Most dives are about movement, but this one stopped me cold. Lying untouched in the sand was a shell unlike anything I’d seen. Perfect curves, intact edges, and colors shaped by years underwater.

Note to readers: Multiple generations of a family of shell collectors gathered earlier this summer in Southwest Florida, combing the beaches on Captiva and Sanibel looking to add to their collections.

CAMP FOSTER, Okinawa — Japanese authorities safely detonated 30 shells believed to be left over from World War II this week on Miyakojima, a popular tourist destination 170 miles southwest of ...