The World Beneath - Richard Smith

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richness of coral reefs globally. The limited coral reefs of the Galápagos Islands, for instance, have one-tenth the number of species as their counterparts in the Coral Triangle, but these peripheral reef locations tend to have many unique and indigenous organisms. Almost 20 percent of the marine life in Galápagos is found nowhere else on Earth. The areas with the highest numbers of such endemics are found at various isolated eastern Pacific islands, as well as Baja California, a Mexican state just south of California; Hawaii; Galápagos; the Red Sea; and Oman.39 Despite their high proportions of indigenous species, these areas all have far fewer total numbers of species than the Coral Triangle, which is blessed with both amazingly high biodiversity and many endemic species.

      Red Sea anthias. Egypt.

      The conspicuous angelfish is found only on the subtropical reefs of central east Australia, New Caledonia, and east to Lord Howe Island. Lord Howe Island, Australia.

      Marine iguana feeding on algae. Fernandina Island, Galapagos Islands.

      The more I have explored coral reefs around the world, the better my appreciation of the world’s varied reefs and how each has its own unique defining attributes. For instance, clouds of bright orange anthias fish, exuberant coral growth, and impossibly blue waters are instantly recognizable as a Red Sea reef. The Red Sea is an area of extreme contrasts. The average rainfall there is less than one centimeter per year, and barely a plant grows on the exceptionally arid land beside it. But the parched and dusty land spills abruptly into the azure sea, which bustles with life more colorful than a painter’s palette. Rather than being hindered by the desolate terrestrial landscape, the coral reefs of the Red Sea are shaped by the conditions above. The dazzling blue water is a result of the very limited rainfall, and without freshwater influx hindering their growth, the corals fringe around the land’s contours almost exactly.

      Red Sea longnose filefish. Egypt.

      What I most enjoy about diving the Red Sea is that 13 percent of its fishes are found nowhere else on earth.40 Over the past several million years, as sea levels have fluctuated, the Red Sea has been cut off by a land barrier at its southern reaches. It is one of the saltiest bodies of water on Earth and its high salinity drives the evolution and adaptation of its inhabitants. Huge clouds of tiny reddish anthias fish are endemic to the region; striking sunrise dottybacks and vivid orange and green spotted longnose filefish that putter about feeding on coral polyps are also indigenous.

      Red Sea mimic blenny. Egypt.

      Black-­line fang blenny. Egypt.

      Another fascinating example of evolution that exists in the Red Sea is the venomous fang blenny of the genus Meiacanthus, whose relatives have been found throughout the world’s reefs. They are quick to bite and potential predators know to avoid them, so they can largely go about their business on the reef without fear of attack. They hold a privileged position and have attracted other envious fishes wishing to exploit the situation. The Red Sea’s fang blenny is an endemic species and has a unique coloration of a blue head, black stripe, and yellow rear half of the body. Red Sea predators know to avoid these colors, so it makes sense that their mimics would need to keep up and copy these colors if they’re to successfully pull the wool over their would-be predators’ eyes.41 A harmless blenny of the genus Ecsenius mimics the venomous fang blenny, allowing it to feed on algae out in the open during the day without fear of predators. The Plagiotremus blenny also exploits the Meiacanthus, mimicking the fang blenny’s coloration to get close to fish that they themselves prey on. Predators avoid the Plagiotremus and its prey species do not fear the Meiacanthus, so they don’t worry about it being near them, allowing the mimic to approach extraordinarily closely and take a bite of a scale. I find it fascinating that because the model Meiacanthus is different in the Red Sea, all its mimics have had to evolve to continue to benefit from mimicking it.

      Subtropical Reefs

      Keen to experience another type of reef system, I visited the remote subtropical reefs of the Izu Islands some 180 miles south of Tokyo, in Japan. Unlike the calm and tranquil diving around the sheltered islands of Indonesia, these high-latitude reefs tend to suffer more adverse conditions. To reach the entry point, I had to rappel in full dive gear down a steep ramp into the ocean, toward the crashing waves below. Holding a rope in one hand and my hefty camera in the other, I wondered if I should have just visited the stunning temples of Kyoto and given this a pass. Once I sank safely under the surface, the clear and surprisingly tranquil water revealed a beautiful and peaceful sloping topography. There were very few hard corals, with algae more dominant than would be expected for a tropical coral reef, but lots of sponges, gorgonians, and soft corals.

      Wrought-­iron and Japanese butterflyfishes. Hachijō-­jima, Japan.

      Many quirky creatures call these Japanese reefs home. The yuzen, or wrought-iron butterflyfish, endemic to Japan’s Izu and Bonin islands, is stunning with its black-and-white body and a tail of bright daffodil yellow. During my dives, I came across the Japanese swallowtail angelfish, Sakura anthias, Japanese eeltail catfish, and Yatabe blenny—all indigenous to the region. Unexpectedly, I also came across a Bargibant’s pygmy seahorse clinging to a gorgonian coral at 110 feet. This find extended the recorded geographic range for the species several hundred miles north from the coral reefs of Okinawa. This vagrant seahorse’s presence in these northern reefs implies some of the processes that have resulted in Japan’s unique marine life.

      Sakura anthias. Izu Peninsula, Japan.

      Japanese eeltail catfish, described in 2008, and bigscale soldierfish. Hachijō-­jima, Japan.

      Huge ocean-scale currents flow across the Pacific Ocean and split as they strike Australasia. The South Pacific Gyre pushes water across the Pacific in a counterclockwise motion and hits New Guinea, becoming the East Australian Current as it flows southward, down toward Tasmania. The North Pacific gyre heads up toward Japan as the Kuroshio Current. It pushes water from the equator northward toward Japan and is the Pacific’s largest current. This current has a significant impact on marine ecosystems, bringing warm water and tropical fishes to where you might not expect them in Japan’s northern reaches. This northward flow also has the effect of creating a barrier to fish trying to migrate in a southerly direction. Since they are effectively isolated in Japanese waters, with the current as a barrier to them moving south and cold polar waters in the north, they have evolved into unique forms. As a result, Japanese reefs have many endemic marine species that exist nowhere else on Earth.

      Bargibant’s pygmy seahorse. Bangka Island, Indonesia.

      Why the Triangle

      There is no doubt that Japan has fascinating reef inhabitants, but the total number of species I encountered on the trip was dramatically lower than I could have seen on a comparable number of dives in Indonesia. There is some debate about the reason for high biodiversity in the Coral Triangle, but there are three leading theories to explain why global patterns of marine richness center in this part of the world.42 43

      The first theory to explain the existence of the Coral

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