Submarine caves in Okinawa offer treasure trove of new species

Asahi Shimbun

16-05-2025

Researchers explore a submarine cave on Kumejima island in Okinawa Prefecture. (Provided by Yoshihisa Fujita)
NAHA—The sight of white crabs with long, slender legs and tiny, dot-like eyes drew a yelp of astonishment from Yoshihisa Fujita, even though the researcher was submerged deep in the sea in a submarine cave.
'I cried out, 'Wow,' underwater in spite of myself,' said Fujita, a professor of marine biology with Okinawa Prefectural University of Arts in Naha. 'That's because the moment I saw them, I knew they belonged to a new species.'
Submarine caves, formed primarily through the submersion of limestone caves and erosion, can prove hazardous to divers. But underwater caves can be home to an unexplored universe of unknown creatures.
A group of Japanese researchers, led by Fujita, has discovered 24 new species of marine creatures over the past decade in submarine caves mainly in Okinawa Prefecture.
Fujita said they have collected more than 100 other animals awaiting publication as new species.
The white crabs seen by Fujita were found living in darkness in the recesses of a submarine cave in the village of Onna on the main Okinawa island.
Fujita and a colleague named the new species Caligoplagusia okinawa in an article published in a scientific journal in February last year.
Their Japanese name for the crab species contains the word 'yomi,' which means 'netherworld.'
Fujita, 51, in 2015 recruited researchers for submarine-cave exploration team. They have since conducted expeditions mostly in Okinawa Prefecture but also abroad.
Their 24 new species include lugworms and a shrimp called Halosbaena okinawaensis found in a submarine cave in the north of the main Okinawa island.
Described as a 'living fossil,' this shrimp species has not changed much in appearance for more than 100 million years, Fujita said.
'I am excited on every expedition, partly because adventures and explorations are fun, and partly because new species turn up one after another,' he said.
USEFUL IN PHARMACEUTICALS
Team member Yuji Ise, a 49-year-old researcher of sponges has discovered a number of new sponge species in submarine caves in Okinawa Prefecture.
Sponges are primitive animals that often attach themselves to rocks.
Sollasipelta subterranea, which Ise and his colleagues described as a new sponge species in May 2023, looks like small, white dumplings.
They also described Rhabderemia ginamaensis, another sponge variety, as a new species in a research paper in January this year.
Ise said he is keeping specimens of more than 50 unknown sponge varieties that he collected in Okinawa's submarine caves.
A substance that serves as a basis for an anti-cancer agent was discovered in a sponge species in a previous study, showing that additional natural compounds found in sponges could become useful as pharmaceuticals.
'Submarine caves are a treasure trove of useful substances that have yet to be known,' Ise said.
PITCH-DARK EVEN IN DAY
Expeditions inside submarine caves carry a constant element of danger.
The cave interiors are pitch-dark even in daytime. Failure of underwater lighting would leave divers visionless and disoriented.
Caves often have labyrinth-like interiors with holes barely big enough for a diver to get through.
In emergencies, divers may have little time to reach the safety of the surface.
'I sometimes frightened at the outset that I might not be able to return safe,' Ise said.
Each expedition lasts between around 20 minutes and one hour.
The divers follow a pitched rope to enter a submarine cave and follow it back on their return.
Fujita has dived more than 6,000 times, but he still often hires a professional diver to accompany him.
Members of the research team are creating 3-D relief maps of submarine caves for more detailed studies. They have already completed such maps for five sites in Okinawa Prefecture.
'We hope to conduct more studies to find out what ecosystems there are inside submarine caves,' Fujita said.