The Dolphin Discovery outdoor aquarium on Isla Mujeres, a 40-minute ferry ride from the Mexican resort of Cancún, has spawned countless vacation photos and Instagram posts. It’s marketed as a paradise where parents and kids can swim among the smart, playful mammals in the turquoise waters of the Caribbean. The gift shop brims with all manner of marine kitsch—dolphin plush toys, T-shirts, key chains and more in myriad colors and sizes. And while you await your turn in the pool, the bar and buffet offer free-flowing margaritas and nachos by the mountainload.
Illustration: Le.BLUE for Bloomberg Businessweek
But what’s unlikely to make it into ...