This February 2020 video says about itself, translated:
Fjord (Norway’s Magical Fjords) – trailer
The Norwegian fjords are one of the most impressive regions in Europe. A surprisingly rich underwater world lurks in the deep, cold waters: from vast coral reefs full of luminescent sea creatures to herring-hunting killer whales and humpback whales. Award-winning nature filmmaker Jan Haft reveals the special diversity hidden in the dark water and shows underwater behaviour that has never been seen before. Fjord is an intimate portrait of a unique wilderness.
On 13 June 2020, I went to see this film about northern Norway. Most chairs in the cinema were kept empty, to make spatial distancing against the coronavirus possible.
This beautiful film shows the importance of the billions of herring wintering in the fjords for the food chain. Killer whales attack them: then, dead herring drift upwards as food for herring gulls. Other dead herring sink to the bottom, as food for seastars, crabs, lantern shanks and flatfish.
Apart from humpbacks and orcas, the film mentions a third cetacean species: harbour porpoises. Unfortunately and unnecessarily, the film says, each year 10,000 porpoises die as bycatch in fishing nets in Norway.
In winter, the fjords are mostly frozen, stopping much sunlight from shining underwater. That attracts a deep-sea species which cannot stand much light: Periphylla periphylla, the helmet jellyfish.