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Jonathan explores a cave in Cozumel containing rare marine life found nowhere else in the
world!
Welcome to Jonathan Bird’s Blue World!
The island of Cozumel, just off the coast of Mexico near Cancun, is known for its crystal
clear water.
Divers flock to this scuba diving paradise to see healthy reefs and lots of marine life.
The Splendid Toadfish, one of the local marine rock stars, is found around only two islands
in the world.
Further offshore, reef sharks sometimes sleep in caves, a behavior that has not been witnessed
anywhere else.
And Cozumel has something else unique in the world—this special cenote, containing species
found nowhere else on Earth!
Cameraman Todd and I head on down to Cozumel for a cave diving adventure.
We team up with our favorite local cave diving guide Christine Loew.
Then we head on over to Aerolito cenote.
It’s bigger than most of the cenotes we dive.
It almost looks like a pond.
And it’s only a couple hundred meters from the ocean, which is one of the things making
Aerolito special.
Even though the surface water is fresh, down deeper it turns to salt water, because it’s
connected directly to the ocean.
And because of that, it has some marine life unique to this environment.
So one of the great things about Aerolito is an added element of excitement.
Apparently there are crocodiles.
We go over our plan.
Christine has been here before, but we haven’t so we will be following her!
Then it’s time to get our gear together and suit up.
Time to get wet!
As we put our gear on and kick up the bottom of the algae-filled water, I try not to think
about crocodiles.
Once we get underwater and swim away from the silt we kicked up, we can see much better,
and follow Christine into a small cave opening.
Due to our proximity to the ocean, the halocline is quite shallow.
We pass through this swirly barrier between the fresh water and the salt water at a depth
of only 20 feet.
Todd and I follow as Christine runs a reel from the entrance back to the permanent cave
line.
The permanent line starts pretty far from the entrance to discourage open water divers
from following it.
It takes a while but eventually we find the permanent line, and Christine ties in.
Even this far in, the greenish tint of the algae-filled pond water persists.
Then, we find something spectactular.
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A cave brittlestar.
This species of brittle star is found nowhere else on Earth except this one cave.
Like many cave-adapted organisms, it has lost much of its pigment.
And it can detect the presence of light.
This survival skill causes the brittle star to run from my flashlight.
As I look around, I realize that there are quite a few of these brittlestars, all running
from our lights.
But here’s the most amazing thing: Aerolito is the only cave in the world, known to have
cave-adapted sea stars.
But it’s not just this one species of brittle star.
There are actually three species of sea stars in here.
And I’m hoping to find all of them.
Our search takes us deeper and shallower, at times getting shallow enough to enter the
halocline again.
But we know the sea stars all live below this depth, in the salt water.
So we travel further into the cave, taking a passage that goes in the opposite direction
as the ocean, traveling further inland, seeking deeper passages.
But the cave never gets very deep, and we stay close to the halocline, not the most
likely place to find our elusive sea stars.
Finally, a crack that drops deeper into the salty later, below the influence of the tides--which
cause the halocline to rise and fall.
Christine scours the walls of the cave with her light, casting an experienced eye for
cave life.
And then, we swim down another crack, even deeper.
Now we are really getting into the realm of the unknown.
We end up in a dark tube, with odd, dark-colored limestone and a gravel bottom.
There are almost no speleothem formations.
It’s a spooky place.
Soon we start seeing signs of ocean life.
Little orange sponges dot the walls.
We press on, watching our limited air supply and pushing deeper into the cave.
I watch the floor of the cave carefully as we go.
At last, a white splotch, that looks like another sponge, but the pentagonal shape gives
it away.
This is one of the rarest sea stars in the entire world—a cave adapted type of asteroid
similar to one seen on reefs around the Caribbean.
But here in Aerolito it has lost all pigmentation and lives entirely in the dark.
What it eats is not known.
And we struck gold, because right nearby, the monster of this cave: Copidaster cavernicola.
This large sea star, reaching about a foot across, is also a cave-adapted relative of
a deep water species seen in the ocean.
But unlike the others, this sea star hasn’t lost all its pigmentation.
That may mean that it hasn’t been long enough to fully adapt.
Give it another two hundred generations over a thousand years and we’ll check back.
Having found our three species of sea stars, we turn and make our long swim back towards
the entrance.
Plastic line arrows always point the way out, so we know we are going the right way.
We pass fields of brittle stars on a sandy section of the cave.
There must be something they like to eat in or on the sand.
And we find another magnificent cavernicola snuggled up to a sponge.
Sponges in fact are everywhere.
As we get closer to the entrance, we are also getting closer to the ocean, and the water
contains more organic materials for the sponges to eat.
And the sponges are crawling with brittle stars.
Finally we make it back to our reel, and Christine unties it from the main line.
We’re back to the cavern zone, where we can see sunlight streaming in.
After a few minutes doing a safety stop, we can head back up into the sunlight—keeping
an eye peeled for crocs of course!
Woo!
I am back from the cave!
Aerolito is a fascinating cenote.
It doesn’t really have any beautiful formations, but its location and conditions are just right
for it to have unique marine life, found nowhere else in the world.
And at the moment at least, it’s the only cave in the world known to contain cave-adapted
sea stars.
You never know what you might find, just exploring the depths of a small algae-filled pond.
It’s another incredible wonder of the blue world.
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