umitaka-maru Indian Ocean sector Oceanic ecosystem Sea ice Climate change
This special issue provides an overview of the ten voyages undertaken by the Umitaka-maru from the austral summers of 2002/2003 to 2014/2015 to promote the next phase of study of the ecosystems in the Indian Ocean sector of the Southern Ocean. The voyages by the Umitaka-maru have mainly targeted three areas in the Indian Ocean sector: off Dumont d’Urville Base (France, 140 E transect), off Casey Station (Australia, 110 E transect), and off Syowa Station (Japan, north of Lützow Holm Bay). The findings of Umitaka-maru's research on the krill-independent food web, animal assemblages, community structure and distribution patterns from the epipelagic to the deeper waters provide invaluable information for elucidating the material cycle and predicting future ecosystem changes. Further studies on assessing the influence of sea ice on food webs in the water column are required, which will provide crucial information for predicting ecosystem changes as a result of projected sea ice changes in the near future. © 2017 Published by Elsevier B.V.
1. Voyages of the training vessel Umitaka-maru The Umitaka-maru IV is a training vessel operated by the Tokyo University of Marine Science and Technology (TUMSAT) which made its first voyage in 2000. The most recent research expedition undertaken in January 2017 was the 20th Southern Ocean voyage since the Tokyo University of Fisheries (which later became TUMSAT) conducted the first voyage in 1956 as part of the Japanese Antarctic Research Expedition. This special issue provides an overview of the ten voyages undertaken by the Umitaka-maru from the austral summers of 2002/2003 to 2014/2015 to promote the next phase of study of the ecosystems in the Indian Ocean sector of the Southern Ocean. The Umitaka-maru has assumed the major part of Japanese ecosystem research in the Southern Ocean in the last decade. The Kaiyodai Antarctic Research Expedition (KARE) in 2002/ 2003 (KARE09; the first Southern Ocean voyage for Umitaka-maru IV) was supported by the Grants-in-Aid for Scientific Research program of the Japan Society for the Promotion of Science [Principal Investigator (PI): Prof. T. Ishimaru of TUMSAT] (Table 1; Kaiyodai is the acronym in Japanese of TUMSAT). KARE09 was composed of a first leg of physical oceanography observations in the Kerguelen Plateau region and a second leg of multidisciplinary surveys along a 140 E transect off Dumont d’Urville Base (France). Thereafter, studies along the 140 E transect continued on KAREs11 (leg 2), 12 (leg 2), 14 (leg 2), and 15 (leg 2). KAREs10, 11 (leg 1), 12 (leg 1), and 13 conducted observations off Lützow Holm Bay (off the Japanese Syowa Station) as a program of the Japanese Antarctic Research Expedition (JARE) (PI: M. Fukuchi of the National Institute of Polar Research, NIPR). Leg 2 of KARE12 was the Collaborative East http://dx.doi.org/10.1016/j.polar.2017.04.002 1873-9652/© 2017 Published by Elsevier B.V.
Antarctic Marine Census (CEAMARC, PI: G. Hosie of the Australian Antarctic Division) of Australia, Japan and Belgium, whose achievements were published in the special issue of Polar Science 5, 2011 (Hosie et al., 2011). Since KARE13, the Umitaka-maru has been performing one of the JARE Routine Observations, the Physical and Chemical Oceanographic Observations, which the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) commissioned to NIPR and TUMSAT. Before NIPR and TUMSAT were given charge of these routine observations, they were performed by the Japanese Coast Guard during the cruises of the icebreakers Fuji and Shirase at five stations between 40 S and 60 S every 300 nautical miles. Since the Physical and Chemical Oceanographic Observations extended the observation area to the vicinity of the ice edge along the 110 E transect (>60 S), ecosystem studies have been conducted mainly in the waters south of 60 S along 110 E or its vicinity. These research voyages by the Umitaka-maru in the Southern Ocean provide practical opportunities of education and training for younger scientists, as well as training voyages in ship navigation for cadets of the Advanced Course of Fisheries Science at TUMSAT. The KARE voyages have mainly targeted three areas in the Indian Ocean sector: off Dumont d’Urville Base (France, 140 E transect), off Casey Station (Australia, 110 E transect), and off Syowa Station (Japan, north of Lützow Holm Bay). Off the Dumont d’Urville Base, the Antarctic Circumpolar Current (ACC) comes close to the continental shelf, and sea ice tends to melt in the continental shelf zone during mid-summer (Nicol et al., 2000a). In fact, the Umitakamaru, which is not an icebreaker, was able to enter the shelf waters on the CEAMARC voyage (JaneFeb, 2008) enabling it to cover a wide area from the oceanic to continental shelf zone (Hosie et al.,
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Table 1 Voyages by the training vessel Umitaka-maru relating to this issue. Voyage code
Year
Area (leg 1/ leg 2)
KARE09 10 11 12 13 14 15 16 17 18
2002/03 2004/05 2005/06 2007/08 2009/10 2010/11 2011/12 2012/13 2013/14 2014/15
Kerguelen Plateu/140 E Lützow Holm Bay Lützow Holm Bay/140 E Lützow Holm Bay/140 E Lützow Holm Bay, Cape Darnley 110 E, 140 E 110 E, 140 E 110 E 110 E 110 E
