How the Disco Clam Uses Light to Fight Super-Strong Predators

[Matt] Clams usually have one line of defense

against a predator, their tough shells,

but this researcher,

My name is Dr. Lindsey Dougherty.

[Matt] just discovered that this clam, the disco clam,

may have a unique defense mechanism,

[disco music]

a mesmerizing light show.

[Lindsey] The fact that this clam was opening

in the middle of an attack

to flash at the predator made no sense to us.

[Matt] Especially given that the predator

is the fearsome manta shrimp,

known for its incredibly powerful punch.

I got hit once and was bruised for a month.

[Matt] But when the disco clam meets a manta shrimp,

Dougherty discovered something bizarre.

[Lindsey] The manta shrimp itself, they actually went

into a catatonic state for up to 15 minutes.

I think this is one of the greatest match-ups

in the animal kingdom.

Can you talk about the combatants we have on both sides?

They're two very popular and very unique creatures.

Manta shrimp are not technically shrimp,

their taxonomic group is stomatopods,

so there are two main types.

There are smashers, which smash things,

so they usually feed on hard-bodied prey,

things like clams, snails.

And then there are spearers,

which look like the Edward Scissorshands, I suppose,

of the underwater world.

In this case, because we're dealing with a clam,

or a hard-bodied predator,

we studied the smashing manta shrimp,

which can actually hit at the speed of a six-caliber bullet

and cause cavitation under water,

so it's a quite unique strike.

It does strike with such force

that it causes these cavitation bubbles.

Can you walk us through what those are,

and what happens when they explode?

The easiest way to explain it is

that they essentially boil the water.

It's actually creating an area of low volume

that creates this boiling,

and when that bubble collapses it actually can create

a shockwave that can stun their prey items.

They can actually break aquarium glass.

We had this happen.

It's a very interesting evolutionary adaptation

to feed on things that are traditionally hard to get at,

like a clam that has a thick, calcium carbonate shell.

Switching to the clams, what is a disco clam,

and why is it called such?

A disco clam is a type of file clam.

Disco is a colloquial term.

People also call them flame scallops

or electric scallops.

They are technically a clam, not a scallop,

but they live in the Indo-Pacific on coral reefs,

and what they typically do is they find

a small hole that they can get inside,

and they'll use bissell threads to attach themselves

inside that hole, and then they'll stick out their tentacles

and they'll be flashing any time there's ambient light.

One side of the issue is reflective.

It actually has tiny silicon nanospheres,

which if you think about it,

are essentially like teeny tiny disco balls

inside their tissue that are really effective

at reflecting light.

And then on the other side, it's absorbent.

They basically show the reflective side and then hide it,

almost like an audience doing a wave at a football game.

And that's why, to our eyes, when it happens very quickly,

it looks as though they're flashing.

They speed up when you scare them or give them food,

so anything that excites them will speed up

that flashing display.

This is fundamentally different

from how most other critters in the sea

that produce light are going about it.

How is this different from bioluminescence?

A lot of people actually thought

it was bioluminescence initially.

The difference is you can see it during the day,

and usually bioluminescence isn't bright enough

to be seen during the day.

This is based fully on structure within the tissue,

whereas bioluminescence is a chemical reaction

that actually produces light instead of heat.

Yeah, it's quite different, it's quite unique.

And you did a study recently that looked at this match-up

between the manta shrimp and the disco clam.

What did you find in this study?

The most interesting interaction was the disco clam

opening mid-attack.

When you think about a clam,

usually their best line of defense is their shell, right?

They can close very tightly, as anyone who's ever tried

to open one knows.

The fact that this clam was opening

in the middle of an attack to flash at the predator

made no sense to us.

That's your best line of defense when you're being attacked

by this voracious predator.

The manta shrimp itself also has a very strange reaction

to that red, external tissue.

They actually went into a catatonic state

for up to 15 minutes.

Given that the manta shrimp

goes into this catatonic state, might that open it up

to its own predation?

That's this weird symptom of the disco clam

doing its thing, and then the predator itself gets eaten.

There's clearly something going on

that the manta shrimp is very unsure of

when they encounter this tissue, so that's why

we wanted to look at the tissue further

and see if we could figure out what was going on

that made it so unique and unpalatable.

