– Plankton glowing in Cairns, Australia
They spill like stardust over the sides of the container. Little flickers of light, electrical sparks responding to the swirling movement of our hands shaking the bucket as we try and get them to bioluminesce…
The “they” in question are plankton, the tiny plants and animals at the mercy of the ocean currents. I am at Shoals Marine Lab on Appledore Island, part of the Isles of Shoals – a group of islands partly in New Hampshire, partly in Maine. I am taking a marine botany course and we’re out underneath dark skies taking a plankton tow. We toss the net behind the boat, drag it through the summer-cold saline water, and bring it back onto the deck. We later take water samples back to the laboratory and find most of our biological light is being produced by diatoms. Diatoms are part of the tiny planktonic marine plants; they have beautiful, delicate silicon shells arranged in various symmetrical configurations.
Another vivid memory: a night dive at the Shoals, my first. It’s easy to be scared; we are out of our element and enveloped in an icy darkness with only a narrow flashlight beam to interrupt the visual silence. At some point during the experience, we turn of the flashlights and as our eyes acclimate to the blackness, the faintest glimmers are present. We wave our gloved hands and sparks fly around our covered fingertips – even at its seemingly blackest, the ocean has a shine…
There are many different types of creatures that cast a natural glow, both on land and at sea (although this is mostly a marine happening). The phenomenon is called bioluminescence and translates literally to “living light”. An enzyme-mediated chemical reaction is generally responsible for its production. There are several different light-producing chemicals that have been isolated in bioluminescent organisms an are usually all referred to by a catch-all term, “luciferins.” In larger organisms these chemicals can be released in mucuses, inks, or concentrated in special light organs known as “chromatophores.” It’s also been discovered that some organisms concentrate luminescent bacteria in specialized organs – forming a symbiotic relationship where the bacteria corner the market on light-making.
The organisms that cast their own glow are diverse. Natural light is produced by fungi, bacteria, plankton, molluscs, fish, insects, and others. So why waste the energy? Why bother being a beacon in the darkness?
- Communication: Some living things use light to send vibrant messages, something like a visual morse code. Fireflies use light to find their special someones. Different species will use different patterns of flashes to find one another, so they’re not wasting their energies on blind dates with incompatible mates.
- To escape predators: The concept here is to blind or distract ( “Look, a diversion!”) things that potentially want to eat you. This seems to be the case with the newly discovered deep sea “green-bomber” worms. Some species of squid will eject clouds of bright ink when startled. Also, it’s possible smaller creatures will try to lure bigger predators to snack on whatever’s currently threatening them.
- To attract prey:We all know it’s easy to get distracted by shiny objects… This is the way anglerfish get their man (or dinner as it were) by dangling a glowing lure. Predators may spy on potential nom noms as well. Some fish are equipped with what amounts to sneak-a-scopes. Red light is often not a color really deep sea fishes can see. Red light is more easily absorbed and less visible in deeper waters than other wavelengths of light falling in the blue-violet part of the spectrum, and as such, many organisms are not adapted to see or detect it. Sneakier fish take use of this and produce red-light lamps they can use to detect prey without alerting the food source to their presence.
- Camouflage – alot of marine creatures employ something called countershading where the top of the organism is darker (when you or in this case, a predator, looks down at it with darker ocean water for background, it appears to blends in) and the bottom of the organisms is pale (to blend in with the incoming light coming from above). A similar effect can be achieved with the production of your own light – it can help you blend in with the light coming from above as a predator stares up at you. This strategy is thought to be used by at least a couple species of squid.
Of course we’re still discovering new variations on the bioluminscence model and developing new ideas about why organisms are putting on light shows…
The following video is from David Attenborough’s Blue Planet Series, and gives a glimpse about bioluminescence in the deep sea. Very little light reaches the murky depths but organisms create light where there is none:
One of my favorite pages on the subject:
University of California at Santa Barbara: The Bioluminescence Web Page – I really enjoy the last question on the Q&A page