The hidden diversity of diatoms in the Canary Islands

by Paula Mendoza-Casanova |

If you grab a world map and look closely at the west coast of North Africa, just across from the sunny Sahara Desert, you’ll find an archipelago floating in the Atlantic Ocean. Welcome to the Canary Islands (Spain)! Famously known for sunny beaches, tourists getting terrible sunburns, and delicious wrinkled potatoes, these volcanic islands hide a much deeper, much smaller secret. While tourists stare at the giant volcanoes, science has spent decades ignoring the microscopic residents that actually run the aquatic ecosystems. Yes, we are talking about regions criminally understudied by science when it comes to the tiny diatoms.

From an evolutionary perspective, these volcanic islands are basically nature’s version of Big Brother TV show. They rise aggressively out of the ocean floor, completely empty, shouting, “Who wants to colonize me?!” This makes them absolutely essential laboratories for studying how populations move, adapt, and occasionally start genetic drama. For a long time, scientists used these islands to study larger animals and plants. But what about the single-celled micro-algae living inside gorgeous, intricate silicate glass houses? How do they handle the landscape of islands that are literally born from fire?

To solve this mystery, we packed our bags and went on a microscopic safari across three very distinct Canarian islands: La Gomera, La Palma, and Tenerife. But we didn’t just look through a standard microscope and guess their names based on their looks. For the first time in this region, we combined morphology  with metabarcoding.

Map that shows where the Canary Islands are located.

And guess what? The diatoms did not disappoint. Our double-method investigation revealed three completely distinct diatom communities, each perfectly tailored to the predominant environmental but not exclusive conditions of each island.

Pictures of some of the sampling points. These ravines are very special ecosystems and are locally known as “Barrancos”. 

In La Gomera, mystical laurel forests that look straight out of The Lord of the Rings, the diatoms have a very chill, stable, and moisture-loving community. They enjoy the constant, gentle mists brought by the trade winds, probably sipping micro-cocktails in the humid moss. In La Palma, the geologically rebellious island (which loves a good volcanic eruption every now and then), the diatoms live in the steep streams surronded by endemic pine forests. Finally, we have Tenerife—the big one with the massive volcano towering over everything. Here, the landscape changes drastically from the super-humid, green north to the bone-dry, desert-like south. 

Images of some diatoms: A, Epithemia sorex; B, Epithemia turgida; C, Humidophila contenta; D, Humidophila perpusilla; and E, Nitzschia macaronesica. A and B are indicator species for the Tenerife group, C and D for La Gomera, and E for La Palma.

So, what have we learnt from playing at being detectives with the Canarian microalgae? Firstly, that you should never underestimate a living organism simply because it is smaller than a speck of dust. Diatoms play an essential role in aquatic ecosystems, and potential endemic species to the Macaronesian region, such as Nitzschia macaronesica, have been discovered. Secondly, that volcanic islands shape life on every scale, however small. This has been confirmed by the discovery of several distinct diatom communities that correspond to the predominant—though not exclusive—conditions of each island. 

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