You know those old movies about how some species is exposed to human-made chemicals and radiation and mutates and takes over the world? Do you remember thinking that's pretty old-fashioned? It is. It already happened in 1980.
Caulerpa taxifolia managed to lay waste to the world’s oceans by, at first, posing as a friend of humanity. It’s a tropical type of algae that builds to look like lush, bright green sea weed. It generally does very well in warm water, but dies out in the cold. That is, it died out until it was exposed to the constant chemicals and ultraviolet light of the Stuttgart Aquarium. There, in one cold-water tank, a mutant strain flourished despite the cold. Aquarium workers, who had to deal with nothing but problems from their exhibits, were happy that one aspect was so simple. The algae made fish sick, so no fish would eat it, and it only required occasional cutting back to be maintained.
Wanting to share their good fortune with other aquariums, the staff passed caulerpa taxifolia around. Having established strategic bases in many different aquariums, it finally made a break for it in Monaco. A small patch was spotted growing in the sea outside the aquarium. By the time people had realized there was a serious problem, it had been carried all over the world.
The algae can also go asexual, which means that if one piece clings to a boat, it can be carried across the ocean and establish more and more colonies. It displaces plants that local marine life can eat, and poisons any fish that take more than a little nibble.
People still don’t know what to do about this algae. Only a predator from its native tropical shore can eat it, and most predators won’t survive in colder oceans. Even in places like Hawaii, which has seas warm enough to support such a predator, general opinion is that introducing another potential invasive species isn’t a solution so much as an expansion of the problem. One group of scientists managed to kill a outbreak by putting a tarp over the patch and pumping it full of chlorine. Other than that, hope is dim. Perhaps we could expose local wildlife to chemicals and radiation until they develop the ability to eat the algae. What harm could that do?