Coming up next on Jonathan Bird's Blue World,
a look at symbiosis in the ocean!
Hi, I'm Jonathan Bird and welcome to my world!
( music ♪ )
Many creatures in the ocean
survive by forming relationships or partnerships
with other creatures. Perhaps the most famous is that
of the anemone and the anemonefish (sometimes called a clownfish).
An anemone is an invertebrate that looks
like a carpet, with stinging tentacles. It’s basically a
jellyfish that can’t swim. It stings and kills fish to eat
with these tentacles. But this fish,
the clownfish, lives in the anemone’s tentacles without injury because
its coated with a special slime that tells the anemone not to sting.
The anemone provides protection for the fish. This is a perfect
example of symbiosis. The word
symbiosis comes from the Greek, meaning “living together” but it refers
to creatures that have a relationship, not just the ones that are living together.
In the case of the clownfish and the anemone, they do live
together. This is how most people think of symbiosis.
But take the example of the cleaning station.At a cleaning station,
one kind of fish gets cleaned by another--such as this manta ray being
cleaned by a bunch of wrasses. It hovers over the reef
and the wrasses come right over to pick the parasites from its gills.
This is symbiosis, but the two animals definitely don’t live together.
And that’s not the only thing confusing about symbiotic relationships!
Although we tend to think of symbiotic relationships as being
beneficial to both parties, that’s not always the case.
Take the case of the remora. A remora is a fish with a suction cup
on its head that allows it to stick to larger animals like sharks,
dolphins and turtles. The remora survives by mooching food
scraps and a free ride from its host. They may provide some
cleaning services to their host, but for the most part, they seem to be
freeloaders. This is definitely a symbiotic relationship,
but it’s really only good for one party. If the remora were
to harm the host in some way, you would call it a parasite. If the remora
merely helps itself without harming the host, then this would be
called a commensal relationship or commensalism.
Parasites are common in the ocean,
but sometimes harder to film. Meet the Anilocra isopod,
a blood-sucking crustacean that attaches itself permanently to a reef
fish. Like a mosquito, it lives by sucking its host’s blood,
but the poor fish can never get rid of it! Now that’s
a parasite—it helps itself but harms the other animal.
A partnership that’s good for both parties
is called mutualism.
For example, take this hermit crab. She has a garden of small
anemones on her shell that she carries everywhere she goes. The anemones
give her protection from predators like octopus because their stinging
tentacles pack a punch.
But the anemones have a great life living on her shell because they gather
some of the scraps from her messy eating, and they travel around with her to the
next meal.
Since the hermit crab uses an old snail
shell for a home, she needs to find a larger shell every once in a while
as she grows. When she finds one, it’s as simple as
hopping out of the old shell and into the new one. But what to do about
the anemones? The anemones are so important to the hermit crab
that she must also move them to the new shell.
Without them, she is defenseless.Slowly, with a combination of
tapping on the anemones and peeling their edges, the hermit crab convinces them
to release their grip. Only the crab knows how to coax
the anemones into letting go. They will not submit to any other creature
pulling on them. Once the anemone lets go of the old shell,
the hermit crab deposits it on her new shell. She simply plops
it in place and holds it until the anemone grabs on.
The anemone will then crawl around on the shell and find a good spot all on its own,
while the hermit crab turns her attention to working on the next anemone.
Fifteen minutes later,
with the anemones planted on her new shell, the hermit crab has completed
her move. She leaves her old shell for the next hermit crab a bit
smaller than herself.
Another crab has a different
symbiotic strategy for survival. This decorator
crab grows living sponges, hydroids, algae, and tunicates
on its body to create camouflage. When the crab holds still,
you will never see it against the similar background.
Only when it moves does it give itself away.
In the ocean, perhaps the animals
most commonly involved in symbiotic relationships are shrimp.
Shrimp are found associated with sea cucumbers,
sea urchins, sea stars, crinoids,
nudibranchs, anemones,
coral…you name it. They are everywhere.
Why? Well, because they make great snacks.
Fish love to eat shrimp, so shrimp need to be
clever to keep from becoming lunch.
Out on the sandy sea floor of the Philippines, a fire urchin slowly
makes its way across the bottom, feeding on algae.
The urchin’s venomous spines protect it from most predators.
On top of the urchin, a pair of Coleman shrimp ride
like first class passengers. The shrimp have used their claws
to clear the spines off a little spot they call home.
This is a commensal relationship because the shrimp get protection from the urchin,
but they don’t offer anything in return to the urchin.
Neither do they harm the urchin, so they are not parasites either.
Another shrimp, another free ride. This Spanish Dancer is a large nudibranch--
a snail without a shell. It’s about the size of your hand.
On its back rides an Imperial shrimp.
The shrimp survives by eating the nudibranch’s poop.
It gets a free ride and a meal from the nudibranch, but it gives
nothing in return.
Here’s a shrimp with a little more to offer.
This shrimp lives with a Goby,
a small fish, in a burrow in the sand on the sea floor.
The shrimp works hard to keep the
place clean and tidy, constantly arranging the rocks at the entrance and
shoveling out the sand that gets inside.
Why do all this
work for the goby? The shrimp needs someone to stand guard.
While it works, the shrimp keeps one antenna
in contact with the goby while the fish keeps its eyes peeled.
If the goby moves, the shrimp retreats.
This is classic mutualistic symbiosis because both animals
get something out of their relationship.
High above the shrimp’s head is a much larger animal—
a whale shark, the size of a bus. Swimming around it
are a few fish called jacks. These fish are using the whale shark as a
body guard. They know that nothing will dare attack the
whale shark—it’s too big. So if they hang around, they are safe too.
The whale shark eats only plankton and tiny fish,
so the jacks are safe from the shark’s humongous appetite.
These are only a handful
of examples of the symbiotic relationships in the ocean.
There are thousands of different animals all working together to survive,
and its one of the things that makes the blue world so
exciting to explore.
( music ♪)