NankaiNN covered the result of the collaborative research with Dr. Kahng from University of Hawai’i.

June 25, 2020

KIKAI Institute worked together with Dr. Kahng, discovering that a species of reef building corals in the deep water with scarce sunlight have been growing as fast as those in the shallow water. The result might be a strong indication of their abilities to adapt themselves to the adverse environment and recover quickly from the damages.

Click here to read the entire article (Japanese only).

To the visitors of the institute: important requests

August 5,2020

KIKAI Institute sets a guideline for the prevention of COVID-19 pandemic, taking into consideration its status and the responses of Kagoshima Prefecture and Kikaicho.

It is our utmost priority that the visitors can look around and use our facilities and enjoy our events. Therefore, we request every one of them to observe the following:

This guideline is subject to change, depending on the circumstances. We wish you all to stay healthy, and we will continue to distribute our energy to the rest of the world. We appreciate your understanding.


KIKAI Institute for Coral Reef Sciences

Publication: the illustrated guide for corals in Kikaijima 

August 7, 2020

Anyone can access this book online for FREE!

Click NOW the link below to download a copy!


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,

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.

Senior Lecturer Tsuyoshi Watanabe

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

KIKAI Institute for coral reef sciences

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


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.
Senior Lecturer Tsuyoshi Watanabe

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

KIKAI Institute for coral reef sciences

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


Recruiting interns!

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!

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


We decide their task depends on individual ability and what our institute needs.
6 hours per day for work and 5 days a week (no payment, holiday: Sunday and Monday)
We provide a lodging place.

How to Apply

Please contact college(at) with information about your interests.

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

We send an application form as received your contact email.
If you have any questions, please feel free to ask us.

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) (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
skahng(at) 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).

World Oceans Day 2020

World Oceans Day 2020

Taking action from the small coral reef island, Kikaijima!

We have started a new project to promote sustainability and care for coral reefs and our oceans.

Japan has beautiful coral reefs that extend latitudinally from the tip of Okinawa to the southern edge of Honshu, the main island of Japan. Kikaijima, or “Kikai Island,” is one of the Amami Islands located north of Okinawa and south of Kyushu. Kikaijima is a raised coral island, the land continuously expanding with the uplifting of coral reef terraces. The climate of Kikaijima borders between tropical and temperate ocean and is classified as a humid subtropical climate. The coral reef ecosystem responds sensitively to changes in the climate. Kikaijima is a small island without river discharge and runoff to disturb the reef environment, a common source of damage to coral. A healthy coral reef ecosystem has been maintained for a long time, making Kikajima one of the best locations to detect ecological shifts as a response to change in global climate and ocean environment in the northwestern Pacific Ocean.

The KIKAI Institute has created education programs about coral reefs and the beautiful nature of Kikaijima. Many children visit our island from all over the world to learn about coral reef research. We could not meet them this year due to COVID-19. Japanese coral reef researchers belonging to our institute started an online seminar (webinar) for school students in March 2020. Since then, over 200 children have joined us to learn about the science of coral reefs, animals that use coral reefs as their homes (such as reef fish, bivalves, etc.), carbon and nutrient cycles within coral reefs, and so on. These programs will continue at least until next March. We are eagerly waiting for these future scientists to work with us!

As a new project this year, we have started making an encyclopedia of symbiotic reef corals in Kikaijima. KIKAI Institute is working with the National Institute for Environmental Studies to conduct and support this project. The coral ecologist team, Prof. Hironobu Fukami, Prof. Naoko Isomura, Dr. Takuma Fujii, and Dr. Yuko Kitano, have started a field survey to collect coral specimens and DNA samples for species identification. The process of the making the encyclopedia is open and always available in our newsletter, so everyone can join in to provide editorial and financial support. Kikajima’s high school students have also joined to help us take photos of the beautiful, white coral skeletons for the encyclopedia.

We hope that the encyclopedia will be a letter to the future oceans and the people who take care of them. The last record of the number of reef coral species in the Amami Islands was done 25 years ago. We want to make a record of modern ecosystem conditions in our encyclopedia, and want to continue to update it in the coming decades and centuries. At the end of this project we want to send our encyclopedia to school libraries as a gift of education. We hope the next generation and many generations after that will be interested in coral reefs, and will continue to observe and conserve our wonderful home– the ocean. Please join us to support this project and preserve our precious ocean far into the future.

Please see more details on our website and in our newsletters:

Atsuko Yamazaki and Tsuyoshi Watanabe
KIKAI Institute for Coral Reef Sciences

Special thanks to Katrina Little.

Central Caribbean Marine Institute

Central Caribbean Marine Institute


喜界島サンゴ礁科学研究所はCentral Caribbean Marine Instituteと共同研究をおこなっています。

キューバの南60kmほどに位置するリトルケイマン島は喜界島と同じく、離島で河川がなく、海の透明度は抜群です。この人口130人ほどの小さな島であるリトルケイマン島には、Central Caribbean Marine Institute(CCMI) という海洋研究所があります。喜界島サンゴ礁科学研究所はCCMIと共同研究をおこなっています。


喜界島サンゴ礁科学研究所を開設するにあたり、CCMIから多くのヒントをもらいました。CCMI所長のCarrie Manfrino博士、CCMIと引き合わせてくれたGEOMARのSteffen Hetzinger博士に感謝いたします。

Central Caribbean Marine Institute ウェブサイト