If this video does not work, try other source from the menu or open it from the alternative links below.
Blue Planet II: Season 1, Episode 5
1 - 5: Green Seas
In the undersea forests of kelp, algae and sea-grass, there is competition between species and sea otters are seen helping Garibaldi fish protect their seaweed garden from sea urchins while the common octopus uses shells to create a coat of armour against sharks.