 There are many organisms in nature that are
capable of lighting themselves up through 
their own bioluminescent means. 
But not many have the distinction of having
helped guide a future astronaut to safety. 
Jim Lovell is perhaps best known for his flights
to and around the moon, including the 1970 
Apollo 13 mission, which experienced a critical
failure that prevented it from actually landing 
on the moon. 
But in 1954, he was a fighter pilot on a training
mission off the coast of Japan when his navigation 
systems failed. 
With darkness around him and no guide to the
aircraft carrier he was meant to land on, 
Lovell turned off the lights in his cabin, only
to notice a glimmer of green in the waters 
below, acting like a trail of glow-in-the
dark breadcrumbs left behind by the carrier 
as it moved through the water. 
That light was the bioluminescence of planktonic
life, and fortunately, you don’t have to 
be a stranded fighter pilot to see it in action. 
That surface oceanic light is most likely
attributable to a certain kind of single-celled 
eukaryote called a dinoflagellate. 
There are more than 2000 living species of
dinoflagellates, and while a few are found 
in freshwater, most are some form of marine plankton.
Dinoflagellates survive on a mix of diets.
Some are purely phototrophic, consuming food
produced by their own chloroplasts. 
But most are mixotrophic, meaning that they
rely on a mix of photosynthesis and consumption. 
In either capacity, dinoflagellates are hugely
important for their local ecosystems. 
As marine primary producers, they are second only to diatoms.
And when dinoflagellates consume other organisms,
they link together various facets of production 
and consumption in the ocean, sending energy up the food chain.
But nature is built on balance, and excess
dinoflagellates can also become disruptive
to local ecosystems when they accumulate into
large toxic blooms, also known as “red tides”. 
These can choke off resources to other animals,
and sometimes even produce toxins that poison 
their neighbors. 
Aside from their importance, dinoflagellates are kind of quirky.
For one thing, they have a really weird nucleus.
Like so weird that it has its own name: the
dinokaryon. 
If “dinokaryon” sounds majestic to you, well… that is apt.
The dinokaryon can hold a truly absurd amount
of DNA for a eukaryotic nucleus. 
A human nucleus, just for reference, holds about 3 picograms of DNA.
Meanwhile, some dinoflagellates species can
hold somewhere from 100-200 picograms of DNA 
in their dinokaryon. 
And where most eukaryotes pack our DNA into
little structures connected together like 
beads on a string, dinoflagellate DNA does
not have that clear of an architecture. 
Even more weird: they have the genes to make
that kind of orderly arrangement possible, 
they just rarely seem to use them. 
Dinoflagellates also swim kind of funny. 
It’s part of why we can’t show them too
often because they’re always whirling in 
and out of focus. 
One is held in a structure around the organism’s
equator, spinning and moving the organism forward.
The other flagella, which you can see here
coming out the end of the dinoflagellate, 
helps the organism steer around. 
While most dinoflagellates are capable of
photosynthesis, they do not all go about their 
chloroplasts the same way. 
Yes, some dinoflagellates have their own chloroplasts
and use them as you would expect to carry 
out photosynthesis. 
But others, like the freshwater Nusuttodinium, are a little bit less honest.
They steal their chloroplasts.
These dinoflagellates will start out chloroplast-less and colorless.
But as they begin to consume their favorite
meal, some local photosynthetic algae, the 
dinoflagellates don’t just consume their
nutrients: they steal the algae’s chloroplasts. 
These, appropriately enough, are called kleptochloroplasts,
and they’ll stay with the dinoflagellate 
until they divide and the daughter cells have to steal some new ones.
But of course, the most striking dinoflagellate
trait is their bioluminescence. 
When the organisms were first described by
Henry Baker in the 19th century, he called 
them “animalcules which cause the sparkling light in sea water”.
That sparkling light is the product of a molecule
called luciferin, which is usually set into 
glowing action by some kind of mechanical stimulation.
It could be the breaking of waves, a passing
aircraft carrier, or—most relevant to the 
dinoflagellates themselves—a potential predator. 
Scientists have hypothesized that dinoflagellates
flash their lights as a kind of “burglar 
alarm” in response to predators, attracting
the attention of other organisms that will 
eat the dinoflagellates’ own enemies. 
So, no, they’re not scaring away their predators.
They are attracting the predators of their
predators. 
This system of bioluminescence and the molecules
underlying it has its parallels across a lot 
of other animals, including fireflies. 
And whether they are taking in light for photosynthesis
or producing it through their own pathways, 
dinoflagellates have evolved their own mastery of illumination.

