Koji Sugie | Central Research Institute of Electric Powor Industry (original) (raw)

Papers by Koji Sugie

Limnology and Oceanography, 2016

ICES Journal of Marine Science: Journal du Conseil, 2016

Deep Sea Research Part I: Oceanographic Research Papers, 2014

ABSTRACT Increase in seawater pCO2 and the corresponding decrease in pH caused by the increasing ... more ABSTRACT Increase in seawater pCO2 and the corresponding decrease in pH caused by the increasing atmospheric CO2 concentration (i.e., ocean acidification) may affect organic matter production by phytoplankton communities. Organic matter production forms the basis of marine food webs and plays a crucial role in oceanic CO2 uptake through the biological carbon pump, and hence will potentially affect future marine ecosystem dynamics. However, responses of organic matter production in open ocean plankton ecosystems to CO2 increase have not been fully examined. We conducted on-deck microcosm experiments using high nutrient, low chlorophyll (HNLC) waters in the western subarctic Pacific and oceanic Bering Sea basin in summer 2008 and 2009, respectively, to examine the impacts of elevated CO2 on particulate and dissolved organic matter (i.e., POM and DOM, respectively) production. Iron deficient natural plankton communities were incubated for 7–14 days under multiple CO2 levels with and without iron enrichments (hereafter +Fe and −Fe treatments, respectively). By combining with our previous experiments at two sites, we created a comprehensive dataset on responses of organic matter production to CO2 increase during macronutrient replete conditions in HNLC waters. Significant differences in net particulate organic carbon production among CO2 treatments were observed only in the −Fe treatments, whereas that in net dissolved organic carbon production were mainly observed in the +Fe treatments, suggesting that CO2 may affect different processes depending on the Fe nutritional status. However, impacts of CO2 were not consistent among experiments and were much smaller than the consistent positive effects of Fe enrichment. In contrast, no significant differences among the CO2 treatments were observed for organic carbon partitioning into POM and DOM, and carbon to nitrogen ratio of net produced POM. We conclude that CO2 does not play a primary role, but could have secondary effects on controlling the organic matter production under macronutrient replete conditions in HNLC waters. On the other hand, in a nutrient-depleted, declining phase of the phytoplankton bloom induced by Fe enrichment, carbon overconsumption was found in an experiment with elevated CO2 conditions suggesting that CO2 impacts might become more significant in such environments.

PloS one, 2016

Next-generation sequencing (NGS) technologies have enabled us to determine phytoplankton communit... more Next-generation sequencing (NGS) technologies have enabled us to determine phytoplankton community compositions at high resolution. However, few studies have adopted this approach to assess the responses of natural phytoplankton communities to environmental change. Here, we report the impact of different CO2 levels on spring diatoms in the Oyashio region of the western North Pacific as estimated by NGS of the diatom-specific rbcL gene (DNA), which encodes the large subunit of RubisCO. We also examined the abundance and composition of rbcL transcripts (cDNA) in diatoms to assess their physiological responses to changing CO2 levels. A short-term (3-day) incubation experiment was carried out on-deck using surface Oyashio waters under different pCO2 levels (180, 350, 750, and 1000 μatm) in May 2011. During the incubation, the transcript abundance of the diatom-specific rbcL gene decreased with an increase in seawater pCO2 levels. These results suggest that CO2 fixation capacity of diato...

Isij International, Mar 15, 2011

Isij International, Mar 1, 2011

Atmospheric CO2 is increasing because of anthropogenic activities including the burning of fossil... more Atmospheric CO2 is increasing because of anthropogenic activities including the burning of fossil fuels, which cause global warming and ocean acidification.1,2) To regulate cli-mate change to an acceptable level, the following carbon mitigation strategies have been proposed: (1) ...