2011; Ono and Moteki, 2017a; Tachibana et al., 2017; Toda et al., 2014). Off Casey Station, the edge of the sea ice retreats approximately in accordance with the bottom topography, with sea ice retreats occurring earlier around 110 E where bathymetric lines indent south, and sea ice tending to remain to both the east and the west of areas where banks are present (Moteki et al., 2017b). Based on satellite image analysis, Ojima et al. (2017) showed that sea ice drifting in these waters during austral summer was transferred from Porpoise Bay, 127 Ee129 E, in 172e250 days by the westward moving Coastal Current. The topographic characteristics of the waters off Syowa Station are very similar to those off Casey Base; sea ice tends to remain in both the east and the west. Makabe et al. (2017) reported that distribution patterns of mesozooplankton and the developmental state of dominant copepod species in the waters off north of Lützow Holm Bay were related to sea ice dynamics at the local scale. It was suggested that greater annual fluctuation in the timing of sea ice retreat in these waters affects the biomass of zooplankton through fluctuations in primary production (Ono and Moteki, 2017b; Toda et al., 2010). 2. Krill-independent food web and sea ice in the Indian Ocean sector In recent years, ecosystem studies have advanced significantly, particularly in the western Antarctic Peninsula and Scotia Sea, where the krill species Euphausia superba dominates and is widely distributed compared with that in East Antarctic waters (Atkinson et al., 2008). In contrast, the Indian Ocean sector of the East Antarctic Ocean has a relatively short history of ecosystem research, although large-scale campaigns such as Baseline Research on Oceanography, Krill and Environment (BROKE) and BROKE-West have been conducted (Nicol et al., 2000b, 2010). In the Scotia Sea, both krill-dependent and krill-independent food webs have been proposed, depending on krill abundance (Murphy et al., 2007). The krill-independent food web becomes dominant when krill is less abundant, and copepods and myctophid fish are key components. It is considered that this food web is more dominant in the Indian Ocean sector than in the western Antarctic Peninsula or Scotia Sea because, during austral summer off Dumont d’Urville Base and Lützow Holm Bay, the distribution of krill is limited to along the continental slope and total biomass is relatively small (Amakasu et al., 2011; Atkinson et al., 2008; Ono et al., 2011; Ono and Moteki, 2017b). Murphy et al. (2007) placed icefish (Channichthyidae) in the krill-independent food web as a component below top predators. However, this may not be applicable to the Indian Ocean sector, at least along the 140 E transect off Dumont d’Urville Base. Here, notothenioid fish, including icefish, and myctophids (mesopelagic) have allopatric distributions in the neritic (continental shelf) and oceanic zones, respectively (Moteki et al., 2011). Similar distinctive distribution patterns were observed in these waters by copepods
and pelagic cnidarians (Tachibana et al., 2017; Toda et al., 2014). In contrast, in the Scotia Sea, islands and wide shelf areas interrupting the eastward flow of the ACC produce complicated oceanic frontal structures (Murphy et al., 2012), which likely result in neritic and oceanic species having sympatric distributions. These distributions indicate that myctophids are more important in the krillindependent food web in the oceanic zone in the Indian Ocean sector. Thus, in the neritic zone of the Indian Ocean sector, there is another food web in which Antarctic silverfish, Pleuragramma antarcticum, or ice krill, Euphausia crystallorophias, are a key component, as observed in the Ross Sea (Smith, Jr. et al., 2012). Myctophid fish have become recognised as an important component in the Southern Ocean food web with their huge biomass and high energy content, and as the targets of foraging by higher trophic animals (Saunders et al., 2014). Electrona antarctica is the most dominant myctophid in the Southern Ocean. Moteki et al. (2017a, 2017b) studied the early life history of this species. In one paper (2017a), they described the development of the external morphology and osteology from the larval to juvenile stages, and discussed changes in the swimming and feeding functions with development. They also first described the transformation stage between the larval and juvenile stages, and reported that morphological changes such as transformation are related to ontogenetic vertical migration to deeper water (Moteki et al., 2009). Moteki et al. (2017b) conducted discrete depth samplings along 140 E and 110 E transects, and observed that larvae were distributed mainly in a specific water mass, the Modified Circumpolar Deep Water (MCDW), and did not participate in diurnal vertical migration (DVM). The study also detected DVM in juvenile/adult fish using a quantitative echo-sounder in conjunction with net sampling. MCDW is generally located close to the area of the ice edge or drifting sea ice in our research waters during summer, suggesting that the early life history of E. antarctica is related to the presence of sea ice. Makabe et al. (2017) discussed mesozooplankton distribution patterns and the developmental stage composition of dominant herbivorous copepods in relation to timing and longevity of ice edge bloom in the waters north of Lützow Holm Bay. They also suggested that such differences in primary productivity in this region would be caused by local heterogeneity in sea ice dynamics, which is closely related with the local hydrography and topography. Although most of the studies on sea ice biota (SIB) have focused on those in fast sea ice or larger stable ice floes, Ojima et al. (2017) investigated the fauna in smaller areas of drifting sea ice at the sea ice edge during summer to provide fundamental information on the role of SIB in the water column. The latter two studies indicate the importance of assessing the influence of sea ice on food webs in the water column, and provide crucial information for predicting ecosystem changes as a result of projected changes in sea ice in the near future. 