Development of a Shizugawa Bay Digital Twin using an integrated watershed-ocean-ecosystem model (part 3)

School of Environment and Society, Institute of Science Tokyo

Asso.Prof.Takashi Nakamura

I would like to express my sincere gratitude for your consideration in awarding me the EMECS Grants-in-Aid for young researchers. I am deeply appreciative of the invaluable support provided by the International EMECS Center, which has enabled me to continue my research on the coastal ecosystem in Shizugawa Bay, Minamisanriku, Miyagi.
It has been observed that semi-closed bays, such as Shizugawa Bay, are characterized by a complex flow and water quality environment, influenced by various factors, including the inflow of freshwater from land, nutrients, organic matter, sediment, and biochemical reactions within the bay, as well as the intrusion of open-ocean water. To sustainably utilize marine resources and aquaculture, it is essential to understand these processes and the bay environment with a high degree of accuracy. Furthermore, it is possible that global warming and ocean acidification associated with recent increases in atmospheric CO2 concentrations may enhance stratification, especially in summer, and induce serious hypoxia and acidification in the bottom layer. We need to recognize that ongoing acidification has the potential to have significant consequences for marine ecosystems, particularly for calcifying organisms, such as oysters. This study aims to develop a digital twin of Shizugawa Bay to seek the optimal sustainable use of marine resources and aquaculture in the present and the future under climate change. The proposed approach involves the utilization of an integrated watershed-ocean-ecosystem model, intending to comprehensively reproduce the bay environment and ecosystem, including the dynamics of marine resources.
One of the interesting phenomena of oyster farming in Shizugawa Bay is that oyster yield increased when the number of oyster rafts was reduced with the great decision of local fishermen after the earthquake disaster. This means that it is very important to understand the negative impact of overcrowded aquaculture and to know the best density for aquaculture. The effects of overcrowding in aquaculture must be biological, such as competition for the availability of oyster food (phytoplankton), and physical, such as the weakening of water circulation by the drag of oyster rafts. Additionally, we need to think about how wakame seaweed and phytoplankton, which are a food source for oysters, compete for nutrients. Considering both physical and biological aspects, we try to seek the optimum aquaculture density and the best solution for sustainable aquaculture in Shizugawa Bay.

Elucidating the Carbon Budget in Coastal Areas: A Case Study of Toyama Bay

Faculty of Science, University of Toyama

Special Assit.Prof.Hidetaka Kobayashi

The ocean functions as one of the Earth’s largest carbon reservoirs, absorbing roughly 30% of anthropogenic CO2 emissions. Understanding the mechanisms behind this variability is essential for predicting future atmospheric concentrations. Coastal regions play a particularly important role as dynamic CO2 sinks. Within this context, my research centers on Toyama Bay, where I aim to uncover the processes that shape carbon-centered material cycles through a combination of long-term field observations and numerical modeling.
Over the past research period, I have focused on building a comprehensive observational dataset. This includes continuous monitoring of major rivers in Toyama Prefecture as well as bay waters, measuring discharge, water quality, dissolved inorganic carbon, nutrient concentrations, and chlorophyll. These records highlight both seasonal and interannual variability in nutrient delivery from land, which previous studies suggest may account for up to 20% of phytoplankton blooms. By extending these observations across multiple years, I seek to narrow the uncertainty surrounding this contribution.
These observational efforts provide the foundation for my modeling work. By constraining terrestrial inputs such as riverine discharge and submarine groundwater, I aim to improve the reproducibility of primary production and CO2 fluxes in the bay. Although the modeling system is still in progress, gradually incorporating field data is beginning to reveal the unique structure of material cycles in Toyama Bay.
Looking ahead, I intend to combine observations and modeling in a complementary way to quantify the causal relationships between terrestrial fluxes of nutrients and carbon and the oceanic responses they trigger. Such results will not only advance our understanding of carbon cycling in coastal zones but also contribute to more accurate projections of global climate change. Beyond the global perspective, the findings will also provide a scientific basis for sustaining fisheries resources and protecting coastal environments, ensuring that the research contributes to both regional communities and the broader Earth system.

