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Click below to go to the Cruise Logs - (photo credit: Lophelia Coral - Open-File Report 2008-1148 & OCS Study MMS 2008-015)

DISCOVRE 2009



Cruise Log: 12/02/2009    



Mysterious Lights in the Deep

Cheryl Lewis Ames

Deep-sea corals can also produce bioluminescence, as shown in this image of Gerarida sp taken in the Bahamas. Photo credit: Sönke Johnsen, Duke University. - click to enlarge
Deep-sea corals can also produce bioluminescence, as shown in this image of Gerarida sp taken in the Bahamas. Photo credit: Sönke Johnsen, Duke University. - click to enlarge
Trailing our boat at nighttime is a brilliant blue wake…a phenomenon known as bioluminescence. Perhaps you have seen something similar while strolling on a beach at night, as a faint green glow at the surface of the water. This eerie glow results from a chemical reaction within animals producing photons, or light particles. We sometimes observe it as flashes of blue, green or red light from the porthole of our submersible as it ascends to the surface.

Bioluminescence is common in marine organisms. The creatures responsible for these aquatic "light shows" vary as much in size as they do in taxonomic classification. These animals range from tiny dinoflagellates found close to the sea surface, to deep-sea fishes, crustaceans and squids of various sizes that undergo vertical migration from the ocean's twilight zone to the sea surface at night.

What roles does bioluminescence play in the deep sea?
You would think that for an organism trying to be discreet, making light isn't exactly a great idea. However, bioluminescence is an important form of communication in the deep ocean where little or no light penetrates. Researchers have been studying how bioluminescence affects the biology and ecology of deep-sea animals over the past several decades. The following examples including defense, predation, and mate location are the most common uses of bioluminescence in the ocean.

Defense
Ironically, camouflage may be the most common use of bioluminescence in the ocean. For example, euphausid shrimps that undergo nightly vertical migrations up and down through the water column have a series of light producing organs, or photophores. Those photophores are located on the part of the organisms facing downwards - their "bellies"- known to biologists as their "ventral surface." Light emitted from these organs helps disguise these euphausids by preventing upward-looking predators from distinguishing the silhouette of their potential prey against the relatively bright moon light on the surface.

Certain squid can change the color of their luminescent photophores to match moonlight and sunlight depending on their position in the water column.

This parapandulus shrimp spews a luminescent  mucous to deter predators. Photo credit: Sönke Johnsen, Duke University. - click to enlarge
This parapandulus shrimp spews a luminescent mucous to deter predators. Photo credit: Sönke Johnsen, Duke University. - click to enlarge
Some species of oceanic squid release a cloud of "ink" composed of mucus and luminescent bacteria that seems to serve as a shield for their escape in the dark waters where black ink would be useless for defense. Various shrimps also employ a glowing cloud to escape predators in the depths of the twilight zone.

Predation
Bioluminescent blue “lures”, used to attract prey, are common in deep-sea fish and squid. Recent studies have revealed that the siphonophore jellyfish Erenna actually uses red “lures” to catch prey. Another jellyfish found in the deep sea, Aequorea, has a bell margin that glows green as a result of a luminescent molecule coupled with a green fluorescent protein (known as GFP). Although the function of bioluminescence is not well-understood in this jellyfish, the researchers unraveling the mysteries of the compound responsible for the glow earned the Nobel Prize in Chemistry.

Mate Location
Another obvious role of bioluminescence is helping animals find a mate. The elaborate mating signals generated by their bioluminescent light organ of “seed shrimp” or ostrocods have been studied extensively.

Whether glowing, flashing or setting up luminescent “smoke-shields”, these deep-sea organisms continue to peak our curiosity. Much remains to be learned about the function and roles of bioluminescence in the deep sea. Information and specimens we collect on this expedition will certainly add to our growing knowledge base.

For more on bioluminescence visit: The Bioluminescence Web Page



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