Tuesday, January 19, 2010

A Shining Light

Here at Communicate Science, there is nothing we like better than a night at the movies. So, stuffed to the metaphorical gills with popcorn and ice cream, I recently settled down in front of James Cameron's epic Avatar.

It's a good film (it should be since it cost a reported $300 million to make and another $150 to market) but I know you didn't come here for a film review. One of the startling images of the film is the use of special effects to create bioluminescent plant and animal life on the alien planet Pandora (I think, strictly speaking, it's a moon, but that's not important).

As the cast of characters move through the lush forest, the plant life is glowing around them. As they brush against leaves and fronds, the plants glow stronger as if influenced by the contact.

Whereas bioluminescence (that's the ability of living organisms to generate light) isn't as common or spectacular as illustrated in the film, it is evident in nature.It's estimated that up to 90% of deep sea creatures exhibit some form of bioluminescence.

During the (all too brief) Summer we had in 2009, I was lucky enough to take a night-time kayaking trip in the waters surrounding Castletownshend in West Cork. The whole aim of the trip was to look for bioluminescent algae which are at their brightest during late summer. As we paddled through the water and the night got darker, I was amazed to catch flecks of silver spilling from the paddle and lapping at the side of the boat. In places, these flecks became almost like a thick soup of silver sparks. It was as if a child had emptied a jar of glitter into the water, except on a massive scale.

Once we ceased moving, the algae too switched off, and we returned to darkness. But, by trailing your hand through the water again, I could set off a beautiful cascade of stars to rise to the surface of the black water.

You can try this out for yourself by taking a trip with Atlantic Kayaking. So what were the algae up to? There are three basic reasons for organisms to produce their own light: to locate food, to attract a mate or to defend itself against attack.

Unfortunately, no plant or animal produces its own light on land. So, James Cameron was certainly in the land of make believe there. However, it's reported that he was influenced by marine life that bioluminesce when designing his forest scenes.

Anglerfish are an example of deep water fish which utilise bioluminescence to attract food. At the bottom of deep, dark oceans, the ugly looking creature waves about a brightly lit lure at the end of an extended 'fishing rod' attached to the front of its head.

Once the preyfish has spotted this tasty bait (often disguised as a small fish itself) it moves closer to investigate. This is generally the last thing it does, as out of the darkness, the anglerfish's mouth opens and the prey is gobbled up in an instant.

In fact, the anglerfish is a tad unusual because it doesn't make its own light. It actually has some light producing bacteria inside the lure to do the job for it.

Back on land, scientists have now identified almost 70 species of fungi that are bioluminescent. Quite why they glow seems to be a bit of a mystery. In some cases, just the cap of a mushroom glows, suggesting that it may have something to do with the dispersal of spores. Alternatively, some scientists suggest that the glowing may just be a byproduct of normal metabolic function of the fungi and serve no purpose. I'm inclined to be suspicious of this theory - these things do usually have some sort of evolutionary advantage.

In West Cork, and in many other parts of the world, the bioluminescent single-celled algae which create such wonderful displays are called dinoflagellates. The light show in this species has been described as a sort of 'burglar alarm' designed to light up the water around a potential threat (or kayak). This is a shout for help.

The dinoflagellates are working on the theory that the best chance of avoiding getting eaten themselves is to attract something bigger to eat their enemy. Hence the big light show.

What's happening at the cellular level is that a chemical known as a luciferin is converted to oxyluciferin by the enzyme luciferase. This basic reaction involves the release of energy in the form of light.

As we've seen, at the organism level, this phenomenon can be used for a variety of purposes. The result is often quiet beautiful. Almost as spectacular as the movies.


Anonymous February 7, 2011 at 8:08 AM  

there are actually a number, although small, of bioluminescent land animals. fireflies and glowworms are probably the two most commonly known examples.

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