Deep-sea shrimp are covered in organs that see light

Many deep-sea creatures have organs all over their bodies that emit light. Now scientists believe these same organs can actually see.

The organs, called photophores, cannot see shapes but FIU marine scientist Heather Bracken-Grissom says they are capable of detecting light. She led a research team that took a closer look at these luminous organs in deep-sea shrimp.

While the shrimp have eyes, the photophores appear to work as extraocular photoreceptors allowing these animals to detect and respond to light outside ocular tissues.

“We were looking for proteins that are known to be light sensitive, and we found them in the photophores,” said Danielle DeLeo, a co-author of the study and post-doctoral researcher in Bracken-Grissom’s lab. “For the first time in deep-sea invertebrates, we are seeing that these light-emitting organs are light-sensitive.”

Bioluminescence is the production of light by living creatures and most commonly found in the dark depths of the ocean. By mimicking natural light from above, animals can match their backgrounds and hide their appetizing silhouettes from predators below — a form of camouflage called counterillumination.

Many of these deep-sea animals participate in the largest migration on the planet, a daily vertical ascent from the deep sea to shallow water to feed. During the journey, they adjust their camouflage to both the progression of day to night and the varying degrees of light intensity throughout the water column.

It has long been known that photophores play a critical role in counterillumination as the structures that emit light. However, with new evidence that these structures can also detect light, Bracken-Grissom says scientists are now reconsidering the role photophores play in an organism's ability to counterilluminate and survive in the deep sea. The research team suggests photophore photosensitivity may provide the shrimp with sight beyond their own eyes and serve as a mechanism for fine-tuning light emissions during counterillumination.

“Our study raises the exciting possibility that light organ photosensitivity is present across diverse groups, and should be investigated in other bioluminescent animals,” Bracken-Grissom said. “Because light organs can be found within several lineages across the animal Tree of Life, results from this study have the potential to reach far beyond our model system.”

The study was co-authored by researchers from the University of Hawaii and Nova Southeastern University. The findings were published this week in Scientific Reports.