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The world of the shallow seas is one of the richest and most productive on earth, with an array of diverse wildlife habitats populated by a myriad of bizarre characters, seemingly straight from the pages of Welsh mythology.

We journey into this strange environment - one that sits remarkably close to shore. In the giant kelp forest, we join a female catshark as she lays an egg deep in the forest floor and watch as we witness a tangled web of hermaphrodite sea hares taking part in a three-day ‘love-athon’.

On the dramatic underwater cliffs off Pembrokeshire, we find the Great Barrier Reef of Wales, chocked with exotic gardens of sponges and soft corals. The alien-like predators on this rocky landscape include a rare spiny lobster and a large star fish, making a stealth attack on a hapless-looking scallop with a surprise up his sleeve.

Just beyond the beaches of Abersoch, an underwater desert stretches out to sea. With nowhere to hide, many marine inhabitants have found incredible ways to camouflage themselves from the visiting catshark. Meanwhile a gang of painted goby use extraordinary drum-like vocalisations to attract a female.

In Anglesey, Arctic terns have arrived to breed. These elegant sea birds have the longest migration of any bird on earth. They spend the summer fishing in the shallows to feed their young. On the wreck of the SS Gwynfaen, we meet a range of colourful and exciting characters including a three-meter-long conger eel.