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 millennia.

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].