Thanks to Brilliant for supporting  this episode of SciShow.

Head to Brilliant.org/SciShow to check out their interactive Algorithm Fundamentals course! [♪ INTRO]. Life in the ocean is a little  different than it is up here.

For one thing, water holds onto heat a lot  better than air, so temperatures tend to stay the same from day to day rather  than fluctuating with the sun. But this doesn’t mean that ocean-dwelling  organisms are less susceptible to rising temperatures brought about by the climate crisis. In fact, most marine critters  are adapted to live at a very narrow temperature range, so even  a tiny change can quickly spell trouble.

And we might not have  understood just how much trouble without the help of an unassuming little snail. The threeline mud snail is a small,  spiral-shelled snail commonly found crawling around beneath the waves  on the North Atlantic seafloor. While the adults spend their  lives on the bottom of the ocean, their larvae start out life  swimming around up in the water.

These babies are so small that they are at the mercy of the waves and ocean currents. This snail species typically spawns  in the summer, when the water temperatures warm up enough to signal to  their bodies that it’s baby-making time. And the summertime ocean currents in the  North Atlantic gently tow the freshly hatched larvae out to cooler, deeper  waters found at the edge of the continental shelf, where the babies can then feed, grow and eventually settle onto the  seafloor as adult snails.

However, in a 2020 study, researchers  from Rutgers University uncovered a disturbing trend happening with  the threeline mud snail, along with potentially dozens of other bottom-dwelling  species living in the North Atlantic. They found that this little snail  was missing from the deeper, colder waters of the North Atlantic outer shelf. They expected to see increasing  populations of these creatures in the deeper waters because the  deep waters are places of refuge.

They’re cooler than the shallow waters, whose temperatures have risen  dramatically in recent years. Instead, the researchers  found higher populations of these snails in the warmer waters close to shore. Which is not good, because remember, most marine creatures are adapted to survive  at narrow temperature ranges.

And the baby mud snails are particularly fragile. They’re less likely to make it to adulthood  in warm waters than colder waters. The researchers believe that  this shift in habitat is an unexpected consequence of climate change.

But this is not something  the snail is choosing to do. See, in response to changing temperatures, some organisms choose to travel north or south toward the poles to seek refuge in cooler waters. But these snails are too small to travel that far.

Instead, the snail’s physiology makes  them easily influenced by changes in the ocean’s physics, and it’s making them  migrate in the completely wrong direction. First, their spawning behavior is  temperature dependent, so when the ocean waters warm earlier in the year, they  trigger an earlier spawning event. This means those little baby snails  are floating around in the water in the springtime instead of in the summer.

And the currents in the North Atlantic vary  throughout the year, changing directions depending on the prevailing winds, as well as the amount of water running  into the ocean from the rivers on land. Which leads to the second issue: the baby snails are being pushed  around by springtime ocean currents, which are different from summertime currents. The spring currents funnel  these babies towards the shore instead of away from it, as they do in the summer.

And the waters closer to  shore are shallower and warmer than the deeper edge of the shelf waters. That means fewer babies will survive to adulthood, and the survivors will spend the rest of  their lives at those higher temperatures. Which means that those adults will  spawn even earlier in the year than past generations, trapping the threeline  mud snail in a feedback loop that they cannot escape from.

This unfortunate circumstance could  spell the beginning of the end for the threeline mud snail, and  potentially several other bottom-dwelling North Atlantic species. That’s because other seafloor-dwellers,  like sea stars, clams, and worms, have similar spawning and larval  behavior to the threeline mud snail. In fact, researchers have  found that since the 1960’s, around 80% of bottom-dwelling  species have disappeared from the deep waters of North Atlantic, potentially all unwilling victims of  this wrong-way migration phenomenon.

And it may not be just a  North Atlantic occurrence. This could be happening in other  locations around the world. Through no fault or choice of  their own, bottom-dwelling species are being pushed to the limits of their  survival, thanks to the climate crisis.

But at least this is helping us to understand  the many unexpected ways the climate crisis can affect the creatures  who share the planet with us. And maybe help us understand how to help them. If you like learning more about the surprising things the world  around us has to offer, you might enjoy a course from Brilliant.

They’re overhauling some of their classic  courses to be even more interactive. Like Algorithm Fundamentals, which  requires no prior coding experience. They make it easy to learn  how to make your computer do what you want with  rearrangeable blocks of code.

If you’re interested, you can get started at brilliant.org/scishow to get 20%  off an annual Premium subscription. And checking them out helps us too, so thank you. [♪ OUTRO].