Noctiluca scintillans – An algae, but not a plant!

The new Avatar movie was just released, and as if it was an advertiser, suddenly the beach in the Maldives was glowing as blue as Pandora.

“The plankton is here!” people said, and my short and simple quest, I mean long and difficult quest for a story started.

To be honest I wasn’t sure whether I’ll be writing about a plant or an animal.

We’re going back to the utmost basics of taxonomy. What are we?

Living beings are distinguished by the structure of their cells: we have prokaryotes and eukaryotes. The latter come with a cell nucleos. Prokaryotes contains two domains, and emerged before the “invention” of the nucleos. Those two domains are bacteria and archaea, some kind of not-bacteria. Arachaea are not new, they are known since 1977. So we have three domains of life, eukaryotes, bacteria, aracheae.

Humans are eukaryotes, and so are mushrooms, apes, bed bugs, trees, and sharks. Everyone who has nuclei in their cells. Believe it or not, eukaryotic life forms might have emerged from the archaea, meaning we might only have two domains of live. Viruses BTW are no living beings and thus not included here.

Within “our” domain, we have four Kingdoms: Animalia, fungi, plantae, and protista. Sounds like pizza, doesn’t it? Animalia, plants and fungi are quite self exploratory. But our glowing-in-the-dark particle is a protist. What is that?

We can say protists are neither plants, animals, fungi or bacteria. They are protists. What makes it difficult is that there are also unicellular plants and fungi. Examples for protists are diatoms, amoebas, slime molds, plasmodiums (the malaria “parasite”), and dinoflagellates. What a family! Have a look at Wikipedia to understand how far away we are from a certain classification system. You can find several opinions on how many kingdoms there are.

Noctiluca scintillans belongs to the superclass dinoflagellates. It is said to be the common cause for the “Glowing beach” in the Maldives. But more than ever, I have have done no further identification so no guarantee. It could as well be any other species!

First thing you read on Wikipedia is that N. scintillans are considered algae! Aaaaahhhrg. I thought they weren’t?!

Language is confusing. A while ago Linnaeus separated life into animals and plants. And algae were of course plants. Splitting life forms into more kingdoms (1860 protista, 1938 prokaryotes, 1969 fungi were added) separated some algae from another. Some are plants, some are protista. So, our blue dot is an algae, but not a plant. Phew.

No surprise, there are more than 1,500 species of dinoflagellates, and for sure more to come. Ours, again with no guarantee on ID, was initially thought to be a jellyfish, and described as Medusa marina by Martinus Slabber in 1771. In 1810 Macartney described it as Medusa scintillans, and after some confusion Noctiluca scintillans (Macartney) Kofoid & Swezy, 1921 was established. Many people were involved here.

Unlike other algae N. scintillans is not photosynthetic. They feed on diatoms, and other plankton. More like an animal, isn’t it? Or a carnivorous plant. They grow to a size up to 1500 μm.

The obvious characteristic is the bioluminiscence. While you often see a few blue dots during a night dive, you sometimes have mass events like the one in the picture. It might be initiated by a blooming of a food source like diatoms, which humans might no notice at all. Our dinoflagellate has an either red or green center. While the green form is harmless, the red form in high numbers, called red tide, can make living for other organisms difficult.

The light emission is activated by motion, and supposedly a defense mechanism. Either the blue light confuses predators, or it attracts predators of their predators. The waves are glowing, and so are the soles of your feet when you walk along the beach. Two substances are needed for this special effect: A molecule that emits light when cracked, and an enzyme to crack it. The enzyme is luciferase, and several unrelated molecules are called luciferine. The luciferine our dinoflagellate is using is related to chlorophyll. Other organisms use different luciferines.

Translating dinoflagellates gives us “whirling whip”, what describes their microscopic swimming-arms. The chemicals causing the luminescence are called after lucifer, what means “light-bearer”. A light-bearer with a whirling whip is causing the glowing beach! And it is absolutely amazing.

A glowing beach