Giant clams tell the story of past typhoons

Giant clams tell the story of past typhoons

Research Press Release | May 24, 2018

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.

Original article:
Komagoe T. et al., Geochemical and Microstructural Signals in Giant Clam Tridacna maxima Recorded Typhoon Events at Okinotori Island, Japan. Journal of Geophysical Research: Biogeosciences, April 19, 2018.
DOI: 10.1029/2017JG004082

Funding information:
This study was supported by JSPS KAHENHI grants JP 25257207 and 15H03742.

Contacts:
Senior Lecturer Tsuyoshi Watanabe

1508 Shiomichi, Kikai-cho, Oshima-gun, Kagoshima 897-6151, JAPAN

KIKAI Institute for coral reef sciences

pr(at)kikaireefs.org (please change (at) to @ when you send e-mail.)

+81-997-66-0200

Strong winter dust storms may have caused the collapse of the Akkadian Empire

Strong winter dust storms may have caused the collapse of the Akkadian Empire

Research Press Release | October 24, 2019

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.
Contacts:
Senior Lecturer Tsuyoshi Watanabe

1508 Shiomichi, Kikai-cho, Oshima-gun, Kagoshima 897-6151, JAPAN

KIKAI Institute for coral reef sciences

pr(at)kikaireefs.org (please change (at) to @ when you send e-mail.)

+81-997-66-0200

Surprising growth rates discovered in world’s deepest photosynthetic corals

Surprising growth rates discovered in world’s deepest photosynthetic corals

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 Kahng
Figure 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).

https://doi.org/10.1007/s00338-020-01960-4

【論文発表のお知らせ】世界最深の有藻性サンゴが驚異的な速度で成長することを発見

【論文発表のお知らせ】世界最深の有藻性サンゴが驚異的な速度で成長することを発見

喜界島サンゴ礁科学研究所・ハワイパシフィック⼤学・ハワイ⼤学・ワイキキ⽔族館・北海道⼤学・国⽴台湾⼤学の研究チームは、世界で最も深い水深に生息している有藻性サンゴが驚くべき早さで⾻格を形成していることを明らかにしました。

■背景
センベイサンゴ属は、インド洋から太平洋にかけて生息し、太陽の光が届く範囲で最も深いところに群集を形成することのできる有藻性イシサンゴの一属です。有藻性イシサンゴは、共生する褐虫藻の光合成によって、エネルギーを得ていますが、水深が深くなると、利用できる光が少なくなります。センベイサンゴの生息水深の下限では、利用できる太陽光は、海洋表面の0.2%未満とわずかです。一般的に、光が少ない環境では、有藻性イシサンゴの成長は遅くなるという傾向があります。よって、センベイサンゴは、深い海では、年間1 mmという非常にゆっくり成長していると考えられてきました。しかし、水深68 mを超える深度に住むセンベイサンゴの成長率はこれまでほとんど報告されていませんでした。

■研究手法
研究チームは、ハワイのAu’au海峡で、ハワイ大学の調査潜水艇Pisces IV / Vを用いて、水深68 m〜110 mに生息するセンベイサンゴのコロニーを採取し、ウラン-トリウム放射年代測定法により放射状の成長方向に沿ってサンゴの骨格の年齢を極めて正確に調べました。

Fig.1 ハワイ・アウアウ海峡にハワイセンベイサンゴの群体(Credit:HURL UH)
Fig.2 深場に棲むセンベイサンゴ属の群体。中心から放射状に伸びる骨格の凹凸と散在する個体(ポリプ)が観察できる(Credit:Sam Kahng)

■研究成果
光の少ない環境を考慮すると、以前の想定では、極端に深いところにいる大きなセンベイサンゴは、成長速度が非常に遅いため、非常に年齢が高いと考えられてきました。しかし、私たちの結果では、驚くべきことに、サンゴは比較的若く、成長率は浅海に棲むセンベイサンゴの成長率に匹敵します。成長率は、水深68 mで年間2.5 cm近く、水深110 m で年間7.6 mmという結果が出ました。

Fig.3 深場に棲むセンベイサンゴ属の個体(ポリプ)の拡大画像。一部のポリプに触手が見える。 また、ポリプ同士の間にも新しいポリプの中心が小さく見える。(Credit:Sam Kahng)

■今後の期待
この結果は、センベイサンゴは深い海に適応し、この水深を支配していることを示しています。薄いプレートのような骨格は、光を吸収することのできる表面積を大きくし、放射状に成長します。その表面には細かい凹凸があり、降り注ぐ光を効率的に吸収できる構造になっています。センベイサンゴのこのような戦略は、光の少ない環境でも成長率を保つことを可能にし、他の成長の遅い生物との競争に勝つことができたと考えられます。本研究成果はサンゴ礁をサンゴの柔軟な適応戦略を示し、サンゴ群集がダメージを受けたとしても、これまで考えられていた以上に早く回復することができると考えられます。

