The results indicate that light organ patterns on shrimp bodies were the best predictor of eye size. Image: UNCW

Tiny, shiny shrimp that live in the darkest depths of the oceans shed light on how life works in one of the last frontiers, the deep sea.

Research examining the eye size of more than 16 species of planktonic, nearly transparent shrimp called sergestide shrimp reveals how deep-sea animals have adapted to survive in low light conditions.

“We don’t know much about the deep sea because it’s incredibly difficult to study,” said Lorian Schweikert, assistant professor of biology and marine biology at the University of North Carolina at Wilmington. “A really good place to start is to look at vision, light and sight and that’s because, from what we understand, sight and light sensing are critical to survival on the high seas. “

Schweikert was part of a three-week research expedition funded by the National Oceanic and Atmospheric Administration’s Office of Ocean Exploration and Research in June 2019, which allowed groups of researchers to focus on their particular areas of research. offshore study in the Gulf of Mexico. Coincidentally, this was the same expedition where one of these research groups captured a giant squid on video, a sighting that made national news.

Schweikert’s team, which included marine biologists from the University of Texas and Florida International University, was there to study the eye size patterns of sergestide shrimp shot at different depths off the coast of Louisiana.

Deep-sea animals have developed the ability to glow and they use bioluminescent signals to communicate with each other.

This means that their vision is essential to their survival. This is how they find food and each other in the depths.

“That’s really why we were looking at vision models,” Schweikert said.

The research team targeted sergestide shrimp because they swim in large numbers in the water column of the world’s oceans.

They are found in a variety of deep-sea habitats – on the seafloor, in deep open and more shallow areas – making them particularly ideal to study when comparing survival patterns in the deep-sea environment.

Sergestide shrimp participate in a nocturnal phenomenon called the Daily Vertical Migration, the largest mass animal migration on Earth, when creatures of the deep leave the safety of the cold, darkest depths of the ocean to avoid predators and get closer. from the surface to feed. under better lighting conditions.

“These shrimp, like all the animals out there, differ in how much they do this migration behavior, how far they migrate each night,” Schweikert explained.

Researchers have used giant trawl container nets, which seal when animals are brought to the surface to keep them in a light-tight environment, to pull shrimp at depths ranging from 200 meters, about 660 feet, the night at between 1,000 meters, or about 3,300 feet and 2,000 meters during the day.

The captured shrimp were taken to a wet lab aboard the research vessel and released into tanks where they lit up like a constellation, Schweikert said.

In total, the research team examined more than 450 shrimp.

“We looked at the vision patterns of these shrimp and compared them to different aspects of their life, different aspects of ecology, because we wanted to know what it was like about life in the deep sea that drives the importance vision,” she said.

They compared the size of the eyes of shrimp caught at different depths of the ocean and compared their migration through the water column.

The research focused on sergestide shrimp shot at various depths off the coast of Louisiana.  Photo: UNCW
The research focused on sergestide shrimp shot at various depths off the coast of Louisiana. Photo: UNCW

“We found that above all other aspects of light that we compared, the light organ patterns on their bodies were the best predictor of their eye condition,” Schweikert said. “In other words, it told us that the light signals they can send to each other are, by far, the most important aspect of their lives in determining their visual mobility.”

Shrimp with larger organs that put out more bioluminescence have smaller eyes.

This proves, Schweikert said, that species with smaller, and therefore potentially weaker, organs had to evolve larger eyes to detect subtle glimmers of light from a distance.

“The size of the light organs was, by far, the best predictor of how the eyes would differ in these animals,” she said. “But, we saw weaker relationships for depth and for migration range.”

The researchers found that, overall, species that lived at greater depths – around 1,000 meters – had larger eyes.

Their discoveries now allow biologists to understand, because the eyes of these crustaceans correspond to the luminosity emitted by their organs, they use their bioluminescence to communicate with each other.

Yet this is just a glimpse into the mysterious world of the deep sea, the tip of the iceberg.

“We know more about the surface of the moon than about the topography of the seabed,” Schweikert said.

Next, the researchers will study how deep-sea creatures produce bioluminescence and how they communicate using light from their bodies.

Schweikert said continued research will ultimately help people better manage plans for how humans exploit deep sea resources, including fish, gas and oil, and rare minerals.

“These have an impact on the environment that we don’t fully understand,” she said.