3 Degrees of Japan's Seas

The waters off the coast vary from frigid to temperate to tropical. The marine life is uniformly extraordinary.

This story appears in the November 2010 issue of National Geographic magazine.

Sunlight streams between cracks in the ice. Thicker chunks glow emerald green, bejeweled by algae. The characters of this frosty realm begin to appear: a translucent, blue swimming snail, a pink fish with a tail like a geisha's fan, a bright orange lumpsucker that looks as if it leaped out of a Pokémon cartoon.

This is the underwater world that awaits photographer Brian Skerry, who is lumbering across the beach near a fishing town called Rausu, in Japan's northeastern corner. Wearing a hooded dry suit and carrying an air tank, hoses, regulator, and 32 pounds of weights, he pulls on his fins and slowly submerges his face to get used to the 29°F water. His lips go numb. And then, camera in hand, Skerry dives between the ice floes into the waters of the Sea of Okhotsk, bordering the Shiretoko Peninsula.

Most people think of Japan as a compact collection of large islands, but a map of the country shows otherwise. Japan stretches over 1,500 miles and includes more than 5,000 islands. As land mingles with sea over these vast distances, it embraces at least three distinct ecosystems. In the frigid north, sea-eagles, with their seven-foot wingspans, and king crabs frequent the ice-covered seas off the remote Shiretoko Peninsula. In the mild central waters of the Izu Peninsula and Toyama Bay, a few hours' drive from the skyscrapers of Tokyo, firefly squid swarm, and soft coral forests grow. In the balmy south, delicate butterflyfish and huge sand tiger sharks share coral reefs in the Bonin Islands, a collection of 30 or more islands about 500 miles south of Tokyo.

Ocean currents are key to the marine diversity, bathing Japan's shores in temperatures of water that range from around 30°F to 85°F. The currents also bring the country a couple of world records. The powerful Kuroshio shoots warm water northward, allowing coral reefs to thrive where they would not normally be found. The East Sakhalin Current draws cold water down toward Japan, helping make the Shiretoko Peninsula the southernmost spot with winter sea ice.

These currents control more than water temperature. They transport distant marine life as well. Inlets pockmark Japan's volcanic shoreline, explains Florida Institute of Technology professor Robert van Woesik. On islands surrounded by coral reefs, the lagoons "act like baseball mitts catching coral and fish larvae."

As in so much of the world's oceans, these ecosystems are at risk. Japan is filling in lagoons to create more land to build upon. When this happens, fish, coral, and crab larvae glide past without settling down.

For now, the array of ocean life is thriving, as Brian Skerry's photographs show. When he surfaces from the frigid waters, he's grateful for the teahouse on the beach. Stripped of his gear, he warms up by sipping miso soup as he sits on the floor watching the snow fall. All the while, the orange lumpsucker swims, and the ice glows green undersea.