Ecosystem Group Seminar (FY 2016)

* The schedule is subject to change if we have a guest speaker.

Miyako Satoh
"2016 fiscal year work report"

Yuriko Nakamura
"Various samples scanned with MXCT"

Tomoko Yoshiki
"Effect of variation in copepod community structure on the downward carbon flux in the western subarctic Pacific Ocean"

Abstract

Variations in lower trophic structure and biological diversity of marine plankton in the last decade may influence on the some services of planktonic ecosystem such as biogenic carbon flux. To assess the effect of the variation in zooplankton community structure on the carbon export, seasonal and spatio-temporal variabilities in biomass, biodiversity and the minimum turnover time of carbon incorporated in copepods community were examined in western subarctic ocean area by using CPR data. Additionally, impact of ontogenetically migrating of large-sized Neocalanus copepods on carbon export was estimated. The biomass of warm-water species were increased from summer and autumn season. The biodiversity increased and the turnover time was tended to be short concurrent with the warm-water species increment. These results indicate that the copepod-related downward carbon export could be reduced in smaller-sized community concurrent with the rise of sea surface temperature in warming climate system. The maximum of the turnover time of the western North Pacific area was approximately 2 folds of the value in the subarctic Atlantic area. This implies that contribution of the copepods to biological carbon pump in the western North Pacific is quite higher than Atlantic Ocean.

S. Lan Smith, Taketo Hashioka, Bingzhang Chen
"Untangling the effects of individual-level acclimation and inter-specific competition on the modeled dynamics of phytoplankton community size structure"

Abstract

A variety of ecosystem models have been developed that resolve the size distribution of phytoplankton using multiple (now up to hundreds of) discrete size classes. Although such models have proven useful as research tools, they require a great many calculations for large-scale and long term modeling studies. As an alternative, continuous size-distribution models, which require many fewer calculations, could in principle be used for faster large-scale simulations. However, few such models even exist, and their ability to reproduce observations has not been well tested. This study compares the discrete and continuous approaches, and furthermore aims to clarify the relative importance of acclimation (at the individual or species level) and competition between multiple size-classes (or species) for the dynamics of size-based phytoplankton communities. We compare the performance of discrete and continuous size-distribution models, each formulated with and without flexible physiological response (acclimation) for each size class. All four models were implemented in a 0-D (box) model of the oceanic mixed layer and fitted to data from two contrasting time-series observation stations in the North Pacific, including size fractionated chlorophyll observations. Unexpectedly, the continuous size distribution model with acclimation reproduces the observations better than the corresponding discrete model. However, accounting for acclimation response makes more difference for model results than does the choice of discrete or continuous size representation. Finally we compare modeled relationships to observed patterns of size-fractionated chlorophyll vs. total chlorophyll, to clarify how the acclimation response and inter-specific competition impact the dynamic size structure of phytoplankton communities.

Tetsuichi Fujiki
"In situ observation of autumn phytoplankton blooms in the western subarctic North Pacific"

Abstract

The western subarctic North Pacific is a cyclonic upwelling gyre (western subarctic gyre; WSG) that extends from the northeast of Japan to near the international dateline. It is well known that the WSG is a region of high-nutrient and low-chlorophyll waters, as is the Alaskan gyre (AG), which is located in the eastern subarctic North Pacific. One of the major differences between the WSG and AG systems is the occurrence of seasonal phytoplankton blooms. In the AG, chlorophyll a (Chl a) concentrations in surface waters remain relatively constant throughout the year. In contrast, in the WSG, transient increases of surface Chl a occur in late spring and autumn. Although the occurring mechanisms of the late-spring blooms have been relatively well-studied, those of the autumn blooms are still unknown due to the lack of observation data in autumn. To overcome this limitation, we deployed a hybrid profiling buoy system at time-series station K2 (47oN, 160oE) in the WSG and carried out time-series observations of phytoplankton productivity from July to October 2015. Our study will provide a better understanding of the mechanisms that regulate seasonal phytoplankton dynamics in the WSG.

Katsunori Kimoto
"Anticyclonic eddies and spatial distribution of microzooplankton in the North Pacific: Preliminary result"

Abstract

Mesoscale anticyclonic eddies have been observed at south of the Aleutian Islands and shift the position to Southwestward. Those anticyclonic eddies are called “Aleutian Eddy” and have longer lifetime. Satellite image of these eddies indicates high surface chlorophyll and primary production from spring to summer, therefore behavior of these eddies are thought one of the keys to induce higher primary production in the western subarctic gyre.
A research cruise by the T/S Oshoro Maru had conducted from June to July, 2016 to clarify the relationships between Aleutian eddies and biological productions. During this cruise, we performed plankton tow observations by VMPS and NORPAC in two mesoscale eddies (Eddy A and B) appeared in the North Pacific. The purpose of this study is 1) reveal spatial distributions of microzooplankton, particularly planktic foraminifers, and 2) make comparisons biomass between inside and outside of eddies.
The lower limit of existence of planktic foraminifers in K2 and KNOT where there were no influences of eddies were ca. ~150 m in this cruise. On the other hand, in Eddy A and B, planktic foraminifers occurred at ~500 m and much deeper than other areas. Furthermore, standing stocks of planktic foraminifers in the eddies were abundant compare to K2 and KNOT. In this presentation, I will show the additional chemical and physical properties of eddies and discuss the relationship between spatial distributions of planktic foraminifers and mesoscale eddies.

