A. 深海もしくは外洋に棲むウナギ目（ウナギの仲間）はフウセンウナギ科、フクロウナギ科、シギウナギ科、タンガクウナギ科などなど実は数多くのグループと種がおりますが、どれも食用に利用されないので、一般的に見かける機会はほぼない魚ばかりです。面白いことに、我々に馴染み深い蒲焼のウナギは、沿岸に棲んでいるアナゴ類よりも、これらの外洋に棲む「ウナギらしくないウナギ目の魚」の方が血筋としては近いことが近年わかりました。
2020年9月、喜界島サンゴ礁科学研究所の教育プログラムを再編し、KIKAI college を開設しました！ 通年でサンゴ礁研究と科学英語を学ぶサンゴ塾コースや、研究者によるセミナー、サマーキャンプ、島留学など、サンゴ礁科学研究所の豊富なプログラムが受講できます！ 未来の研究者の卵のみなさん！KIKAI collegeでお待ちしています！ KIKAI college ウェブサイトはこちら！
A highly precise method to determine past typhoon occurrences from giant clam shells has been developed, with the hope of using this method to predict future cyclone activity.
The waters surrounding Okinotori Island are home to a large number of Tridacna maxima, or giant clam. The isolated island is also located in a highly active typhoon region. (Photo credit: Ministry of Land, Infrastructure, Transport and Tourism Kanto Regional Development Bureau, http://www.ktr.mlit.go.jp/keihin/keihin_index005.html)
A team of researchers led by Tsuyoshi Watanabe of Hokkaido University has discovered that giant clams record short-term environmental changes, such as those caused by typhoons, in their shells. Analyzing the shell’s microstructure and chemical composition could reveal data about typhoons that occurred before written records were available.
Scientists are concerned that major tropical cyclones such as typhoons and hurricanes will increase with global warming. To better predict the frequency of these weather patterns, understanding typhoons in the past warmer periods of Earth’s history is particularly important.
The giant clam Tridacna maxima species was specifically chosen due to its fast and highly precise shell growth rate; daily growth increments in the shell can be seen, similar to tree rings, allowing researchers to accurately investigate the clam’s paleoenvironment. Live specimens were sampled from the waters surrounding Okinotori Island, which lies in the middle of a common path taken by typhoons before making landfall in Japan and other parts of Asia. The team analyzed the shell growth increment of each year, measuring its thickness, stable isotope ratio, and the barium/calcium ratio. They then compared the data with the past environmental records such as typhoons and water temperatures.
The whole Tridacna maxima valve. The shell was cut in two sections along the maximum growth axis. (Komagoe T. et al., Journal of Geophysical Research: Biogeosciences, April 19, 2018)
With these methods, the team found the growth pattern and chemical compositions in the shells were altered by short-term environmental changes in the area. Cooler ocean temperatures and other environmental stresses brought on by typhoons disrupted shell growth and increased the barium/calcium ratio as well as the stable isotope ratio.
Enlarged image of the shell edge showing a stripe pattern of growth increments. Geochemical analysis of increments reveals the clam’s paleoenvironment. (Komagoe T. et al., Journal of Geophysical Research: Biogeosciences, April 19, 2018)
“Since microstructural and geochemical features are well preserved in giant clam fossils, it may now be possible to reconstruct the timing and occurrence of past typhoons to a level of accuracy that was previously impossible,” says Tsuyoshi Watanabe of Hokkaido University.
This study, conducted in collaboration with The University of Tokyo, KIKAI institute for Coral Reef Sciences, and Kyusyu University, was published April 19, 2018 in the Journal of Geophysical Research: Biogeosciences.
Fossil coral records provide new evidence that frequent winter shamals, or dust storms, and a prolonged cold winter season contributed to the collapse of the ancient Akkadian Empire in Mesopotamia.
The Akkadian Empire (24th to 22nd century B.C.E.) was the first united empire in Mesopotamia and thrived with the development of irrigation. Yet, settlements appear to have been suddenly abandoned ca. 4,200 years ago, causing its collapse. The area would also not experience resettlement until about 300 years later.
Past studies have shown that the Akkadian Empire likely collapsed due to abrupt drought and civil turmoil. However, the climatic dynamics which caused widespread agricultural failures and the end of an era have yet to be sufficiently explored.
Researchers from Hokkaido University, the KIKAI Institute for Coral Reef Sciences, Kyushu University, and Kiel University made paleoclimatic reconstructions of the temperature and hydrological changes of the areas around the archaeological site of Tell Leilan, the center of the Akkadian Empire. They sampled six 4,100-year-old fossil Porites corals from the Gulf of Oman, just directly downwind. The samples were aged by radiocarbon dating and geochemically analyzed to confirm they have not been significantly altered from their present state.
4,100-year-old Oman coral fossil
The coral data was then compared to modern coral samples and meteorological information. Although it is normal for the survey area to receive a significant amount of rainfall in the winter, the coral data suggests that, during the time of the empire’s collapse, the area suffered from significant dry spells. The data before and since the collapse are furthermore comparable to modern coral data, showing the dry spells would have been sudden and intense.
Map showing the sample sites (red stars) in respect to Mesopotamia (green dots) and wind direction. (Watanabe T.K. et al, The Geological Society of America. September 2, 2019)
The fossil evidence shows that there was a prolonged winter shamal season accompanied by frequent shamal days. The impact of the dust storms and the lack of rainfall would have caused major agricultural problems possibly leading to social instability and famine, both factors which have been previously associated with the collapse of the empire.
There is a clear correlation between ancient winter climate anomalies (green, blue, and red) and the civilization area of Mesopotamia and the Akkadian Empire (black) via time, with the right-hand side of the graph representing the present day. The anomalies are presented relative to present day values.
