In the dark depths of the South Atlantic Ocean off Argentina’s coast, a hidden wonderland thrives. This deep-sea haven is home to bustling crabs, slender sea stars, ethereal jellyfish gliding through ocean currents, elusive fish, curious octopuses, and most notably, coral.
Among these corals is the rarely seen, cold-water species Bathelia candida. Its extensive reefs provide sanctuary for entire ecosystems in the ocean’s darkness.
This newly discovered site hosts the largest Bathelia candida reef ever found, spanning approximately 0.4 square kilometers (0.15 square miles), nearly matching the size of Vatican City.
“I would say that it is one of the most vibrant and lush environments in the deep sea that I’ve ever seen,” remarked Santiago Herrera, a deep-sea biologist from Lehigh University in the US, in an interview with Mongabay.
“When we go down into the deep, we know that food becomes increasingly scarce, and so that means that life becomes increasingly scarce. So it’s a big surprise when you suddenly find large amounts of animals all together, clearly interacting in a very vibrant and dynamic ecosystem.”
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The ocean floors are notorious for their mysteries. Sunlight only reaches a limited depth, scattering and absorbing as it goes. Below this point lies perpetual darkness and cold, with crushing pressures from the water above.
In recent decades, technology has enabled scientists to explore these dark waters, revealing a surprisingly vibrant biosphere. Without photosynthesis, which most land-based food webs depend on, life in these depths relies on chemosynthesis, using chemical energy to survive.
Some undersea oases are hydrothermal vents, where volcanic activity introduces heat and chemicals into the water. Others are cold seeps, where methane and other chemicals seep from beneath the seafloor.
During their search for cold seeps, researchers aboard the Schmidt Ocean Institute’s research vessel Falkor (too) used the remotely operated vehicle SuBastian, leading to the discovery of this remarkable coral kingdom.
“We were not expecting to see this level of biodiversity in the Argentine deep sea, and are so excited to see it teeming with life,” said marine scientist MarĂa Emilia Bravo from the University of Buenos Aires and Argentina’s National Scientific and Technical Research Council (CONICET) in a statement.
“Seeing all the biodiversity, ecosystem functions, and connectivity unfolding together was incredible. We opened a window into our country’s biodiversity only to find there are so many more windows left to be opened.”
Corals in shallower waters depend on symbiotic relationships with photosynthetic algae for energy. Scientists have known about deep-sea corals for over 250 years, but they were often seen as isolated oddities. Recent discoveries show that some can form extensive reefs in deep, dark oceans, feeding on marine snow and other organic material falling from above.
These reefs become a hub for biodiversity, forming another type of deep-sea oasis.
The species observed at the Bathelia candida reef demonstrated a flourishing ecosystem. Basket stars fed on marine snow alongside the coral, while crabs, octopuses, and fish joined in the feast. The reef is situated beneath a productive fishing area in Argentina, possibly contributing to the abundant life below.
Interestingly, this reef is near an active cold seep with its own ecosystem, including a large group of chemosynthetic clams. However, the connection between cold seeps and deep-sea coral reefs remains unclear.
The expedition, covering 900 kilometers (560 miles) of ocean floor, also uncovered another oasis: a whale fall, the remains of one of the ocean’s largest creatures, providing sustenance for animals and microbes for years. This is the first deep-water whale fall recorded in Argentine waters.
Located 3,890 meters deep, the whale fall consists of bones that now shelter other organisms, and it may have been there for decades.
The expedition also captured images of the giant phantom jellyfish (Stygiomedusa gigantea), one of the largest and least observed jellyfish on Earth. These enigmatic creatures can exceed 10 meters in length but are rarely seen, with fewer than 120 recorded sightings.
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This discovery may only scratch the surface. Among the expedition’s findings were 28 species potentially new to science, gathered from various coral beds throughout the survey. These specimens are still under examination, suggesting that the mysterious world beneath the South Atlantic has many more wonders to unveil.