Taketo Hashioka
"Preliminary experiment of ocean acidification in the western North Pacific"

Abstract

Responses of marine phytoplankton to ocean acidification is reported from an on-board manipulation experiment by Dr. Koji Sugie (JAMSTEC) in the western North Pacific. They suggested that an increase in nano-/pico-phytoplankton and a decrease in diatoms under high pCO2 conditions (1420 and 2850 μatm), respectively. In this study, we parameterized the responses of phytoplankton to acidification, and conducted a simplified ocean acidification experiment using a 1D ecosystem model (Shigemitsu et al., 2012) at the Station A04 (42.15N, 145.07E). The results showed a potential of delay in spring bloom with decrease in the magnitude, and an importance of acidification on not only calcifiers but also on general phytoplankton.

Minoru Kitamura
"Temporal changes in radiocaecium contamination derived from the Fukushima Dai-ichi Nuclear Power Plant accident in oceanic zooplankton in the western North Pacific"

Abstract

We investigated temporal changes in radiocaesium contamination derived from the Fukushima Dai-ichi Nuclear Power Plant accident in oceanic zooplankton from 1 month to 3 years after the accident at subtropical and subarctic stations (900–1000 and 1900km from the plant, respectively) in the western North Pacific. The maximum activity concentrations of 137Cs in zooplankton were 2 orders of magnitude higher than the pre-accident level. In the first 3 months of the study period, the activity concentrations of radiocaesium in subtropical zooplankton rapidly decreased, whereas no such drastic change was observed at the subarctic station. The atmospheric deposition–derived radiocaesium rapidly decreased as a result of seawater mixing. Thus, most of the subtropical zooplankton (with short life-spans) that had taken up radiocaesium just after the accident might have been replaced by newly hatched zooplankton by 3 months after the accident, whereas subarctic zooplankton (with long life-spans) that were highly contaminated with radiocaesium were still alive after 3 months. By the end of the study, 137Cs activity concentrations in subtropical zooplankton remained high, whereas the activity concentrations in subarctic zooplankton had decreased nearly to the pre-accident level. The former concentrations were probably influenced by a secondary supply of radiocaesium resulting from advection of subtropical mode water that was highly contaminated with Fukushima-derived radiocaesium. Unexpectedly, at the subarctic station, the radiocaesium activity concentrations in surface zooplankton were lower than those in subsurface zooplankton, whereas the opposite relationship was observed for surface and subsurface seawater. Because carnivores predominated in the subsurface community, we contend that the higher radiocaesium activity concentrations in subsurface zooplankton were influenced by bioaccumulation. We conclude that radiocaesium activity concentrations in zooplankton are influenced not only by the supply of radiocaesium to the environment but also by the characteristics of the zooplankton community.

Koji Sugie
"Effects of temperature, CO₂, and salinity on the dynamics of phytoplankton communities in the western Arctic Ocean"

Abstract

The rapid climate change such as warming, sea ice reduction and ocean acidification in the Arctic Ocean can influence ecosystem dynamics including biogeochemical cycling. This study examined the effects of temperature, CO₂ and salinity on plankton communities in the Arctic Ocean using on-board manipulation experiment during R/V Mirai MR15-03 and MR16-06 cruises. Temperature (control and + ~4°C), CO₂ (control and + 300/500 μatm), and salinity (control and −5%) were manipulated using thermostatic circulator, the addition of high-CO₂ seawater, and pure water, respectively. The higher temperature enhanced the growth of total phytoplankton community in both incubations. Nano-sized (~2–10 μm) phytoplankton growth was increased due to the higher temperature in the MR15-3 community, whereas the higher CO₂ levels enhanced their growth in the MR16-06 community. Pico-sized (＜ 2 μm) phytoplankton growth was unchanged in the MR15-03 community, but that was enhanced in the MR16-06 community under the higher temperature conditions. The effect of lower salinity rarely affected phytoplankton growth rates. Phytoplankton pigment and nutrient drawdown ratio imply that the contribution of diatom biomass to the total phytoplankton was slightly decreased because of the higher temperature in the MR15-03 community. The growth of larger phytoplankton group (＞ 10 μm) responded only against temperature increases in both incubations. Our results showed that phytoplankton dynamics in the Arctic Ocean could be altered by each of any perturbations but the responded community differed each other. The higher temperature and CO₂ levels could act as a negative feedback on atmospheric CO₂ concentrations via decreasing large-sized phytoplankton such as diatoms.

Carmen Garcia-Comas Rubio
"Species-level functional traits affect differently species-ranking in subarctic and subtropical communities of copepods"

Abstract

Understanding the mechanisms driving biodiversity changes is an open question in ecology. Communities are usually structured by a few common species and many rare species. And according to niche theory, common species dominate due to more adapted functional traits. Here, we investigate how six categorical functional traits at species level (i.e., body size, diet, feeding mode, myelination, egg spawning and thermal-biogeographic-range) affect the abundance ranking of species from common to rare, and thus community structuring in subarctic versus subtropical copepod communities of the western North Pacific. Different trait categories dominate subarctic and subtropical communities except for the trophic strategies. Overall, we observe that in subarctic communities trait-categories distribute unevenly in the species ranking, with the dominant species (rank 1) belonging to favourable trait-categories more often than expected by chance. In contrast, in subtropical communities trait-categories distribute more evenly in the species ranking, and communities are niche-saturated for certain traits (e.g., most species are small and warm-water). We conclude that those species-level functional traits have a stronger role in structuring subarctic than subtropical communities. Combining species and functional trait information may contribute to understanding mechanisms behind patterns of diversity change such as the latitudinal gradient of biodiversity.