Primary production of microphytobenthos on tidal flats influenced　by tides and submarine groundwater discharge (Part II)

Prefectural University of Kumamoto
Graduate School of Environmental & Symbiotic Sciences　Division of Environmental & Symbiotic Sciences

Doctoral Degree ProgramsTatsuya Ozaki

I would like to offer my sincere gratitude regarding my selection for EMECS Grants-in-Aid for young researchers. I belong to the doctoral course of the Graduate School of Environmental Symbiosis, Prefectural University of Kumamoto, and I am working on quantifying the primary producers of tidal flats in the Midori River tidal flat of the Ariake Bay, which has the largest tidal flat area in Japan.
Tidal flats support high fishery productivity, mainly through the harvest of bivalves. The growth of these bivalves is sustained by the horizontal transport of primary producers within the tidal flats. In this system, bivalve habitats function as “sinks” that consume primary producers, whereas muddy flats without bivalves and submarine groundwater discharge (SGD) areas act as “sources” that supply them. Recent studies have suggested that nutrient-rich SGD, particularly in nearshore areas adjacent to subterranean estuaries, promotes primary production and significantly contributes to its spatial distribution. Thus, conserving the tidal flat ecosystem requires not only the protection of bivalve habitats but also the preservation of these sources. However, because such sources are often located nearshore, they are increasingly threatened by coastal development worldwide. Furthermore, the quantification of primary production in tidal flats and its relationship with SGD have not been sufficiently evaluated scientifically, and evaluating the production balance between sources and sinks is an urgent research priority.
The Ariake Bay, which serve as my study site, contains approximately 40 % of Japan’s tidal flats. Although it was once a major bivalve fishing ground, its catches have drastically declined in recent decades. The tidal flats of the Ariake Bay are broadly categorized into sandy and muddy flats: the sandy flats serve as bivalve habitats, while the muddy flats function as sources of primary producers. In my research last year, I successfully quantified long-term primary production in sandy flats (i.e., the sink) of the Ariake Bay. Comparison with the secondary production of Ruditapes philippinarum at the same site revealed that primary production was substantially lower than the clam’s secondary production, demonstrating that an external supply of primary producers is indispensable for sustaining bivalve populations.
Field investigations have also confirmed the presence of nutrient-rich SGD in the southern Ariake Bay, leading me to hypothesize that “SGD areas, together with muddy flats, function as important sources of primary producers.” In the present study, I aim to quantify primary production within these sources and conduct a broad-scale assessment of primary production across the Ariake Bay. Through this research, I seek to contribute to a deeper understanding of the mechanisms sustaining tidal flat ecosystems and provide knowledge essential for their conservation.

Effects of Dissolved Silica on the Growth and Eicosapentaenoic Acid (EPA) Production of Benthic Diatoms in Tidal Flats

Department of Urban and Environmental Engineering
Faculty of Engineering　Kyushu University

Asso.Prof.Megumu Fujibayashi

I am honored to have been selected for the EMECS Grants-in-Aid for young researchers, and I am deeply grateful for this opportunity to pursue my research.
My interest lies in the dynamics and ecological roles of fatty acids in aquatic ecosystems, with a particular focus on highly unsaturated fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These fatty acids are essential nutrients for many aquatic animals; however, animals cannot synthesize them de novo or cannot meet their requirements through endogenous synthesis.
EPA is mainly synthesized by diatoms and supplied to aquatic food webs through trophic transfer. Adequate dietary EPA has been shown to enhance the fitness of aquatic animals and potentially increase community diversity. In this study, I aim to clarify how dissolved silica (DSi)—an essential nutrient for diatoms—affects their growth and EPA production.
Diatoms, the primary producers of EPA, require silica to build their siliceous frustules. In Japanese rivers, the concentration of silica is generally higher relative to nitrogen and phosphorus, so DSi has rarely been considered a limiting factor for diatom growth. Here, the comparison “silica is relatively more abundant than nitrogen and phosphorus” is based on the Redfield ratio, which estimates that diatoms require N:P:Si ≈ 16:1:15 (molar). According to Liebig’s law of the minimum, the nutrient in shortest supply—typically nitrogen or phosphorus—would limit growth. However, recent culture experiments have yielded results inconsistent with this Redfield requirement, and concepts such as multiple-nutrient limitation have been proposed. This suggests that it is necessary to investigate the nutrient requirements of benthic diatoms in tidal flats, which underpin coastal food webs and supply EPA.
The purpose of this project is to elucidate, through field surveys of nutrient concentrations (nitrogen, phosphorus, and silica) and laboratory culture experiments, the nutrient requirements of benthic diatoms in tidal flats, focusing mainly on sites in Kyushu, Japan. I have already received valuable advice from my advisors and am proceeding with field and laboratory work with the utmost commitment.

