Why Are Scientists Exploring Bioluminescence in Deep-Sea Benthic Communities?
A key purpose of NOAA Ocean Exploration Initiative is to investigate the more than 95 percent of Earth's underwater world that until now has remained virtually unknown and unseen. Such exploration may reveal clues to the origin of life on Earth, cures for human diseases, answers on how to achieve sustainable use of resources, links to our maritime history, and information to protect endangered species.
Deep ocean environments are almost completely dark; yet light is still important in these environments. Many marine species are able to produce "living light" through a process known as bioluminescence, but very little is known about specific ways that deep-sea organisms use this ability. Part of the problem is that these organisms are difficult to observe: turning on bright lights can cause mobile animals to move away, and may permanently blind light-sensitive sight organs. In addition, transparent and camouflaged organisms may be virtually invisible even with strong lights, and many types of bioluminescence can't be seen under ordinary visible light. Overcoming these obstacles is a primary objective of the Bioluminescence 2009: Living Light on the Deep Sea Floor Expedition.
Like the 2004 and 2005 Ocean Exploration Deep Scope Expeditions Bioluminescence 2009 will use advanced optical techniques to observe animals under extremely dim light, focussing on the deep-sea benthos (organisms that live on the bottom). Very little is known about bioluminescence among the benthos, because traditional benthic collecting techniques (trawls, dredges, grabs) usually damage or destroy the organisms they collect. The new techniques used by the Bioluminescence 2009 expedition are expected to reveal organisms and behaviors that have never been seen before, and allow scientists to study animals whose vision is based on processes that are very different from human vision.
These techniques are based on a number of basic concepts related to the production of light by chemical reactions, a process known as chemiluminescence. When these reactions occur in living organisms, the process is called bioluminescence. A familiar example is the bioluminescence of fireflies; another is "foxfire," which is caused by bioluminescence in fungi growing on wood. Bioluminescence is relatively rare in terrestrial ecosystems, but is much more common in marine organisms, including bacteria, algae, cnidarians, annelids, crustaceans, and fishes.
A primary goal of the Bioluminescence 2009 expedition is to explore bioluminescence in the deep-sea benthos, about which very little is known. To achieve this goal, the expedition will pursue three objectives:
- Quantify deep-sea benthic fauna in unexplored areas;
- Discover fundamental new information about the bioluminescence potential of benthic organisms; and
- Discover fundamental new knowledge about the visual systems of benthic organisms and their relationship to bioluminescence.
These objectives involve laboratory as well as underwater activities including:
- Visual surveys of the deep benthic fauna off Rose Atoll (American Samoa);
- In situ observations of bioluminescence using videography, still photography, and long-term in situ observations;
- Collection of live specimens from deep benthic communities;
- Shipboard electroretinograms to determine spectral sensitivity and how well animals can track flashing or glowing prey; and
- Laboratory studies of bioluminescence in live specimens including kinetics and flash patterns, emission spectra, and identification of new bioluminescent photoproteins.
Key technological components of the Bioluminescence 2009 expedition are:
Johnson Sea-Link Submersible (JSL)
This is a highly maneuverable submersible owned and operated by Harbor Branch Oceanographic Institution. JSL can dive to a depth of 3,000 ft with a maximum speed of one knot. The submersible has two separate pressure hulls and can carry four people. The front chamber contains the sub's controls and is enclosed by a 5-ft-diameter sphere made of five-in thick, clear acrylic providing a panoramic view for the pilot and one observer. The second chamber in the stern houses another crewmember and a second observer. For more information, visit: http://oceanexplorer.noaa.gov/technology/subs/sealink/sealink.html.
Scientists will take advantage of several recently developed cameras that provide good video and still images in very low light. The video camera actually intensifies an image before recording it. A Nikon D700 SLR has a large and extremely sensitive sensor that is capable of an ISO rating of 25,600 (ordinary photographic film has a maximum ISO rating of about 400). For more information, see the essay, "Seeing in the Dark: Imaging and Vision at Low Light Levels."
