February 22, 2013
Shark Carries “Lightsaber” Spikes For Defense
Lee Rannals for redOrbit.com — Your Universe Online
It's been decades since the first Star Wars movies came out, but the mark they left is still relevant in the world, even finding a little fandom in the deep waters of the ocean.
Researchers reported in the journal Nature about how they discovered light organs adjacent to the dorsal defensive spines of a small deep-sea lanternshark.
The shark species, Etmopterus spinax, or velvet belly lanternshark, lives in the mesopelagic zone of the ocean, ranging between 650- and 3,200-feet in depth.
The glow-in-the-dark shark can measure up to about a couple feet, but most are just within a little under a foot-and-a-half. Velvet belly lantersharks have mineralized spines in front of their dorsal fins, and a ventral surface covered by thousands of tiny photophores. Once these organs are stimulated by melatonin or prolactin, they produce light, providing the shark with "counterilluminating camouflage," the researchers said.
"When investigating this species' bioluminescence, we were surprised to observe glows from the frontal edges of the dorsal fins, forming conspicuous arcs immediately behind the spines," the authors said in the journal. "This dorsal luminescent display seems in direct conflict with the camouflage role of the ventral photophores."
They looked at the histology and light emission of the dorsal photophores, and determined the 3D structure and spectral transmittance of their associated spines.
"Using these structural and in vivo luminescence data, ocular measurements from local fishes and marine mammals and a recent theory for visual detection in pelagic habitats17, we then determined the detection range of the luminescence produced by the spine-associated photophores (SAPs) in the shark's environment, characterizing their in situ performance and suggesting their ecological role," they wrote.
According to the team, the functional significance of these lightsaber defense mechanisms is to try and ward off potential predators. Their lights, both around and through the spines, work as a "predators-eyes-only" beacon to deter approaching predators, but without jeopardizing potential prey. They believe the luminescence works by highlighting the spines themselves, almost like an "advertisement" for its predators that these spines "would be particularly advantageous."
"When you live in this dark place, what you try to do is to avoid being seen by other animals, because there are no places to hide," Dr Julien Claes, a shark biologist from the Catholic University of Louvain in Belgium, and the lead author of the study, told the BBC.
The deepest parts of our oceans still hold some of the biggest mysteries on our planet. However, even some of these unexplored depths will soon be explored. Virgin Oceanic is working on a submarine to explore these depths, and the company says it will be hitting up the Mariana Trench early in 2013. This part of the ocean sits 36,201 feet below the water surface, just north of Australia and east of Hawaii. It is the deepest part of the world's oceans.