Increasing atmospheric CO2 over the Anthropocene due to human activities has reduced seawater pH ... more Increasing atmospheric CO2 over the Anthropocene due to human activities has reduced seawater pH and it continues as long as burning fossil fuels. In this review, we summarize and discuss the methodology of ocean acidification study and the effects of ocean acidification on phytoplankton and biogeochemical cycle of nutrients. In addition, we compare the pH variability and phytoplankton dynamics over the past 60 million years with the recent phenomenon of ocean acidification. We found that: (1) there is a significant lack of knowledge on the effect of ocean acidification because previous studies were not examined using subpolar to polar phytoplankton species and also not considered their habitat and life cycle. (2) We should study the effect of pH on dissolved inorganic Fe(II) bioavailability relative to dissolved inorganic Fe(III) species and the availability of Fe(III)-ligand complex. The role of Fe(II) and chemical structure of the ligand are also important issues. (3) Particulate...

PLOS ONE, 2015

Traditionally, biodiversity has often been estimated on the basis of abundance partly due to the ... more Traditionally, biodiversity has often been estimated on the basis of abundance partly due to the need for complicated measurements of biomass. Here, we conducted robust measurements of the community composition and of the size structure of diatoms in the North Pacific to evaluate the importance of biomass on the biodiversity. We found that the two most useful evenness indices increased in most cases where small species were numerically dominant when calculations were based on biomass compared with those on abundance. Size-abundance spectra of diatoms revealed that numerically dominant small species rarely dominated in terms of biomass. On the other hand, intermediate to large diatom species generally played a dominant role in terms of biomass in diatom community. The results suggest that the size of the dominant species is a crucial factor in determining the role of diatoms in the ecosystem functioning. Because such size variability can also be observed in other organisms, we need to pay attention to the effect of size structures on biodiversity.

Iron (Fe) can limit phytoplankton productivity in approximately 40 % of the global ocean, includi... more Iron (Fe) can limit phytoplankton productivity in approximately 40 % of the global ocean, including in highnutrient, low-chlorophyll (HNLC) waters. However, there is little information available on the impact of CO 2 -induced seawater acidification on natural phytoplankton assemblages in HNLC regions. We therefore conducted an on-deck experiment manipulating CO 2 and Fe using Fe-deficient Bering Sea water during the summer of 2009. The concentrations of CO 2 in the incubation bottles were set at 380 and 600 ppm in the non-Fe-added (control) bottles and 180, 380, 600, and 1000 ppm in the Fe-added bottles. The phytoplankton assemblages were primarily composed of diatoms followed by haptophytes in all incubation bottles as estimated by pigment signatures throughout the 5-day (control) or 6-day (Fe-added treatment) incubation period. At the end of incubation, the relative contribution of diatoms to chlorophyll a biomass was significantly higher in the 380 ppm CO 2 treatment than in the 600 ppm treatment in the controls, whereas minimal changes were found in the Fe-added treatments. These results indicate that, under Fe-deficient conditions, the growth of diatoms could be negatively affected by the increase in CO 2 availability. To further support this finding, we estimated the expression and phylogeny of rbcL (which encodes the large subunit of RuBisCO) mRNA in diatoms by quantitative reverse transcription polymerase chain reaction (PCR) and clone library techniques, respectively. Interestingly, regardless of Fe availability, the transcript abundance of rbcL decreased in the high CO 2 treatments (600 and 1000 ppm). The present study suggests that the projected future increase in seawater pCO 2 could reduce the RuBisCO transcription of diatoms, resulting in a decrease in primary productivity and a shift in the food web structure of the Bering Sea.

Journal of Phycology, 2013

Partial pressure of CO 2 (pCO 2 ) and iron availability in seawater show corresponding 32 changes... more Partial pressure of CO 2 (pCO 2 ) and iron availability in seawater show corresponding 32 changes due to biological and anthropogenic activities. The simultaneous change in these 33 factors precludes an understanding of their independent effects on the ecophysiology of 34 phytoplankton. In addition, there is a lack of data regarding the interactive effects of 35 these factors on phytoplankton cellular stoichiometry, which is a key driving factor for 36 the biogeochemical cycling of oceanic nutrients. Here, we investigated the effects of 37 pCO 2 and iron availability on the elemental composition (C, N, P and Si) of the diatom 38

