Tag Archives: photophores

Bioluminscent sharks and their photon hunting abilities

This is the eye of a velvet belly lanternshark. Credit: Dr. J. Mallefet (FNRS/UCL); CC-BY

This is the eye of a velvet belly lanternshark.
Credit: Dr. J. Mallefet (FNRS/UCL); CC-BY

The velvet belly is a bioluminscent shark, i.e., it projects some light. Here’s a description from its Wikipedia entry (Note: Links have been removed),

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. … 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.

An Aug. 6, 2014 news item on ScienceDaily highlights some recent featuring the velvet belly,

The eyes of deep-sea bioluminescent sharks have a higher rod density when compared to non-bioluminescent sharks, according to a study published August 6, 2014 in the open-access journal PLOS ONE by Julien M. Claes, postdoctoral researcher from the FNRS at Université catholique de Louvain (Belgium), and colleagues. This adaptation is one of many these sharks use to produce and perceive bioluminescent light in order to communicate, find prey, and camouflage themselves against predators.

An Aug. 6, 2014 news item on phys.org elucidates further,

The mesopelagic twilight zone, or about 200-1000 meters deep in the sea, is a vast, dim habitat, where, with increasing depth, sunlight is progressively replaced by point-like bioluminescent emissions. To better understand strategies used by bioluminescent predators inhabiting this region that help optimize photon capture, the authors of this study analyzed the eye shape, structure, and retinal cell mapping in the visual systems of five deep-sea bioluminescent sharks, including four Lanternsharks (Etmopteridae) and one kitefin shark (Dalatiidae).

The researchers found that the sharks’ eyes contained a translucent area present in the upper eye orbit of the lantern sharks, which might aid in adjusting counter-illumination, or in using bioluminescence to camouflage the fish. They also found several ocular specializations, such as a gap between the lens and iris that allows extra light to the retina, which was previously unknown in sharks. Comparisons with previous data on non-bioluminescent sharks reveals that bioluminescent sharks possess higher rod densities in their eyes, which might provide them with improved temporal resolution, particularly useful for bioluminescent communication during social interactions.

“Every bioluminescent signal needs to reach a target photoreceptor to be ecologically efficient. Here, we clearly found evidence that the visual system of bioluminescent sharks has co-evolved with their light-producing capability, even though more work is needed to understand the full story,” said Dr. Claes.

Here’s a link to and a citation for the paper,

Photon Hunting in the Twilight Zone: Visual Features of Mesopelagic Bioluminescent Sharks by Julien M. Claes, Julian C. Partridge, Nathan S. Hart, Eduardo Garza-Gisholt, Hsuan-Ching Ho, Jérôme Mallefet, and Shaun P. Collin. PLOS ONE DOI: 10.1371/journal.pone.0104213 Published: August 06, 2014

This study is open access as is the journal where it appears, PLOS (Public Library of Science) ONE.