Bioluminescence in lanternsharks appears to help with reproduction
Scientia — A small team of researchers with members from Belgium, Sweden and Germany has a found what they believe is a possible explanation for bioluminescence in lanternsharks. In their paper, Julien Claes, Dan-Eric Nilsson, Jérôme Mallefet and Nicolas Straube describe field experiments they conducted watching the sharks to learn if the luminescence was tied to their behavior, genetic testing they conducted and what they found in doing so.
Lanternsharks live in the ocean off the coast of Iceland and northern Europe all the way down to South Africa, generally in deep water—water so deep that there is no light. As the researchers report, most species of the small shark have developed bioluminescence, though until now, the reason for it has remained a mystery—it does not appear to offer a means of attracting prey or warding off predators and it would seem counterproductive towards hiding from predators.
To find out, the team studied the sharks in their natural environment and also in large holding tanks—on the lookout for any behaviors that might be related to their ability to light up. They noted that males and females have light producing organs known as photophores on different parts of their bodies, and that both have the organs very near their external sex organs.
After the careful study of the sharks, the team determined that the purpose of the bioluminescence was to help with finding a mate—with light coming from different body parts it becomes much easier for the sharks to differentiate between genders in the dark. They also noted that the sharks shimmy as they swim, twisting their bodies back and forth which causes the light they emit to appear to flick on and off, which the team believes is meant to confuse predators—in some cases it might be mistaken for light matching the surroundings causing the shark to appear invisible.
Genetic testing of the sharks showed much more species diversity than was thought—they found 36 in all and suspect the bioluminescence was partly responsible, because it allows for maintaining reproductive isolation. But it also contributes to a slow reproductive rate, which the team notes, has led to them being classified as “near threatened” in northern waters.
What is a Bioluminescence lanternshark?
A Bioluminescence Lanternshark also known as the velvet belly lanternshark (or simply velvet belly, Etmopterus spinax) is a species of dogfish shark in the family Etmopteridae.
One of the most common deepwater sharks in the northeastern Atlantic Ocean, the velvet belly is found from Iceland and Norway to Gabon and South Africa at a depth of 70–2,490 m (230–8,170 ft).
A small shark generally no more than 45 cm (18 in) long, the velvet belly is so named because its black underside is abruptly distinct from the brown coloration on the rest of its body. The body of this species is fairly stout, with a moderately long snout and tail, and very small gill slits. Like other lanternsharks, the velvet belly is bioluminescent, with light-emitting photophores forming a species-specific pattern over its flanks and abdomen. These photophores are thought to function in counter-illumination, which camouflages the shark against predators. They may also play a role in social interactions.
Young velvet bellies feed mainly on krill and small bony fish, transitioning to squid and shrimp as they grow larger. There is evidence that individuals also move into deeper water as they age. This species exhibits a number of adaptations to living in the deep sea, such as specialized T-cells and liver proteins for dealing with the higher concentrations of heavy metals found there. Velvet bellies often carry a heavy parasite load. It is ovoviviparous, giving birth to litters of six to 20 young every two to three years. This species has virtually no commercial value, but large numbers are caught as bycatch in deepwater commercial fisheries. Although it has been assessed as of Least Concern by the International Union for Conservation of Nature, the heavy fishing pressure throughout its range and its slow reproductive rate are raising conservation concerns.
Species: E. spinax
Habitat of the lanternshark
The range of the velvet belly is in the eastern Atlantic, extending from Iceland and Norway to Gabon, including the Mediterranean Sea, the Azores, the Canary Islands, and Cape Verde. It has also been reported off Cape Province, South Africa. This shark mainly inhabits the outer continental and insular shelves and upper slopes over mud or clay, from close to the bottom to the middle of the water column. It is most common at a depth of 200–500 m (660–1,640 ft), though in the Rockall Trough, it is only found at a depth of 500–750 m (1,640–2,460 ft). This species has been reported from as shallow as 70 m (230 ft), and as deep as 2,490 m (8,170 ft).
Pictures of lanternsharks
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More information: The presence of lateral photophores correlates with increased speciation in deep-sea bioluminescent sharks, DOI: 10.1098/rsos.150219