Photon hunting in the twilight zone

August 06, 2014

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.

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.

These results reveal an unexpected diversity of photon capture strategies and indicate that like other deep-sea animals, deep-sea sharks possess a number of adaptations to cope with the twilight zone.
-end-
In your coverage please use this URL to provide access to the freely available paper: http://dx.plos.org/10.1371/journal.pone.0104213

Citation: Claes JM, Partridge JC, Hart NS, Garza-Gisholt E, Ho H-C, et al. (2014) Photon Hunting in the Twilight Zone: Visual Features of Mesopelagic Bioluminescent Sharks. PLoS ONE 9(8): e104213. doi:10.1371/journal.pone.0104213

Funding: Financial support (specimen collection, open access fee) was provided by the Fonds National de la Recherche Scientifique (FNRS, Belgium) through a Fonds de la Recherche Fondamentale Collective grant (FRFC - 2.4525.12) and travel grants to JMC (postdoctoral researcher at FNRS) and JM (research associate at FNRS). Part of the research (data collection and analysis) was supported by an Australian Research Council grant (DP110103294) to SPC, NSH and others, the Western Australian State Government to SPC, and the National Museum of Marine Biology and Aquarium to HCH. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests: The authors have declared that no competing interests exist.

PLOS

Related Sharks Articles from Brightsurf:

Ancient bony fish forces rethink of how sharks evolved
Sharks' non-bony skeletons were thought to be the template before bony internal skeletons evolved, but a new fossil discovery suggests otherwise.

Reef sharks in decline
Though many people find them intimidating, menacing or just plain scary, sharks are vital to the health of the world's oceans.

Sharks almost gone from many reefs
A massive global study of the world's reefs has found sharks are 'functionally extinct' on nearly one in five of the reefs surveyed.

Plastics found in sea-bed sharks
Microplastics have been found in the guts of sharks that live near the seabed off the UK coast.

Life in the shallows becomes a trap for baby sharks
Baby reef sharks tolerate living in the sometimes-extreme environments of their nurseries -- but these habitats face an uncertain future which may leave newborn sharks 'trapped'.

Caribbean sharks in need of large marine protected areas
Governments must provide larger spatial protections in the Greater Caribbean for threatened, highly migratory species such as sharks, is the call from a diverse group of marine scientists including Stony Brook University School of Marine and Atmospheric Sciences (SoMAS) PhD Candidate, Oliver Shipley.

Recreational fishers catching more sharks and rays
Recreational fishers are increasingly targeting sharks and rays, a situation that is causing concern among researchers.

Walking sharks discovered in the tropics
Four new species of tropical sharks that use their fins to walk are causing a stir in waters off northern Australia and New Guinea.

Lonesome no more: White sharks hang with buddies
White sharks form communities, researchers have revealed. Although normally solitary predators, white sharks (Carcharodon carcharias) gather in large numbers at certain times of year in order to feast on baby seals.

The private lives of sharks
White sharks are top predators in the marine environment, but unlike their terrestrial counterparts, very little is known about their predatory activity underwater, with current knowledge limited to surface predation events.

Read More: Sharks News and Sharks Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.