A trip in search of dolphins instead led a conservationist and film-maker into the “bizarre and beautiful phenomenon” of coral spawning.

Andrew Stevenson, a whale researcher, said he found sea covered in floating pink streaks from the annual event when he went offshore last Friday.

Mr Stevenson said: “It was everywhere, acres of it. I travelled a long distance, maybe seven miles, and I kept coming across it.”

The tiny coral larvae, known as planulae, float for days or weeks before they sink to the ocean floor.

Mr Stevenson said the corals took their cue from the lunar cycle and the water temperature, but that the spawning was not completely understood by scientists.

He said all the corals released a “blizzard” of tiny eggs and sperm to fertilise on the surface.

Mr Stevenson added: “It was a dead calm day off St David’s and along the South Shore, close to the Bermuda platform, which is where you would expect to find coral spawning.

“I didn’t see any dolphins, but it was pretty amazing out there.”