Bioluminescent Organisms, Japan Photograph by Paul A. Zahl The transparent shells of tiny Cypridina hilgendorfii, found in the coastal waters and sands of Japan, hold a creature that emits a luminous blue substance when disturbed. During World War II, the Japanese harvested these creatures for soldiers to use when reading maps and messages at night. (Photo shot on assignment for “Nature’s Night Lights—Probing the Secrets of Bioluminescence,” July 1971, National Geographic magazine)
Bloody Bay wall in the Cayman Islands
Credit: Jim Hellemn, portraitofacoralreef.com
Wall of color
Pictured is the Cayman Islands’ Bloody Bay Wall, a species-rich, 1,000-foot-tall wall of coral that is home to many bioluminescent and biofluorescent animals. To take this amazing photograph, photographers in scuba gear flooded the reef in violet light and captured the corals’ conversion of the light into red and green.
Glowing is a common trick in nature. Bioluminescence, the ability to give off light through a simple chemical reaction, is so useful that it has evolved independently at least 50 different times, and can be found among such diverse lifeforms as mushrooms, fireflies and terrifying deep sea creatures. Whether to ward off predators, attract prey, rid cells of oxygen, or simply cope with living in the perpetual darkness of the deep ocean, bioluminescence is one of life’s most ingenious tools.
These purple, green-rimmed creatures live off the Pacific Coast of North America. Called crystal jellies, they dazzle the deep sea with two distinct kinds of glowing. First, they’re bioluminescent, producing purplish-blue light through a chemical reaction between calcium and the protein aequorian. This light in turn triggers fluorescence around the jelly’s rim: A molecule called green fluorescent protein (GFP) absorbs the purple-blue light and transforms it into green. Since scientists discovered what makes the crystal jelly glow, aequorian and GFP have become important tools in research. For example, they can be injected into other creatures and used to visualize processes inside the body
The Hawaiian Bobtail Squid uses bioluminescence in a unique way to avoid predators.
The squid harbours a population of Vivio Fischeri -a luminescent bacteria- in glands underneath its body. These bacteria, like many others, are able to communicate with one another through Quorum Sensing. Quorum Sensing involves the secretion of molecules called autoinducers into the extracellular environment. The bacteria then use specialised receptors to detect the concentration of autoinducers in their surroundings, which allows them to estimate the local population density of their own species or other bacteria-because other individuals in the area have also been secreting autoinducers.
What Quorom Sensing allows bacteria to do is to regulate gene activity on a community level. Once a certain population is reached, all the individuals in the colony know about it, and this information (the concentration of autoinducer) triggers the transcription of genes that were previously inactive. Viruses for example, only begin attacking the body when they know that there are enough of them around to actually have an effect on the host. Similarly, bioluminescence is only turned on when there is a threshold amount of bacteria in the glands of the squid.
Incredibly, the squid has managed to sync the bacterial bio-luminescence with its Circadian rhythm, expelling just the right amount of bacteria during the day (it would actually be harmful to keep them in for long periods), so that by night time, they’ve multiplied to exactly the right number to activate bio-luminescence via quorum sensing. Depending on the level of moonlight or starlight, the squid is then able to use this bio-luminescence to create the illusion that it does not create a shadow- allowing it to avoid predators.
And we thought humans were innovative.