3. Global warming and ecosystem changes The key species E. superba has declined significantly in abundance since the 1970s (Atkinson et al., 2004). In contrast, Antarctic salps, Salpa thompsoni, which are considered competitors to krill in terms of space and/or food, have increased their range southward (Atkinson et al., 2004). Ono and Moteki (2013, 2017a) observed the distribution of salps south of the Southern Boundary of the ACC (SBACC), which had previously been considered the southern limit of the species in the Indian Ocean sector, and suggested they can reproduce south of the SBACC. However, they appeared to be less competitive with krill, at least in spatial distribution (Ono and Moteki, 2017a). The study also mentioned a need for monitoring in terms of population dynamics. Large-scale research campaigns focusing on krill generally
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sample the epipelagic layer (0e200 m depth) to cover a wide study area (e.g. BROKE, Nicol et al., 2000b) because krill are mainly distributed in this layer. Consequently, very few studies on meso- and bathypelagic fauna have been conducted in the Southern Ocean. Umitaka-maru has contributed as an observation platform to reveal meso- and bathypelagic fauna using several large nets. These studies have observed high diversity of pelagic cnidarians, copepods and pelagic fish (Moteki et al., 2009, 2011; Tachibana et al., 2017; Toda et al., 2010, 2014), and elucidated the distribution patterns and demography of euphausiids using samples from epipelagic to meso- and bathypelagic waters (Ono and Moteki, 2017b; Ono et al., 2011). These findings on the animal assemblages, community structure and distribution patterns in deeper waters provide invaluable information for elucidating the cycling of material and predicting future ecosystem changes related to the biological pump. Part of the Umitaka-maru research has comprised net sampling in deeper waters in the Southern Ocean. However, net sampling only looks at a snapshot of biological features in the sea. Acoustic techniques can potentially address this limitation. In fact, quantitative echo-sounder sampling is applied as an international standard for the estimation of krill abundance (Hewitt et al., 2004). Although conventional echo-sounders use narrowband sound of discrete frequencies (e.g. 38, 70, 120 and 200 kHz), the use of broadband sound has recently been focused for measuring continuous spectra of echoes. Amakasu et al. (2017) developed a broadband echosounder and applied it to infer the length-frequency distribution of krill. This technique could be useful for monitoring krill population structures. Climate change is observed as changes in sea ice in the Southern Ocean, although no remarkable changes have occurred to date in East Antarctica (Massom et al., 2013). However, Umitaka-maru research expeditions have contributed to detecting the freshening of Antarctic Bottom Water off Dumont d’Urville Base (Aoki et al., 2013), which draws attention to ecosystem changes in the Indian Ocean sector. Katayama et al. (2017) verified experimentally the effects of the shallowing of the surface mixed layer depth due to global warming on the photosystem of phytoplankton, which suggested that photosystem II damaged by high light could have induced the faster recovery observed north of the Polar Front (PF) compared to that south of the front. Ocean acidification caused by increasing pCO2 in the atmosphere causes failure of the aragonite shell of thecosome pteropods to develop properly. Akiha et al. (2017) investigated the distribution and biomass of shelled pteropods including the veliger stage using a relatively fine mesh net (100 mm). These data could provide a basis for detecting ecosystem changes in the future, as well as information on the biomass of small-sized pteropods, which is often omitted in studies yet is essential for understanding the cycling of material in the ocean. KARE did not incorporate monitoring observations before the JARE initiated Continuous Plankton Recorder (CPR) observations in 2003 (KARE09) on the Umitaka-maru because inter-annual continuity was not guaranteed before KARE08. CPR observations are an effective and efficient method for zooplankton monitoring to detect ecosystem change over large ocean scales. On the Umitaka-maru, CPR has contributed significantly to surface zooplankton monitoring in the Southern Ocean (Takahashi et al., 2010, 2011; Hosie et al., 2014). Regular sampling on the Shirase and the Umitakamaru along single transect provide the opportunity to conduct time-series CPR towing. Takahashi et al. (2017) compared CPR samples from three different seasons along the same 110 E transect collected from two research vessels. Multi-ship observations will be required in future research in the Southern Ocean because long-term voyages with a single ship are rarely scheduled due to various difficulties, such as the need for resupplying stations, budget limits and competition for ship time.