Yoshikazu Sasai
"Nutrient dynamics at cyclonic eddy off the east coast of Taiwan using an eddy-resolving coupled physical-biological model"

Abstract

In the oligotrophic ocean, subtropical gyre, the mechanism of nutrient supply from deeper layer to euphotic layer is an important to sustain biological production. Eddy-induced upwelling supplies a significant fraction of nutrients to sustain primary production in the Sargasso Sea [McGillicuddy and Robbinson, 1997; McGillicuddy et al., 1999, 2007]. There are two different types of eddies (cyclones and mode-water eddies) that generate plankton blooms with mode-water eddies tending to produce a stronger biological response [McGillicuddy et al., 2007]. In the subtropical region of the western North Pacific, the shipboard high-resolution hydrographic survey conducted to investigate the biogeochemical response with the passage of the cyclonic eddy [Sukigara et al., 2014]. This result presents that the enhanced primary productivity due to the passage of cyclonic eddy is likely to have an important role in the ecosystem and material cycling in the subtropical region. Our study focuses on the cyclonic eddy off the east coast of Taiwan in the subtropical region of the western North Pacific and analyzes the response of biogeochemical processes with its temporal and spatial evolution using an eddy-resolving coupled physical-biological model (OFES). Our focused the cyclonic eddy (hereafter Eddy-A) in the OFES has about 200 km diameter and its life-time is about 3 months (from May to July) off the east coast of Taiwan. Temporal variability of the Eddy-A has 3 states (spin-up period, stable period, and spin-down period). Vertical nutrient supply within the Eddy-A is related to the strength of its relative vorticity. During the spin-up period of the Eddy-A (increasing relative vorticity), nutrient supply from deep layer is the largest and the biological production increases. Variability of ecosystem (phytoplankton, zooplankton and detritus) within the Eddy-A is linked to vertical nutrient supply.

Bingzhang Chen
"Why primary production peaks at surface during summer in the subtropical, oligotrophic open ocean?"

Abstract

Classic understanding on the phytoplankton dynamics in the oligotrophic open ocean such as the central North Pacific gyre is that phytoplankton growth rate is limited by the upward supply of inorganic nutrients delivered largely by diffusion. Since nutrient supply mostly comes from below and light attenuates from surface to the depth, phytoplankton growth rate should peak at some intermediate depth, coinciding with the deep chlorophyll maximum (DCM) layer. However, examination on the data of net primary production (NPP) measured at two stations (ALOHA and S1) in the subtropical North Pacific reveals that NPP peaks within the surface mixed layer in spite of the negligible nutrient concentration at surface and a pronounced deep chlorophyll maximum (DCM) around 100 m. While the formation of DCM might be largely accounted for by phytoplankton photoacclimation (adjustments of chlorophyll-to-carbon ratios), the surface peak of phytoplankton growth rates suggests that the phytoplankton growth rate is not really limited by nutrient availability but could be light-limited. I developed a 1D model that couples ocean physics with two different kinds of ecosystem models (one species vs. two species of phytoplankton) built upon nutrient-phytoplankton-zooplankton-detritus (NPZD) plankton models. Model parameters were optimized by a Delayed Rejection Adaptive Monte-Carlo (DRAM) algorithm. Preliminary results suggest that the two-species model can better reproduce the vertical patterns of NPP. The implications are: 1) phytoplankton nutrient limitation may not be as severe as previously expected and light could play a more important role in controlling NPP in the oligotrophic open ocean; 2) phytoplankton diversity seems critical in faithfully reproducing NPP patterns.

Eko Siswanto
"Unique dispersion of low salinity and high primary productivity water in the East China Sea in summer 2010"

Abstract

Nutrient-limited regime of the East China Sea (ECS) including the Kuroshio water normally has low phytoplankton primary productivity (PP) of < 400 mgC m-2 d-1 all-year round. Combination of satellite observation and PP model revealed unique dispersion of high phytoplankton biomass (Chl) and PP (> 500 ~ 1000 mgC m-2 d-1) in summer 2010 over the normally nutrient-limited regime of the ECS, and that the high PP water was likely dispersed along the Kuroshio axis. Applying SeaWiFS ocean color data, colored dissolved organic matter (gelbstof) absorption coefficient (ag) algorithm, and relationship between ag and salinity, unusually southeastward dispersion of high ag and low salinity water was observed in summer 2010. This high ag and low salinity water which is associated with high nutrient water from the Yangtze River plume was likely also transported northeastward by Kuroshio water. This high nutrient was likely responsible for the high PP in the outer-shelf and Kuroshio water of the ECS in summer 2010. Unusually large southeastward extension of low salinity (thereby high in nutrient) water was caused by high Yangtze River discharge associated with 2010 La Niña.

