The magical forest realm hiding at the bottom of the ocean - Luka Seamus Wright and Salomé Buglass

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>> In [music] the mid-20th century, the first scuba technology allowed deep-sea divers in the Mediterranean to reach previously impossible [music] depths.

And after descending into the mesophotic zone, an ocean region spanning 30 to 150 m, these aquanauts [music] made a remarkable discovery.

Up to 90 m below the surface, where sometimes only 0.1% of surface sunlight can reach, they found a forest of huge kelps, over twice the size of a giraffe.

Today, kelps are known to be the largest marine plants, and there had already been talk of such giants being pulled up from enormous depths in the late 19th century.

But following the Mediterranean discovery, fishermen, naval officers, and scientists began dredging up more massive [music] mesophotic kelps in the Philippine Sea and off the coasts of Brazil, Australia, and North America.

There were even claims of plants this large being brought up from as deep as 150 m. That's deeper than the Great Pyramid [music] of Giza is tall.

These forests should be impossible. Like any other plant, kelps require light to grow. Yet these [music] specimens grow as and often even larger than their shallow counterparts. [music] All with less light than they should require just to stay alive.

Then again, the mesophotic is the border between two worlds. One where life depends on the energy provided by sunlight, and another where life has learned to live in darkness.

So, how have these large, light-dependent organisms >> [music] >> adapted to thrive at such depths?

Researchers are still investigating the answer to this question, but they do have theories. Mesophotic kelps [music] photosynthesize more efficiently than their shallow counterparts, and some have suggested this might be due to having very large surface area relative to biomass, [music]

which allows deep kelps to maximize light harvesting and minimize respiration. By taking these adaptations into account, existing research still suggests that deep kelp forests don't photosynthesize enough to sustain [music] their growth and respiration, even at peak sunlight.