“Oceans” scenes 1-6: Currents, Plankton, Reef Building Corals, Symbiotic Relationships.

G'day, my name is Josh Jensen. I'm a marine biologist and the underwater cameraman for Undersea Productions in Australia. I filmed the "Nature's Aquarium" series, and I'm going to talk you through some of what's going on in the underwater scenes of this film. "Oceans" is basically a collection of some of our favourite seascapes from the countries we visited and filmed over the past five years. I think it's a privilege to be able to dive and see what's under that big blue blanket, and I think that privilege gives all divers an obligation to document that beauty to share with others if we can. Our oceans are in serious trouble, and it's only through an awareness and understanding of marine ecosystems that we can learn to use marine resources sustainably. You can probably see that the current is running pretty hard in this shot: the red sea whips are bent over, the fish are swimming pretty hard but not really going anywhere.

Current can be challenging, but it brings rewards. In fact, pretty much the whole coral reef system—and in fact the entire marine world— relies on currents, and specifically the plankton that the current brings with it. Plankton is any organism that gets moved around more by the current than by its own propulsion. There are literally millions of tiny planktonic organisms flowing through this scene every second. All those particles you can see, and even more way too small to see. Plankton is what turns the water from crystal clear into the maybe 30m/100ft visibility that you can see in this shot. Some plankton are tiny things, smaller than bacteria, that get filtered by sponges; next up in size are the single-celled plants called phytoplankton, which might get filtered or eaten by microscopic animals called zooplankton; and all those zooplankton are eaten by small fish, which are eaten by the bigger fish.

Think of coral reefs as massive filters. I'll often talk about plankton predators called planktivores. Throughout the film, I'll also refer to a lot of critters as filter feeders, and it is plankton that they are filtering and feeding on. This is a typical remote Indonesian coral reef. The school of small orange fish are one of the most common and conspicuous species of planktivores you'll find. They're called Scalefin anthias, and these are all females. For every 20 or so orange females, you'll see a mostly purple male, and the male usually swims just above his harem, every now and then you'll see them make frantic runs up and down as a display to the females and to rival males. Each hard coral is actually a colony of hundreds to millions of tiny animals called polyps.

They're called reef building corals because their stony skeleton creates habitat for the incredible diversity of reef fish. Each fish has evolved to fill a specific niche created by the diverse coral growth forms. All these cardinalfish, for example— and there are at least six different species in there— they shelter amongst this staghorn coral during the day… and at night they'll move up into the water column to feed, and the daytime planktivores will move down into the staghorn coral to sleep. Most species canʼt survive alone. This anemone, for example, is in a mutualistic symbiotic relationship with clownfish— that means both species benefit from the partnership. The clownish defends the anemone from butterflyfish attack, and the clownfish get a safe place to live and lay their eggs. Itʼs a really well-studied and well-understood field..

. but there are strange things going on in this shot: The White-belly damselfish, for example— thatʼs the single grey fish here—they arenʼt normally associated with anemones, but this guy is most likely waiting to be cleaned. There are usually cleaner shrimp on anemones, but itʼs probably the juvenile Blunthead wrasse—those are the black and white ones— or the juvenile cleaner wrasse that will dance in shortly— that will do the cleaning in this particular station. Whatʼs extra unusual about this shot is the Sixstripe wrasse—the little pink and green fish swimming throughout the tentacles— heʼs not supposed to be able to do that without getting stung and eaten. There are hundreds of species of animals that we never see— mostly worms, but also crustaceans and molluscs—that live inside the rock-like coral skeleton. If you were to slice down into that coral rock youʼd find it looks like Swiss cheese: lots of holes in it.

The big fella feeding here is a Titan triggerfish and he is biting off chunks of that rock with incredibly strong teeth and powerful jaws to find big juicy worms that he knows live inside. But in searching for those big worms, he is also exposing lots of smaller worms and other critters, and thatʼs food for all the other fish species you can see here. Thereʼs a Moorish idol, a pair of Pacific double-saddled butterflyfish, a Checkerboard wrasse… there will also be smaller wrasse and hawkfish hanging around looking for scraps, too. Titan triggerfish almost always have an entourage of these opportunists which are attracted to the scene by the crunching sound of coral being broken..