Origin and composition of Transparent Exopolymer Particles (TEPs) produced in eelgrass meadows

Akkeshi Marine Station
Field Science Center for Northern Biosphere
Hokkaido University

Asso.Prof.Tomonori Isada

Firstly, I express my sincere gratitude to the International EMECS Center for its generous Grants-in-Aid for young researchers. My research focuses on the dynamics of marine phytoplankton and seagrass in Akkeshi-ko estuary and Akkeshi Bay, located in the eastern region of Hokkaido, Japan. My objective is to obtain a better understanding of the carbon cycle within the coastal marine ecosystem.
Macroalgae beds and seagrass meadows play an important role in carbon burial and sequestration, serving as blue carbon that mitigate climate change. Notably, Japan is recognized as a significant blue carbon area due to its extensive coastline, ranking sixth globally. Consequently, elucidating the carbon cycle of macroalgae beds and seagrass meadows in estuarine and shallow coastal areas is of paramount importance.
This project focuses on the dynamics of Transparent Exopolymer Particles (TEPs) within eelgrass meadows in Akkeshi-ko estuary and Akkeshi Bay. TEPs are composed of acid polysaccharides and are characterized by their sticky particles with > 0.4 µm diameter. This particle aggregation phenomenon closely relates to marine snow. Our previous surveys have shown that the TEP concentrations in the eelgrass meadows of Akkeshi-ko estuary and Akkeshi Bay were highest in summer. We have also found that TEPs contribute to the particle flux in the eelgrass meadow. Next, we aim to investigate the origin and composition of TEPs produced in eelgrass meadows for better understanding the carbon cycle in eelgrass meadows.

Restoration of stock of asari clams and tidal flats ecosystem through nutrient management -A study of ecosystem response and function in　　 tidal flat mesocosm experiments

Aichi Fisheries Research Institute

Chief researcherRyota Sone

The stock of asari clams Ruditapes philippinarum, a key marine species, has significantly declined, impacting coastal fisheries and recreational activities such as clam digging. Moreover, asari clams play an important role in coastal carbon cycling, raising concerns that their decline may lead to the degradation of tidal flats and seagrass beds-ecosystems recognized as part of the blue carbon framework. One major factor contributing to the decline in asari crams stocks is thought to be a shortage of food due to reduced nutrient levels. In response, wastewater treatment facilities in Ise and Mikawa Bays have begun operating with increased nitrogen or phosphorus levels to improve the feeding environment for asari clams. These efforts are expected not only to enhance biological productivity but also to restore ecosystem functions and promote healthy material cycling. Increased primary production may also contribute to decarbonization by enhancing CO₂ absorption at the air–sea interface and increasing carbon sequestration in sediments through the growth of benthic organisms. However, the extent to which differences in nutrient supply and food availability affect biological productivity and ecosystem functions in tidal flats-and how these changes influence material cycling-remains poorly understood. Field surveys in natural coastal areas are often complicated by disturbances such as weather variability and fishing activity, making it difficult to evaluate these processes. Aichi Fisheries Research Institute possesses large-scale tidal flat mesocosms, which have been used to study biological colonization, ecosystem development, and material cycling. This study aims to use these mesocosms to eliminate natural disturbances and conduct controlled experiments manipulating nutrient levels and primary production. We will assess the responses and functions of tidal flat ecosystems, focusing on asari clams. Experimental plots will be established with varying nutrient or food supply conditions, and changes in species composition and biomass of benthic organisms will be monitored. Simultaneously, we will track changes of carbon and nitrogen in water and sediment and evaluate shifts in material cycling driven by ecosystem functions. Direct measurements of CO₂ flux at the air–sea interface will also be conducted to examine carbon budgets, including atmospheric exchange. Through this research, we hope to evaluate how nutrient management can support both productive coastal ecosystems and broader environmental goals such as decarbonization. Ultimately, we aim to contribute to the advancement of integrated fisheries and environmental policies.

