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1 The Ocean Represents 99 Percent of the Biosphere
Over the last decade, I’ve been trying to write novels that resituate human beings inside the interconnected webs of a living planet. After exploring dense forest networks in The Overstory and confronting mass extinction and ecoanxiety in Bewilderment, I realized that I needed to turn my attention to the immense wellspring of all life on Earth: the oceans.
Like most people, I knew from way back in grade school that the oceans cover more than 70 percent of the planet’s surface. And I had a good sense of their depth—a little more than 12,000 feet. What I didn’t appreciate until I started writing Playground was just how much livable space that represented, compared to terrestrial habitats.
On land, multicellular life stays pretty close to the surface. But every depth of the ocean is inhabited, in numbers that we are just beginning to appreciate. There are dragon fish, carnivorous sponges, zombie worms, and countless other kinds of exotic organisms—most of them still undiscovered—living throughout the Mariana Trench, the deepest trench in the world. (The wildest of these deep-sea creatures might be the various species of barreleye fish, with their telescoping eyes, bioluminescent organs, and large transparent heads.) Even at the very bottom, in the Challenger Deep, nearly 7 miles below the surface where it was long thought nothing could live, shrimp and sea cucumbers abound.
Comparing the inhabitable terrain of the ocean to that of the land yields a startling statistic: The ocean represents something very close to 99 percent of the biosphere. Spread out as far as we might, we humans still can’t occupy more than 1 or 2 percent of the livable space on Earth.
As large as the volume of inhabitable water is, a global system of currents slowly and perpetually mixes it. Thermohaline circulation, sometimes called the global ocean conveyor belt, moves an immense amount of water—more than a dozen times the flow of all the world’s rivers combined—at the speed of a few centimeters per second on a path that traverses all the latitudes and threads through all the globe’s oceans. Any given quantity of water is estimated to take somewhere between 1,000 and 1,500 years to make the entire circuit.
The largest synchronous movement of biomass on the planet happens every night, as countless tons of zooplankton rise from the deep up to the surface and sink down again every morning. Fish, crustaceans, and mollusks follow them in what is called the diel vertical migration, covering distances over half a mile in each direction. Until I wrote this book, I thought of the great living journeys as moving mostly north to south, when in reality it’s up and down.
2 I Fell in Love with Manta Rays
There are more kinds of fish than all the mammals, birds, reptiles, and amphibians put together. Three fifths of every creature with a backbone is a fish. Their ability to sense the world exceeds our own in many ways. Most bony fish are tetrachromats; they see in four different color channels, perceiving color much more vividly than most of us. Many can see light in the near ultraviolet spectrum, which we cannot. In some ways, their hearing surpasses ours, and they have more ways of making sounds than any other group of vertebrates. Fish can be trained to distinguish between different kinds of musical styles. And that’s not to mention their extraordinary powers of chemical and electroreception. Their taste and smell can surpass our own by as many as four magnitudes.
It stunned me to read about their powers of cognition. Swimming over a tidal pool at high tide, a goby can memorize the entire layout of the terrain after only one exposure. So can a frillfin, calculating precisely where the pools will be at low tide. Archerfish can learn a skill by watching others at a distance, an ability known as perspective-taking.
What impressed me the most about the oceans while I researched this book was how little we know about them.
While writing Playground, I fell in love with manta rays, whose cognitive abilities went way beyond what I ever imagined. They have the largest brain of any fish, one of the two or three largest relative to their body size. They are exceptionally playful and curious, and they practice coordinated social behavior. Manta rays in at least three different aquariums around the world have learned how to swim onto stretchers for transport. Mantas even display contingency checking and other signs of self-awareness in front of a mirror, passing the so-called mirror self-recognition test. While the full significance of such tests are controversial, it’s worth pointing out that many kinds of primates and very smart mammals including dogs cannot pass them.
3 Almost All of the Ocean Is Unexplored
What impressed me the most about the oceans while I researched this book was how little we know about them. According to NOAA, we have explored only 5 percent of the oceans and mapped only about one quarter of the seafloor in high resolution. Scientists estimate that roughly 1 million species live in the oceans (excluding microorganisms, which would push the total far higher). Of that number, two thirds or more remain to be discovered or described. (I’ve seen estimates up to 90 percent.) Almost 2,000 new species are being identified every year.
Even for well-known sea creatures, our sense of aquatic populations are often crude at best. There may be more fish living in the twilight zone between about 650 and 3,300 feet than in all the rest of the ocean combined. Three times as many kinds of life live on or near the ocean bottom as live in the upper ocean, and the great majority of those species have not yet been identified. The biological processes at these depths play a central role in the sequestration of the globe’s carbon and the regulation of Earth’s atmosphere, but we have very little knowledge of the specifics of those processes.
Our greatest and most catastrophic ignorance is how little we know about our own impact on a place we once thought we could never much alter. Some scientists talk about “dark plastic,” estimating that 99 percent of the plastic we have put into the ocean can’t subsequently be located or traced. Just half a dozen years ago, researchers discovered whole new ecosystems based on floating plastic debris, replete with coastal creatures floating in the middle of the ocean. And even as we are finally beginning to model the incredibly complex ocean engine that regulates the climate of the planet, we are tipping the world’s currents in directions that we can’t yet predict with necessary precision.
Our knowledge about the ocean is expanding rapidly, but so is our impact upon it. Maybe the biggest revelation I had while writing Playground was a bit of wisdom that Polynesians have known for a very long time. In her essential book, How the Ocean Works, Helen Czerski quotes the Hawaiian phrase, He moku he wa’a, he wa’a he moku. “A canoe is an island, and an island is a canoe.” This unknown water planet is an island in the emptiness of incalculable space. It’s also our canoe. 
Lead image: JENG BO YUAN / Shutterstock
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