Diver, lead author R Pyle and HURL's submersible explore deep reefs. Photo courtesy of Robert K. Whitton/UH

Diver, lead author R Pyle and HURL’s submersible explore deep reefs. Photo courtesy of Robert K. Whitton/UH

A team of 16 researchers has completed a comprehensive investigation of deep coral-reef environments — known as mesophotic coral ecosystems — throughout the Hawaiian Archipelago. A major focus of the study was to cover deep-sea environments off Kaua‘i and Maui.

The study, published in the open-access journal PeerJ, spanned more than two decades and involved a combination of submersibles, remotely operated vehicles, drop- cameras, data recorders, and advanced mixed-gas diving to study these difficult-to-reach environments, as reported by the University of Hawai‘i.

Researchers documented vast areas of 100 percent coral-cover and extensive algal communities at depths of 50-90 meters (165-300 feet) extending for tens of square kilometers, and found that the deep-reef habitats are home to many unique and distinct species not found on shallow reefs. The findings of the study have important implications for the protection and management of coral reefs in Hawai‘i and elsewhere.

Deep coral reefs in Maui are home to high endemism and coral cover. Photo courtesy of HURL

Deep coral reefs in Maui are home to high endemism and coral cover. Photo courtesy of HURL

“This is one of the largest and most comprehensive studies of its kind,” said Richard Pyle, Bishop Museum researcher and lead author of the publication. “It involved scientists in many different disciplines and from multiple federal, state, and private organizations working together with a range of different technologies across the entire Hawaiian Archipelago.”

The primary objective of the study was to characterize deep coral reef habitat, known as “mesophotic coral ecosystems” or the coral-reef “Twilight Zone.” Coral reefs at depths of 30 to 150 meters (100 t