Elucidation of the effects of changes in the feeding environment on bivalve larvae and development of an index to evaluate the larval settlement.

Coastal Productivity Research Group, Coastal and Inland Fisheries Ecosystems Division, Environmental Fisheries Applied Techniques Research Department,
Fisheries Technology Institute, National Research and Development Agency, Japan Fisheries Research and Education Agency

ResearcherTomohiro Okamura

I would like to appreciate to be selected for the “EMECS Grants-in-Aid for young researchers”.
In the Seto Inland Sea, the production of bivalves such as asari clam have been decreasing. Various factors have been pointed out as reasons for this decrease, and changes in the feeding environment is one of them.
Our previous study has shown that < 10 μm sized diatoms (nanoplanktonic diatoms) are important food for bivalve larvae and their biomass affects the larval settlement which could influences bivalve resources. Last year, we conducted filed observation to test our hypothesis that “Changes in the feeding environment during the larval stage affect the physiological activity and settlement of bivalve larvae”. As a result, it was confirmed that oyster larvae that occurred during the periods when the nanoplanktonic diatoms Cyclotella sp.A and Skeletonema menzelii were dominant (i.e., oyster larvae that appeared to have fed mainly on these diatoms) tended to have high physiological activity and achieve successful settlement. On the other hand, the larvae occurred when Chaetoceros tenuissimus was dominant tended to be less physiological activity and fail to settlement. Thus, although the results of field study supported the hypothesis, analysis of field data alone could not exclude the effects of fluctuating water temperature and salinity on larvae, and it was not able to genuinely evaluate the effects of each nanoplanktonic diatom on the larvae. In this study, in order to investigate the effects of different diets on the physiological activity, growth and survival of the oyster larvae, we will feed each of above three nanoplanktonic diatoms to oyster larvae under rearing conditions with uniform water temperature and salinity. Last year’s field observation also confirmed that oyster larvae with high physiological activity tended to have a high success rate in settlement. Therefore, we considered that it is possible to evaluate whether the coastal areas are suitable for bivalve production by investigating the physiological activity of the larvae that occurred there. This year, we will continue to accumulate the data on the physiological activity and success or failure in settlement of oyster larvae, and verify whether the physiological activity of bivalve larvae is an effective indicator for assessing bivalve production areas.

The results of this study will lead to the presentation of environment conditions for sustainable bivalve production and the development of methods for assessing the coastal areas. We believe this study will contribute to maintenance of a healthy coastal areas in which bivalve resources can be used sustainably.

Spawning and migration ecology of anadromous Japanese grenadier anchovy in the Ariake Sea (3)

Atmosphere and Ocean Research Institute、 University of Tokyo

Asst. Prof.Hikaru Itakura

I’m Hikaru Itakura, working at Atmosphere and Ocean Research Institute (AORI), University of Tokyo. I received my PhD from University of Tokyo in 2014, and then worked at Kobe University and University of Maryland, USA as a JSPS Research Fellow. My research topic is understanding response mechanisms of fisheries resources to environmental change, with primary interest of how diversity in migration and life history contribute to resilience in exploited fishes under environmental change. I have been studying effects of climate change and habitat modification on distribution, migration, and growth of migratory fishes such as freshwater eels and striped bass that migrate between marine and freshwater habitats.