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4. Conclusion Research voyages in the Southern Ocean undertaken by the Umitaka-maru have been conducted as a leg of the long-distance training voyages for the Advanced Course of Fisheries Science at TUMSAT, but have had limitations in terms of the observation season, length of voyage and location. However, scientists have conducted detailed observations intensely using the various types of nets available on the Umitaka-maru, and collected important data on an almost annual basis. The Umitaka-maru has contributed to advances in deep-water sampling that had previously been performed by only a few studies in the Indian Ocean sector. It is crucial to continue the Southern Ocean observations to monitor the ecosystem changes caused by global warming. The Umitaka-maru sails almost every year in the Southern Ocean, which provides a valuable opportunity for the education and training of graduate students and young scientists. An international framework for a multi-ship observation system is required to develop effective efforts to monitor marine ecosystems. TUMSAT committed to participate in the Antarctic Climate and Ecosystem Cooperative Research Centre (ACE CRC, http://acecrc.org.au/) in 2016, and TUMSAT began collaborative studies with Australian scientists and graduate students onboard the Umitaka-maru in the same year. The abundance of E. superba, a key species in the Southern Ocean food web, is small in the Indian Ocean sector of the Antarctic Ocean compared to the western Antarctic Peninsula region and Scotia Sea, which results in the relative importance of the krillindependent food web in this region. The early life history of E. antarctica, one of the key components in this food web, has been suggested to be related to sea ice or food webs near the sea ice, which implies that ecosystem changes are related to changes in sea ice. It is crucial to determine the significance of sea ice in marginal ice zone ecosystems using onboard experiments and monitoring. Acknowledgements We are grateful to the captain, officers and crew of the Umitakamaru for all of their efforts, which ensured that KARE voyages were always productive. Takashi Ishimaru of TUMSAT established the early stages of KARE, and the guest managing editor inherited his achievements on the Umitaka-maru. Nobue Takasawa, Kaori Uchiyama, Tomoko Satoh, Keishi Shimada, Takuji Hosaka and Jota Kanda of the Observation and Research Centre for Ocean Systems of TUMSAT assisted in organizing KARE. We are also grateful to the scientists and graduate students who worked on board and the cadets on the ship for scientific discussions and help with observations. In addition, we acknowledge the support of the Polar Science office in Tokyo, the Editor-in-chief Takashi Yamanouchi and his secretary Ayumi Ando. The field observations of this special issue were supported in part by a Grant-in-Aid for Science (No. 15H05239 for M. Moteki and No. 24255001 for T. Odate) and by the National Institute of Polar Research through project research numbers AJ-02, AP-25, AP-46, AP-0923, AMB-2-5, AMB-0902, KPe4 and KP-308, and by the MEXT for JARE Routine Observations, the Physical and Chemical Oceanographic Observations. References Akiha, F., Hashida, G., Makabe, R., Hattori, H., Sasaki, H., 2017. Distribution in the abundance and biomass of shelled pteropods in surface waters of the Indian sector of the Antarctic Ocean in mid-summer. Polar Sci. 12, 12e18. Amakasu, K., Ono, A., Hirano, D., Moteki, M., Ishimaru, T., 2011. Distribution and density of Antarctic krill (Euphausia superba) and ice krill (E. crystallorophias) lie Land in austral summer 2008 estimated by acoustical methods. Polar off Ade Sci. 5, 187e194.
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Masato Moteki* Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato, Tokyo 108-8477, Japan National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan Tsuneo Odate National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan Department of Polar Science, School of Multidisciplinary Sciences, Graduate University for Advanced Studies (SOKENDAI), 10-3 Midoricho, Tachikawa, Tokyo 190-8518, Japan Graham W. Hosie Emeritus Life Fellow, Sir Alister Hardy Foundation for Ocean Science, Plymouth, UK Kunio T. Takahashi National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan Department of Polar Science, School of Multidisciplinary Sciences, Graduate University for Advanced Studies (SOKENDAI), 10-3 Midoricho, Tachikawa, Tokyo 190-8518, Japan Kerrie M. Swadling Antarctic Climate & Ecosystems Cooperative Research Centre and Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 129, Hobart, TAS 7001, Australia Atsushi Tanimura National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan Department of Polar Science, School of Multidisciplinary Sciences, Graduate University for Advanced Studies (SOKENDAI), 10-3 Midoricho, Tachikawa, Tokyo 190-8518, Japan *
Corresponding author. Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato, Tokyo 108-8477, Japan. E-mail address: [email protected] (M. Moteki).
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Editorial
Ecosystem studies in the Indian Ocean sector of the Southern Ocean undertaken by the training vessel Umitaka-maru a b s t r a c t Keywords: Umitaka-maru Indian Ocean sector Oceanic ecosystem Sea ice Climate change
This special issue provides an overview of the ten voyages undertaken by the Umitaka-maru from the austral summers of 2002/2003 to 2014/2015 to promote the next phase of study of the ecosystems in the Indian Ocean sector of the Southern Ocean. The voyages by the Umitaka-maru have mainly targeted three areas in the Indian Ocean sector: off Dumont d’Urville Base (France, 140 E transect), off Casey Station (Australia, 110 E transect), and off Syowa Station (Japan, north of Lützow Holm Bay). The findings of Umitaka-maru's research on the krill-independent food web, animal assemblages, community structure and distribution patterns from the epipelagic to the deeper waters provide invaluable information for elucidating the material cycle and predicting future ecosystem changes. Further studies on assessing the influence of sea ice on food webs in the water column are required, which will provide crucial information for predicting ecosystem changes as a result of projected sea ice changes in the near future. © 2017 Published by Elsevier B.V.
