Toru Kobari
Kagoshima University
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Featured researches published by Toru Kobari.
Progress in Oceanography | 2003
Toru Kobari; Akiyoshi Shinada; Atsushi Tsuda
Grazing experiments and production estimation based on life-history analysis of Neocalanus copepods (N. cristatus, N. plumchrus and N. flemingeri) were carried out in the Oyashio region to understand the carbon flows associated with the interzonal migrating copepods. These copepods, and also Eucalanus bungii, fed on nano- and micro-sized organisms non-selectively throughout the season. However, diatoms were the dominant food resource until May and organisms, such as ciliates were the major resource after May. Daily growth rate was estimated from the Ikeda-Motoda, Huntley-Lopez and Hirst-Sheader models. Since the growth rates were considered to be overestimates for the Huntley-Lopez model and underestimates for the other two models, we applied the weight-specific growth rates previously reported for these species in the Bering Shelf. Surface biomass of Neocalanus increased rapidly in June during the appearance of C5, and a successive increase of overwintering stock was evident in the deeper layer. The deep biomass decreased gradually from September to May during the dormant and reproduction period. N. cirstatus has the largest annual mean biomass (2.3 gC m -2 ), followed by N. plumchrus (1.1) and N. flemingeri (0.4). Daily production rate of Neocalanus varied from 0.4 to 363.4 mgC m -2 day -1 , to which N. cristatus was the largest contributor. Annual production was estimated as 11.5 gC m -2 year -1 for N. cirstatus, 5.7 for N. plumchrus and 2.1 for N. flemingeri, yielding annual P/B ratio of 5 for each species. The annual production of Neocalanus accounted for 13.2% of the primary production in the Oyashio region. Their fecal pellets were estimated to account for 14.9% (0.7 gC m -2 year -1 ) of sinking flux of organic carbon at 1000-m depth. Moreover, their export flux by ontogenetic vertical migration, which is not measured by sediment trap observations, is estimated to be 91.5% (4.3 gC m -2 year -1 ) of carbon flux of sinking particles at 1000-m depth. These results suggest the important role of interzonal migrating copepods in the export flux of carbon.
Journal of Oceanography | 2003
Toru Kobari; Kazuaki Tadokoro; Akihiro Shiomoto; Shinji Hashimoto
Geographical variations in prosome length and body weight of Neocalanus copepods (N. cristatus, N. plumchrus and N. flemingeri) were investigated on samples from North-South and East-West transects in the North Pacific during spring to early summer in 1998 and 1999. Southward and eastward increasing patterns were pronounced for water temperature, although no significant pattern was observed for chlorophyll a concentrations. All Neocalanus species showed large geographical variations in prosome length and body weight, being smaller in the southern and eastern waters. Comparing the relationship between prosome length and body weight, large deviations (lower body weight at a given prosome length) were evident for the eastern specimens of N. cristatus and N. plumchrus. In stepwise regression analysis, the geographical variations of prosome length and body weight revealed a significantly negative correlation with temperature variations. These results suggest that temperature is a more important environmental factor than chlorophyll a concentration in its effect on geographical variations in prosome length and body weight of Neocalanus copepods in the North Pacific.
Journal of Oceanography | 2016
Minoru Kitamura; Toru Kobari; Makio C. Honda; Kazuhiko Matsumoto; Kosei Sasaoka; Rie Nakamura; Kazuyuki Tanabe
Seasonal changes in mesozooplankton biomass and their community structures were observed at time-series stations K2 (subarctic) and S1 (subtropical) in the western North Pacific Ocean. At K2, the maximum biomass was observed during the spring when primary productivity was still low. The annual mean biomasses in the euphotic and 200- to 1000-m layers were 1.39 (day) and 2.49 (night) g C m−2 and 4.00 (day) and 3.63 (night) g C m−2, respectively. Mesozooplankton vertical distribution was bimodal and mesopelagic peak was observed in a 200- to 300-m layer; it mainly comprised dormant copepods. Copepods predominated in most sampling layers, but euphausiids were dominant at the surface during the night. At S1, the maximum biomass was observed during the spring and the peak timing of biomass followed those of chlorophyll a and primary productivity. The annual mean biomasses in the euphotic and 200- to 1000-m layers were 0.10 (day) and 0.21 (night) g C m−2 and 0.47 (day) and 0.26 (night) g C m−2, respectively. Copepods were dominant in most sampling layers, but their mean proportion was lower than that in K2. Mesozooplankton community characteristics at both sites were compared with those at other time-series stations in the North Pacific and with each other. The annual mean primary productivities and sinking POC fluxes were equivalent at both sites; however, mesozooplankton biomasses were higher at K2 than at S1. The difference of biomasses was probably caused by differences of individual carbon losses, population turnover rates, and trophic structures of communities between the two sites.