Naomi Harada
"Seasonal change in biomass and assemblage of Arctic Eukaryota estimated by metagenome extracted from formalin-preserved particles"

Abstract

Loss of marine biodiversity caused by climate change is an urgent issue. Identifying changes in marine biodiversity such as biomass, assemblages, and geographic distributions due to multiple environmental stressors is necessary to sustain ecosystem services, but we lack an effective method for surveying temporal changes in marine biodiversity by comparing historical and modern data. Here we report on a new technique for extracting a metagenome from marine particles stored in formalin for long periods. By using rescued 18S rDNA, we were able to quantify the relative biomass of individual lower trophic level organisms identified at the phylum or division level. We analyzed a time series of 18S rDNA extracted from settling particles collected by sediment trap from October 2010 to September 2011 in the western Arctic Ocean. The time-series 18S rDNA data revealed seasonal and/or annual changes in biomass and assemblages, including those of organisms undeterminable by traditional methods such as microscopic observation. By allowing genomic analysis of formalin-preserved tissue, the metagenome rescue technique developed here should lead to breakthroughs in other fields as well.

Simone Taglialatela (Instituto de Ciencias Marinas de Andalucía, Department of Coastal Ecology and Management, Consejo Superior de Investigaciones Cientificas (CSIC) - Spanish National Research Council)
"Characterization of mesozooplankton communities through image analysis technique: an assessment in transitional and offshore waters"

Abstract

This work includes the results proceeding from different researches carried out under the common denominator of the methodological assessment of a technique of images analysis applied to mesozooplankton samples. The major methodological features involved in the semi-automatic identification and count of the mesozooplankton have been evaluated. The assessment provided a series of guidelines aimed to maximize the efficiency of the technique and to minimize the processing times. The methodological assessment was further expanded to the study of three different mesozooplankton communities to accomplish different objectives and to validate the efficiency of the technique under different conditions. The communities aim of the studies, were characterized by different species composition and abundances. The results proved the robustness of the technique, confirming it as a valid alternative to the traditional microscopy. With relatively brief processing times, a high level of accuracy was achieved through the semi-automatic identification of the samples. Furthermore, the broad versatility of the technique permitted the accomplishment of specific objectives related to the three different communities investigated.

Abigail McQuatters-Gollop (Centre for Marine Conservation and Policy, Plymouth University, UK)
"Using science to inform marine policy: a case study of marine ecosystem monitoring in the UK"

Abstract

Unprecedented basin-scale ecological changes are occurring in our seas. As temperatures warm ocean pH is lowering, sea ice is decreasing, and marine stratification and nutrient regimes are changing. These unparalleled changes present new challenges for managing our seas as we are only just beginning to understand their ecological manifestations. Management toward a healthy ecosystem will take place against a background of climate-driven macroecological change. When setting environmental policy targets an understanding of large-scale ecological change in the marine ecosystem is also necessary. Knowledge exchange activities are often limited in funding, and the communication formats respected in the scientific community, such as peer-reviewed publications and scientific conference talks, are not appropriate to disseminate research to policy and decision makers. Consequently, scientific research may not be integrated in to the decision making process, with end users left either unaware of or not clearly understanding how science can support and inform management, adaptation and mitigation options. Much of our knowledge of macroecological change in the North Atlantic is a result of research using data gathered by the UK’s Continuous Plankton Recorder (CPR) survey, a near-surface plankton monitoring program which has been sampling in the North Atlantic since 1931. CPR data indicate that North Atlantic and North Sea plankton dynamics are responding to both climate and human-induced changes, presenting challenges to the development of pelagic targets for achievement of a good environmental status in European Seas. The CPR time-series is a crucial scientific tool for informing and supporting the sustainable management of our seas through policy mechanisms. Translating and transferring scientific data into the management process is challenging, important for managing our seas.

Dr. Hongbin Liu (Hong Kong University of Science and Technology)
"Geographical niche differentiation of Synechococcus communities in the Western Pacific Marginal Seas"

Abstract

Synechococcus, a cosmopolitan pico-unicellular cyanobacteria, are important primary producers in marine environments. They are both highly phylogenetically and phenotypically diverse. In order to draw a map about the abundance, pigment phenotypic diversity (revealed by cpe genes), and phylogenetic diversity (revealed by rpoC1 gene) of Synechococcus in the western Pacific Ocean and its marginal seas, we collected surface samples in eight cruises from 2009 to 2014, and studied both the phylogenetic and phenotypes (pigment genetics) of Synechococcus using 454 pyrosequencing and clone library construction and sequencing methods. Synechococcus abundance in this vast area was also determined through flow cytometric analysis. Our results show that the abundance and genetic diversity of Synechococcus were the highest in the East China Sea. Clades I and II were the dominant lineages in the western Pacific Ocean surface waters. Clade I Synechococcus may contain six different subclades corresponding to cold and warm water ecotypes. Clade IV Synechococcus were rarely found in this study, though it often co-occurs with clade I. Clade III, VI, VII and S5.3 were also the major Synechococcus lineages in the warm waters of the western Pacific Ocean, but with relatively narrower niche than clade II. There is a latitudinal niche partitioning in Synechococcus pigment phenotypic compositions. Pigment type 3a was abundant in the ECS, while type 3c and/or type 3dB was largely dominant at the SCS. Most strikingly, chromatic acclimaters of the 3dA type constituted almost the sole pigment type in the western subarctic Pacific and the Bering Sea. Our results also showed that Synechococcus communities with a similar phylogenetic composition might be composed of distinct pigment phenotypes, suggesting that the PE-encoding genes have undergone multiple lateral transfers between Synechococcus lineages during the evolution of this genus. The GC and GC3 contents of cpe genes of Synechococcus communities in the ECS are higher than those in other geographic locations, indicating that the pigment genes in the ECS suffered the least pressure. Our results show a geographical differentiation in bothphylogenetic composition and pigment genotype of Synechococcus in the western Pacific Ocean, which can be explained by the adaptation of different clades/types to environmental conditions

Kana Nagashima
"The amount and sources of Asian dust transported to the North Pacific"

Abstract

Asian dust affects the climate/environment throughout the northern hemisphere, such as primary productivity in the North Pacific through supply of micronutrient iron. For further investigation and evaluation of the effect of Asian dust on marine primary productivity, it is critical to determine the amount and main sources of Asian dust transported over long distances using marine sediments from the North Pacific.