1. Voyages of the training vessel Umitaka-maru The Umitaka-maru IV is a training vessel operated by the Tokyo University of Marine Science and Technology (TUMSAT) which made its first voyage in 2000. The most recent research expedition undertaken in January 2017 was the 20th Southern Ocean voyage since the Tokyo University of Fisheries (which later became TUMSAT) conducted the first voyage in 1956 as part of the Japanese Antarctic Research Expedition. This special issue provides an overview of the ten voyages undertaken by the Umitaka-maru from the austral summers of 2002/2003 to 2014/2015 to promote the next phase of study of the ecosystems in the Indian Ocean sector of the Southern Ocean. The Umitaka-maru has assumed the major part of Japanese ecosystem research in the Southern Ocean in the last decade. The Kaiyodai Antarctic Research Expedition (KARE) in 2002/ 2003 (KARE09; the first Southern Ocean voyage for Umitaka-maru IV) was supported by the Grants-in-Aid for Scientific Research program of the Japan Society for the Promotion of Science [Principal Investigator (PI): Prof. T. Ishimaru of TUMSAT] (Table 1; Kaiyodai is the acronym in Japanese of TUMSAT). KARE09 was composed of a first leg of physical oceanography observations in the Kerguelen Plateau region and a second leg of multidisciplinary surveys along a 140 E transect off Dumont d’Urville Base (France). Thereafter, studies along the 140 E transect continued on KAREs11 (leg 2), 12 (leg 2), 14 (leg 2), and 15 (leg 2). KAREs10, 11 (leg 1), 12 (leg 1), and 13 conducted observations off Lützow Holm Bay (off the Japanese Syowa Station) as a program of the Japanese Antarctic Research Expedition (JARE) (PI: M. Fukuchi of the National Institute of Polar Research, NIPR). Leg 2 of KARE12 was the Collaborative East http://dx.doi.org/10.1016/j.polar.2017.04.002 1873-9652/© 2017 Published by Elsevier B.V.
Antarctic Marine Census (CEAMARC, PI: G. Hosie of the Australian Antarctic Division) of Australia, Japan and Belgium, whose achievements were published in the special issue of Polar Science 5, 2011 (Hosie et al., 2011). Since KARE13, the Umitaka-maru has been performing one of the JARE Routine Observations, the Physical and Chemical Oceanographic Observations, which the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) commissioned to NIPR and TUMSAT. Before NIPR and TUMSAT were given charge of these routine observations, they were performed by the Japanese Coast Guard during the cruises of the icebreakers Fuji and Shirase at five stations between 40 S and 60 S every 300 nautical miles. Since the Physical and Chemical Oceanographic Observations extended the observation area to the vicinity of the ice edge along the 110 E transect (>60 S), ecosystem studies have been conducted mainly in the waters south of 60 S along 110 E or its vicinity. These research voyages by the Umitaka-maru in the Southern Ocean provide practical opportunities of education and training for younger scientists, as well as training voyages in ship navigation for cadets of the Advanced Course of Fisheries Science at TUMSAT. The KARE voyages have mainly targeted three areas in the Indian Ocean sector: off Dumont d’Urville Base (France, 140 E transect), off Casey Station (Australia, 110 E transect), and off Syowa Station (Japan, north of Lützow Holm Bay). Off the Dumont d’Urville Base, the Antarctic Circumpolar Current (ACC) comes close to the continental shelf, and sea ice tends to melt in the continental shelf zone during mid-summer (Nicol et al., 2000a). In fact, the Umitakamaru, which is not an icebreaker, was able to enter the shelf waters on the CEAMARC voyage (JaneFeb, 2008) enabling it to cover a wide area from the oceanic to continental shelf zone (Hosie et al.,
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Table 1 Voyages by the training vessel Umitaka-maru relating to this issue. Voyage code
Year
Area (leg 1/ leg 2)
KARE09 10 11 12 13 14 15 16 17 18
2002/03 2004/05 2005/06 2007/08 2009/10 2010/11 2011/12 2012/13 2013/14 2014/15
Kerguelen Plateu/140 E Lützow Holm Bay Lützow Holm Bay/140 E Lützow Holm Bay/140 E Lützow Holm Bay, Cape Darnley 110 E, 140 E 110 E, 140 E 110 E 110 E 110 E
2011; Ono and Moteki, 2017a; Tachibana et al., 2017; Toda et al., 2014). Off Casey Station, the edge of the sea ice retreats approximately in accordance with the bottom topography, with sea ice retreats occurring earlier around 110 E where bathymetric lines indent south, and sea ice tending to remain to both the east and the west of areas where banks are present (Moteki et al., 2017b). Based on satellite image analysis, Ojima et al. (2017) showed that sea ice drifting in these waters during austral summer was transferred from Porpoise Bay, 127 Ee129 E, in 172e250 days by the westward moving Coastal Current. The topographic characteristics of the waters off Syowa Station are very similar to those off Casey Base; sea ice tends to remain in both the east and the west. Makabe et al. (2017) reported that distribution patterns of mesozooplankton and the developmental state of dominant copepod species in the waters off north of Lützow Holm Bay were related to sea ice dynamics at the local scale. It was suggested that greater annual fluctuation in the timing of sea ice retreat in these waters affects the biomass of zooplankton through fluctuations in primary production (Ono and Moteki, 2017b; Toda et al., 2010). 