At nine in the morning, an hour before the Monterey Bay Aquarium opens to the public, the curator of husbandry operations walks across a tiled tundra of empty exhibit halls. Watery displays drench the floors in blue-green light, and a groggy-eyed sculpture of a whale the size of a bus hangs from the ceiling overhead. Paul Clarkson seems to be trespassing on a defunct discotheque. But then he swings open two steel double doors to reveal a hidden maze of bubbling tanks and whooshing pipes. This is where the party’s at, and jellyfish are the life of it.

People love aquariums. Almost two million visitors flock to this one each year for the chance to press their noses against glass displays housing 35,000 animals and plants. The jellyfish exhibit ranks among the most popular in aquarium history. But pilgrims seldom ponder how aquariums keep all of those tanks populated—an especially difficult task when so many species have natural life spans of only a few months.

“You don’t go to Petco,” Clarkson says. And in some cases, the aquarium can’t turn to the wild either. Case in point: sea nettles, brilliantly orange jellyfish the size of dinner platters that once teemed in the Monterey Bay. Warming water trends have exiled the animals for the past two years. So the aquarium stocks sea nettles and many other animals through large-scale, trial-and-error breeding efforts, whose experiments unfold in rows of tanks that the public never sees. The aquarium welcomes more babies than any American hospital.

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