Great Blue Wild - Season 3 Episode 4 -

To a marine biologist, any attempt at mapping an oceanic food chain begins and ends with plankton, from tiny bacterial algae to soft-bodied animals such as jellyfish. These microscopic miracles are responsible for producing two-thirds of atmospheric oxygen. Their place at the bottom of the chain has the greatest impact on marine life, whether they're providing nourishment for filter-feeders such as sardines and manta rays or predators like dolphins and sharks.