Squid Run -- Market Squid, United States
Divers descend into the nighttime morass of a hundred thousand small slimy creatures extending in all directions. It's a squid run, a rarely seen soiree now at great risk due to climate change. The Darwin team has combed the depths searching for clues to explain this massive gathering. The result? Incredible footage of a range of mating behaviors, from aggressive multi-armed battles and intimate pairings to a mother's delicate depositing of egg casings in a blossom-like pattern on the sea floor.