A study of the entire Hawaiian Archipelago, published in Peer on October 4, 2016, reveals that Hawaii has some of the most extensive deep water reefs in the world. A multi-faceted team of geologists, botanists and biologists completed the investigation of the deep water coral of Hawaii’s ‘twilight zone’ with findings that have important implications for the protection and management of coral reefs worldwide.
“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. Plus see our recent and related story on Richard Pyle, a pioneer in developing re-breather technology and the discoveries that this technology has allowed Richard to make in the Twilight Zone. See: Richard Pyle Explores Mysterious, Deep Coral Reefs
Update: Celebrating The Year of the Reef
During 2018 we are celebrating The International Year of The Reef. Over the next few months we will increase the frequency of our articles on the world’s coral reef ecosystems. We will include current news on the health of reefs and the worldwide efforts to maintain and restore them. In addition, we will republish a variety of our past, but still very pertinent and helpful articles on coral reefs. Our hope is that this effort will focus more attention on these very important issues.
Too Deep for Conventional Exploration
The goal of the 20-year study was to explore this deep coral reef habitat, technically referred to as ‘mesophotic coral ecosystems’, that until now have been barely explored. The lag time in getting to know these reefs has been due to their depth. Found at 100 to 500 feet, they are too deep to be explored by conventional scuba gear, and yet too shallow for most submersible-based explorations.
This new frontier for coral science required new approaches: The research involved the use of multibeam bathymetry mapping, submersibles, remotely operated vehicles, towed and remotely operated cameras, environmental data recorders, and advanced mixed-gas closed-circuit rebreather diving to study these difficult-to-reach environments.
The use of mixed gas rebreathers allowed the team to try out a new research approach, combining divers and submersibles together on coordinated dives. Two research submersibles descended alongside divers, acting as lighting and support vehicles, freeing up the divers to do the hands-on science.
“Free-swimming divers and submersibles don’t often work side-by-side on scientific research projects,” said Pyle. “Submersibles can go much deeper and stay much longer, but divers can perform more complex tasks to conduct experiments and collect specimens. Combining both together on the same dives allowed us to achieve tasks that could not have been performed by either technology alone.”
The new diving co-op led to some amazing discoveries. The study reveals dramatic areas of reef building corals, along with extensive algae meadows, that all require the sun to survive – and yet they were found to be thriving at the darker depths of 165-300 feet (50-90 meters).
The Largest Uninterrupted Coral System ever found
In a channel off Maui, the researchers found the largest uninterrupted coral system ever recorded – measuring more than 3 square miles – and an astonishing 100% coral cover in places.
Researchers found the coral ecosystem to be a deep water refuge for biodiversity. On a shallow Hawaiian reef, 17% of the fish are unique to Hawaii. But researchers discovered 50% endemic Hawaiian fish on some of the deep water reefs. In the Northwestern Hawaiian Islands, surveys revealed 100% of the fish species unique to the region — the highest level of endemism ever recorded in any marine ecosystem.
A Deep Reef Refuge
One theory that they are exploring is something called the “deep reef refuge” hypothesis. “If shallow coral reefs are more vulnerable to threats from, say, runoff or overfishing or whatever, then down deep these reefs could potentially serve as refuges for those species,” Pyle said.
Corals face many threats but the findings of this research will help to ensure that future activities in the region, such as cable laying, dredging dump sites, and deep sewer outfalls, do not irreparably damage these reefs.
Fish swim in a mesophotic coral ecosystem about 230 feet deep in the in Auau Channel off Maui. Coral reefs in Hawaii’s oceanic twilight zone, the deep area of ocean where light still penetrates and photosynthesis occurs, are abundant and home to a wide variety of regionally unique fish species.
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