Walking a 100-mile stretch of coastline reveals how a pioneering project is transforming the seascape, rivers and land

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On a blustery morning in May on Shoreham-by-Sea’s west beach, Eric Smith and George Short are pointing out treasures the waves have left on the tideline. Cuttlefish bones and balls of whelk eggs, they say, are evidence of recovering marine habitats.

“Just give nature a bit of space and it will come back,” says Smith, 76, a former lorry driver by trade, freediver by choice. He first started diving off the Sussex coast at the age of 11, and still recalls the underwater “garden of Eden” of his childhood, a kelp forest teeming with bream, lobsters and cuttlefish that stretched for 25 miles (40km) between Shoreham and Selsey Bill. It vanished after years of intensive trawling, a destructive form of fishing involving dragging heavy nets along the seabed.

Whelk eggs and seaweed. Photograph: Urszula Sołtys/the Guardian