Sunday, December 17, 2017

More common than you think



ILLUMINATED: The bioluminescent glow of the Ortoire River, Mayaro, surrounds a bather at night. The luminescence is caused by a plankton that emits a brief flash of light when disturbed. The river has bloomed with billions of these organisms and has been putting on an amazing light show at night, which has brought thousands of people to the east coast of Trinidad. —Photo: Richard Charan

Mark Fraser

 As seen in recent weeks, scores of people from all corners of Trinidad visited Mayaro to see the Ortoire River. This river quickly becoming known as the glowing river, is the sight of a phenomenon called bioluminescence. 

Bioluminescence is light produced by a chemical reaction within a living organism and is basically a type of chemiluminescence or a chemical reaction wherein light is produced. In the case of Ortorie River, the bioluminescence was caused by a species of dinoflagellate.

Bioluminescent dinoflagellate ecosystems are rare, forming mostly in warm-water lagoons with narrow openings to the open sea. In light of this, residents have been offering boat trips upriver to view the occurrence of this natural light. However, most person visiting the Ortoire River would have encountered bioluminescence before and not even know it.  

Have you ever seen a candle fly? If you have—then you have encountered a bioluminescent organism. In fact, bioluminescence in the ocean is quite common and most species of animals ranging from sharks to bacteria include at least one bioluminescent species. So, what exactly causes bioluminescence? Within some dinoflagellate algae is an enzyme called luciferase. When luciferase interacts with oxidised luciferin it forms an compound known as oxyluciferin which glows. But what is the importance of this light? Does it have a function other than to enthuse nature lovers and inspire family road trips?

The reasons for bioluminescence are not known for all animals; however there are some animals that have very unique ways in which they use bioluminescence. The “burglar-alarm” theory is a possible explanation for how lighting up helps dinoflagellate to survive. For example, if a small fish begins to feed on the algae, they emit a flash of light. The light from the algae attracts larger fish, which are likely to be the predators of the smaller fish. In other words, the flash of light works is an alarm alerts nearby bigger animals of the presence of smaller animals. 

Other animals use bioluminescence in a process called counter illumination camouflage. Cookiecutter sharks use photophores (small light producing organs that appear as single, bright dots of light) to lure in a potential prey. Though, almost the entire body of the cookiecutter shark is covered in these photophores: these sharks have a dark band of skin forming a collar near their heads that does not light up. One possible explanation is that the absence of bioluminescence in the shark’s head is the source of the lure. It has been hypothesised that when a shark is producing light in all areas surrounding that collar,  the dark band looks like the silhouette of a small fish against the lighter surface waters higher up in the water column when viewed from below by an animal looking up at the cookiecutter. The shark slowly drifts, suspended in the water column, its bioluminescence breaking up its figure by matching the penetrating light. This action enables the cookiecutter shark to turn the tables and feed on fishes that perceive the shark to be smaller than its actually size.

Another importance of bioluminescence is to attract mates. Many of us would be familiar with this phenomenon through our interacting with candle flies as they periodically flash their abdomens to attract mates during the mating season.  Marine animals that utilise bioluminescence to attract a mate is well displayed by ostracods, or ostracodes, sometimes known as “seed” shrimp. These ostracods commonly referred to as “blue sand” or “blue tears” and give off a blue light in the dark. At extreme ocean depths, some fish species attract prey by using their light like a spotlight or in case of the angler fish, as a luminescent lure. Other animals use bioluminescence as a form of defence by release a cloud of bioluminescent fluid, similar to the way squids defend themselves with a cloud of ink or using a bright flash of light to momentarily blind predators. Some animals such as the Bobtail squids do not create light on their own, they instead form symbiotic relationships with a bioluminescent bacteria (Vibrio fischeri), which inhabit a special light organ in the squid’s mantle. The squid benefits from bioluminescence through camouflage similar to the cookiecutter shark while providing the bacteria with shelter and nutrition.

Bioluminescence occurs in many animals that live on land and at sea. We can observe bioluminescence if we look attentively at our environment. In addition to being beautiful to behold as presently in the Ortoire River, one can now appreciate that this natural light plays an important role in attracting a mate, camouflage, attracting prey and even as a warning system. So, while we can safely conclude that these animals have no real desire to awe us, we cannot help but appreciate that the luminance makes them much more than beautiful, in a word—phenomenal!

Submitted by the Institute 

of Marine Affairs