What lies beneath: discovering surprising jewels in the North Sea

Not far from the mouth of the river Tyne, fabulously-coloured nudibranchs and corals can be spotted amongst rusting sunken ships

As I finned alongside the bulky remnants of the ship's boilers - three massive blocks of northern iron - the light had almost gone. The gently rusting masses were riddled with fire-tubes, each seemingly host to a wary crab. In some, the red eyes of a velvet swimming crab (Necora puber) reflected my light; in others edible crabs (Cancer pagurus) retreated from my gaze. Small prawns and a few well-camouflaged fish moved to avoid me, drab browns revealed as reds and oranges under my torch light. And there, on a piece of deck plate, covered by a bright red encrusting sponge, was one of the jewel-like animals I'd set out to capture on film.