Case studies > Dr.Teruhisa Komatsu Interview

2019/2/4

Interview with Dr.Teruhisa Komatsu
Photo of Komatsu Dr.Teruhisa Komatsu
Tokyo University, Atmosphere and Ocean Research Institute,
<Major research themes>
Dr.Teruhisa Komatsu is Associate Professor of Atmosphere
and Ocean Research Institute of UT. He got the Doctor Degree at Kyoto University.
His major research subjects are marine ecology,
the interaction between lives and ocean environments
and the development of biological instrumentation by the remote sensing.
Q Please tell us your current research subjects
Q Our group studies on building-up a sustainable society through an ecological approach and makes developing of new instrumentations for it, as follows:

1. Studies on ecology of seagrass beds and environmental conditions for their formation
In coastal areas, there are plants communities with high biological net-productivity as much as tropical rain forest on the land. Such grass fields or forests consisted of large seagrass and seaweed in the sea is called as ‘seagrass beds’. We investigate the environment in such grass field or forest. We also measure photosynthesis and respiration of the seagrass and seaweed, and research on the contribution of seagrass beds on carbon assimilation from a view point of net-productivity.

2. Ecosystem and distribution of drifting seaweeds
Sargassum bed which is made by Sargassaceae occupies the widest areas among seagrass beds in the Japanese coastal zone. The upper part of the Sargassaceae base or the base-itself is torn off from its substrate by wave motions and currents in the growing season of spring. The seaweed has many air bladders and floats on the sea surface. It is carried to the open ocean and forms ecosystem in the surface layer. Those are called drifting seaweeds and used as shelters for fry of yellowtails and saurel. Therefore this research is a very important issue for fisheries. We research on the distribution, the movement and the ecosystem of these floating seaweeds.

3. Coastal area mapping and management by the remote sensing
A coastal area is a region where many people share conflicting interests. To build a sustainable society, reasonable and integrated management of the coastal area region is needed. Therefore understanding status of coastal area precisely is necessary. Toward this need, we’re analyzing air-born and satellite-born optical sensors images and distribution measurement of sea bottom by supersonic remote sensing.