2. Krill-independent food web and sea ice in the Indian Ocean sector In recent years, ecosystem studies have advanced significantly, particularly in the western Antarctic Peninsula and Scotia Sea, where the krill species Euphausia superba dominates and is widely distributed compared with that in East Antarctic waters (Atkinson et al., 2008). In contrast, the Indian Ocean sector of the East Antarctic Ocean has a relatively short history of ecosystem research, although large-scale campaigns such as Baseline Research on Oceanography, Krill and Environment (BROKE) and BROKE-West have been conducted (Nicol et al., 2000b, 2010). In the Scotia Sea, both krill-dependent and krill-independent food webs have been proposed, depending on krill abundance (Murphy et al., 2007). The krill-independent food web becomes dominant when krill is less abundant, and copepods and myctophid fish are key components. It is considered that this food web is more dominant in the Indian Ocean sector than in the western Antarctic Peninsula or Scotia Sea because, during austral summer off Dumont d’Urville Base and Lützow Holm Bay, the distribution of krill is limited to along the continental slope and total biomass is relatively small (Amakasu et al., 2011; Atkinson et al., 2008; Ono et al., 2011; Ono and Moteki, 2017b). Murphy et al. (2007) placed icefish (Channichthyidae) in the krill-independent food web as a component below top predators. However, this may not be applicable to the Indian Ocean sector, at least along the 140 E transect off Dumont d’Urville Base. Here, notothenioid fish, including icefish, and myctophids (mesopelagic) have allopatric distributions in the neritic (continental shelf) and oceanic zones, respectively (Moteki et al., 2011). Similar distinctive distribution patterns were observed in these waters by copepods
and pelagic cnidarians (Tachibana et al., 2017; Toda et al., 2014). In contrast, in the Scotia Sea, islands and wide shelf areas interrupting the eastward flow of the ACC produce complicated oceanic frontal structures (Murphy et al., 2012), which likely result in neritic and oceanic species having sympatric distributions. These distributions indicate that myctophids are more important in the krillindependent food web in the oceanic zone in the Indian Ocean sector. Thus, in the neritic zone of the Indian Ocean sector, there is another food web in which Antarctic silverfish, Pleuragramma antarcticum, or ice krill, Euphausia crystallorophias, are a key component, as observed in the Ross Sea (Smith, Jr. et al., 2012). Myctophid fish have become recognised as an important component in the Southern Ocean food web with their huge biomass and high energy content, and as the targets of foraging by higher trophic animals (Saunders et al., 2014). Electrona antarctica is the most dominant myctophid in the Southern Ocean. Moteki et al. (2017a, 2017b) studied the early life history of this species. In one paper (2017a), they described the development of the external morphology and osteology from the larval to juvenile stages, and discussed changes in the swimming and feeding functions with development. They also first described the transformation stage between the larval and juvenile stages, and reported that morphological changes such as transformation are related to ontogenetic vertical migration to deeper water (Moteki et al., 2009). Moteki et al. (2017b) conducted discrete depth samplings along 140 E and 110 E transects, and observed that larvae were distributed mainly in a specific water mass, the Modified Circumpolar Deep Water (MCDW), and did not participate in diurnal vertical migration (DVM). The study also detected DVM in juvenile/adult fish using a quantitative echo-sounder in conjunction with net sampling. MCDW is generally located close to the area of the ice edge or drifting sea ice in our research waters during summer, suggesting that the early life history of E. antarctica is related to the presence of sea ice. Makabe et al. (2017) discussed mesozooplankton distribution patterns and the developmental stage composition of dominant herbivorous copepods in relation to timing and longevity of ice edge bloom in the waters north of Lützow Holm Bay. They also suggested that such differences in primary productivity in this region would be caused by local heterogeneity in sea ice dynamics, which is closely related with the local hydrography and topography. Although most of the studies on sea ice biota (SIB) have focused on those in fast sea ice or larger stable ice floes, Ojima et al. (2017) investigated the fauna in smaller areas of drifting sea ice at the sea ice edge during summer to provide fundamental information on the role of SIB in the water column. The latter two studies indicate the importance of assessing the influence of sea ice on food webs in the water column, and provide crucial information for predicting ecosystem changes as a result of projected changes in sea ice in the near future. 