Three years after Hurricane Sandy lashed the Rockaways, the boardwalk marched down the beach in broken segments as the public housing built under Robert Moses was hemmed in by condos. Out in the surf, not much changed as the bathymetry returned to normal, but the predominantly white, male crowd of surfers had.

Part of that shift happened when Louis Harris, 46, founded the East Coast chapter of the Black Surfing Association in 2016.

Mr. Harris bought his first surf board after moving to the Rockaways in 2006. After getting his bearings in remote beaches, he joined the crowd at Beach 90th Street. “That’s when I saw B.J.,” Mr. Harris said.

Brian James — “B.J.” — the only other black man in the water, paddled over to Mr. Harris and asked if he wanted to hang out afterward. “‘If you’re going to be a surfer, you have to take it seriously,’” Mr. Harris recalled him saying . “‘You’re a black guy. Everybody’s eyes are on you.’”