Eye-in-the-Sea Camera System
This system is designed specifically to record bioluminescence using far red illumination in combination with a highly sensitive video camera. Far red light is invisible to most deep-sea dwellers that are adapted to see primarily blue light. The Eye-in-the-Sea (EITS) system can be programmed to record video at regular intervals, or to begin recording when it detects a bioluminescent flash. In the latter mode, the camera records three seconds of video with the lights off (to record luminescence) then turns the lights on to record the source of the flash. The EITS will also make use of an electronic lure that mimics the luminescent displays of jellyfish that may attract other animals. For more information on EITS, see the essay, "ORCA's Eye in the Sea."
Light-tight, Insulated BioBoxes
These are constructed of 5/8" black Plexiglas and are carried in the front collecting basket of the Johnson Sea-Link submersible. Lids on the boxes have o-rings to make a light-tight and water-tight seal when the lids are closed. Pressure relief valves release excess pressure from the boxes as they are brought to the surface. Onboard ship, the boxes can be opened under dim red light to avoid damaging sensitive photoreceptors of the collected animals.
More About Bioluminescence and Light in the Sea
Bioluminescence is a form of chemiluminescence that occurs in living organisms. The fundamental chemiluminescent reaction occurs when an electron in a chemical molecule receives sufficient energy from an external source to drive the electron into a higher-energy orbital. This is typically an unstable condition, and when the electron returns to the original lower-energy state, energy is emitted from the molecule as a photon. Lightning is an example of gas-phase chemiluminescence: an electrical discharge in the atmosphere drives electrons in gas molecules (such as nitrogen and oxygen) to higher-energy orbitals. When the electrons return to their original lower-energy orbitals, energy is released in the form of visible light. The production of light in bioluminescent organisms results from the conversion of chemical energy to light energy. The energy for bioluminescent reactions is typically provided by an exothermic chemical reaction.
Bioluminescence typically requires at least three components: a light-emitting organic molecule known as a luciferin; a source of oxygen (may be O2, but could also be hydrogen peroxide or a similar compound); and a protein catalyst known as a luciferase. In some organisms, these three components are bound together in a complex called a photoprotein (note that luciferin and luciferase are general categories that include many different chemical compounds). Light production may be triggered by the presence of ions (often calcium) or other chemicals. Some bioluminescent systems also contain a fluorescent protein that absorbs the light energy produced by the photoprotein, and re-emits this energy as light at a longer wavelength. The fact that many different chemical systems have been found in marine organisms suggests that bioluminescence may have evolved many times in the sea among different taxonomic groups. Despite these differences, almost all marine bioluminescence is green to blue in color. These colors travel farther through seawater than warmer colors. In fact, most marine organisms are sensitive only to blue light. One interesting exception is a fish known as the black loosejaw, which can see a variety of colors including red. The loosejaw has a red light-emitting organ beneath its eyes, and is able to use this light to locate prey animals that cannot see red.
Fluorescence and phosphorescence are distinctly different from chemiluminescence. These light-producing processes occur when electrons in a molecule are driven to a higher-energy orbital by the absorption of light energy (instead of chemical energy). Atoms of a fluorescent material typically re-emit the absorbed radiation only as long as the atoms are being irradiated (as in a fluorescent lamp). Phosphorescent materials, on the other hand, continue to emit light for a much longer time after the incident radiation is removed (glowing hands on watches and clocks are familiar examples). Both fluorescence and phosphorescence may occur in living organisms.
Triboluminescence is another light-producing process that takes place when physical stress is applied to certain crystals. The mechanical energy from stressing the crystals provides energy that raises electrons in the crystals' molecules to a higher-energy orbital. When the electrons return to a lower-energy state, light energy is emitted from the molecules.
For More Information
Director, Education Programs
NOAA Office of Ocean Exploration and Research