In this research project, I’m studying about spawning and migration ecology of anadromous Japanese grenadier anchovy (Coilia nasus), to contribute to the conservation for enclosed coastal seas and resources management of this species　in Asia. The enclosed coastal seas including estuaries and inner bays are an important ecosystem with high production and biodiversity around globe. In particular, the estuarine turbidity maximum (ETM) formed in brackish water is essential habitats for many aquatic organisms. Fishes of genus Coilia (family Engraulidae), which are widely distributed in Asia, strongly depend on such enclosed coastal seas, especially ETM zones, and migrate between the sea and rivers. Thus, they have a potential to be an indicator species for conservation of health of ETM zones and connectivity between rivers and enclosed coastal seas. In Japan, Japanese grenadier anchovy is distributed only in the inner part of the Ariake Sea and its inflowing rivers, such as the Chikugo River, and adult anchovies migrate upstream for spawning up to the tidal freshwater area in early summer. Owing to such limited occurrence in space and time, they are prized as a summer feature in the local area. However, the fisheries catch of the species has continuously decreased over the past decades. Despite this situation, ecological knowledge of Coilia are scarce. Therefore, I’m exploring their potential spawning rivers, nursery grounds within rivers, migration patterns, and spatial distribution in the Ariake Sea using otolith stable-isotopic ratio and environmental DNA analyses, in order to clarify environmental characteristics that the fish prefer along their life history. In addition, I’m examining the degree of natal homing (contribution of each river stock to the entire population of the fish) to understand population dynamics of the anchovy in Ariake Sea so that the results will contribute to the conservation of enclosed coastal seas and appropriate resource management of Coilia in Asia based on ecological information of this symbolic fish.

Dynamics of Transparent Exopolymer Particles (TEPs) in the eelgrass meadows of Akkeshi-ko estuary、Japan

Akkeshi Marine Station Field Science Center for Northern Biosphere Hokkaido University

Asso. Prof.Tomonori Isada

Firstly, I am deeply grateful to the International EMECS Center for its Grants-in-Aid for young researchers. I am studying marine phytoplankton and seagrass dynamics in Akkeshi-ko estuary and Akkeshi Bay, located in the eastern part of Hokkaido, Japan, to better understand the carbon cycle in the coastal marine ecosystem.

Macroalgae beds and seagrass meadows in estuarine and shallow coastal areas have a significant role in carbon burial and sequestration to mitigate climate change as blue carbon. Especially, Japan is considered to be a major blue carbon area because Japan has the sixth longest coastline in the world. It is therefore important to understand the carbon cycle of macroalgae beds and seagrass meadows in estuarine and shallow coastal areas.

This project focuses on the Transparent Exopolymer Particles (TEPs) dynamics in eelgrass meadows in Akkeshi-ko estuary. TEPs consist of acid polysaccharides and are sticky particles with > 0.4 µm diameter, resulting in particle aggregation like marine snow. TEPs significantly contribute to the carbon flux into deep waters. TEPs stem from dissolved organic matter (DOC) released by aquatic organisms. Previous studies showed that phytoplankton is the main producer of DOC and TEPs in coastal and open oceans. However, little is known about the concentration of TEPs and their controlling factors in seagrass meadows. Since seagrass produces a large amount of DOC, TEP also could be produced in the seagrass meadows. Although seagrass’s root and leaf litter are the main fraction of carbon burial and sequestration, the evaluation of carbon storage by TEPs in the seagrass meadows is required.