In order to extract dust information from sediments, it is necessary to distinguish dust from other terrigenous materials. Until now, many parameters such as major, trace, and rare earth elements (e.g., Zhang et al., 1996); strontium and neodymium isotopes (e.g., Asahara et al., 1995, Nakano et al., 2004); and oxygen isotopes, crystallinity, and electron spin resonance (ESR) signal intensity of quartz (e.g., Mizota et al., 1992, Nagashima et al., 2007, Sun et al., 2007) have been investigated to identify Asian dust and estimate its source desert. I will review such provenance-tracing techniques and introduce our new approach combining multiple parameters; Sr-Nd isotopes, ESR signal intensity of quartz, and mineral compositions. Then, I will discuss relative abundance of Asian dust to the volcanic materials transported from island arcs using a sediment core derived from Shatsky Rise, the oceanic plateau in the northwestern Pacific Ocean, and estimate dust sources.

Maki Noguchi Aita
"Nitrogen and Carbon stable isotope ratios of the lower trophic level food web system in the Oyashio region of the western North Pacific"

Abstract

The Coastal Oyashio water (COY) which has lower salinity (＜33‰) and cold water (＜ 2 deg C) is distributed along the coast of Hokkaido during winter – spring. The origin of COY has been considered as the ice melt water from the Okhotsk Sea (e.g. Ohtani, 1971; Shimizu et al., 2001), and large blooming of phytoplankton was observed early spring at COY. To investigate the COY plays important related to blooming of the Oyasio region, we carried the observations in three water mass: COY, Oyashio water(OY) and Warm-Core Ring(OUT) along the A-line monitoring transect (38N-42.5N, 144.5-147.5E) in March 2015 during cruises of KH15-1 of the R/V Hakuho-maru and WK15-03 of the R/V Wakataka-maru. We analyzed carbon and nitrogen isotopic ratios of plnakton samples, and inspected how Δδ15N / Δδ13C of the zooplankton changed by the difference in the water mass on the basic foodweb.

Markus Pahlow (GEOMAR, Germany)
"Towards Optimality-Based Plankton Modelling on the Global Scale"

Abstract

Optimality-based models of plankton organisms have enabled considerable progress in 0D (laboratory and mesocosm), 1D (ocean time series), and 2D (global satellite data) analysis. At GEOMAR we are currently developing the methodology to use the benefits of optimality-based models, such as realistic biological process descriptions and variable stoichiometry, in global biogeochemical and Earth-system models. For example, realistic biological process representations allow us to ask genuinely biological questions, such as about the role of different feeding strategies by zooplankton in the surface ocean. The presentation will start by reviewing previous achievements with optimality-based modelling. I will then describe and outline solutions to some qualitatively new technical difficulties posed by our optimality-based models. Preliminary simulations with the University of Victoria Earth System model will show the current state and outline future plans and new opportunities in the interpretation of global datasets afforded by the optimality-based approach.

Carmen Garcia-Comas Rubio
" (My) Efforts on understanding functional diversity of plankton"

Abstract

Understanding how species coexist in rich communities and the role of biodiversity on ecosystem-functioning is a long-standing major challenge in ecology. Increasing number of studies have explored the role of functional diversity in these processes, considering that species have different roles in a community and thus measures based only on species numbers may be misleading due to functional redundancy. In addition, theoretical models based on functional traits are proliferating fast. Yet, empirical studies of plankton functional diversity are still scarce, especially those on mesozooplankton.

In this seminar I will briefly show you the state of the art of my work on this matter. First, analyses of copepod species functional traits at the Kuroshio-Oyashio extension revealed that subtropical communities were more niche saturated (e.g., most species were small) and that the distribution of trait values in the species abundance-rank was homogeneous, mirroring the average frequency of those trait values in the species pools; while in subarctic communities the dominant species (rank 1) had favorable trait values more often than expected by chance. Our results suggest that subtropical communities may be niche-saturated towards the most adapted trait values, so that merely having those most adapted trait value confers no strong competitive advantage to a species. Second, I joined the summer A-line cruise of FRA and will show you the plan for sample analysis. Third, preliminary analyses of the individual size structure of mesozooplankton across the north Pacific show that the continuous size diversity reveals spatial structuring hidden on previous analyses of the size spectra slopes.

S. Lan Smith
"Untangling the relative contributions of physiological acclimation and inter-specific competition for modelling size-based phytoplankton communities"

Abstract

Several plankton ecosystem models have been developed that resolve the size distribution of phytoplankton using a number of discrete size classes. Some even resolve hundreds of size classes. Although such models have proven useful as research tools, they require a great deal of calculations for large-scale modeling studies. As an alternative, we in our CREST project have been developing continuous size-distrbitution models, which require many fewer calculations and can therefore be used for faster large-scale simulations. However, few such models even exist, and their ability to reproduce observations has not been well tested. This study aims to compare the discrete and continuous approaches and furthermore to clarify the relative importance of acclimation (at the individual or species level) and competition between multiple size-classes (or species) for modeling size-based phytoplankton communities.

