The Shark and the Jellyfish: More Stories in Natural History

Water World

101 Water World When she first left the island of her birth, the petrel found herself lost on a wild and trackless sea. With no idea how to find her way to her next meal, she set off chasing the other petrels out over the open ocean. They taught her how to survive, and then she taught herself how to prosper—as she learned the subtleties of her world. Now, after years living on the sea, the petrel had learned that the broad vista was covered with signs—crossroads she could follow much more easily than she could navigate the features of the solid ground of her birth. Solid surfaces had become deserts to her—places of short lines of sight frequented by predatory gulls. Vertigo came to her quickly when she chanced to light on land and found the regular heaving and falling motion of the sea abruptly stilled. She had matured into a creature of the open ocean. She had not seen land, smelled dust, or heard surf for months. Sky and sea fused uninterrupted along her horizon as always. Her own flock filled the air around her, while groups of dark terns and shearwaters followed their own pathways over the water in the distance. The longer-winged seabirds, the albatrosses and the boobies, were nowhere to be seen—they had been blown a thousand miles away by the gales of the previous week. The shorter-winged petrels had sliced through those winds, banking close over the crests of the waves to cut through the troughs with one wingtip inches from the water. Parallel ranks of cumulostratus clouds stretching from one edge of the sky to the other were the last remnants of jet-stream winds that had finally abated. But one cumulus column stood out among the rest. It grew higher than the others, drawing the petrel toward it. That billowing tower was born in updrafts that rose from the flanks of a volcanic island standing below the far horizon. The petrel knew that the days of gales had increased the strength of the current flowing around the island. The wake the island left in that current was now swirling with great eddies. Those deep whirlpools were stirring up the bottom, like tornadoes moving across the plains—mixing the deep, nutrient-rich silt back up into the surface layer. That levitated plume of 102 nutrients trailed away across the ocean, fostering a bloom of plankton in the island’s lee. This broad green swath on the sea would be alive with the predators that thrive in the webs of the plankton-based food chain. Without ever seeing the island, the petrel caught the scent of the planktonic highway on the breeze and turned upwind. Soon she found the waves animated with flashing silver fins under a cloud of fluttering white wings. The air above the swells was alive with prion petrels—small, filter-feeding birds that ran across the surface on webbed toes. They dipped up billsful of water and seined out the plankton, pursuing the same feeding strategy as their much bigger brethren, the baleen whales. The petrel climbed above the fray forty, then sixty, feet, more than doubling the distance she could see with every second she rose. She saw the prions gathered by the thousands, but she was looking for something else—her next avenue across the water—the track of dolphins. Cries arose around her as the other petrels turned and dove to the west. As she wheeled to join her flock, the dolphins appeared ahead in the middle distance, their course across the sea marked by trails of mist suspended above their blowholes. The petrels closed the gap, turning downwind to catch up with the pod from behind; then they slowed to keep pace above it. The sleek mammals showed in clear detail through the surface. They were coasting, chasing each other over short sprints, keeping a loose school. Like ribbons trailing from their flanks, dark remora fish clung to some of them, releasing their suction hold occasionally and dashing from one dolphin to another. Diminutive newborn dolphins swam in close formation with their mothers. Because the petrel now coasted, flying the same speed and direction as the wind, the air around her seemed calm. The sigh of the breeze blowing through feathers was stilled in her ears, allowing her to eavesdrop on dolphin vocalizations that carried through the surface. She heard the rapid bursts of dolphin laughter as pairs of them...