Next on Jonathan Bird's Blue World, Jonathan spends
a week underwater at night waiting for the coral to spawn!
Hi, I'm Jonathan Bird and welcome to my world!
[♪ music]
Coral reefs are amazingly beautiful underwater sculptures that grow in tropical waters and
provide essential habitat for fish and invertebrates, as well as form an important part of the tropical
ocean ecosystem.
Some coral, like this bushy gorgonian, may look like a plant.
Other coral, such as this brain coral, looks like a boulder on the sea floor.
But coral is alive, and it's an animal. Look close enough and you'll see hundreds
of little mouths, such as the ones on this star coral colony. Each mouth belongs to an
individual coral animal, called a polyp.
Corals are related to jellies, so think of a coral colony as hundreds or thousands of
tiny jellies all clumped together.
Like jellies, coral has stinging tentacles to catch prey, which it mostly does at night.
But unlike jellies, corals grow attached to the bottom and often create a hard skeleton
to hold themselves down.
This begs the question—how does an animal that can't move reproduce and make a new
colony in a different place.
I'm on a mission to document how coral reproduces....
...so I have come to Bonaire, one of the greatest places in the world to learn about coral spawning.
Biologists have been studying coral reproduction here on Bonaire for more than a decade.
Bonaire is an island in the southern part of the Caribbean near Venezuela.
It's a beautiful place, full of Dutch architecture because it is part of the Netherlands.
The rocky, windward shoreline is rough, desolate and pounded by crashing waves,
but the other side of the island is calm and tranquil, where it is protected from the trade winds.
It's here that I will be diving to observe the coral.
Coral reproduction is not the easiest thing in the world to observe. That's because
coral reproduces by spawning. It only does it at night, and it only happens a couple
nights per year.
I have come to Bonaire a week after the full moon in September, when the corals are predicted
to spawn.
Why a week after the full moon? Well it has
to do with the tides. During a full moon you have what is called a spring tide. That's
when the high tide is really high and the low tide is really low, and you have a huge
amount of water movement between those two tides. A week later you have what's called
a neap tide. That's when the high tide is not quite so high and the low tide is not
quite so low. So you have a smaller amount of movement between the two tides. Less water
movement means less current and less current means that the eggs from the coral have more
time to float around in the water and get fertilized before the current takes them away.
As the sun sets, I prepare my gear. Soon I'll be heading out for a night dive. The corals
spawn under the cover of darkness.
Well, lets go see what's happening on the reef!
I head down the steps of the dock at Captain Don's Habitat. Cameraman Tim and I are diving
from the dock because the reef is only a few hundred feet off shore. We can do as many
dives as we need.
Down on the reef, I start hunting for signs that the coral might be ready to spawn. It's
pretty dark! I can only see as far as my flashlight beam.
I am looking at each coral head closely. If a coral colony is getting ready to spawn,
the polyps will be swollen with the eggs they are going to release. These don't look ready.
Movement catches my eye. A Spiny lobster is walking down the reef slope, so I take a few
minutes to watch. The spiny lobster has no big claws like the lobsters in New England.
Instead, its long antennae are covered in sharp spines for protection.
Nearby, an octopus is on the prowl, hunting for dinner. I follow along with my bright
video lights, but it doesn't take long for the octopus to decide that I'm not helping
its chances of finding a meal. It gives me the slip with a squirt of ink
as it jets away into a hole.
After three hours underwater with no sign of imminent coral spawning, Tim and I decide
to call it a night. We're tired.
Well, that was a long night...but no spawning tonight, so we'll try again tomorrow.
The next day I spend a little time touring around the island to see the sights.
First, a stop at lake Gotomeer to see the flamingos for which Bonaire is famous. Their
pink color comes from the shrimp they eat.
Next, I swing down to the incredible Cargill Salt Works to see the huge piles of salt created
by drying out seawater in vast shallow pools.
And of course to downtown Kralandijk for a few gifts at a colorful gift shop!
But then it's time to head back to the dive shop to prepare for the night dives.
Tim and I examine the predicted coral spawning times published by the Bonaire National Park.
Okay, tonight on the 29th, it is predicted to be the peak spawn, okay, so you'll notice
we have almost all of the species.
If we can't nail it tonight we'll never nail it.
No, tomorrow night the star corals and the brain corals should still be spawning. In
fact tomorrow night is the peak for the brain corals.
After dark, I suit up again for another long night.
Well, tonight's supposed to be the peak spawn. I'm hoping for a great show! Let's
check it out!
As I swim out to the reef, I'm joined by a school of gigantic tarpon. These big silvery
fish are as long as a bicycle, and have learned to use divers' lights to find smaller fish
to eat. They follow Tim and I around all night.
On any other night I would film these magnificent fish for the entire dive, but tonight I have
work to do. This is my fourth night observing the coral and my last chance to capture the
coral spawn.
I examine a coral head and I can see swollen polyps filled with big blobs that look like
eggs. They are actually called gamete bundles. I get ready with my camera and wait. The big
moment is definitely coming soon!
There! The colony has released its bundles! Since most corals are hermaphroditic, the
bundles contain both eggs and sperm. They float up into the water and separate. This
allows eggs and sperm from different coral colonies to mix together and cross-fertilize
in the water column.
They all release at the same time in order to overwhelm predators that come in to feed
on this nutritious food source.
Soon the water is filled with coral spawn! Not all corals are hermaphroditic though.
Some are gonochoric, meaning that they have separate male and female colonies.
The male colonies are easy to spot. When they release their sperm, it looks like they are
smoldering.
I train my camera on a big colony of Greater Star Coral and wait. In spite of my camera's
lights, it spawns, releasing clouds of sperm into the water.
While I'm waiting for this coral to spawn, a Tarpon passes by, checking out what I'm up to.
Once all of these eggs are fertilized, they will drift in the current for a while and
eventually settle down. If they are not eaten, and if they don't settle into water that
is too deep, or land on sand where they can't anchor themselves, they might land on a nice
hard surface and take hold.
A new coral colony will start growing.
After several hours observing the coral spawning, it's time to head to shore with our mission
accomplished!
What an amazing spectacle! Millions and millions of coral polyps all releasing their eggs at
the same time synchronized to the phase of the moon. Just an astonishing thing to see
and it just goes to show you, patience pays off because our perseverance over several
nights finally resulted in nature giving us an incredible show!
As I exit the water and head for a hot shower, I am thrilled to have witnessed one of nature's
secret spectacles. It was worth all those long nights of diving. But now, I'm ready
for bed!
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