I will compare the performance of discrete and continuous models, each formulated with and without flexible physiological response (acclimation) for each size class. The newly developed Ecologically Flexible Type (EFT) model incorporates both physiological flexibility of each size class and a continuous size distribution. The FlexPFT model (Smith et al. J. Plankton Res. 2015) uses the same rate equations for a set of discrete size classes. As a control, the equations typical of a discrete Nutrient-Phytoplankton-Zooplankton-Detritus (NPZD) model have been used to construct both a continuous size-distribution model and a discrete model with multiple size classes. All four models were implemented in a 0-D (box) model of the oceanic mixed layer and fitted to data from observation stations K2 (subarctic) and S1 (subtropical) in the North Pacific as in Smith et al. (2015), with the addition of size-fractionated chlorophyll observations. Unexpectedly, the continuous size-distribution models consistently reproduced the observations better than the discrete models. However, the flexible models consistently outperformed the corresponding inflexible control models by a much wider margin, in both discrete and continuous versions. For size-based modeling of phytoplankton communities, continuous distribution models are viable alternatives to the more common discrete approaches, although accounting for acclimation response is much more important than how the size distribution is represented.

Inah Seo (the guest from Korea Institute of Ocean Science and Technology)
"Tropical Pacific paleoceanography during the last deglaciation: From the surface to the deep"

Abstract

The future climate would be predicted reliably only with the in-depth understanding of past climate change. Especially, in relation to present global warming, the last deglaciation (18-12 ka) is one of the periods which have received considerable attention because it provides the most recent record of abrupt CO₂ rise and warming climate. Recently my researches are focused on the last deglacial paleoceanography of tropical Pacific, where the heat and moisture are converged and transported to the higher latitudes via atmospheric and oceanic motion.

The surface ocean environment at a central equatorial Pacific site (6°40′N, 177°28′W) during the last deglaciation was reconstructed using the planktic foraminifera. The planktic foraminifera assemblage and their geochemical composition during the period resembles modern composition at subtropical central Pacific sites that are strongly influenced by the northeasterly Trades and North Equatorial Current (NEC). We suggest that the study site, presently under the control of the Intertropical Convergence Zone (ITCZ)–North Equatorial Countercurrent, had been influenced by the northeasterly Trades and NEC during the 18–12 ka interval.

My research interest in the future lies on the deep ocean circulation that could have affected the deglacial CO₂ rise. Today, the equatorial upwelling region is one of the major pathways of CO₂ from the deep ocean to the atmosphere, and the release of CO₂ in the region is thought to have been increased during the deglacial periods owing to the weakening of ocean stratification. Such ventilation of deep ocean basins and emission of stored CO₂ are often considered as an explanation for the “carbonate preservation spike” in deep-sea sediment. However, a number of records are found without deglacial peaks in CaCO₃ preservation in the tropical western Pacific. One suggests that there had been a significant change in the deep ocean current system originated from the North Pacific during the last deglacial period, which would have resulted in the decrease of Pacific [CO₃^2-]. To investigate the relationship between the deep ocean circulation and the CaCO₃ preservation, my current study is focused on the reconstruction of paleo-[CO₃^2-] and the ventilation age of the deep water in the tropical western Pacific.

Keisuke Shimizu (the guest from R&D Center for Marine Biosciences)
"Genetic diversity and population structure of arctic pteropod Limacina helicina"

Abstract

Current high levels of atmospheric CO₂ lead to decrease the average of pH and calcium carbonate saturation state (Ω_ar or Ω_ca) at the subsurface seawater. These chemical changes are expected to impact some calcifying marine organisms to varying degrees, because it triggers the inhibition of their calcification or the dissolution of their calcified structure like shell. In some marine calcifying organisms, however, different response patterns against experimentally high pCO₂ seawater environment have reported between species or between populations of same species. Although their patterns are likely related to their genetic background, their population structure and genetic diversity remain unclear. In this seminar, I introduce the results of phylogeograpic analyses using arctic pteropod Limacina helicina and the effect of different CO₂ levels on the shell development in L. helicina.

Koji Sugie
"Emerging impact of CO2 on the elemental composition of marine diatoms after nutrient depletion"

Abstract

Partitioning of algal production into dissolved and particulate matters could affect food web dynamics and biogeochemical cycling of bioelements. Although the impact of increasing CO2 in seawater due to the anthropogenic activities (i.e., ocean acidification), on marine phytoplankton has been intensively investigated in the past two decades, there are very limited data available concerning the dissolved and particulate matter partitioning of algal production. In this study, we investigated the effects of different CO2 levels (180, 380, 600 and 1000 ppm) on the production of dissolved organic and particulate matters using two marine diatoms Chaetoceros affinis and Ditylum brightwellii under nutrient-replete and –depleted conditions. We found that both species increased specific growth rate with increasing CO2 levels. Particulate organic carbon production increased with increasing CO2 levels especially under nutrient-depleted conditions, whereas dissolved organic carbon production decreased (C. affinis) or unchanged (D. brightwellii) in the higher CO2 conditions. Particulate organic carbon to particulate nitrogen ratio increased with increasing CO2 levels partly due to the decrease in intracellular nitrogen concentration under high CO2 conditions. Production of transparent exopolymer particles (extracellular carbon-rich material) tended to decrease with increasing CO2 levels under nutrient-depleted conditions. The enhanced carbon production was partitioned into intracellular particulate phase rather than into the dissolved organic matters, suggesting that the high CO2 levels could have positive impacts on carbon transfer to the higher trophic levels and to the ocean depth.

