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Cherishing Okinawa’s diverse marine life


Special To The Japan Times

Diving in Okinawa this summer, I came face to face with my favorite undersea creature: the octopus.

I was diving at Maeda Point on the main island when my guide directed my attention to something that was right in front of me.

I stared but could only see coral. I made an open-palm gesture, as if to say, “I can’t see anything,” and the movement caused what I had previously thought to be a rock to burst into life.

Now on the move, the octopus’ skin started changing color as it swam over the rocks. It soon found a narrow crevice and squeezed itself inside. Upon approach, all I could see was a solitary eye — with its alien-like horizontal pupil — peering out. The color of the octopus’ skin throbbed vibrantly.

Octopuses and other cephalopods such as squid and cuttlefish have remarkable eyes. In eyes of vertebrates, the nerve fibers route in front of the retina, blocking some light and creating a blind spot where the fibers pass through the retina. In cephalopods, however, the nerve fibers are wired the other way round, routing behind the retina so that the image appears brighter and there is no blind spot.

I’m always glad to see an octopus when diving, but I was particularly pleased to see one on this trip because I was primarily in Japan to visit the Okinawa Institute of Science and Technology (OIST), and it was during my trip that scientists published the octopus’ genome sequence.

Arguably, the most impressive thing about these animals is their intelligence. Although octopuses are essentially a mollusk, they have been around for approximately 300 million years — primates are believed to have been around for 65 million years or so — and, perhaps not surprisingly, are extraordinarily smart. As Nobel laureate Sydney Brenner, founding president of OIST, said when the octopus’ genome sequence was published, “They were the first intelligent beings on the planet.”

Octopuses have the biggest brains of all invertebrates relative to their body size. Some cephalopods hunt fish, which requires cooperation. The tentacles give octopuses extraordinary dexterity; they are able to manipulate objects and even use tools. Each tentacle, it seems, has its own “brain” — its own dedicated part of the central nervous system.

Incidentally, the plural of octopus is not octopi. The English word for octopus comes from a Greek word and, therefore, it’s preferable to refer to more than one animal as octopuses (or even octopodes). Things might be different if the word had Latin origins — but it doesn’t.

The octopus genome includes several large gene families that may hold a clue to understanding the animal’s unique central nervous system. Individually, these gene families are known to assist brain development in other animals, but octopuses have more than most.

OIST scientists also detected hundreds of genes that are common in cephalopods but haven’t been found in other animals. Some of these genes are believed to assist color change. Cephalopods primarily change color to hide, but also when engaging in courtship or trying to ward off an attack by a predator.

Another extraordinary finding relates to a mysterious genetic feature called transposons. Most of the genes in our genome only duplicate when instructed to by the cell that they’re living in, but transposons are mobile genetic elements that have a life of their own. About half of the octopus’ genome — a huge amount — is made up of these rogue transposons, and many of these relate to the brain.

OIST and University of Tokyo scientists have now sequenced the genome of another unusual marine animal, a brachiopod called Lingula. This mysterious mollusk-like creature, collected from the Amami islands north of Okinawa, has changed very little in appearance since it evolved more than 400 million years ago. Charles Darwin called them “living fossils,” but the brachiopod’s genome sequence shows that while the marine animal’s appearance hasn’t changed, it has been genetically evolving.

Noriyuki Satoh, head of OIST’s Marine Genomics Unit, said the study shows that animals appear to take independent evolutionary paths.

“Conserving the natural habitat for animal diversity is important,” he says. “This research illustrates the well-nurtured tradition of zoological studies in Japan.”

The waters around Okinawa are scientifically important insofar as coral is concerned but, until recently, the marine ecosystem hasn’t been monitored as well as it could have been. OIST has helped to create a targeted system in order to collect data on such marine information as salinity, temperature and oxygen content.

Marine biodiversity is under threat, with a recent study showing that more than 17,000 species around the world have little or no protection. I was surprised by the diversity of life I saw during my dive in Okinawa last summer. Often these days, you see bleached, dead coral and few fish during dives, but Okinawa appears still to be thriving. Long may it continue.

Rowan Hooper is the news editor of New Scientist magazine. The second volume of Natural Selections columns translated into Japanese is published by Shinchosha. The title is “Hito wa Ima mo Shinka Shiteru” (“The Evolving Human”). Follow Rowan on Twitter @rowhoop.