If you were at a restaurant,  sitting down, and, like, jellyfish was on the menu, you would  probably order literally anything else.

Like I can’t tell you what you’d definitely  do, but there’s basically nothing there. They’re 95% water.

Nothing you can sink your teeth into.. Now celery is also 95% water, but at  least it goes well with wings and ranch. You know, not just by itself.

Yet some species of sea turtles, like  the loggerhead and the leatherback, eat almost nothing but jellyfish, leaving  scientists asking how in the world they can live on something  similarly lacking in oomph. Which, like, we need to know, because  human activity is changing the way nutrients move through the  oceans, and jellyfish can teach us a surprising amount about what ends up where. [♪ INTRO] Considering jellies are made up of water  and, like… stings, it’s no wonder scientists used to be pretty convinced that jellyfish  were dead weight within their food webs. At best they were believed to contribute very  little to the ecosystem; at worst, it was thought they shunted nutrients away  from other species in the food web.

Remember that food webs are all about how nutrients move through an ecosystem. From things like carbon and  nitrogen to more minor nutrients, everything’s constantly moving in a cycle. At least, it’s best for everyone  involved if that’s the case.

So how is it that certain animals  can survive perfectly well on a diet so heavy in jellyfish sea-celery? Ok, well, jellyfish do provide some nutrients, and not all of them are from the jelly itself. Jellyfish primarily eat plankton  and other small food sources.

They catch their prey by stabbing them  with their stinging nematocyst cells in their tentacles and then  trapping them in their mucus. The leftover dissolved and digested prey  leave behind a lot of carbon in that mucus, enough to support the growth  of bacteria in the surrounding waters. What’s more, predators of jellyfish seem to know how to get the best bang for their buck.

They’ve been observed eating only the  most nutritious parts of the jellyfish, often leaving behind the  less-nutritious upper bell portion. They get up to five times more nutrients  this way, and probably a healthy dose of collagen, too - a building block for  cartilage that jellyfish are full of. Now, a potential problem arises,  though, when jellyfish bloom.

Jellyfish can explode in population  numbers when warm water conditions permit. When this happens, jellies  may over-hunt their prey, and funnel those nutrients into what’s  called a sink, preventing carbon and other nutrients from going to  other consumers in the food web. If jellyfish blooms were sequestering  nutrients and energy in the environment, it could spell disaster for all  of the organisms connected to them if nutrients weren’t available  for other members of the food web.

And with warmer oceans thought to  be driving more and more blooms, this could be yet another nasty  effect of the climate crisis. Thankfully, marine scientists are using  more sophisticated tools to observe and closely measure how you get  nutrients back out of a jellyfish. Which happens more than we used to think!

Now, untangling food webs can be pretty tricky. The first problem is that since  jellyfish are pretty much jelly, there isn’t much left behind  to find in predator stomachs. Being mostly water, jellyfish  are digested really quickly.

It takes a keen eye with a microscope  to look through recent stomach contents of predators for evidence of tentacles  and their stinging nematocysts. Stable isotope analysis is an  advanced tool that can help identify what kind of food  sources make up an animal’s diet. Isotopes, or variants of elements  like carbon and nitrogen, appear in predictable ratios in  an animal’s tissue depending on if the animal is an herbivore  or a carnivore, for example.

This is how we know that some  supposedly herbivorous sea turtles are actually eating a whole lot of jellyfish. Species that were believed  to be completely vegetarian, including the green and black sea turtles,  have been found to opportunistically make use of jellyfish as food  when blooms provide lots of them. And we’ve found that it’s more than  just turtles who enjoy a jelly snack.

All good blooms must come to an end. When conditions return to normal,  jellies can die off en masse, providing a lot of easy food to  animals living on the deep ocean floor. Some deep-dwelling animals,  including hagfish, crabs, and lobsters will take advantage of this bounty.

Then there’s the bluefin  tuna, who hunt live jellies. This is actually a good way  to get back at jellyfish, who also like to eat tuna eggs and larvae! Speaking of babies, lobster larvae  also enjoy a jellyfish delicacy.

They even have specializations to disarm  jellyfish stings, making them safe to eat. Findings made possible by new  methodology show that even albatross and penguins have been found to prey on jellyfish  when the opportunity presents itself. They’re super easy to catch, and  quick to digest, making them, if anything, a rather nice  addition to a balanced diet.

Turns out, just because we couldn’t  figure out how at first, doesn’t mean that jellyfish aren’t actually  a valuable and integrated part of their food webs in numbers big and small. And being able to understand their  place in the ecosystem makes them an important consideration as  conservationists monitor changes in ocean temperature, fishing trends,  and marine animal population changes. Not bad for a bit of sea-celery.

Now jellyfish may be the balloons of the sea, but if you want to see the balloons of  space, we have a sticker sheet of unlikely space balloons in our merch  store at dftba.com/scishow! They are holographic and  shiny and extremely good for sticking on your water bottle or laptop. That’s only one of many fine  SciShow-themed products, and in fact, we’re looking to expand our offerings.

So hit us up with any requests  or ideas in the comments! If you want to check out the sticker  sheet, and everything else yet to come, head to the link in the description. And thank you for watching. [♪ OUTRO]