The Lanternshark is the subject of a new study in Scientific Reports, an online journal for scientific documents and studies. Specifically, the study discusses the ‘lightsabers’ on the dorsal, or back, of the shark.
There are many species of lanternshark. Most are found in both the Atlantic and Pacific Oceans. Each species has a slightly different shape and features. All lanternsharks are of the genus Etmopterus, a diverse group of dogfish sharks. Some examples of lanternsharks include: Etmopterus bigelowi, also known as the blurred lanternshark; Etmopterus fusus, the pygmy lanternshark; and Etmopterus pusillus, the smooth lanternshark. There are over thirty species of lanternshark, each with its own individual characteristics.
The recent study was conducted by Julien M. Claes, Mason N. Dean, Dan-Eric Nilsson, Nathan S. Hart, and Jérôme Mallefet with affiliations from various prestigious organizations in Belgium, Germany, Sweden, and Australia. The study focused on the light organs, or photophores, next to the dorsal defensive spines. The sharks in this study were the small deep-sea lanternsharks of the species Etmopterus spinax.
The darkness of the deep sea at 200 to 1,000 meters in depth has necessitated the evolution of many species from the smallest bacteria to larger fish to develop an ability to produce light. This bioluminescence generally is produced by a chemical reaction. The light produced by these creatures is hypothesized to provide evasion from predators, ability to acquire food, and assistance in reproduction.
The light display originates from behind the two to four dorsal fins in arc patterns. The light shines to the sides, rather than straight up, when the fish is still. Because the fins rotate during swimming, the light can be seen intermittently from above. What is interesting is that this adaptation seems counterintuitive to safety as it makes the shark visible to predators. Apparently, rather than lure predators, the light display actually seems to warn off potential predators while the location of the light (adjacent to the dorsal spines, which are defensive). The light is brighter and may be seen by predators from several meters away. The unique pattern of light created by the fin movement likely signals to predators that the sharp spine is nearby, and after some unsuccessful attacks, the predator may have learned that this signal is one to stay away from.
As for prey, since the light is produced from the top of the lanternshark, prey will see a pattern of shadow and light, as if from the sun. Prey can only see this glow from less than 2 meters, making escape nearly impossible.
The bioluminescence may also play a role in reproduction in differing displays by male and female lanternfish. The size and brightness are part of mate selection and sexual communication.
It is very unique to find a single creature that uses light both to ward off predators and hide from prey at the same time. Add the reproduction factor, and this amazing quality becomes even more multipurpose and amazing. A shark with light sabers! Who would have imagined that?
