We follow Atlantic grey seals through the year, from courtship to pregnancy and birth. Will a curious snowy-white seal pup make it safely through to adulthood?

The strange environment of the shallow seas is 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.

As the water starts to warm in the summer, marine giants arrive at the Celtic deep. Some have travelled for thousands of miles to feast on plankton and abundant shoals of fish.

Presented by Dame Sian Phillips, this episode looks at some of the biggest challenges and issues facing the marine environment in Wales and the rest of the world today.