WITH A HEART THE SIZE OF a piano tucked inside a two-hundred-ton body, the elusive blue whale (Balaenoptera musculus) is the largest known animal to have ever inhabited Earth. If you are fortunate enough to see one careen into a great cloud of krill, it might be tempting to label such a hungry behemoth as a quintessential taker, but the truth is, in her ninety years of life a blue endows as much as she acquires. As a baleen whale swims, her many keratin plates filter seawater, transporting nutrients and biomass across depths and along vast migration routes between breeding and feeding grounds. Along the way her sloughed dead skin provides a feast for zooplankton, while her nitrogen-rich excrement helps sustain the phytoplankton at the core of the marine food web.

In an age of accelerating endangerment, the loss of any whale is something to mourn, but even beyond the edge, a blue whale creates life. In death, her body recedes from sunlight, sinking slowly down, down, down through benthic zones until it lands in darkness upon the ocean floor. Call it bounty or boon, bonanza, if you will—this is a whale fall.

Mobile scavengers are the first to arrive. For several weeks or months, toothy sleeper and sixgill sharks yank at flesh, as slimy, eelish hagfish burrow headfirst into blubber, reveling in the surprise smorgasbord. Then come the octopuses and isopods, sea pigs and eelpouts, small crustaceans and other wiggly ones, ready to scrape and rasp every last scrap. When the carcass is clean, the bone-eaters take over—Osedax worms amass along knotty vertebrae, and together wag like a reanimated pelt of fuzzy red fur. Lacking mouths, females penetrate the skeleton with rootlike structures, delivering symbiotic bacteria that break down the bones’ fatty lipids, releasing a slurry of sulfides that provide a secondary feast for more highly specialized, chemosynthetic deep-sea weirdos. What remains, years later, provides a scaffolding for suspension feeders. This is the marvel of how a single whale may for a century feed and seed an entire secret world.