21:10 PM

Newly Named "Coral Reef Twilight Zone" Is Full of Fish Nobody Has Ever Seen

Sarah Sloat for Inverse Science


To date, humans have explored less than five percent of the ocean. That’s less surprising when you consider that 95 percent of the livable space on Earth is in the ocean, which itself takes up 70 percent of the planet’s surface. Scientists exploring one small fraction of that livable space reported on Tuesday that they’ve discovered never-before-seen species of life lurking in the depths, as well as an entirely new ocean life zone.

This new zone is newly named the “rariphotic,” and it exists between 130 to 309 meters below the surface. Smithsonian scientists identified it while exploring the reef system alongside Curaçao, a Dutch Caribbean island separated from mainland South America by a deep ocean trench. Using a manned submersible, the research team came across an entirely new world of biodiversity, which includes the 30 fish species that they describe in their study in Scientific Reports.

“About one in every five fish we’re finding in the rariphotic of the Caribbean is a new species,” explained co-author and Smithsonian marine biologist D. Ross Robertson, Ph.D., in a statement released Tuesday. Robertson and his team are associated with the Deep Reef Observation Project, an effort to explore life in understudied deep reefs and monitor the ecosystem changes there.

While the biodiversity the scientists discovered is astounding, the real focus of the new study was to identify and characterize the rariphotic zone, where these reef fish live. This strange zone exists just below a previously defined reef zone called the mesophotic, which extends from 40 to 150 meters below the surface. They scientists hypothesize that it could be a “coral reef twilight zone” — a refuge where shallow-water organisms can seek relief from warming surface waters and deteriorating coral reefs — but its exact purpose is still unclear.

“Reef ecosystems just below the mesophotic are globally under-explored, and the conventional view based on the few studies that mention them was that mesophotic ecosystems transition directly into those of the deep sea,” explained lead author and curator of fishes at the Smithsonian’s National Museum of Natural History Carole Baldwin, Ph.D., in the statement. “Our study reveals a previously unrecognized zone comprising reef vs. deep-sea fishes that links mesophotic and deep-sea ecosystems.”

Read the full article, originally published March 21, 2018, on Inverse.