Light-emitting creatures crowding Lake Pontchartrain

They’re gooey, slimy, all over Lake Pontchartrain, and they glow in the dark, but they’re harmless, said biology professor at the University of New Orleans Michael Poirrier.

You may have noticed that comb jellies, more specifically Ctenophores called Mnemiopsis Macradyi, are crowding the banks of the lake on both the north and south shores.

Don’t worry, it’s normal, Poirrier said. The tiny creatures are prevalent this time of year and will likely hang around through the winter.

Although most refer to the clear, gummy blobs as jellyfish, they’re actually not true jellyfish, Poirrier said, and are in an entirely different phylum, Cnidaria, than the Ctenophores.

Besides using cilia for locomotion, there’s something else that makes the harmless, clear invertebrates peculiar.

“They emit light. It’s a chemical reaction, and they do it deliberately, but nobody knows the exact reason behind it,” Poirrier said. Bioluminescence is the emission of light by a living organism thanks to chemical reactions that convert chemical energy to light energy.

Just like fireflies and several other organisms, the comb jellies can also make their own light. You can even provoke them to do it, Poirrier said, by poking the creatures at night. Or you could do like Poirrier’s students and gather a few in a glass jar then shake it in a dark room.

After nearly 40 years of teaching and studying biology, Poirrier said the little blobs are mostly harmless and very abundant in the Gulf of Mexico and local estuaries.

They become abundant in the lake this time every year, he said, but he admitted this year’s prevalence of the Ctenophores exceeds recent years.

The abundance can have an impact on oyster and other shellfish populations because the organisms feed on the larval offspring of shellfish and other creatures, but Poirrier said that’s not a problem because there aren’t many oysters that live in Lake Pontchartrain.

The tiny creatures are more helpful than harmful because they play a vital role in filtering the water, Poirrier said.