Development of a Shizugawa Bay Digital Twin using an integrated watershed-ocean-ecosystem model (part 2)

School of Environment and Society, Tokyo Institute of Technology

Assoc. Prof.Takashi Nakamura

I would like to thank you again for selecting me for the EMECS Grants-in-Aid for young researchers, and, I am grateful to continuously study the coastal ecosystem in Shizugawa Bay, Minamisanriku, Miyagi with the great support by International EMECS Center.
It is known that semi-closed bays, such as Shizugawa Bay, have a complex flow and water quality environment due to various influences such as the inflow of freshwater from land, nutrients, organic matter, sediment, biochemical reactions in the bay, and open-ocean water intrusion. For sustainable utilization of marine resources and aquaculture, it is essential to understand these processes and to understand the bay environment with a high degree of accuracy. Furthermore, global warming and ocean acidification associated with recent increases in atmospheric CO2 concentrations may enhance stratification, especially in summer, and worsen hypoxia and acidification in the bottom layer. The progress of acidification may have serious impacts on marine resources, especially calcifyers, such as oysters. Based on this awareness of such issues, this study aims to develop a digital twin of Shizugawa Bay using an integrated watershed-ocean-ecosystem model to fully reproduce the bay environment and ecosystem including the dynamics of marine resources. In addition, this digital will be able to numerically seek the optimal sustainable use of marine resources and aquaculture in the present and the future under climate change.
One of the interesting phenomena of oyster farming in Shizugawa Bay is that oyster yield increased when the number of oyster rafts was reduced with the great decision of local fishermen after the earthquake disaster. This fact indicates that understanding the negative impact of overcrowded aquaculture and estimating the optimum density of aquaculture is very important. The effects of overcrowding in aquaculture must be biological, such as competition for the availability of oyster food (phytoplankton), and physical, such as the weakening of water circulation by the drag of oyster rafts. This year I will mainly focus on modeling the effects of overcrowding by incorporating both biological and physical processes.

Elucidating the Carbon Budget in Coastal Areas: A Case Study of Toyama Bay (part 2)

Faculty of Science, Academic Assembly University of Toyama

Asst. Prof. Hidetaka Kobayashi

From the perspective of carbon dioxide uptake in the ocean, coastal areas are regions where nutrients necessary for phytoplankton growth are abundantly supplied, leading to high primary production. Through gas exchange between the atmosphere and the ocean, coastal areas are expected to function as sinks for carbon dioxide. This project aims to elucidate the formation and variability mechanisms of the ocean biogeochemical cycle in Toyama Bay through both model experiments and observational data.

We construct an ocean biogeochemical cycle model to quantify the budget of nutrients and carbon related to the ecosystem. Toyama Bay receives abundant nutrient supplies from riverine and groundwater inputs from the land. It has been shown that up to 20% of the plankton bloom in the bay is supported by nutrient supply from terrestrial sources. By constraining these input amounts through observations and incorporating them into the model, we aim to evaluate the impact of terrestrial nutrient supply on the coastal ecosystem of Toyama Bay.

We have advanced the construction of the model, calculated the climatological distribution of the physical and biogeochemical fields, and examined the differences in results concerning freshwater input from the Jinzu River and the spatial resolution of the model. Additionally, we collected and organized existing observational data in Toyama Bay and compared the monthly variations in biogeochemical fields between the model and observational data.

In Toyama Prefecture, significant crustal deformation was observed due to the Noto Peninsula Earthquake in 2024. Changes in groundwater levels and quality have been confirmed, raising concerns about changes in the flow and quality of groundwater from land to coastal shallow sea areas. Submarine slope failures have also been identified, suggesting changes in submarine groundwater discharge points. These changes in nutrient supply to coastal waters are likely to induce variations in primary production and carbon dioxide fluxes in coastal areas. Therefore, this year, we plan to conduct surveys of terrestrial and submarine groundwater discharge and observations in Toyama Bay. By comparing with past observational data, we aim to understand the impact of the Earthquake and evaluate its impacts on the coastal ecosystem using models.