Jose Luis Otero-Ferrer (The guest from Departamento de Ecoloxía e Bioloxía Animal, Universidade de Vigo, Spain)
"Which main factors control the picoplankton community structure in the ocean?"

Abstract

Picoplankton are the most abundant organisms in the ocean, often dominate planktonic biomass and primary production, and they could represent a substantial contribution to the global export of carbon. Today, we have a limited understanding about the factors that control the picoplankton community structure. A recent analysis indicates that light and temperature are the main factors explaining Prochlorococcus and Synechococcus distributions, whereas nutrient concentrations play a minor role (Flombaum et al., PNAS 2013). Methodological difficulties to quantify mixing in the field have motivated the use of indirect approaches to determine the input of nutrients into the euphotic zone and moreover, nutrient concentrations are not always directly related to nutrient supply. Classical competition ecology, physiological studies and nutrient competition experiments indicate that nutrient supply dynamic plays a significant role on determining the taxonomic composition of eukaryotic microphytoplankton. In order to investigate the role of nutrient supply in the composition of picoplankton groups, we used 3 different approaches: database analysis, nutrient competition experiments and ecological modelling. Our results indicate that nutrient supply also plays a role in the distribution of picoplankton functional groups in the ocean.　

Bing-Zhang Chen
"On the pitfalls of estimating model parameters from data using ordinary linear least-squares regression: the errors in X matter"

Abstract

Mechanistic models need parameters as input. The parameters are usually obtained by fitting laboratory and/or field data to a specific model, the simplest form being a linear model with only one predictor (X). Many parameters such as the coefficient of temperature dependence and the allometric scaling factor are estimated by running ordinary least-squares (OLS) regression on the (log-transformed) data. However, the primary assumption of the OLS regression is that the predictor X is error-free, which is rarely satisfied in real data analysis. It is noteworthy that the errors include not only measurement error but also natural variability. In a seminar paper, Ricker (1973) already pointed out that when the X values are predetermined instead of being measured, the OLS regression estimates the true relationship between the response variable (Y) and X even in the presence of errors in X. However, when the X values are just measured, the OLS regression will underestimate the slope between Y and X when X has error. I will illustrate two cases in which the parameters estimated from OLS regressions can be misleading. The first case is the estimation of temperature sensitivity of phytoplankton growth (i.e. Q10 or activation energy). The second case is the estimation of zooplankton grazing half-saturation constant. Care must be taken to estimate these seemingly simple parameters that nonetheless greatly influence model results.

Naomi Harada
"Is alkenone valid as a thermometer of the past temperature of lake Ichinomegata?"

Abstract

Well preserved lake or pond sediment cores with high time resolution are good recorders to know natural disasters occurred in the past. Lake Ichinomegata located on the coast in Akita prefecture is famous to preserve perfect sediment that has seasonal lamination with no disturbance caused by bioturbation, wave, wind, gas vent, and water vent on the lake floor. We collected sediment core at the center of Lake Ichinomegata in summer 2013. To understand the past environment surrounding area of Lake Ichinomegata, we tried to reconstruct lake surface temperature by biomarker, alkenone that has been utilized commonly as a paleo thermometer under ocean. I will talk about the empirical equation to show the relationship between temperature and alkenone index, UK’37 of suspended particles collected in lake Ichinomegata and results of lake surface temperature over the past a couple of decaces using this equation.

Minoru Kitamura
"Acoustic observations to understand zooplankton dynamics"

Abstract

I will introduce our two acoustic observations for zooplankton research. One of them was conducted to describe vertical distribution and diel migration of zooplankton by using the moored ADCP at S1. The comparison with net samples indicated that the backscatter strength likely represents the bulk zooplankton biomass. There was seasonality in the vertical distribution of zooplankton. Seasonal changes in daylight hours affected the timing of the diel migration and lunar cycle affected nighttime vertical distribution in the surface layer. Physical events, such as mixed-layer deepening/restratification and the passage of a mesoscale eddy, also affected vertical distribution of zooplankton. Another acoustical observation was conducted in the Chukchi Sea by using the AZFP (Acoustic Zooplankton Fish Profiler) which was a multi-frequency eco-sounder. Acoustic backscattering strength from marine organism is known to be size and frequency dependent, and the dependence can be used to make inferences about classification of organisms. We attempted to identify the dominant scatterers in the study site and the results will be introduced.

