As we travel from the surface of the ocean down through the water column, the amount
of light available decreases with depth.
Very little light from the surface penetrates between 200 and 1,000 meters, in what’s
known as the twilight zone.
And once we reach about 1,000 meters depth, light from above has disappeared entirely.
But throughout the open ocean -- even in its darkest depths -- we encounter a different
kind of light.
The displays you see here are examples of bioluminescence, an adaptation that scientists
estimate is found in more than 75% of the animals that live in the water column.
Bioluminescence is a form of chemiluminescence, which is the production of visible light by
a chemical reaction.
Scientists call the process “bioluminescence” when the reaction occurs within a living organism.
While relatively rare on land, bioluminescence is quite common throughout the open ocean
-- particularly among fishes, jellies, squids, tunicates, and crustaceans.
Along the coast you might even see the work of bioluminescent dinoflagellates -- tiny
planktonic organisms -- that can cause the sea -- to glow.
To tell us more about how bioluminescence is used by marine organisms and what questions
keep scientists up at night, let's talk to an expert.
Welcome Rene!
Before we delve into the topic of bioluminescence, can you first tell us a bit more about yourself?
Yeah, of course.
So I'm a PhD student at the University of Kansas and I work here in the natural history
museum.
My research primarily focuses on the evolution of deep-sea fishes and I focus on a group
called the lantern fishes.
So where in the ocean do we most frequently see bioluminescence occurring?
The majority of bioluminescence and where it occurs in the ocean, um, actually happens
a lot in what we consider the open ocean mid-water zone.
So these zones, um, specifically are called the Mesopelagic or the Twilight zone, and
the bathypelagic called the midnight zone.
And I actually looked this up recently and 4,000 meters is basically the entire length
of central park in New York city.
And so if you just, like, stood central park on its head and then went all the way down,
that's approximately 4,000 meters.
And it's just, it's kind of crazy to think about how much open space there is down there
and how much water there is down there.
And it's also important to note that many of these organisms aren't restricted to just
one depth in the ocean.
This is a three-dimensional world.
And so many of them perform something called a daily vertical migration, where they swim
up into the surface at night to feed on a bunch of the zooplankton and other organisms
that survive and are very abundant up there.
And then they swim back down into the deep sea during the day.
And that's usually to hide from predators.
And this mass migration is thought to be the largest migration on earth because it is constantly
happening around the globe as we're rotating.
Can you tell us what are some of the reasons why these animals actually bioluminesce?
So if you're an organism that lives in the deep sea, one of the major benefits of evolving
bioluminescence is to use it for a type of camouflage.
Many of the organisms that live in this area have something called photophores or light
organs on their stomachs.
And much of the light that's produced by these stomach light organs specifically matches
both the color and the intensity of light that's coming from the surface of the ocean.
So this type of camouflage that they're doing is called counter illumination.
Uh, some of the other cool behaviors or some of the things that bioluminescence is used
for, if you think of an angler fish.
So the one from finding nemo that has the esca on its head, uh, they use those to attract
prey.
It's also known to be used for defense mechanisms.
So some species and some organisms will actually shoot out bioluminescent goo to make bright
flashes to distract or stun different types of predators.
And also living in the deep sea, it means you’ve got to get creative in order to communicate.
And so many of the organisms that use bioluminescence use it, to communicate with each other.
Can you explain how bioluminescence is actually produced by animals?
In the simplest sense?
Bioluminescence is actually created as a byproduct of a chemical reaction between the molecules
luciferin and luciferase.
Luciferin is called a substrate molecule, and it's the molecule that emits light.
And this happens when it's combined with a luciferase, which is an enzyme and oxygen.
So light along with oxyluciferin byproducts of that reaction.
Alexandra Purit...: 23:22 Is the chemical reaction for bioluminescence the same for
every species?
Luciferase and luciferase are general terms.
And there's actually a range of structures that fill the roles of each of these.
And the fact that we see so many different kinds of luciferins and luciferases hints
that the evolution of this trait didn't just happen once.
Recent studies actually have shown that bioluminescence has evolved at least 94 different times across
the tree of life.
It's an insane number and it's actually a number that will probably increase as we identify
new species and find new organisms, especially since the deep sea is one of the least explored
areas on earth.
So I'm curious to know what are some of the things that scientists are still uncertain
about with regards to bioluminescence, and also to hear a little bit more about some
of the current areas of research in this field?
Yeah, of course -- we still don't actually know how many times bioluminescence has evolved
or how many species are bioluminescent. 94 is just like our current hypothesis based
on information that we have.
We're constantly also finding those new chemical compounds of luciferin and luciferase, new
light organ structures, new species that can bioluminesce, um, not only that, but we continue
to find new ways that bioluminescence is used, different types of cells that can do it.
And we still actually don't know much about how organisms store luciferins in their bodies.
And so there's actually ongoing research in basically every single one of these areas.
Rene, thank you so much for joining us today.
It was really great speaking with you and learning more about the fascinating topic
of bioluminescence.
I hope I was able to bring light to some of the topics of bioluminescence.
It's clear that in this dark and open environment, a little bit of light can go a long way.
One of nature's most amazing phenomena, there's still a lot we don't know about bioluminescence,
particularly in deep-sea organisms.
The answers to our scientific mysteries begin with curiosity: What questions spark your
curiosity about bioluminescence?