Luminous Life - Light Generation

© Eandephotography | Dreamstime.com

The luminous creatures and life forms we've surveyed so far all make use of a specific chemical reaction to produce light. If they don't create the reaction themselves, they have a symbiotic relationship with light-generating bacteria that are housed in a special light organ within the host animal.

But it turns out that there is another biological mechanism that generates photons, or the basic unit of light. Ultraweak photon emission is the term for the process that creates biophotons - photons created by biological systems. Scientists think that all living cells, plant and animal, do create light in the visible range of the electromagnetic spectrum. But the light is so weak, special detectors are needed to pick it up.

So while we may envy those amazing sea creatures and fireflies that flash beautiful light, we ourselves are emitting a very low level of light. You're doing it, right now, even as you read this. In humans, the fingertips, forehead and soles of the feet seem to give off the most light.

Biophoton image of a hand.

The light is thought to be created by a chemical reaction, like bioluminescence, but the reaction is tied to the DNA molecules that reside in the nuclei of our cells. The hypothesis is that DNA both stores and releases the photons to form a network of light that is used for communication and to regulate various processes within the body. Some potential applications for the science of biophotonics include non-invasive medical diagnostics, food and water quality testing and cancer research.

Our journey to explore the luminous life around us has ended with ourselves, with tiny packets of light pulsing through the very stuff of life within us. We're so much more interesting than we realize.

Luminous Life - The Glittering Sea

A bioluminescent hydromedusa.

So far, our examination of bioluminescence has focused on land dwellers - fungi, worms, various insects. As rare as the ability is here on dry ground, up to 90 percent of ocean life is capable of producing light. Against the backdrop of a black sea, life forms use self-generated light to hunt, find mates and defend themselves.

Red tide bioluminescence taken at midnight at a
Carlsbad, California beach. Image by Flickr user msauder.

And it starts at the bottom of the food chain. Some forms of plankton can create light, as in the image above. The sea appears to glow, especially when disturbed, and if conditions are right, the phenomenon can cover such a large area that it can be seen from space.

A ctenophores light display is actually diffraction
of ambient light, not bioluminescence.

Even when sea creatures are not producing their own light, they are able to make use of what dim light reaches them. Some organisms can put on quite a display by reflecting any existing light.

Blackdevil angler fish with bioluminescent lure.
Image by Edith Widder/HBOI.

As beautiful as a bioluminescent display can be, it can mask a hungry predator. The angler fish lights its lure to draw in prey. This little fishy looks like it swam straight out of a bad dream.

We can thank Edith Widder for bringing us this scary guy. For more of her images and the challenges she faces trying to capture shimmering sea creatures and photograph them, check out this link.

To go with the still images, here are 2 short videos of bioluminescence in action. The first one features a magnificent jellyfish shown in both direct light and in darkness.



This second video is of a dazzling comb jelly that almost appears to be an alien life form.



As I was thinking about how, even in the darkest depths of the ocean, the sea inhabitants were using their own light, it made me wonder why they would develop the ability in the first place. Why not develop some other sensory method to accomplish all the tasks they need to accomplish? Electrical signals, pressure changes, scent, hearing - something that didn't depend on light, which is so noticeably absent in that environment.

Not being a biologist, I can only speculate that the rhythm of the Earth's day/night cycle was a powerful influence on evolution, even when life was found only in the sea. The dichotomy was so strong that life forms internalized it so that even in the darkness, light can exist.

Luminous Life - Into the Woods

© Luxgene 2000

Softly glowing mushrooms rising from the forest floor - no wonder people in bygone times concluded that they had suddenly been transported to the realm of the faeries.

The strange bioluminescence of mushrooms and other fungi defies understanding. The usual reasons given for bioluminescence - mating, predation, defense, communication - don't seem to apply to luminous mushrooms, and no one seems to understand why they developed this ability.

© D. Hibbett

Mushrooms aren't the only light-generating organisms in the woods. Slime molds, which are no longer considered fungi but classified as protista, are capable of bioluminescence, but that's mostly the tropical varieties. It can get confusing. One of my favorite stories about a cold-light encounter comes from the magazine The Smithsonian, which ran a photo essay some years ago featuring slime molds (images similar to these). In the next issue, there was a letter from a couple who told a story about how they went to their local parks department to get free wood chip mulch, which they spread in their yard. One night not long after, they noticed that a region of the wood chips was glowing. Not sure what to do and apparently alarmed, they turned the hose on it.

They wondered whether they had sprayed away a slime mold. But those intrepid suburbanites were most likely dealing with foxfire, another type of fungi that emits light.

Bruce McAdam/Creative Commons License

Foxfire can be found on rotting wood in damp forests. The fungi will glow at temperatures as low as 34 degrees F, but the optimal temperature is 77. If you want to hunt foxfire, there are some great tips in this extension bulletin from the University of Georgia's School of Forest Resources. The tips include going out on overcast or moonless nights to spot the low-intensity green glow, and staying away from artificial lights to give your eyes time to adjust to the dark.

In the depths of the nighttime forest, mysterious lights beckon, inviting us to explore their domain. No need to grab the hose - just marvel at how the mundane by day becomes the wondrous by night.

Luminous Life - Light-Up Slime

As I've been researching bioluminescence, the ability of some organisms to produce light with virtually no heat (there's a powerful metaphor right there), I learned that there are different types of bioluminescence: intrinstic or internal, where the organism has specialized cell structures to produce its own light; bacterial, where the organism needs to partner with bacteria to generate light; and extracellular, where the organism creates luminous slime.

Yes, glowing slime. It sounds like the next big thing in toys. But a surprising number of creatures secrete bioluminescent slime, and it's not always clear why.

The image above shows bamboo coral that, if touched, will produce "astonishing" amounts of slime, but scientists don't understand its purpose. Another sea creature, the Venus fly trap anemone, was also found to be bioluminescent not that long ago, again by way of slime and again for unknown reasons.

Certain centipedes, squids, shrimp, earthworms and tube worms can produce luminous secretions. Possible uses include defense against predators, communication and mating, which is the case with the Bermuda glow worm. In the summer months, these sea-dwellers swim to the surface to mate, with the females exuding a glowing slime to attract the males. The males respond with their own flashes of blue light, seen below.

That makes sense, and it's also interesting that their mating ritual occurs 2 to 3 days after the full moon and exactly 56 minutes after sunset. There are boat tours to view the phenomenon, it's that regular.

Still, that leaves a lot of radiant slime whose purpose remains clouded. Why would worms, like the ones above, ooze light? There is no satisfactory answer; I can only accept that these supposed lowly creatures have, by their unusual capacity, caused me to rethink the sources of light that exist in the world, as I consider beautiful light transported via mucus, protecting and otherwise serving its creator.

Luminous Life - An Intro to Bioluminescence

To me, bioluminescence, the ability of some microbes, plants and animals to emit visible light, is one of the most interesting phenomena in the natural world. It's time to explore how some life forms have developed this talent, which evolved first in the blackness of the deep sea, and then among land plants and animals that glow against the backdrop of the night.

Most people are familiar with the fireflies that grace summer evenings. But the greenish glow doesn't end there. The image above shows eerie fungi found in a state park in Brazil - as if the woods in the nighttime weren't mysterious enough.

To get started, here's a video that showcases some deep sea bioluminescent creatures, as well as some octopi camoflaging themselves in amazing ways. There's more to come as we survey the luminous life around us.