In our final episode, The Changing Sea , we discover that the ocean is sending us clear signals. Off the rugged and beautiful coast of British Columbia we meet scientists and fishermen who are shocked at the recent arrival of a voracious new creature – the Humboldt squid. This monster-sized squid native to the equatorial waters of Mexico has moved north and ushered in a cascade of changes to the ecosystem. Their arrival is part of a disturbing pattern that is emerging with species movement being tracked around the world. In The Changing Sea we illustrate how the ocean’s chemistry and systems are being compromised by increased acidity, less oxygen and warming temperatures. The changes to the timeless rhythms of birth and renewal are being felt everywhere – even on coral reefs. In the idyllic waters of the Bay of Naples, we get a glimpse of our future ocean, thanks to the mythic Mount Vesuvius. As scientists swim through lush green seagrass beds, they collect creatures whose shells are dissolving, and we discover that this amazing place has a terrible secret. It has been naturally acidified for millennia – could this be our ocean’s future?