After a halt devoted to educational outreach, Tara’s scientific research in Japan is starting up again. The schooner will travel south along the Japanese coast, looking for clues about the health of the coral. In the southern region of the Bay of Tokyo, each site studied displays the characteristics of the ocean of the future. Scientists will study simultaneously the effects of temperature changes and increasing acidity (pH) of water on marine ecosystems..

Beneath the surface, the concept of “climate change”; becomes very clear, affecting the corals in an extremely visible way. The 2 factors particularly impacting the corals today are ocean warming and acidification.


Tara in Shikine studying effects of acidification on coral. © François Aurat / Fondation Tara Expéditions

Warming and bleaching
To understand what’s happening here, we must explain exactly what coral is. Let’s draw closer and observe with a magnifying glass this animal that, from a distance, resembles a pebble. Coral is a distinct animal, a sort of small, upside down jellyfish called a « polyp » which builds a skeleton outside of its body. Another particularity is the fact that it can’t feed itself. Coral needs micro-algae to supply its energy: the zooxanthella. Using photosynthesis*, this algae provides the nutrients necessary for its survival. This collaboration between algae and coral is called «symbiosis».

But their marriage is fragile. An increase of only 1°C in the ocean’s temperature can lead to the death of a reef in just a few days. Stressed by the heat, corals and algae sign their divorce. Corals lose their micro-algae, or maybe the corals throw them out. Researchers are still questioning this process. Deprived of algae and thus of nutrients, the corals become white and die. This is called “bleaching”.


Shikine, 7 meters depth. © Nicolas Floch / Fondation Tara Expéditions

CO2 and acidification
Acidification is the other major threat. This concept is fairly recent: the earliest research on the subject dates only from the 1990s. CO2 released by human activities acidifies the oceans and impacts the growth of corals. Reef health is threatened.

Sylvain Agostini, Tara’s scientific coordinator in Japan, explains: «There are only a few other sites known to exist in the world like Shikine in Japan—one in Italy and the other in Papua New Guinea. The site of Shikine is located in a volcanic zone. The magma burning under the Earth’s crust releases CO2 and forms bubbles that escape from the seabed. The surrounding area is therefore naturally acidified! Usually scientists work on the issue of acidification in aquariums, examining only a few species. In Shikine, the whole ecosystem has been bathing in this acidic water for several generations.»

Diving into the waters of Shikine, Taranauts will take a leap into the future. Acidification of the chosen site corresponds to the estimates predicted globally for the year 2100. So, for the researchers embarking aboard Tara, this area has strong scientific potential and constitutes a natural underwater laboratory.


Maggie Nugges completing a coral-algae transect. © Nicolas Floch / Fondation Tara Expéditions 

Noëlie Pansiot

*Photosynthesis: a bioenergetic process that allows plants and algae to synthesize organic matter using sunlight.