The Phillipine coral reef tank inside the California Academy of Sciences in San Francisco is 25 feet deep and holds 212,000 gallons of water, making it one of the largest exhibits of living coral anywhere in the world. It is the centerpiece of the academy’s Steinhart Aquarium and hosts hundreds of coral species, a couple thousand colorful fish, plus sharks, stingrays, and numerous smaller creatures, like sea anemones and snails. There are five windows affording looks inside, the biggest of which, at 16 and a half feet tall and almost 30 feet wide, makes a sweeping arc in front of a dimly lit standing area backed by several rows of benches. It was designed to offer visitors a panoramic, theater-like view of life in the tank and is among the museum’s most popular attractions. It’s Wallace J. Nichols’s favorite spot in the building.

Nichols, 44, is a biologist and research associate at the academy who made a name for himself in the mid-1990s when he tracked a loggerhead turtle that swam from Baja, Mexico, to Japan, the first time anyone had recorded an animal swimming an entire ocean. He has done fieldwork in waters around the globe and spends most of his waking hours thinking and talking about the ocean, but when he’s in front of that big window at the aquarium, he doesn’t watch the fish. He watches the people.

“Whether it’s a 92-year-old or a two-year-old, when they come into that blue space, something happens,” Nichols says. They grow quiet and calm, but there’s more to it than that. When couples walk in, they frequently start holding hands. He says that if you ask people here what they’re feeling, they’ll struggle for words. Nichols finds this fascinating. He also believes that if we can understand what really happens to us in the presence of the ocean—which brain processes underlie our emotional reactions—it could bring about a radical shift in conservation efforts. If we learn precisely why we love the ocean, his thinking goes...