Researchers go to new depths in coral reef study
To the researchers submerged hundreds of feet below the surface in the cool depths of the ‘Au’au Channel, everything looked blue. But the second they flicked their lights on, the reefs were awash with a “rainbow of color.” Schools of vibrant fish wove through great bowls of coral nearly 6 feet high. Meadows of algae spread out across the ocean floor.
What the lights did to the reef is what researchers in a new study are doing for science — revealing the rich array of marine life in the rarely explored deep-sea coral reefs around Hawaii.
“Each time you go down, it’s still like you’re a child in a candy shop,” said Heather Spalding, co-author of the new deep coral reef study and a phycologist with the University of Hawaii at Manoa’s Department of Botany. “We still find at least one new species every dive that we do. We haven’t hit a plateau in terms of looking at where these reefs are and the types of communities (they hold).”
The study, which was released this month, focuses in large part on Maui, Kauai and Oahu. One of the most comprehensive of its kind, the study pulls together two decades’ worth of research and 16 different experts, who documented some of the most extensive reef habitats in the main and Northwestern Hawaiian Islands and discovered many new species, including a fish that they plan to name in honor of President Barack Obama.
In the past, most studies have focused on shallow-water reefs because diving beyond 100 feet requires special equipment, Spalding explained. But the deeper reefs, between 100 to 500 feet, hold as much as 80 percent of the total coral reef system. Understanding these mesophotic coral ecosystems, or the “twilight zone” reefs, is crucial for both researchers and conservationists.
“It’s often said that you can’t protect what you don’t understand,” said Richard Pyle, the study’s lead author and an associate zoologist in icthyology at Bishop Museum. “But even more fundamentally, you won’t protect what you don’t even know exists.”
The ‘Au’au Channel between Maui and Lanai is prime ground for these deep-sea coral reefs. The channel features a gently sloping bottom with clear waters, allowing light to seep in and nurture coral growth, Spalding said. It’s well protected from wind, and the waters are generally calm. Stony, platelike corals make up much of the channel’s reef.
While things like sediment runoff and algae bloom put stress on shallow reefs, deeper reefs are better protected offshore, Spalding explained. Far beneath Maui’s southwest waters, wide swaths of near-complete coral cover extend for tens of square kilometers, with big meadows of algae in between. The reefs are rife with hundreds of different species of fish, coral and limu.
“I haven’t seen any other place in the world that looks like this,” Spalding said. “Half of what we brought up was new to science or new records for Hawaii.”
Researchers collected samples across all depths. Many species changed with each new level, but scientists also noticed that some of the deeper-water fish were also found in shallower waters. Spalding said this means they could possibly help repopulate some declining species. Some of the species are so new to researchers that they have yet to be identified.
One of the “novel approaches” researchers used was the combination of submersibles and rebreather divers, Pyle explained. While scuba divers use systems that expel oxygen out into the water, rebreather divers use systems that recycle gases. The system cleans the carbon dioxide out of the exhaled gas, mixes it with different gases based on the depth and sends it back to the diver.
The submersibles have time to scout out locations for research, while divers can deal directly with the marine life. In one experiment, the sub carried down an acrylic dome that was too large for the divers, who then followed to perform carefully timed tasks.“This could not have been done using either technology alone,” Pyle said.
Researchers also found that the rate of endemism — species found nowhere else on Earth — “increases substantially on the deep reefs.” In the shallower reefs at depths of 100 feet or less, only 17 percent of the fish surveyed were Hawaiian endemics. In reefs past 230 feet of depth, more than half of the species were endemics. The number is even greater in the Northwestern Hawaiian Islands, where 100 percent of the fish at some deep reefs are found only in Hawaii.
In the Northwestern Hawaiian Islands, Pyle found a small basslet that researchers plan to name in honor of Obama, who expanded the Papahanaumokuakea Marine National Monument earlier this year.
“It’s a beautiful fish,” Spalding said. “Obama should be proud.”
The findings not only help researchers understand the biodiversity of deep-sea reefs, but can also guide decisions on management. Knowing where the reefs are can prevent them from being destroyed by undersea cable laying, dredging and future development such as wave-energy stations, Spalding said.
Researchers plan to continue documenting these reefs, answering important questions such as what influences the growth of these corals, how fast they grow and whether they’d grow back if they were crushed.
“We’re just scratching the surface,” Spalding said. “If we don’t document and we don’t know what
* Colleen Uechi can be reached at email@example.com.