Awardee of 14th Biwako Prize for Ecology in 2007

Dr. Atsushi Tsuda/
/ Dr. Ming-Shiou Jeng

■ Japan
■ Associate Professor, Ocean Research Institute, The University of Tokyo

● Research Area
Marine Planktology (Study on the effect of iron enrichment on plankton community and the effectiveness of iron enrichment as a CO2 reduction technology)

● Principal Achievements
Tsuda et al. conducted iron enrichment experiments in the open ocean, where iron is a major factor limiting biological productivity, to evaluate the ecological effect and effectiveness of the technology for improving the CO2absorption capability of marine organisms by spreading iron on the ocean. Various methods of reducing the increase in CO2concentration have been proposed. Among them, one technology that has been attracting attention increases the rate of CO2absorption from the atmosphere into the water by increasing the concentration of iron (trace metal), which limits CO2fixation by marine organisms. In this research, in the subarctic Pacific Ocean, where the suppression of CO2fixation is prominent due to lack of iron, iron-enrichment experiments were carried out three times: in 2001 (Western subarctic Pacific, SEEDS 1), in 2002 (Eastern subarctic Pacific, SERIES) and in 2004 (Western subarctic Pacific, SEEDS 2), to clarify the effects of iron enrichment on the ecosystem and to evaluate the effectiveness of iron concentration control as a method for improving oceanic CO2absorption function.

1.
SEEDS 1 is the first iron-enrichment experiment conducted in the North Pacific Ocean. Compared with past experiments in other sea regions, the highest density of phytoplankton was recorded here. A shift of dominant phytoplankton species from pinnate diatom (Pseudonitzshia turgidula) to centric diatom (Chaetoceros debilis) was first observed. The multiplication rate of P.debilis was very high, at 2.6 per day, and Chlorophyll-a concentration reached 20 mg m-3 at maximum. In the end, a slight declining trend in plankton production, due to lack of silicon, was observed.

2.
The SERIES experiment was conducted jointly with a Canadian research team to determine the fate of fixed carbon, which was not clarified in the SEEDS 1 experiment. In the SERIES experiment, a shift from the growth phase to declining phases of the phytoplankton bloom was clearly observed for the first time in iron enrichment experiments. The amount of sedimented carbon was less than initially expected, and the amount of carbon transferred to zooplankton (predatory system) and bacteria (degradation system) was large. It became evident for the first time that the efficiency of the CO2 reduction technology (amount of carbon sedimented per unit iron addition) was lower than expected.

3.
In the SEEDS 2 experiment, conducted jointly with a U.S. research team, the same amount of iron was released in the same region, during the same season as the SEEDS 1 experiment. The population of zooplankton increased and phytoplankton displayed high photosynthetic activity, but the biomass quantity increased only two to three times. Comparison with SEEDS 1 shows that these results are attributable to the fact that in natural ocean waters, zooplankton existed more than 10 times in the surface layer (high predation pressure), with high multiplication rate phytoplankton types not present.

● Academic/Social Contributions and Prospects for the Future
The scientific basis of technology for increasing the absorption of CO2from the atmosphere to the ocean by iron enrichment was Martin’s Hypothesis (1990). Martin’s hypothesis postulated that the increased iron supply during the last glacial period relieved the iron limitation on phytoplankton production in the Southern Ocean and that the corresponding increase in carbon sedimentation brought about low atmospheric CO2levels during that period. A series of Tsuda’s experiments support the first half of Martin’s hypothesis, i.e. relief of iron limitation, but has shown scientifically, for the first time, that the latter half, i.e. increase in carbon sedimentation, is problematic. These findings were published in the academically and socially influential magazines Science and Nature. Their publication acted as a deterrent to an easygoing attitude of trying to reduce CO2in the atmosphere by iron enrichment, based on Martin’s hypothesis. Dr. Tsuda played a leading role in all phases of the three experiments, from planning to execution, including organizing researchers from other institutions in Japan, and conducting negotiations with Canadian and U.S. research teams. It is obvious that he has superior project management ability. Dr. Tsuda has made it clear that, on the basis of iron enrichment experiments, iron functions as the fourth limiting nutrient - in addition to nitrogen, phosphorous and silicon - not only in open oceans, but also in coastal waters around Japan. His research has progressed to the study of iron-supply mechanism in Japanese waters. He is also planning a long-term research project to further clarify the fate of fixed carbon by controlling iron concentration. Future development of his research is greatly anticipated.

■ Republic of China, Taiwan
■ Research Fellow, Research Center for Biodiversity, Academia Sinica,Taiwan

● Principal Achievements
Dr. Ming-Shiou Jeng has conducted surveys on all coral reefs and coasts in Taiwan for 30 years, to assess ecological changes in invertebrates (mainly crustaceans) that occurred during this period. Through the surveys, he identified 295 species in Kenting National Park at the southern tip of Taiwan, 231 species along the northeastern coast of Taiwan and 112 species in the Penghu Archipelago in the Taiwan Strait, confirming that coastal waters around Taiwan are rich in species diversity. He has also amassed an enormous collection of marine invertebrates at National Science Council. One of his ecological achievements is a study on the ecology of the crab, Xenograpsus testudinatus. After several years of observing the behavior of Xenograpsus crabs, which live in shallow waters off the northeastern coast of Taiwan, he discovered that Xenograpsus crabs feed on zooplankton that have been killed by toxic sulphurous plumes emitted from hydrothermal vents. His interesting findings regarding the ecology of Xenograpsus testudinatus were published in the science journal Nature. In an applied ecological study, he examined the amount of heavy metals accumulated in invertebrates in coastal areas and found that heavy metal accumulation in invertebrates has reached a dangerous level. He is also strongly engaged in social activities; he is actively involved in public relations activities regarding environmental issues, the establishment of National Tungsha Ocean Park in the Penghu Archipelago and support activities for the Green Island Ocean Conservation Area, now under construction.

● Academic/Social Contributions and Prospects for the Future
Dr. Ming-Shiou Jeng has described numerous marine organisms taxonomically, and has found that coastal waters around Taiwan are high in species diversity. These are significant academic contributions. His research findings have also improved public awareness and understanding of the importance of the ecosystem of Taiwan coastal.