The manta shrimp is famous for being a voracious predator,

it's eating a lot of different things in the sea.

Are there any indications that it's off-put

by any other potential prey items other than the disco clam?

They're not what I would call picky eaters.

I know my PhD P.I. fed one a blue ring octopus,

which has enough tetrodotoxin to kill eight adult humans,

so not something most people would willfully eat.

The fact that we saw this strange interaction

with the disco clam fascinated us

from a behavioral point of view

because there's just not much that will throw off

the manta shrimp, especially to the point

of going into a catatonic state

and cleaning their mouth parts and just clearly

being very annoyed at what they were encountering.

I think it's also interesting

because these are intelligent, as we can define it,

creatures that I've seen them actually blow limbs

off of crabs and things like that.

They're crafty animals, and it's just interesting

to see them fall to pieces when they come across

a disco clam.

Yeah, so they can be very manipulative

with the morphology of any creature that they encounter.

I think they have to be in order to get various things open,

and avoid getting hurt themselves

while they're predating upon something.

To see them not only go catatonic, but just seem

to be completely lost, I don't know how to deal

with this bright red clam that's flashing at me,

I don't know what to do with this.

It's a pretty fascinating behavior to encounter.

In general, animals usually don't do something

unless there's some sort of benefit to them, right?

You don't want to expend too much energy

unless it benefits you in some manner.

And it's not always the case, but most of the time

that's true, so it could be that this flashing

is just a really catchy evolutionary thing

to show predators, don't eat me, you'll regret it.

I was actually gonna ask about the evolutionary side

of things.

Could it be that the disco clam has evolved this defense

specifically for something like a manta shrimp,

to be able to confuse it?

One thing that's really important in animal behavior

is to remember to consider the visual capability

of the predator you're assuming is attacking.

All of these different groups that could potentially eat

disco clams all have different visual capacity.

Manta shrimp in particular have up to 16 photo receptors,

which we as humans have three,

so they've got us a little bit beat there.

This is an Indo-Pacific species that has evolved

this display, and Indo-Pacific reefs are incredibly colorful

and you have to do a lot to stand out.

If you're trying to advertise that you're poisonous

or distasteful, you have to be creative in order to do it.

Given the uniqueness of the structure in the disco clam

that's producing this light,

might there be some inspiration here for human designs

for disco balls or otherwise?

[Lindsey laughs]

A disco clam disco ball.

Yes, I like to say that anything we can do,

nature does better.

There's a lot that we can learn about structural coloration

from things like morpho-butterflies that use

a very specific interaction between tissue and light

in order to create really amazing displays of color.

There's actually a qualcomm display

that's based on movable mirrors that can create

more light when there's a bright light outside.

If you think about using a tablet,

if you're trying to read a book on your tablet,

and you go outside and there's too much light,

you suddenly can't see the screen.

If we learn from nature and how animals

use structural coloration, given more ambient light,

the screen can actually get brighter

if that screen itself can interact with the light

that's coming in.

With disco clams, we initially studied the size

of the silicon nanospheres,

their spacing against one another.

All of that showed us essentially that they're optimized

for a blue light environment, and that they're reflection

is really quite impressive for a natural animal.

In spectrometry we look at something

called a white standard, which essentially should reflect

every color of the visible spectrum, which gives you white.

The disco clam was quite close to that ideal standard,

and it's pretty amazing to have a reflector

that is that powerful, especially under water

where your light environment is quite limited.

In the ocean, being able to reflect

the entire visible spectrum is particularly impressive

because red light attenuates so quickly,

as do other wavelengths as you go little bit deeper.

The thing that I was most interested in

is the actual flashing display,

and unfortunately, the disco clam is the only bi-valve

I know of that has anything like that.

In a perfect world, I would love

to look at different potential predators

and see how they measure up against the disco clam,

but yeah, it's something we can potentially do

in the future.

Generally speaking, the disco clam is staying alive?

[Lindsey laughs]

I'm sorry, I'll show myself out now.

[Lindsey laughs]

Thanks for being here with us.

Thanks for having me.

[disco music]