I saw the most amazingly beautiful sight last week.
We spent the Fourth of July weekend in New Jersey visiting family. My brother-in-law took us all out on his boat to see the fireworks over Barnegat Bay.
The weather was perfect, the water was calm (i.e. no one got sea sick) and we all had a wonderful time. We picked our spot early and watched the sunset as the kids played.
The fireworks display was great. Not only could we see the main show, but there were at least 3 other visible fireworks displays along the coast surrounding our spot.
But for my eyes, the real show didn’t start until we turned the boat around and were heading for home. I was looking out off the back of the boat as we motored along and I began to see hundreds of beautiful glowing orbs being churned up by the boat. They flashed their own fireworks as they traveled along. I immediately thought of fluorescent jellyfish – but I was only half right.
Comb jellies. I spent a while researching which jellyfish that produce light could be found off the coast of NJ. I learned many things, including the fact that the stinging jellyfish known as Lion’s mane jellyfish is invading NJ coastal waters.
But they don’t glow.
Then I came across this: “You cannot go diving in New Jersey waters without seeing Comb Jellies…..At night they may phosphoresce – watch the boat wake as agitated Comb Jellies flash in the dark like depth charges.” And I realized that I probably saw comb jellies.
Comb jellies are not true jellyfish; they have a phylum of their own called Ctenophora. They do not sting. They can survive in many different temperatures of water and are found from Cape Cod to the Carolina’s along the North American coast.
They were named for their “combs” which are actually groups of cilia that they use for swimming. They are the largest animals that use cilia for locomotion. They can be as large as 1.5 meters (almost 5 feet tall!)
Although they look similar to jellyfish, comb jellies are not closely related to them. Comb jellies have been highlighted in scientific journals lately as genome sequencing has revealed that they have a nervous system like no other animal.
Bioluminescence. It’s no wonder I was fascinated by the underwater light show. It is the marine equivalent of one of my favorite summer time insects: fireflies.
Both glow due to bioluminescence.
Bioluminescence is the ability of a plant or animal to produce light (usually green or blue) through a chemical reaction. Two proteins that are usually kept apart are joined. This reaction releases energy in the form of light. Kind of like a glow stick that only glows once you crack the inner chamber allowing the two liquids to mix.
Bioluminescence is more common in the marine world. Comb jellies, many jellyfish, dinoflagellates and marine bacteria can produce their own light. Fireflies are one of the few terrestrial dwellers with bioluminescence.
Bioluminescence is not fluorescence. I mistakenly thought I was seeing fluorescent jellyfish behind our boat. This was because I was familiar with green fluorescent protein (GFP) through using it in the lab and I knew it was isolated from jellyfish. But I was wrong.
Bioluminescence and fluorescence are very similar and can be used by the same animals. No wonder I was confused!
Bioluminescence is a chemical reaction between two proteins that produces light. As mentioned above, comb jellies and other organisms produce light through bioluminescence.
Fluorescence occurs when a pigment absorbs light from an outside source (like sunlight). The absorbed light excites electrons in the pigments. As the electrons return to their original state they give off light. Jellyfish off the northwest coast of America became famous when GFP was isolated from them. GFP has become an invaluable tool in the lab and has also been incorporated into many other animals.
Why do comb jellies make light? Fireflies make light to communicate with one another. Male and female flies signal to one another in an annual summer mating ritual.
Scientists are not quite sure why comb jellies produce light. They don’t sense light, so it is not used for communication. Their (our) best guess is that bioluminescence is used as a defense tactic. A bright flash of light might startle a predator or attract an even larger predator to help fend off an attacker.
The light I saw seemed to be produced in response to the water being churned up.
Lucky me that they had this startle response for my own personal fireworks display!