Yoshikazu Sasai
"Nutrient dynamics at cyclonic eddy off the east coast of Taiwan using an eddy-resolving coupled physical-biological model"

Abstract

In the oligotrophic ocean, subtropical gyre, the mechanism of nutrient supply from deeper layer to euphotic layer is an important to sustain biological production. Eddy-induced upwelling supplies a significant fraction of nutrients to sustain primary production in the Sargasso Sea [McGillicuddy and Robbinson, 1997; McGillicuddy et al., 1999, 2007]. There are two different types of eddies (cyclones and mode-water eddies) that generate plankton blooms with mode-water eddies tending to produce a stronger biological response [McGillicuddy et al., 2007]. In the subtropical region of the western North Pacific, the shipboard high-resolution hydrographic survey conducted to investigate the biogeochemical response with the passage of the cyclonic eddy [Sukigara et al., 2014]. This result presents that the enhanced primary productivity due to the passage of cyclonic eddy is likely to have an important role in the ecosystem and material cycling in the subtropical region. Our study focuses on the cyclonic eddy off the east coast of Taiwan in the subtropical region of the western North Pacific and analyzes the response of biogeochemical processes with its temporal and spatial evolution using an eddy-resolving coupled physical-biological model (OFES). Our focused the cyclonic eddy (hereafter Eddy-A) in the OFES has about 200 km diameter and its life-time is about 3 months (from May to July) off the east coast of Taiwan. Temporal variability of the Eddy-A has 3 states (spin-up period, stable period, and spin-down period). Vertical nutrient supply within the Eddy-A is related to the strength of its relative vorticity. During the spin-up period of the Eddy-A (increasing relative vorticity), nutrient supply from deep layer is the largest and the biological production increases. Variability of ecosystem (phytoplankton, zooplankton and detritus) within the Eddy-A is linked to vertical nutrient supply.

Eko Siswanto
"Ongoing ocean color studies under the APN-climate adaptation framework"

Abstract

In this seminar, ongoing activities based on ocean color remote sensing observations will be introduced. Activities are partially supported by the Asia-Pacific Network for Global Change Research (APN)-Climate Adaptation Framework (CAF), with one of outputs will be a free-gap high resolution ocean color remote sensing dataset. Recent and future studies (e.g., in the East and South China Seas, northwest Pacific Ocean) under this APN-CAF will also be briefly presented.

Katsunori Kimoto
"Vulnerability of Pteropod shell in the Arctic Ocean: Results of culture experiment under natural seawater"

Abstract

Culture experiment for Limacina helicina, Thecosomata Pteropod living in the Arctic Ocean was performed in 13 days at the shipboard laboratory to observe shell degradation under three different pH and aragonite saturation states (Ωara) of seawater. Aragonite shell degradation was observed under the unsaturated water conditions within 48 hours after the experiment started, and five degradation states were identified under the microscope. All individuals spawned egg mass during the culturing. It strongly suggests that sensitive of aragonite shells might have received severe impacts in rapid environmental changes in the Arctic Ocean, but on the other hand, they are robust enough to ensure survival of the next generation.
At the onshore laboratory, all cultured shell density of L. helicina had analyzed to detect aragonite shell density by the Microfocus X-ray CT (MXCT). I will discuss about shell density changes during the culture experiment.

Tetsuichi Fujiki
"Seasonal variability of phytoplankton community structure in the subtropical western North Pacific"

Abstract

During 2010–2012 in the northwestern region of the North Pacific subtropical gyre, we examined seasonal variability of the phytoplankton community with respect to structure and photo-physiological status using the chemotaxonomy program CHEMTAX and fast-repetition-rate fluorometry. Total chlorophyll a standing stock in the upper 150 m (ʃTChl a) varied from 25.5 to 89.0 mg m−2 during periods of relatively deep vertical mixing (40–207 m), but was fairly constant (18.6–27.2 mg m−2) during stratification periods. Prymnesiophytes, chlorophytes, chrysophytes, prasinophytes, and/or diatoms comprised major portions of the ʃTChl a during mixing periods. Diatoms became the most abundant group (29–43 %) in February 2011, when large phytoplankton blooms were observed, whereas Prochlorococcus was the dominant component (15–46 %) during stratification periods. During mixing periods, nitrate and nitrite (NO3 + NO2) concentrations occasionally exceeded 0.5 μmol kg−1 in surface waters, and Fv/Fm (photochemical efficiency of photosystem II) ranged from approximately 0.40–0.50 within the euphotic zone. During stratification periods, however, NO3 + NO2 concentrations were very low (＜0.1 μmol kg−1) from the surface to 50–95 m, and Fv/Fm was in the range of 0.25–0.40 in the upper mixed layer. The seasonal variability of phytoplankton community structure in this region was related to the nutrient supply from deep waters. Additionally, we compared our data to published values at the time-series station ALOHA, located in the eastern region of the NPSG. At Sta. ALOHA in 2011, ʃTChl a was almost constant (19.5–26.4 mg m−2) throughout the year and was consistently dominated by Prochlorococcus (61–81 %). These results suggest that the phytoplankton community in the northwestern region of the NPSG is seasonally variable and composed of diverse groups compared with the eastern region of the NPSG.

Taketo Hashioka
"Re-estimation of global distribution of N2 fixation based on wide area observations in the North Pacific"

Abstract

Luo et al. (2014) estimated a global distribution of nitrogen fixation using wide area observations with a multiple regression analysis. This result is widely used for validation of nitrogen fixation model of the global scale. However, a new data-set by Dr. Shiozaki showed a significantly different spatial pattern of nitrogen fixation in the North Pacific. As the observational sites in Luo et al. (2014) are mainly located in the Atlantic, there is a possibility that information in the Pacific was not fully reflected to their estimation. In this study, we re-estimate the global distribution of nitrogen fixation based on the new data-set of the Pacific with a method of SOM (Self-organizing maps).