3. Global warming and ecosystem changes The key species E. superba has declined significantly in abundance since the 1970s (Atkinson et al., 2004). In contrast, Antarctic salps, Salpa thompsoni, which are considered competitors to krill in terms of space and/or food, have increased their range southward (Atkinson et al., 2004). Ono and Moteki (2013, 2017a) observed the distribution of salps south of the Southern Boundary of the ACC (SBACC), which had previously been considered the southern limit of the species in the Indian Ocean sector, and suggested they can reproduce south of the SBACC. However, they appeared to be less competitive with krill, at least in spatial distribution (Ono and Moteki, 2017a). The study also mentioned a need for monitoring in terms of population dynamics. Large-scale research campaigns focusing on krill generally
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sample the epipelagic layer (0e200 m depth) to cover a wide study area (e.g. BROKE, Nicol et al., 2000b) because krill are mainly distributed in this layer. Consequently, very few studies on meso- and bathypelagic fauna have been conducted in the Southern Ocean. Umitaka-maru has contributed as an observation platform to reveal meso- and bathypelagic fauna using several large nets. These studies have observed high diversity of pelagic cnidarians, copepods and pelagic fish (Moteki et al., 2009, 2011; Tachibana et al., 2017; Toda et al., 2010, 2014), and elucidated the distribution patterns and demography of euphausiids using samples from epipelagic to meso- and bathypelagic waters (Ono and Moteki, 2017b; Ono et al., 2011). These findings on the animal assemblages, community structure and distribution patterns in deeper waters provide invaluable information for elucidating the cycling of material and predicting future ecosystem changes related to the biological pump. Part of the Umitaka-maru research has comprised net sampling in deeper waters in the Southern Ocean. However, net sampling only looks at a snapshot of biological features in the sea. Acoustic techniques can potentially address this limitation. In fact, quantitative echo-sounder sampling is applied as an international standard for the estimation of krill abundance (Hewitt et al., 2004). Although conventional echo-sounders use narrowband sound of discrete frequencies (e.g. 38, 70, 120 and 200 kHz), the use of broadband sound has recently been focused for measuring continuous spectra of echoes. Amakasu et al. (2017) developed a broadband echosounder and applied it to infer the length-frequency distribution of krill. This technique could be useful for monitoring krill population structures. Climate change is observed as changes in sea ice in the Southern Ocean, although no remarkable changes have occurred to date in East Antarctica (Massom et al., 2013). However, Umitaka-maru research expeditions have contributed to detecting the freshening of Antarctic Bottom Water off Dumont d’Urville Base (Aoki et al., 2013), which draws attention to ecosystem changes in the Indian Ocean sector. Katayama et al. (2017) verified experimentally the effects of the shallowing of the surface mixed layer depth due to global warming on the photosystem of phytoplankton, which suggested that photosystem II damaged by high light could have induced the faster recovery observed north of the Polar Front (PF) compared to that south of the front. Ocean acidification caused by increasing pCO2 in the atmosphere causes failure of the aragonite shell of thecosome pteropods to develop properly. Akiha et al. (2017) investigated the distribution and biomass of shelled pteropods including the veliger stage using a relatively fine mesh net (100 mm). These data could provide a basis for detecting ecosystem changes in the future, as well as information on the biomass of small-sized pteropods, which is often omitted in studies yet is essential for understanding the cycling of material in the ocean. KARE did not incorporate monitoring observations before the JARE initiated Continuous Plankton Recorder (CPR) observations in 2003 (KARE09) on the Umitaka-maru because inter-annual continuity was not guaranteed before KARE08. CPR observations are an effective and efficient method for zooplankton monitoring to detect ecosystem change over large ocean scales. On the Umitaka-maru, CPR has contributed significantly to surface zooplankton monitoring in the Southern Ocean (Takahashi et al., 2010, 2011; Hosie et al., 2014). Regular sampling on the Shirase and the Umitakamaru along single transect provide the opportunity to conduct time-series CPR towing. Takahashi et al. (2017) compared CPR samples from three different seasons along the same 110 E transect collected from two research vessels. Multi-ship observations will be required in future research in the Southern Ocean because long-term voyages with a single ship are rarely scheduled due to various difficulties, such as the need for resupplying stations, budget limits and competition for ship time.