ISIJ International, 2011

Fisheries Science, 2008

The significance of Mn and Fe for the growth of a coastal marine diatom Thalassiosira weissflogii... more The significance of Mn and Fe for the growth of a coastal marine diatom Thalassiosira weissflogii was investigated by performing culture experiments containing macronutrients with either Mn or Fe, or both. Only the addition of both Mn and Fe induced the highest growth rates and maximal cell yields. Maximal growth was maintained in continuous culture media, which were repeatedly prepared by an inoculation of pre-culture and the addition of both Mn and Fe to the control culture medium containing macronutrients. In particular, it was found that the full growth recovery in Mn-sufficient medium (without added Fe) is accomplished by the addition of Fe even after several days' incubation. On the contrary, there was no sufficient growth recovery by the addition of Mn after a long incubation time in Fe-sufficient medium but without additional Mn. These results suggest that T. weissflogii in Mn-sufficient waters retains the ability for full physiological recovery for a long time, probably resulting from the decrease in the oxidative stress of phytoplankton by the production of antioxidant enzyme Mn superoxide dismutase during a long incubation period.

Biogeosciences, 2013

Little is known concerning the effect of CO 2 on phytoplankton ecophysiological processes under n... more Little is known concerning the effect of CO 2 on phytoplankton ecophysiological processes under nutrient and trace element-limited conditions, because most of the CO 2 manipulation experiments have been conducted under these element-replete conditions. To investigate the effects of CO 2 and iron availability on phytoplankton eco-5 physiology, we conducted an experiment using a phytoplankton community in the ironlimited, high-nutrient, low-chlorophyll (HNLC) region of the Bering Sea basin in September 2009. Carbonate chemistry was controlled by the bubbling of the several levels of CO 2 concentration (180, 380, 600, and 1000 ppm) controlled air, and two iron conditions were established with or without the addition of inorganic iron. We demonstrated 10 that in the iron-limited control conditions, the specific growth rate and the maximum photochemical quantum efficiency (F v /F m ) of photosystem (PS) II decreased with increasing CO 2 levels, suggesting a further decrease in iron bioavailability under the high CO 2 conditions. In addition, biogenic silica to particulate nitrogen and biogenic silica to particulate organic carbon ratios increased from 2.65 to 3.75 and 0.39 to 0.50, re-15 spectively with an increase in CO 2 level in the iron-limited controls. In contrast, in the iron-added treatments, specific growth rate, F v /F m values and elemental compositions did not change in response to the CO 2 variations, indicating that the addition of iron cancelled out the effect of the modulation of iron bioavailability due to the change in carbonate chemistry. Our results suggest that high CO 2 conditions can alter the biogeo-20 chemical cycling of nutrients through decreasing iron bioavailability in the iron-limited HNLC regions in the future.

… Journal of the …, 2008

We estimated probable length of continuation of steelmaking slag as an iron fertilizer enhancing ... more We estimated probable length of continuation of steelmaking slag as an iron fertilizer enhancing marine phytoplankton growth. Bioavailability of the slag was determined by a recovery in growth rate by repeated addition of macronutrients other than iron during a prolonged culture period. Degree of the recovery was gradually reduced by repeated nutrient spikes possibly because concentration of the iron released from the slag decreased with culture age. No recovery can be performed when iron supply from the slag was exhausted. Therefore, we could calculate the final day of the bioavailability of the slag by extrapolating the reduction course of the recovery. We also made SEM observations on the slag particles before and after the culture experiments. Results indicate that the slag particles added to phytoplankton cultures at the concentration of 20 mg L Ϫ1 continually release bioavailable iron for up to 50 d. In the slag we used, submicron particles were often found, while predominant fraction was 5-20 mm before experiments. In the 5-20 mm fraction, three types of the particles were recognized by SEM: amorphous, crystalline and cotton-ball types. After the culture, only the crystalline type of the particle was observed insoluble. Surface structure and size of these particles are likely determinative in bioavailability and durability of the iron contained in the steelmaking slag.

Journal of Geophysical …, Jan 1, 2009

Journal of plankton research, Jan 1, 2008

Deep Sea Research Part II …, Jan 1, 2010