Dead Whales Make for an Underwater Feast
When whales decay the seafloor, their enormous carcasses give life to mysterious worlds inhabited by an assortment of bizarre creatures.
On a chilly September morning, 12 miles off the coast of Monterey Bay, California, the notoriously rocky research ship I'm on tosses about, causing seasickness for even the seasoned crew. But below us, all appears eerily quiet in the waters of Monterey Canyon, which plunges to depths of more than two miles. On giant screens inside the control room, we watch the ship's robotic submersible make its 45-minute descent through the inky darkness. Nothing is visible aside from a steady drizzle of "marine snow," nutrient-rich pellets of organic matter, gliding past like an upside-down snowstorm. The vehicle settles gently onto the soft, silty bottom 1,900 feet below us and cruises toward its destination: the skeleton of a 33-foot-long juvenile humpback whale. The research crew has come to study this "whale fall," the term given to the sumptuous feast left behind when a whale dies and sinks to the seafloor.
Under the submersible's marauding lights the scene takes on a ghoulish green hue. As it nears the whale fall, barren ground gives way to signs of life. Sea stars, sea urchins, and flatfish stud the bottom like quiet sentinels. A jellyfish pulses gracefully across the screen. A lone hagfish darts into the headlights and quickly races away, and in the distance a sablefish cruises by, seemingly oblivious to the glaring headlights. The vehicle sidles up to the oceanic graveyard, revealing a complete whale skeleton obscured by a tangle of seaweed.
"Can I play?" asks Shannon Johnson, a molecular ecologist from the Monterey Bay Aquarium Research Institute in Moss Landing, taking the pilot's seat. "There they are," she exclaims with the exuberance of a proud parent. "Hello, girls." She's referring to one of the more flamboyant inhabitants she's here to collect--worms of the genus Osedax (Latin for "bone devourer"), which cover the bone like a shag carpet. While the peacock-plumed females are about the width of a nail and the length of a pinky finger, the males are mere microscopic threads inside the females' egg sacs that seem to function as little more than sperm factories. A five-foot-long robotic arm deftly retrieves a rib blanketed with hundreds of Osedax, their iridescent tubes waving madly in the current. Minutes later, a second, less nimble arm, which the crew aptly calls Mongo, begins breaking the four-foot-long bone into manageable pieces. After a painstaking half-hour, Mongo snaps the worm-covered bone in two and clumsily drops the pieces into a treasure chest-sized "bio box" that hauls samples to the surface.
As the vehicle settles gently on the deck, Johnson hurries over, sticking her bare hand into the stinging cold seawater to inspect the bones covered in snotty green worms--less striking in the flesh than in their bigger-than-life visage onscreen. She also quickly processes sediment cores, slicing them into thin hockey puck-like samples used to study mud-dwelling microbes. While perhaps the least glamorous members of whale fall communities, these bacteria are the workhorses of the whole ecosystem. "Bacteria are the beginning and the end of the food chain," says Johnson. "Everything has to live with or off of bacteria to survive."
Whales roaming surface waters are supporting ecosystems far below that, until 1987, scientists didn't even know existed. A diverse assortment of bacteria helps sustain these communities. Some provide nutrition to organisms in exchange for safe housing, while others become food for grazers like snails and crabs, which dine on the juicy bacterial mats and are, in turn, eaten by larger creatures. This life-after-death progression recycles carbon and disperses it throughout the ocean--some may even make its way back to the surface to provide nutrition for living whales.
Johnson is among a small cadre of researchers employing extreme--and sometimes unpleasant--measures to understand whale fall ecology. Some 70,000 whales die every year along migratory routes, usually from starvation, injury, or disease. Yet finding a whale fall in the abyssal depths of the ocean isn't easy, since the animals sink at random and can be spaced many miles apart. Despite the challenges, researchers are continually making new discoveries about this environment and its inhabitants. Of the roughly 60 new species discovered so far, many may be uniquely adapted to whale falls. And further research will likely turn up hundreds more species, says Johnson. "We can't understand how the ocean works if we don't understand the little things," she says. "We've barely scratched the surface."
The death of a single whale brings a bonanza of nutrients to the barren waters of the deep sea, delivering an organic parcel equivalent to thousands of years' worth of marine snow. When a whale, elephant seal, or any large animal falls, it supports a range of fauna, from tiny bacteria (and potentially even viruses) to mobile scavengers like sharks and hagfish, creating an ecosystem that can survive for decades. When a whale dies, the scavengers, including squat lobsters, sleeper sharks, and crabs, rip apart the flesh in a feeding frenzy that can last a decade--the "horror movie stage," as marine biologist Adrian Glover, of London's Natural History Museum, puts it. As bits of soft tissue rain down, bringing a pulse of nutrients, a motley entourage of opportunistic worms, mollusks, and crustaceans move in.