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4. Conclusion Research voyages in the Southern Ocean undertaken by the Umitaka-maru have been conducted as a leg of the long-distance training voyages for the Advanced Course of Fisheries Science at TUMSAT, but have had limitations in terms of the observation season, length of voyage and location. However, scientists have conducted detailed observations intensely using the various types of nets available on the Umitaka-maru, and collected important data on an almost annual basis. The Umitaka-maru has contributed to advances in deep-water sampling that had previously been performed by only a few studies in the Indian Ocean sector. It is crucial to continue the Southern Ocean observations to monitor the ecosystem changes caused by global warming. The Umitaka-maru sails almost every year in the Southern Ocean, which provides a valuable opportunity for the education and training of graduate students and young scientists. An international framework for a multi-ship observation system is required to develop effective efforts to monitor marine ecosystems. TUMSAT committed to participate in the Antarctic Climate and Ecosystem Cooperative Research Centre (ACE CRC, http://acecrc.org.au/) in 2016, and TUMSAT began collaborative studies with Australian scientists and graduate students onboard the Umitaka-maru in the same year. The abundance of E. superba, a key species in the Southern Ocean food web, is small in the Indian Ocean sector of the Antarctic Ocean compared to the western Antarctic Peninsula region and Scotia Sea, which results in the relative importance of the krillindependent food web in this region. The early life history of E. antarctica, one of the key components in this food web, has been suggested to be related to sea ice or food webs near the sea ice, which implies that ecosystem changes are related to changes in sea ice. It is crucial to determine the significance of sea ice in marginal ice zone ecosystems using onboard experiments and monitoring. Acknowledgements We are grateful to the captain, officers and crew of the Umitakamaru for all of their efforts, which ensured that KARE voyages were always productive. Takashi Ishimaru of TUMSAT established the early stages of KARE, and the guest managing editor inherited his achievements on the Umitaka-maru. Nobue Takasawa, Kaori Uchiyama, Tomoko Satoh, Keishi Shimada, Takuji Hosaka and Jota Kanda of the Observation and Research Centre for Ocean Systems of TUMSAT assisted in organizing KARE. We are also grateful to the scientists and graduate students who worked on board and the cadets on the ship for scientific discussions and help with observations. In addition, we acknowledge the support of the Polar Science office in Tokyo, the Editor-in-chief Takashi Yamanouchi and his secretary Ayumi Ando. The field observations of this special issue were supported in part by a Grant-in-Aid for Science (No. 15H05239 for M. Moteki and No. 24255001 for T. Odate) and by the National Institute of Polar Research through project research numbers AJ-02, AP-25, AP-46, AP-0923, AMB-2-5, AMB-0902, KPe4 and KP-308, and by the MEXT for JARE Routine Observations, the Physical and Chemical Oceanographic Observations. References Akiha, F., Hashida, G., Makabe, R., Hattori, H., Sasaki, H., 2017. Distribution in the abundance and biomass of shelled pteropods in surface waters of the Indian sector of the Antarctic Ocean in mid-summer. Polar Sci. 12, 12e18. Amakasu, K., Ono, A., Hirano, D., Moteki, M., Ishimaru, T., 2011. Distribution and density of Antarctic krill (Euphausia superba) and ice krill (E. crystallorophias) lie Land in austral summer 2008 estimated by acoustical methods. Polar off Ade Sci. 5, 187e194.
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Amakasu, K., Mukai, T., Moteki, M., 2017. Measurement of the volumebackscattering spectrum from an aggregation of Antarctic krill and inference of their length-frequency distribution. Polar Sci. 12, 79e87. Aoki, S., Kitade, Y., Shimada, K., Ohshima, K.I., Tamura, T., Bajish, C.C., Moteki, M., Rintoul, S.R., 2013. Widespread freshening in the Seasonal Ice Zone near 140 E off the Adelie Land Coast, Antarctica, from 1994 to 2012. J. Geophys. Res. 118, 6046e6063. Atkinson, A., Siegel, V., Pakhomov, E., Rothery, P., 2004. Long-term decline in krill stock and increase in salps within the Southern Ocean. Nature 432, 100e103. Atkinson, A., Siegel, V., Pakhomov, E.A., Rothery, P., Loeb, V., Ross, R.M., Quetin, L.B., Schmidt, K., Fretwell, P., Murphy, E.J., Tarling, G.A., Fleming, A.H., 2008. Oceanic circumpolar habitats of Antarctic krill. Mar. Ecol. Prog. Ser. 362, 1e23. 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Masato Moteki* Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato, Tokyo 108-8477, Japan National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan Tsuneo Odate National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan Department of Polar Science, School of Multidisciplinary Sciences, Graduate University for Advanced Studies (SOKENDAI), 10-3 Midoricho, Tachikawa, Tokyo 190-8518, Japan Graham W. Hosie Emeritus Life Fellow, Sir Alister Hardy Foundation for Ocean Science, Plymouth, UK Kunio T. Takahashi National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan Department of Polar Science, School of Multidisciplinary Sciences, Graduate University for Advanced Studies (SOKENDAI), 10-3 Midoricho, Tachikawa, Tokyo 190-8518, Japan Kerrie M. Swadling Antarctic Climate & Ecosystems Cooperative Research Centre and Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 129, Hobart, TAS 7001, Australia Atsushi Tanimura National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan Department of Polar Science, School of Multidisciplinary Sciences, Graduate University for Advanced Studies (SOKENDAI), 10-3 Midoricho, Tachikawa, Tokyo 190-8518, Japan *
Corresponding author. Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato, Tokyo 108-8477, Japan. E-mail address: [email protected] (M. Moteki).