LONGPORT — Mainland kids spend many summer days on the beach at 30th Avenue. On Monday, hundreds of parents and youths gathered there to wade in the cold water and remember four Mainland Regional High School students who died Saturday.

The ceremony is known as a ‘paddle-out,’ in which surfers gather their boards in a circle on the water to honor lost friends — in this case, Casey Brenner, 17, of Northfield; Edgar Bozzi, 17, of Somers Point; Nicholas Conner, 16, of Northfield; and Dean Khoury, 15, of Linwood, who died Saturday in a crash on the Garden State Parkway following football practice.

“All the kids come to 30th,” said Longport lifeguard Max Mittelman, of Northfield. “That’s what they do, just hang out and have a good time. So we wanted to have a celebratory service here at the beach. ... It seemed like the thing to do: have a happy remembrance, tell stories, and celebrate their lives.”

“I watched these kids grow up in front of me,” lifeguard Dan Gordon, of Northfield, said. “These were good, good kids. It’s so sad to see what happened, but at the same time, it’s great to bring the whole community together to honor four great kids.”

Before the ceremony, friends and family of the teens gathered around an old surfboard that Casey Brenner’s father, John, had found sitting in his backyard — a weather-beaten green board about 50 years old that the family had bought at a yard sale.

“We did this in the backyard today,” John Brenner said. “(A) neighbor got some stencils, and we put the kids’ names on it” and their jersey numbers.

“CB 20,” “DK 67,” “EB 34” and “NC 47,” are stenciled onto the board, along with “’Stangs 2011 — Family 4Ever.”

Brenner carried it into the surf as dozens upon dozens of people paddled out to a point just offshore, where they gathered around several lifeboats, one of which carried his wife, Lynn, and Dean Khoury’s mother, Denise. Crash survivor Alex DeNafo, 16, of Northfield, was among those who went out, Mittelman said.

Participants and lifeguards said they shared a moment of silence before tossing rose petals into the rolling waters. Stray rose petals lay strewn across the beach as they returned — the surfers paddling slowly back in, John Brenner carrying his board, and the mothers in their lifeboat, giving each other a heartfelt hug.

“It’s a great honor,” Lynn Brenner said before the ceremony. “My child is beside himself right now. This is the best thing in the world for him. This is what they wanted to do.”

The four teens’ schoolmates agreed.

“We did it for them,” said 16-year-old Dylan Swenson, of Northfield.

“Anything that helps to put the pain away is absolutely crucial,” said Will McDonnell, a 17-year-old senior. “It just shows how many lives were affected by this.”

As he waded out of the surf, John Brenner thanked everyone who had helped and supported the four families during the past few days, including law-enforcement agencies.

“No parent ever expects anything like this,” he said. “It’s the hardest thing I ever went through in my life. But as hard as this is, all those people (who have helped us) have made this much easier for us and the other families.”

As for the old surfboard, Brenner said he was going to ask the boys’ classmates to add their signatures to the relic, which he hopes will be displayed for all to see.

“At first, we were going to put it in our son’s room,” Casey’s father said. “But it doesn’t belong in our son’s room. It belongs somewhere with three of his best friends and their family members. We want to try to pull good memories and something good out of a tragedy that affected so many people.”

Perhaps Casey’s uncle, Mike Brenner, best described how the ceremony affected those who took part.

“The water was supposed to be cold, but I don’t think anybody out there thought it was,” the Northfield resident said. “It was very peaceful. It was the one moment in this whole process when every single person was at peace.”

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