4. Studies on estimation and conservation of the biomass of the marine organism by acousto-optic instrumentation and bio-logging
It is necessary to understand accurately the amount of marine organisms distribution for sustainably using biological resources. We study on methods of estimating the distribution of marine organisms by integrating the GIS data and the mapping of the instrumentation data by use of a narrow-multibeam echo sounder with various acoustic beams and a quantitative echo sounder. Especially, we begin to research on the behavior of fish with a micro acceleration sensor and a bio-logging device such as a pinger, because the understanding of the piscine behavior is indispensable for the estimation of the biomass and the conservation of fish.
Q Please tell me what made you involved in the field of remote sensing
Q When I did my research on the marine environment of the sargassum bed in a PhD program in Kyoto University (the 1980’s), Dr. Thoma Vercheres in the National French Oceanic Laboratory came to Japan and introduced a study on sargassum bed mapping by using of the SPOT satellite of France. This research attracted me very much, but I could not use satellite data images by SPOT (satellite in France). I got very interested in the study and wanted to devote myself to do the similar one, but satellite images were so expensive to purchase at that time and I could not afford them.
After receiving a PhD degree, I worked for Behavior, Ecology, and Observations Systems group in the Ocean Research Institute, the University of Tokyo, where the acoustic measurement had been studied. I then began to work on the research of seagrass beds by acoustic remote sensing. However, observing seagass beds globally was difficult only by acoustic remote sensing, I started the research on methods of mapping large-scale distribution of seagrass beds by satellite images, which I had been interested in. I have mainly used IKONOS satellite images, and recently also uses ALOS images. Also, I am currently working on seagrass bed mapping not only in coastal areas of Japan but also the Tunisian coast of the Mediterranean, Malaysia and Indonesia with researchers in those countries. As the depth of the sea increases and light intensity decreases, satellite data is usually not suitable for mapping, but the radiation correction method which we have recently developed enables the detection of seagrass beds up to 15 to 16 meter-deep. I hope that our method can be applied for regular monitoring of seagrass beds in the future.
Q Please tell us the prospects the study by remote sensing.
Q I think it is important to monitor habitats using remote sensing techniques.
The Tenth Conference of the Parties (COP10) of Convention on Biological Diversity will be held in Nagoya this October, and because of that, the word “biodiversity” is being heard more often. However, for maintaining the biological diversity of the ocean, it is necessary to conserve the habitat for living things such as seagrass beds, tidal flats, mangroves, and coral reeves. Maintaining diversity of habitats is also important. Marine habitats helps to keep marine biodiversity and also provides ecosystem services such as supplying food resource and protecting the coastlines from erosion by waves, and are indispensable environment for the sustainable society.
In Southeast Asia where economical developments and population increases will be expected in the future, habitats are predicted to be decreased by anthropogenic influences – direct influence of reclaiming and indirect influence of river water, similar to the rapid economic growth in 1960s in Japan, along the coastal zones with high population density. Therefore, we prepare the baseline data for habitat distribution and continue monitoring them. If habitats decrease in the future, it is necessary to identify the cause, prevent the negative effects, and develop the countermeasures to restore the natural environment. I think that understanding the spatial distribution of habitats by remote sensing is useful for the realization of the sustainable society.
The East China Sea is an important spawning ground of the fisheries such as yellowtail and horse mackerel. The juvenile fish grows by accompanying drifting seagrass – in Sargassaceae torn off from the sea floor. Though it has been found out by our research that the origin of the drifting seaweed seems to be originated from China, yellowtail and horse mackerel are shared stocks among the countries around the East China Sea. Both direct/indirect influences such as reclamation, dam-construction, drainage water from factories and urban areas on the coast of the East China Sea destroy seagrass beds of Sargassum horneri and lead to decrease of drifting seagrass. As a result, fish stock of yellowtail and horse mackerel decreases. Therefore, I think that it is necessary to develop an international framework such as NOWPAP and to share monitoring data of habitat on the coast of the East China Sea, and also to urge the stakeholders to take effective measures against the decrease of habits. The conservation of seagrass beds contributes to the conservation of not only the migrational fish such as horse mackerel and yellowtail but also of other fish resources in the coastal areas, and will result in the increase of production of fish resources in the entire region. I think that establishment of organizations and activities for habitat monitoring is one of the ideal schemes of international cooperation.
Researchers on remote sensing in Southeast Asian countries such as Indonesia and Malaysia are interested in seagrass beds and habitat mapping is becoming popular. In the remote sensing workshop of the 7th IOC/WESTPAC International Science Symposium (May 2008, Kotakinabalu, Malaysia), it was decided to initiate actions on habitat mapping by remote sensing from now on. This will be proposed as a project for a three-year project at WESTPAC-VIII (The 8th Intergovernmental Session of UNESCO/IOC Sub-Commission for the Western Pacific, which will be held in Bali in Indonesia on 10-13 May, 2010.
Q Research activities will start from the next year in the new KASHIWA Campus. Could you please give students some words?
Q Let’s do habitat mapping by remote sensing together with me not only in Japan but also in the world!
( Interview date: March 14, 2010 )
Student interview
Soumaya Lahbib Photo Ms. Soumaya Lahbib
Department of Aquatic Bioscience,
Graduate School of Agricultural and Life Science, University of Tokyo
Q Why did you choose the Prof. Komatsu’s laboratory for your study?
Q I have had much interest in the investigation of the coastal ecosystem distribution and its change by remote sensing, so I chose this laboratory. I especially got interested in research study of mapping technique of the coastal area by using acoustic technology, which the researchers in the laboratory have studied, and the study of seagrass bed mapping using high resolution satellite images of IKONOS and ALOS. Prof. Teruhisa Komatsu is an expert of this field and visited Tunis several times for the collaborative study with the Tunisia National Institute of Marine Research on seagrass bed mapping in the Gulf of Gabes. He had a chance to listen to his study and decided to take an exam of Japanese Government Scholarship. Now Dr. Komatsu is my advisor of the graduate course. When I earn a doctorate degree at the University of Tokyo, I would like to work on the coastal ecosystem mapping of Tunisia together with Japanese scientists.
Q Please tell me a theme of your study.
Q My research subject is development of a mapping technique by remote sensing for the conservation of the coastal ecosystem. I would like to develop the system which can provide necessary information on ecosystem distribution to fishermen and/or decision makers.
Q What would you like to learn by satellite image analysis?
Q Not only information on distribution of the coastal ecosystem but also information on distribution of physical and biological parameters such as sea surface temperature, sea-level departure, flows, waves, chlorophyll-a, and turbidity can be obtained by satellite imagery analysis. I will judge vulnerability of the ecosystem based on integration and analysis of such information and distribution of the coastal ecosystem on GIS system, and would like to contribute to the conservation of the coastal ecosystem.。
( Interview date: March 14, 2010 )