“Although the official mark of the collapse of the Akkadian Empire is the invasion of Mesopotamia by other populations, our fossil samples are windows in time showing that variations in climate significantly contributed to the empire’s decline,” said Tsuyoshi Watanabe of Hokkaido University’s Department of Natural History Sciences. “Further interdisciplinary research will help improve our understanding of connections between climate changes and human societies in the past.”
Tsuyoshi Watanabe (center) and his collaborators with the Mausoleum of Bibi Maryam at Qalhat in Oman in the background.
We, KIKAI Institute for coral reef sciences, can provide precious opportunities to work in the marine environment and various land research fields with researchers.
We would love to support your interests and future career by working together!
Criteria
Duration: for more than a month
Start Date: since September 1st, at anytime
Qualifying target: university students or more (at age 18 and older)
Number of interns available: as needed
Tasks
We decide their task depends on individual ability and what our institute needs.
Others:
6 hours per day for work and 5 days a week (no payment, holiday: Sunday and Monday)
We provide a lodging place.
The collaboration work with Dr. Samuel Kahng, our mentor of Coral Reef Science Camp, is published in the journal “Coral Reefs”.
New research published in the journal Coral Reefs revealed unexpectedly high growth rates for deep water photosynthetic corals. The study, led by Samuel Kahng, affiliate graduate faculty in the University of Hawai‘i at Mānoa School of Ocean and Earth Science and Technology (SOEST), alters the assumption that deep corals living on the brink of darkness grow extremely slowly.
Leptoseris is a group of zooxanthellate coral species which dominate the coral community near the deepest reaches of the sun’s light throughout the Indo-Pacific. Symbiotic microalgae (called zooxanthellae) live within the transparent tissues some coral—giving corals their primary color and providing the machinery for photosynthesis, and in turn, energy.
Deeper in the ocean, less light is available. At the lower end of their depth range, the sunlight available to the Leptoseris species examined in the recent study is less than 0.2% of surface light levels. Less light dictates a general trend of slower growth among species that rely on light for photosynthesis.
Previous studies suggested that photosynthetic corals at the bottom of the ocean’s sunlit layer grow extremely slowly – about 0.04 inch per year for one species of Leptoseris. Until recently, there were very few data on growth rates of corals at depths greater than about 225 feet given the logistical challenges of performing traditional time series growth measurements at these depths.
Kahng, who is also an associate professor at Hawai‘i Pacific University, collaborated with SOEST’s Hawai‘i Undersea Research Laboratory (HURL), the Waikiki Aquarium, National Taiwan University, Hokkaido University and KIKAI institute for Coral Reef Sciences to collected colonies of Leptoseris at depths between 225 and 360 feet in the Au‘au Channel, Hawai‘i using HURL’s Pisces IV/V submersibles. The research team used uranium-thorium radiometric dating to accurately determine the age of the coral skeletons at multiple points along its radial growth axis – much like one might determine the age of tree rings within a tree trunk.
“Considering the low light environment, the previous assumption was that large corals at these extreme depths should be very old due to extremely slow growth rates,” said Kahng. “Surprisingly, the corals were found to be relatively young with growth rates comparable to that of many non-branching shallow water corals. Growth rates were measured to be between nearly 1 inch per year at 225 feet depth and 0.3 inches per year at 360 feet depth.”
The research team found that these low light, deep water specialists employ an interesting strategy to dominate their preferred habitat. Their thin skeletons and plate-like shape allow for an efficient use of calcium carbonate to maximize surface area for light absorption while using minimal resources to form their skeleton. These thin corals only grow radially outward, not upward, and do not thicken over time like encrusting or massive corals.
“Additionally, the optical geometry of their thin, flat, white skeletons form fine parallel ridges that grow outward from a central origin,” said Kahng. “In some cases, these ridges form convex spaces between them which effectively trap light in reflective chambers and cause light to pass repeatedly through the coral tissue until it is absorbed by the photosynthetic machinery.”
The strategic efficiency of Leptoseris enabling its robust growth rates in such low light has important implications for its ability to compete for space and over-shade slower growing organisms.
“It also illustrates the flexibility of reef building corals and suggests that these communities may be able to develop and recover from mortality events much faster than previously thought,” said Kahng.
Researcher contact:
Tsuyoshi Watanabe, PhD
KIKAI institute for Coral Reef Sciences
Faculty of Science, Hokkaido University
nabe(at)kikaireefs.org (please change (at) to @ when you send e-mail.)
Samuel E. Kahng, PhD
Affiliate graduate faculty, University of Hawai‘i at Mānoa, School of Ocean and Earth Science and Technology
Associate Professor of Oceanography, Hawaii Pacific University
808-236-3562
skahng(at)hpu.edu(please change (at) to @ when you send e-mail.)
Figure 1. A colony of Leptoseris hawaiiensis at 315 feet in the Au’au Channel Hawaii. Credit: HURL UH Figure 2. A colony of deep water Leptoseris sp. Note fine rows of septocostae radiating outward from a central origin and the low density of polyps. Credit: Sam KahngFigure 3. A magnified view of the polyps from a deep water Leptoseris sp. Note what appears to be vestigial tentacles (which do not extend) surrounding some of the polyps. There are identical bulbs of tissue protruding between some of the septocostae in between the polyps. Credit: Sam Kahng
Kahng, S.E., Watanabe, T.K., Hu, H. et al. Moderate zooxanthellate coral growth rates in the lower photic zone. Coral Reefs (2020).
先週の初級中級クラスの様子をお伝えします！
