Name: 我们对珊瑚有很多误解（There is So Much We Got Wrong about Corals...）
Uploaded: 2021-05-16T09:10:58.000Z
Duration: 11 min 47 s
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When you think about coral reefs, you probably imagine a sparkling tropical oasis

副詞型分詞構句

that you can easily see while snorkeling or diving.

But that's just part of the picture when it comes to corals.

Reefs can be found as deep as 8000 meters.

In many ways, the corals of the deep are similar to shallower corals,

but they also form their own weird, wonderful ecosystems.

And while they might seem really far away, they're not immune

to what happens above, nor are we outside their sphere of influence.

We're just beginning to understand how important deep reefs are

But already, we know that we rely on the health and wellbeing

of all coral ecosystems, whether we can see them or not.

And unfortunately, all corals are struggling as a result of human activities — even those

tucked hundreds of meters below the surface.

No matter where you are in the world, there's probably a deep reef nearby

And the animals that build them have a lot in common

Like, both shallow and deep corals are foundational species which create

ecosystems and provide vital habitat for a huge variety of creatures.

Also, in both cases, what we'd call a single “coral” is actually a colony

of identical anemone-like animals called polyps!

The biggest difference between deep sea and shallow water corals

Shallow water corals all have symbiotic relationships

with single celled algae known as zooxanthellae.

These algae live inside the coral's tissues.

And in exchange for a safe place to live and access to plentiful sunlight,

they provide some food to the coral through photosynthesis,

as well as manage any waste produced by their coral hosts.

In fact, they're largely responsible for the corals' vibrant colors.

If they leave or are ejected from the coral's mostly clear tissues,

we see the hard, white calcium carbonate skeleton below.

And it occurs when a coral gets stressed;

like when the waters they live in become too warm.

Shallow corals are so dependent on these algae

that if one goes too long without them, it will die.

But sunlight quickly disappears the deeper you go.

So things are a bit different with deep corals.

The shallower deep corals, the ones living between 50 and 150 meters down,

And they do have zooxanthellae in their tissues.

Trouble is, the amount of sunlight that reaches these algae

isn't ideal for photosynthesis, which makes it hard for them to hold up

The corals have evolved a nifty workaround though.

They have fluorescent proteins in their tissues

that convert the available light into more algae-friendly wavelengths!.

Still, once you descend past about 200 meters, there's basically zero sunlight.

At those depths, not even fluorescent proteins can drive enough photosynthesis.

But most deep corals are found below this point!

So, the majority of species have ditched their algal buddies altogether.

Since they don't have any colorful symbionts,

they can't bleach like their shallower cousins.

But, that's not to say they're all a boring white!

Deep sea corals actually come in a stunning array of brilliant colors.

For example, the so-called black corals aren't black in life;

They get their namesake from the color of their skeletons,

which are different from the skeletons of most shallow water corals.

Instead of using the white mineral calcium carbonate, they build their skeletons

with protein and a fibrous substance called chitin

These chitin and protein skeletons are more flexible than carbonate ones,

yet still tough enough to support the animals.

So they allow black corals to live where they prefer:

in strong water currents that provide them with more food.

Other deep corals called octocorals, named for the 8 tentacles on each polyp,

Like, there's one species that is a stunning shade of purple.

These, too, are a little different than your average shallow coral.

which means they don't have a hard internal skeleton.

Instead, the polyps are supported by little needle-like pieces

No one is fully certain why deep corals are so colorful,

While pigments aren't visually helpful in the deep sea,

they may be acting as antioxidants and antibacterial compounds.

You see, the pigments found in deep corals are carotenoids

the same class of compounds often responsible for the brilliant colors

In fact, much like us, corals have to get carotenoids from their diet.

So it's likely part of the reason deep corals vary so much in color

is that the local snacks contain different pigments!.

Now, you might be imagining all of these colorful deep corals growing

on top of one another, like shallow corals do.

But in the deep, that kind of reef building is the exception.

In fact, out of the over 3300 deep sea coral species described so far,

there are only six that build that kind of reef.

Instead, most are found standing separate from each other, like trees in a forest.

They can pepper the seafloor or cling to the sides

We still call the habitats they create reefs, though.

And just like shallow reefs, they provide essential habitat

for ecologically and commercially important species.

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我们对珊瑚有很多误解（There is So Much We Got Wrong about Corals...）

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