本研究成果はCoral Reefs誌に掲載されました。(2020年6月15日発行)
Kahng, S.E., Watanabe, T.K., Hu, H. et al. Moderate zooxanthellate coral growth rates in the lower photic zone. Coral Reefs (2020). https://doi.org/10.1007/s00338-020-01960-4
論文掲載誌のURL:https://link.springer.com/article/10.1007/s00338-020-01960-4

このリリースのお問い合わせ先 : 喜界島サンゴ礁科学研究所 理事長 渡邊剛
〒891-6151
鹿児島県大島郡喜界町大字塩道1508 / TEL:0997-66-0200(担当 安田)
メールアドレス: pr@kikaireefs.org

奄美大島住用湾のサンゴ調査結果が南海日日新聞・奄美新聞に掲載されました。

奄美大島住用湾のサンゴ調査結果が南海日日新聞・奄美新聞に掲載されました。

奄美新聞2020年5月17日付
南海日日新聞2020年5月18日付

■詳細はこちら
北海道大学 プレスリリース(研究発表)

■論文はこちら

■NaNature Research Ecology & Evolution Community記事
Influence of local industrial changes on reef coral calcification

【論文発表のお知らせ】人為起源によるサンゴ礁の撹乱の変遷をサンゴ骨格から検出 ~奄美大島住用湾における産業発展・土地利用変遷に対するサンゴの応答~

【論文発表のお知らせ】人為起源によるサンゴ礁の撹乱の変遷をサンゴ骨格から検出 ~奄美大島住用湾における産業発展・土地利用変遷に対するサンゴの応答~

奄美大島住用湾のサンゴ骨格記録
持続可能なサンゴ礁と産業発展に向けて

喜界島サンゴ礁科学研究所 渡邊剛 理事長の研究グループは、奄美大島住用湾の造礁サンゴの骨格から、過去46年間の産業発展と集中豪雨・洪水がもたらす土砂の流出が、サンゴの生息環境と骨格成長へ影響を与えることを明らかにしました。

奄美大島住用湾は造礁サンゴの生息域であり、マングローブ林が広がる住用川と役勝川の河口域に位置しています。住用湾沿岸域では過去46年間にわたり、大島紬の生産や農業など様々な産業が発展してきました。この地域では、集中豪雨・洪水がもたらす土砂の流出による造礁サンゴへの影響が懸念され、これまで、リーフチェックや白化現象のモニタリングにより明らかにされてきました。

しかし、奄美大島住用湾のように河川や湾における定期的な水質モニタリングが実施されていない地域では、集中豪雨・洪水や産業発展がサンゴに対応する長期的かつ定量的なサンゴの成長の詳細はあまり明らかになっていませんでした。そこで研究グループは、奄美大島住用湾の造礁サンゴ骨格を用い、骨格成長の記録と過去の洪水および湾沿岸域の産業史を詳細に比較しました。サンゴの骨格には樹木のように年輪が刻まれており、過去の海洋環境の変動が1週間~1ヶ月間程度の細かい精度で記録されています。

比較の結果、サンゴの骨格成長は土砂流量を反映している可能性が示唆され、住用湾内の土砂流量はサンゴの骨格成長を制御する要因の一つであることがわかりました。過去46年間におけるサンゴ骨格の化学組成の変化は河口域の海水温や海水中の土砂流量・集中豪雨・洪水による海洋環境の変化を記録していました。これらの結果と住用川流域の産業の変遷から,産業の発展は海水中の土砂流量を変化させ、造礁サンゴ骨格はそれに応答する形で成長していることがわかりました。

サンゴ骨格の柱状試料

本研究結果は、気候変動による局地的な豪雨の頻発や人類活動の増加が予想される将来の熱帯・亜熱帯域において、サンゴ礁と人間社会が持続的な相互関係を築いていくための重要な知見となることが期待されます。

なお、本研究成果は,2020年5月12日(火)公開のScientific Reports誌に掲載されました。

詳細はこちら
北海道大学 プレスリリース(研究発表)

NaNature Research Ecology & Evolution Communityの記事
Influence of local industrial changes on reef coral calcification

造礁サンゴ骨格の窒素同位体比から復元された過去150年間の黒潮流量の変動

論文発表のお知らせ

 

当研究所の所長山崎敦子、理事長渡邊剛が他団体との共同研究で20世紀の黒潮流量の長期復元に世界で初めて成功いたしました。

 

論文「造礁サンゴ骨格の窒素同位体比から復元された過去150年間の黒潮流量の変動」をプレスリリースいたしましたのでお知らせします。

 

北海道大学 お知らせ/プレスリリース/研究発表

https://www.hokudai.ac.jp/news/160704_sci_pr.pdf

 

CREES サンゴ礁地球環境学 渡邊研究室

https://www.sci.hokudai.ac.jp/grp/crees/CREES-web/Reseach_hightlight.html