Journal of Oceanography | 2016
Toru Kobari; R. Nakamura; K. Unno; Minoru Kitamura; K. Tanabe; H. Nagafuku; A. Niibo; Hajime Kawakami; Kazuhiko Matsumoto; Makio C. Honda
We investigated seasonal changes in carbon demand and flux by mesozooplankton communities at subtropical (S1) and subarctic sites (K2) in the western North Pacific Ocean to compare the impact of mesozooplankton communities on the carbon budget in surface and mesopelagic layers. Fecal pellet fluxes were one order higher at K2 than at S1, and seemed to be enhanced by copepod and euphausiid egestion under high chlorophyll a concentrations. The decrease in pellet volume and the lack of any substantial change in shape composition during sink suggest a decline in fecal pellet flux due to coprorhexy and coprophagy. While respiratory and excretory carbon by diel migrants at depth (i.e., active carbon flux) was similar between the two sites, the actively transported carbon exceeded sinking fecal pellets at S1. Mesozooplankton carbon demand in surface and mesopelagic layers was higher at K2 than S1, and an excess of demand to primary production and sinking POC flux was found during some seasons at K2. We propose that this demand was met by supplementary carbon sources such as feeding on protozoans and fecal pellets at the surface and carnivory of migrants at mesopelagic depths.
Pacific Science | 2013
Yousef A. E. S. M. Buhadi; Toru Kobari; Kei Kawai; Tomoko Yamamoto; Hiroshi Suzuki; Satoru Nishimura; Takashi Torii; Joeli Veitayaki
Abstract: We compared food availability of filter-feeding bivalves, Anadara spp., between two Fijian sites of different mangrove richness to evaluate impacts of environmental variables on Anadara spp. abundance and body size. Suspended particles including planktonic organisms and detritus were more abundant in the fishery grounds of the mangrove-rich site (MR) than in the mangrove-poor site (MP). Athough no substantial difference was observed in abundance of Anadara spp., dry weights of soft tissue were heavier for animals at MR than those at MP. Respiration rates (i.e., minimum metabolic requirements) of Anadara spp. decreased with increasing animal weight. Unicellular planktonic biomass was estimated to support the Anadara community metabolic requirements (i.e., minimum food requirement) for 9.2 to 85.7 days at MR and 1.4 to 67.4 days at MP, indicating that the planktonic biomass cannot support sufficient growth of the bivalve population at some locations. These results suggest that suspended particles support increased shell sizes of Anadara spp. and that resuspended detritus is a supplement or alternative food resource for these bivalves in mangrovecoral associated ecosystems.
Journal of Oceanography | 2017
Makio C. Honda; Masahide Wakita; Kazuhiko Matsumoto; Tetsuichi Fujiki; Eko Siswanto; Kosei Sasaoka; Hajime Kawakami; Yoshihisa Mino; Chiho Sukigara; Minoru Kitamura; Yoshikazu Sasai; Sherwood Lan Smith; Taketo Hashioka; Chisato Yoshikawa; Katsunori Kimoto; Shuichi Watanabe; Toru Kobari; Toshi Nagata; Koji Hamasaki; Ryo Kaneko; Mario Uchimiya; Hideki Fukuda; Osamu Abe; Toshiro Saino
A comparative study of ecosystems and biogeochemistry at time-series stations in the subarctic gyre (K2) and subtropical region (S1) of the western North Pacific Ocean (K2S1 project) was conducted between 2010 and 2013 to collect essential data about the ecosystem and biological pump in each area and to provide a baseline of information for predicting changes in biologically mediated material cycles in the future. From seasonal chemical and biological observations, general oceanographic settings were verified and annual carbon budgets at both stations were determined. Annual mean of phytoplankton biomass and primary productivity at the oligotrophic station S1 were comparable to that at the eutrophic station K2. Based on chemical/physical observations and numerical simulations, the likely “missing nutrient source” was suggested to include regeneration, meso-scale eddy driven upwelling, meteorological events, and eolian inputs in addition to winter vertical mixing. Time-series observation of carbonate chemistry revealed that ocean acidification (OA) was ongoing at both stations, and that the rate of OA was faster at S1 than at K2 although OA at K2 is more critical for calcifying organisms.
Limnology and Oceanography | 2008
Deborah K. Steinberg; Benjamin A. S. Van Mooy; Ken O. Buesseler; Philip W. Boyd; Toru Kobari; David M. Karl
Deep-sea Research Part Ii-topical Studies in Oceanography | 2008
Deborah K. Steinberg; Joseph S. Cope; Stephanie E. Wilson; Toru Kobari
Journal of Plankton Research | 2001
Toru Kobari; Tsutomu Ikeda
Marine Ecology Progress Series | 2001
Toru Kobari; Tsutomu Ikeda