The ecology of green Noctiluca scintillans and environmental shifts during its red tide occurrences: a study in the Inner Gulf of Thailand

Seto Inland Sea Regional Research Center, Kagawa University

Assistant ProfessorMasatoshi NAKAKUNI

I am Masatoshi Nakakuni, a specially appointed assistant professor at Kagawa University. I am deeply grateful for being selected for the EMECS Young Researcher Support program. My research project is titled “The ecology of green Noctiluca scintillans and environmental shifts during its red tide occurrences: a study in the Inner Gulf of Thailand”. This study focuses on Noctiluca scintillans, a species of dinoflagellate. Noctiluca scintillans inhabits coastal waters worldwide and frequently forms red tides. These red tides bring enormous biomass to coastal areas, causing water discoloration and foul odors, which adversely affect various industries including fisheries, aquaculture, and tourism. This issue is not limited to the inner Gulf of Thailand but is also observed in other Southeast Asian coastal areas, necessitating urgent measures to mitigate the damage.

In the Gulf of Thailand, green Noctiluca blooms are concentrated in the inner coastal areas from February to April, with the affected area expanding to the central part of the inner gulf from May to September. These areas coincide with regions where hypoxic water masses form, suggesting that green Noctiluca red tides may be a contributing factor to the formation of hypoxic water masses in the inner Gulf of Thailand.

However, scientific evidence directly linking green Noctiluca red tides to the formation of hypoxic water masses in the inner Gulf of Thailand is still lacking. One reason for this knowledge gap is the insufficient understanding of the ecological characteristics and composition of green Noctiluca during its bloom development in natural environments.

To address this, our research aims to investigate the basic composition characteristics of green Noctiluca in its natural environment and conduct high-density observations from the pre-bloom season to the post-bloom season. This approach will allow us to provide essential field observation data for modeling the red tide occurrence mechanism of green Noctiluca and attempt to elucidate the process of red tide development using the collected dataset

Primary production on tidal flats reflecting tides and submarine groundwater discharge: machine learning and continuous observation approach

Prefectural University of Kumamoto

Tatsuya Ozaki

I would like to offer my sincere gratitude regarding my selection for EMECS Grants-in-Aid for young researchers. I belong to the doctoral course of the Graduate School of Environmental Symbiosis、 Prefectural University of Kumamoto、 and I am working on quantifying the primary producers of tidal flats in the Midori river tidal flat、 which has the largest tidal flat area in Japan. Tidal flats are hotspots of ecosystem services with high biological production. Tidal flats bordering land are vulnerable to development、 and approximately 16% of the world’s tidal flats have been lost since 1984. Conservation of disappearing tidal flats requires accurate quantification of the primary producers (phytoplankton and microphytobenthos inhabiting the sea bottom)、 which are fundamental to the ecosystem function of tidal flats. The main limiting factors for the primary production on tidal flats are light and tides. However、 conventional estimates of primary production ignore the impact of tides、 and there are no studies of quantifying primary production on tidal flats for longer than one year.

In contrast to the conventional in-situ incubation method in the field、 I established the laboratory experimental method using an artificial light source with light intensity equivalent to the sun、 and combined the method with continuous observation of water quality over two years to estimate the primary production with high time resolution. Generally、 the time of ebb tide on tidal flats is daytime in summer (daytime tides) and nighttime in winter (nighttime tides)、 thus the daytime tides are suitable for photosynthesis for microphytobenthos、 while the nighttime tides are unsuitable for photosynthesis. Therefore、 by using established monitoring methods to precisely quantify the primary production on tidal flats over a long-term、 I will verify that the primary production and relative importance of microphytobenthos increases with increasing time of ebb tide in the daytime from the nighttime tides to the daytime tides. In addition、 while light is more intense in summer、 microphytobenthos are exposed to drought stress during ebb tides. In recent years、 nutrient supply from the submarine groundwater discharge (SGD) is reported to increase primary production in coastal areas around the world. Based on this、 I hypothesized that the photosynthetic activity of microphytobenthos increases significantly when the SGD keeps the sediment surface moist and provides abundant supply of nutrients during ebb tides. In this study、 I will test this hypothesis by measuring and comparing the photosynthetic activity of microphytobenthos in SGD area and control area during ebb tides. The results obtained in this study will be used to construct the primary production on tidal flats estimating model reflecting tides and SGD.