Deep submersible dives clarify rarely exploited coral reefs



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Deep submersible dives clarify rarely exploited coral reefs

A researcher prepares to lower the submersible in a dive off the coast of Maui, Hawaii. Credit: Hawaii Submarine Research Laboratory

Just beyond where conventional divers can go, there is an area of ​​the ocean that is still little explored. In such deep waters – from about 100 to at least 500 feet below the surface – little or no light breaks.


Researchers must rely on sophisticated submersible vessels or diving equipment to study oceanic life in these depths, known as the mesophytic zone. These deep areas encompass the world's oceans and harbor extensive communities of coral reefs, although little is known about them because it is very difficult to get there.

A collaborative research team from the University of Washington, Charleston College, University of California at Berkeley, the University of Hawaii and other institutions explored the largest known reef in the Mesopotamian zone, located in the Hawaiian archipelago, through a series of submersible dives. There, they documented life along the coral reef, finding a surprising amount of coral living in areas where light levels are less than 1% of the surface light available.

Their findings were published on April 8 in the journal Limnology and Oceanography.

"Because mesophytic corals live near the limits of what is possible, understanding their physiology will give us clues about the extraordinary strategies that corals use to adapt to low-light environments," said author Jacqueline Padilla-Gamiño, assistant professor at UW . School of Aquatic and Fisheries Sciences.

Knowing how these coral reefs are functional is important because they appear to be biodiversity points and harbor many species found only in those locations, explained Padilla-Gamiño. In addition, almost half of all corals in the ocean have died in the last 30 years, mainly due to the temperature of the hot water that presses their bodies, causing them to discolor and eventually die. This was documented mainly in shallower reefs where more research has taken place. Scientists say more information about deeper reefs in the mesophytic zone are critical to preserving this habitat.

"Mesopotamian reefs in Hawaii are impressive in their size and abundance," said co-author Heather Spalding of the College of Charleston. "While mesophobic environments are not easily seen, they are still potentially impacted by underwater development, such as cabling and anchoring, and need to be protected for future generations. . "

Padilla-Gamiño was on board for two of the team's eight submersible dives off the coast of Maui, which ran from 2000 to 2011. Each dive was a harrowing adventure: researchers spent up to eight hours in tight quarters on the submersible that was played from the side behind a larger boat, then disconnected when the submersible reached the water.

Once in the mesophobic zone, they collected specimens using a robotic arm and captured video images and life pictures that were rarely seen by humans.

Deep submersible dives clarify rarely exploited coral reefs

A robotic arm attached to the submersible collects the corals from the mesophytic zone off the coast of Maui in Hawaii. Credit: Hawaii Submarine Research Laboratory

"It's a really unbelievable place," said Padilla-Gamiño. "What is surprising is that in theory, these corals should not be there because there is so little light. Now we are finally understanding how they work so we can live there."

By collecting coral samples and analyzing their physiology, the researchers found that different corals in the mesophytic zone use different strategies to deal with low amounts of light. For example, some species of coral change the amount of pigment at deeper depths, while other species change the type and size of symbionts, which are microscopic algae that live inside coral tissue, Padilla-Gamiño explained. These changes allow corals to acquire and maximize available light for photosynthesis and energy.

In addition, corals at deeper depths are likely to eat other organisms such as zooplankton to increase their energy intake and survive under very low levels of light. They probably do this by filtration, Padilla-Gamiño said, but more research is needed to be sure.

Deep submersible dives clarify rarely exploited coral reefs

A robotic arm attached to the submersible collects the corals from the mesophytic zone off the coast of Maui. Credit: Hawaii Submarine Research Laboratory

Researchers hope to collect more live coral samples from the mesophytic zone so they can study in the laboratory how the symbionts and corals they live in.

"The more we study this, the more information we can have about how life works. This is a remarkable system with enormous potential for discoveries," Padilla-Gamiño said. "Our studies provide the basis for exploring physiological flexibility, identifying new mechanisms for acquiring light and challenging current paradigms about the limitations of photosynthetic organisms, such as corals that live in deeper waters."


& Quot; Twilight Zone & # 39; can help preserve shallow water reefs


More information:
Jacqueline L. Padilla-Gamiño et al. Echophysiology of reef-building coral reefs in Hawaii is influenced by symbiotic-host associations, photoaclimatization, trophic plasticity, and adaptation, Limnology and Oceanography (2019) DOI: 10.1002 / lno.11164

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University of Washington

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Deep submersible dives clarify rarely exploited coral reefs (2019, June 20)
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