Thanks to the Monterey Bay Aquarium and their research and technology partner
MBARI for partnering with us on this episode of SciShow.
Their excitement for this video is salp-able!
[♪ INTRO]
You might have heard them called “jellyfish eggs”, “sea walnuts,”
or simply “balls of goo”. But the correct term is salp!
Yes, that’s the real name for this real thing, this amazing set of ocean-dwelling
animals that have long been misunderstood and underappreciated—
even though they’re a lot like us, and could help us tackle
some of the biggest scientific challenges we are facing today.
Salps might look pretty alien, at first glance.
They’re barrel-shaped zooplankton: animals that float throughout the ocean.
And they kind of look like jellyfish, minus the tentacles.
But jellies are not close relatives of salps… we are!
Jellies belong to the phylum Cnidaria —
which is the same group as corals and anemones.
But salps are tunicates, which are part of the phylum Chordata —
the one that we humans are in.
The thing that unifies all chordates is the presence of a notochord:
a flexible, rod-like structure made of a material similar to cartilage.
In vertebrates like us, this develops into a backbone.
And though adult salps are squishy little barrels without any bones at all,
larval salps do have a notochord, making these creatures
among our closest living invertebrate relatives!
That means they can teach us a lot about our ancient ancestors
and the mechanisms of evolution that have shaped our phylum for millenia.
But they’re also really important members of ocean ecosystems.
Nowadays, there are around forty-five to fifty different species of salps
scattered throughout the ocean.
There are fewer salps in the arctic, but around Antarctica,
they can sometimes outnumber krill!
They spend their lives gliding about using jet propulsion:
pulling water in through a siphon at one end and pushing it out the other end.
This process goes hand in hand with feeding:
that water passes through an internal mucous mesh
that captures whatever was suspended in it.
The mesh then acts like a conveyor belt, moving the food to the salp’s stomach.
This system allows them to consume everything from tiny bacteria
less than one micrometer across to larvae one thousand times that size.
And individual salps can filter anywhere between one and a half
to fifty-five liters of water every hour — which is even more impressive
when you consider that they’re about ten centimeters long, on average.
In fact, they’re some of the most efficient filter-feeders in the sea,
which is why some call them the “vacuum cleaners of the ocean”.
Their ability to filter extremely tiny particles out of the water
is also why they’re able to survive in the open ocean, where bacteria and tiny,
photosynthesizing phytoplankton are the most common food source.
And when food is really abundant, like during an algae bloom,
salps have a unique way of taking advantage of the sudden glut of resources.
They can reproduce asexually — making little clones over and over again
until there is a long chain of identical salps attached to the original.
Individuals of some salp species can produce up to nine hundred clones,
and chains of salps can reach fifteen meters long!
These chains often form incredible shapes like wheels and double helixes.
At some point, this chain breaks off from the original salp
and continues on its merry way, growing into a long line of fully-functioning adults
in as little as forty-eight hours.
Which, by the way, is really fast.
In fact, salps are one of the fastest-growing multicellular animals on Earth.
They can increase their body length by ten percent every hour!
That would be like you adding another head to your height in 60 minutes.
It’d be like my toddler doubling in size in less than a day. I am now terrified.
This fast growth helps salps mature quickly
and increase their population size rapidly, leading to massive swarms.
A single swarm of salps can cover up to one hundred thousand square kilometers
and contain more than five thousand salps per cubic meter.
These aren’t all clones, mind you.
Cloning is fast and allows salps to take advantage of abundant food resources,
but it leaves them vulnerable from an evolutionary standpoint.
So, our salp cousins keep their gene pool fresh by sexually reproducing as well.
All of the clones in the chain start out as females, but once they mature,
they become males. This is known as sequential hermaphroditism.
Each female clone has an egg that can get fertilized by a sperm from another chain.
The fertilized egg stays inside her until it matures,
at which point it swims off to start the cloning cycle all over again.
Even though these massive swarms of salps have been observed for centuries,
researchers didn’t think that they were very nutritious,
or that very many animals ate them.
It probably didn’t help matters that salp bodies rapidly disintegrate
in the stomachs of the creatures that eat them,
so they are hard to spot and are prone to misidentification.
But closer examination has revealed that salps are actually an incredibly important
food source for hundreds of species of marine animals.
Even more importantly, their fecal pellets provide nutrition
to creatures living thousands of meters below.
That’s because, thanks to the salps voracious appetites and non-stop feeding,
salp fecal pellets are chock full of carbon.
These extra heavy fecal pellets sink quickly, traveling almost a kilometer per day.
And because of that, they don’t have time to break down in the water column
like the light-weight fecal material of other zooplankton.
Yeah, we’re talking about the density of zooplankton poop. It’s important!
So when a bunch of salps are swarming at the surface,
the feces they produce rapidly transports carbon and other nutrients to the deep sea.
Scientists have found that between their poop
and the remains that also sink when the salps die, a single salp swarm
can sustain the seafloor community below it for up to six months.
MBARI researchers actually caught one of these food-fall frenzies on camera!
An unusually large salp bloom off the coast of central California in 2012
resulted in a carpet of dead salps and their poop on the seafloor 4 kilometers below.
And all sorts of critters stopped by to enjoy the bountiful feast.
If all of that information wasn’t enough to convince you that salps are amazing and
important, they are also a secret weapon in the fight against climate change.
As we explained in our episode about marine snow,
the carbon in a salp’s diet is essentially atmospheric carbon dioxide.
So, their fast-sinking poop helps to shuttle this carbon to the deep
where it won’t be seen again for decades or even centuries.
Now it’s unlikely that salps alone are going to be able to keep up
with the ever-increasing amounts of carbon in our atmosphere,
but they are certainly doing more than their fair share of the heavy lifting…
or, heavy pooping?
So we definitely want to make sure we keep them happy,
which includes making sure the ocean doesn’t get too warm or acidic
or full of trash for them to thrive.
And who knows? Maybe scientists can even get creative
and find ways to maximize salps’ carbon-storing abilities.
Either way, it’s clear there’s way more to these weird, alien barrels of goo than you
might think. And we should love and appreciate our gelatinous marine cousins.
Thanks again to MBARI and the Monterey Bay Aquarium
for collaborating with us on this episode of SciShow.
Follow MBARI's research and technology on their amazing YouTube channel.
And help support the Monterey Bay Aquarium’s ongoing animal care and operations
by making a gift at montereybayaquarium.org/donate.
[♪ OUTRO]