Explore a Mysterious Deep Reef That Shouldn’t Exist

[Voiceover] Welcome to the Twilight Zone.

No, not that Twilight Zone.

The oceanic Twilight Zone,

one of the most mysterious ecosystems on Earth.

200 to 500 feet under the surface,

it gets dark during the day, like scary dark.

Usually, coral needs sunlight to survive,

yet here a reef thrives.

Researchers at the California Academy of Sciences

in San Francisco are finding that these deep reef corals

get there energy in a clever way.

When contrast to shallow water reefs,

which are largely driven by sunlight,

Twilight Zone reefs exist kinda as the sunlight

starts to disappear.

As its darker there, there's less photosynthetic corals

and there are more corals that rely upon filter feeding

or catching and eating plankton, bacteria,

detritus and debris that floats down from shallower waters.

[Voiceover] Up until now, the reefs of the twilight zone

have been too deep for normal scuba diving

and too shallow to justify the expensive exploring

with a submersible.

But thanks to some fancy new diving tech,

the Academy of Sciences is finally bringing

the deep reef to the public

with a first of its kind exhibit.

One of the most fascinating animals we got

for this new exhibit are benthic ctenophores.

They have very long tentacles that look like

long fishing lines, and they capture plankton with them.

[Voiceover] Bringing the creatures up from the deep

was a tremendous challenge, particularly with fish,

whose air-filled swim bladders can get kinda, well, bloody.

That swim bladder represents a problem to us

because when we reduce the ambient pressure for a fish,

their swim bladder expands and it crushes

all of the other organs inside the fish.

[Voiceover] So the academy invented

its own mini decompression chamber.

In the deep, divers collect fish and seal them inside.

At that point, that becomes the world's deepest aquarium.

We hand it off to surface support team,

and then they control the decompression of those fish

over a period of up to about 48 hours,

slowly acclimating them to the surface pressure

that they will be living in when they come to our aquarium.

[Voiceover] Diving to such depths also presents

huge problems for the divers themselves.

Typical scuba gear can only get you around

an hour of dive time, breathing oxygen and nitrogen.

But at these depths, divers breathe not nitrogen,

but helium, a very expensive gas.

So the academy's divers use what's known as a rebreather,

which cycles the helium instead of releasing it

all into the water.

So with the rebreather, everything goes

back into the system.

There's a canister in our back

that filters the carbon dioxide out,

and then we keep breathing the same helium

over and over again, and add oxygen as we need it.

We can stay underwater with a rebreather

for five, six, seven hours.

[Voiceover] That's key to being able to reach

the deep reefs since the divers have to spend

so much time decompressing on their way back up.

And the urgency to explore and understand

the Twilight Zone is real.

Shallow coral reefs are suffering terribly

from both warming seas and pollution.

Whether the deep reefs of the Twilight Zone

can avoid the same fate isn't yet clear.

But just maybe this strange place can

serve as a refuge as the oceans transform.

After all, weirder things have happened

in the Twilight Zone.

(soft ambient music)