Amazing Underwater Caves

The Yucatan is a strip of essentially pure limestone that separates the Caribbean from the Gulf of Mexico and it's got all the ingredients you might think you need for a rich and diverse ecosystem. The tropical sun warms the forest, delivering precious energy to each and every leaf. Oxygen escapes from the plants and trees which is breathed in by the forest animals. And where they can, each of them draws deeply from the region's hidden water supply. But there are some of the ingredients you need to grow this tropical forest that are far more important than others. You might think that this place would be awash with water and it does rain a lot and it's incredibly humid, but actually there are no surface rivers at all on the Yucatan Peninsula because the water just seeps into the porous limestone. And that's where these things come in. These are cenotes. They're caverns dissolved out of the limestone by the rain and they collect water and they play a vital role in the ecosystem. I mean the forest changes when you get around the cenote. Just listen to that. Those are frogs and you don't hear those frogs anywhere else in the forest, just around the cenotes. The cenotes are flooded caves that have been cut off from the outside world for thousands of years. Lilies, troglodytic fish, even the occasional turtle all thrive around the openings of these fresh water wells. As I head deeper into the cave, the temperature drops and the light fades. One by one, the ingredients I depend upon begin to disappear. Yet even here, far from the soil and air, strangely coloured algae still find a home in the water. There's one thing that unites every form of life in this cenote. In fact, every form of life out there in the forest. In fact, every form of life we've ever discovered anywhere on planet Earth. It's that it has to be wet.