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With its caustic red waters, Lake Natron doesn’t seem like the ideal place to call home. But some creatures have evolved amazing adaptations that help them survive and thrive in this alkaline lake.

Hosted by: Hank Green

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[♪ INTRO].

Tanzania’s Lake Natron isn’t exactly a pleasant place for a swim. The water is alkaline -- sometimes very alkaline.

Depending on the conditions, its pH can be higher than 10 -- that’s a thousand times more basic than pure water. Also, it is heated by volcanic geysers. The lake’s temperature has been known to hit sixty (60) degrees Celsius.

Any animal corpses unfortunate enough to land in the water end up mummified in a coat of minerals, and touching it is seriously painful for humans. Because of that, it’s hard to imagine that anything can live in this lake. And yet, Lake Natron is full of life.

First, the lake has a distinctive, bright red color, and it gets that from a flourishing community of algae. The lake is home to a genus of brilliant red algae called Arthrospira, which loves salty, alkaline water. But these algae are not alone.

They’re the basis for the lake’s very own ecosystem. Lake Natron, and other alkaline lakes across the region, are home to a genus of fish called Alcolapia, which have evolved unique adaptations to withstand the toxic environment they call home. For example, alkaline lakes are full of ammonia, which is toxic to many forms of life.

Land animals can usually process ammonia by converting it to urea, which is less toxic, but this process takes up a lot of energy. And some saltwater fish have similar adaptations. The problem is, when it comes to freshwater fish, it doesn’t take a lot of ammonia to be toxic-- just half a milligram in a liter of water can start to cause issues.

So Alcolapia have evolved an enzyme that lets them convert ammonia to urea without using too much energy. And that allows them to survive in waters that have been shown to kill other similar species of fish within an hour. Alcolapia have also evolved a higher internal pH compared to most fishes.

That means they don’t need to spend as much energy protecting their internal pH from changing because of the environment they live in. But as you may guess, there’s a trade-off here. These fish are adapted to live in alkaline lakes, and only alkaline lakes.

These fish have adapted to live in an incredibly specialized ecological niche -- a.k.a. their role in the greater ecosystem. Because they live in a place that’s so difficult for other organisms to tolerate, they can thrive without competition from other fish. But that also means that these fish can’t survive anywhere but in Lake Natron and places like it.

Lake Natron is also the breeding grounds of the Lesser Flamingo. Despite their name, there’s nothing inferior about these birds. Like Alcolapia, Lesser Flamingos are specially adapted to take advantage of everything Lake Natron has to offer.

These flamingos have tough skin on their legs to prevent burns from the caustic water. The high temperatures don’t seem to bother them, either -- they can submerge their heads in water that's so hot, it’s almost boiling. How’s that for a tacky lawn ornament?

They have even been observed drinking boiling water from geysers with little to no ill effect, although they prefer water at reasonable temperatures when they can find it. How they manage this is not clear. In a 2006 study, scientists found an unusual structure in the flamingo’s head.

And while they couldn’t determine exactly what it did, they did have some hypotheses, including that it could act as a heat exchanger of some kind. However, they found it more likely that the structure supports the bird’s head as part of its peculiar upside-down style of feeding. Flamingos also prefer their water fresh -- but when it’s not available, the lesser flamingo can adapt and overcome.

They can drink the salty, alkaline water of Lake Natron because of salt glands in their heads, which filter out the excess minerals through their nasal cavity and pass clean water to the rest of their body. Just like Alcolapia, when they’re in Lake Natron, the flamingos’ favorite thing to eat is Arthrospira. And as you might have heard, the brilliant pigments from the algae get passed to the birds’ feathers -- giving our favorite lawn decorations their pink color.

These incredible adaptations mean that flamingos rule the roost at Lake Natron, and in all the other alkaline lakes that make up Africa’s Great Rift Valley. But also like Alcolapia, flamingos have evolved to take advantage of a specialized environment, and that means that their habitat needs to stay stable in order to keep the species healthy. Flamingos depend on these alkaline lakes to breed.

They can’t outcompete other birds anywhere else. Unfortunately, soda ash mining, which extracts sodium carbonate from alkaline lakes like Lake Natron, is encroaching on their breeding grounds. Which means a balance must be struck between human activities and the needs of the bizarre, unique creatures that have adapted to live in alkaline lakes.

Because really, where would we be without flamingos? And where would we at SciShow be without our patrons? Up to our knees in an alkaline lake?

Not literally, but kinda metaphorically! If you’re interested in being one of the people that helps us make these videos from week to week, check out patreon.com/scishow. [♪ OUTRO].