Ichiro TAKEUCHI, Prof.
Laboratory of Ecosystem Conservation
Department of Life Environment Conservation
Faculty of Agriculture, Ehime University
3-5-7 Tarumi, Matsuyama, Ehime 790-8566, JAPAN
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Outline of Research
The shallow water ecosystem holds one of the highest biodiversity and production on the Earth. Nowadays, various human activities are concentrated in or close to this ecosystem. The north-east Asia region including Japan has one of the most developed economic activity on earth which allows us to spend a life filled with rich material affluence. However, the effects of various human activities on this ecosystem have started to surface and many organisms are silently disappearing.
Therefore, urgent and significant studies on species diversity and production as well as assessment on the effects of anthropogenic chemicals and climate change etc. towards the ecosystem are needed to conserve the nature of the shallow water ecosystem. Hence with that in mind, our laboratory is conducting the following studies,
1. Species diversity and taxonomy on the amphipod crustaceans
Among the various organisms that constitute the shallow water ecosystem, the amphipod crustacean is one of the most important secondary producers which link primary producers and higher producers including coastal fishes. Our laboratory has been pursuing studies on biodiversity and taxonomy of amphipods, primarily focusing on caprellid amphipods (skeleton shrimps).
Unlike most marine organisms, skeleton shrimps lack a planktonic larval stage and as such can lead to a high speciation in each region. Recently, we are also conducting studies on dominant species of caprellid amphipods that are widely distributed throughout the Indo-Pacific regions including Japanese waters.
2. Distribution and biomagnification profiles of anthropogenic chemicals and trace elements in the shallow water ecosystem
Our laboratory has been studying the distribution and biomagnification profiles of trace elements such as arsenic and mercury, as well as anthropogenic chemicals such as TBT (tributyltin) and polychlorinated biphenyl (PCBs), in the shallow water ecosystems around Japan and south-east Asia. The trophic level of each organism in the food-web was assessed by using the stable carbon and nitrogen analysis.
Biomagnification profiles of 21 species of trace elements were studied in the Mekong River Delta food web in southern Vietnam. Among them, we found significant biomagnificaiton on only three trace elements; Se, Rb, and Hg. Biomagnification profiles of butyltins on the other hand, were studied along the coasts of Japan. Although chemical characteristics of TBT and triphenyltin (TPT) are close to each other, TPT indicated significant biomagnification through the food-web unlike TBT which does not biomagnificate through the food-web.
Polychlorinated biphenyls (PCBs) mentioned above are composed of 209 species of congeners. We found that the degree of biomagnification by congener level increases with increasing PCB chlorination levels between chlorine numbers1–6, while the ratio decreases at higher chlorination levels.
In order to construct an inventory of each PCB congeners for fishes in Japan, we are now analyzing PCB concentrations of sea bass collected from Japanese waters using a high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS).
3. Impact of climate change to shallow water ecosystem
Recently, it has been pointed out that an increase of air and sea water temperature can greatly influence the structure of our earth’s ecosystem which includes the various life forms of organisms living within it. Our studies have elucidated that there has been an unusual increase of seawater temperature during the winter compared to summer in the Uwa Sea. As a result of that, there was a decreased in Laminaria production in the years that the higher water temperature was recorded in during winter month.