Shedding Light:

Saving Deep-Sea Coral Communities

By Marisa Ferreira

April 2021

In the darkest depths of the ocean, they take their time. Without sunlight, their community grows, some species not even discovered by humans yet. They can live for thousands of years in the deep sea. Their colors are vibrant, their patterns intricate, and their adaptations unique. Deep-sea corals have demonstrated their ability to thrive in the dark, surviving on microscopic organisms and drifting organic matter in the ocean’s deep currents, while expanding habitat diversity and contributing to the carbon cycle in the ocean. Their medicinal properties, role in enhancing deep-sea biodiversity, massive size, and their impressive old age make them yet another fascinating species in the ocean.

Though not as well known as shallow-water coral reefs, deep-sea coral communities can live worldwide from 150 to 10,000 feet below sea level, mostly in rocky environments, where sunlight is nearly non-existent. They enhance marine ecosystem diversity as they provide a habitat for other deep-sea species while simultaneously contributing to the deep-sea ecosystem at large. They host a diversity of microbes that are rich with marine compounds – drugs from the sea that could aid humans in fighting antibiotic-resistant infections, for example, as well as developing antiviral and anticancer therapies. Additionally, some species have growth rings, like trees, that store memories in the form of chemical signatures that reflect environmental conditions of the past.

However, much like their shallow-water coral relatives, deep-sea corals are increasingly vulnerable to climate change and other harmful human-caused impacts. Once damaged by bottom-trawling from fishing gear or other disturbances, recolonization and regrowth of deep-sea corals may require centuries or longer. Our actions have already proven to be consequential to these deep-sea communities.

Examining Deep-Sea Corals

A map showing the location of Sur Ridge located in Monterey Bay National Marine Sanctuary — Sur Ridge, a large rocky underwater feature located approximately 25 miles west of Point Sur, central California within Monterey Bay National Marine Sanctuary. Image: NOAA

In Monterey Bay National Marine Sanctuary, roughly 25 miles west of Point Sur, lies Sur Ridge, 2,600 to 5,200 feet below the ocean’s surface. Studies conducted at Sur Ridge since 2013 by a team of scientists from the Monterey Bay Aquarium Research Institute (MBARI) and Monterey Bay National Marine Sanctuary include detailed biological and ecological examination of deep-sea corals and how damaged corals can be restored at such depths. Recently, the team led one of the first studies involving the transplantation of live deep-sea corals.

This groundbreaking research included the propagation of fragments from different coral species by removing small branches at depth, bringing them to the surface and attaching to cemented pots, then replanting the fragments to the seafloor. All coral fragments were kept submerged at cold temperatures (41°F or 5°C) throughout the process. This study has shed light on the many challenges in restoring deep-sea corals, including the fact that the best technique for transplanting one type of coral may not apply to all other species. Deep-sea corals are greatly understudied and this research helps us understand how this approach to reconstruct damaged coral populations can work.

Andrew DeVogelaere, the sanctuary’s research coordinator and SIMoN director who is a part of the research team, affirms the unique nature of deep-sea coral examination, “We’re just now discovering their age, what eats them, how they protect themselves from predators, what environmental conditions are necessary for them to grow and thrive, and even what to properly name them.” Fortunately, MBARI has the technological capability to set up an underwater observatory in the deep sea to quantify marine snow, ocean currents, growth rates, and reproductive seasonality, all while collecting environmental DNA, seafloor mapping data, and time lapse photographs of the corals. Over the past 20 years, MBARI scientists have diligently created detailed maps for where corals are located at Sur Ridge. DeVogelaere notes, “We’d like to understand the biology of corals and their role in the ecosystem through repeated visits to a highly instrumented area. Nobody has ever done what we’re doing.”

a pink branching coral being held by the manipulator arm of a remotely operated vehicle deep in the ocean — ROV *Doc Ricketts* places a transplanted bubblegum coral, *Paragorgia arborea*, on the seafloor at Sur Ridge. Photo: MBARI © 2018

several small coral fragments resting on the seafloor in an experimental setup — Transplanted bubblegum coral, *Paragorgia arborea*, experiment on the seafloor at Sur Ridge. Photo: MBARI © 2018

Disturbed By Humankind

Bubblegum coral, Paragorgia arborea, attaches to the seafloor, growing upward and branching outward like a tree. Photo: NOAA/MBARI 2006

Many people do not realize that deep-sea corals – despite their incredible adaptability to an extreme environment, are unintentionally being harmed by human activities. For most people, these organisms are often out of sight and out of mind. Deep-sea trawling and mining, ocean pollution (e.g., marine debris and oil), and the effects of climate change and ocean acidification are all impacting deep-sea corals. As the ocean is absorbing massive amounts of anthropogenic carbon dioxide (CO2), conditions are becoming more acidic over time. These changes are being detected throughout the ocean, including in the deep sea. Just like shallow water corals, deep-sea corals have a difficult time building their calcium carbonate skeletons in more acidic ocean conditions that create a strenuous environment.

DeVogelaere recognizes that humans were already impacting deep-sea corals before they even knew they were down there. “Trawling has impacted corals throughout the globe and that’s one way we started learning about them. When we have these impacts, we remove one of these corals and it takes hundreds of years for them to grow back.” These threats to deep sea communities only emphasize the importance of environmental stewardship and how we can affect marine life beyond what our eyes can see.

Sustaining Unseen Species

Precious coral, Corallium sp., hosting basket stars, Gorgonocephalus sp., on the seafloor. Photo: NOAA/MBARI 2006

The sustainability of deep-sea corals may be enhanced not only by protecting existing communities through regulation, but also by repopulating disturbed areas using active restoration methods. Developing and testing restoration strategies like this at Sur Ridge are critical to ensuring the special places and living communities that national marine sanctuaries protect are able to thrive. NOAA and MBARI’s cutting-edge work comes with the intention to educate other scientists and resource managers around the world about proper transplanting and mitigation techniques – as demonstrated in the recent publication Guide to Translocating Coral Fragments for Deep-sea Restoration. “We hope that this work we are doing to save deep-sea corals will inspire people to care about the deep sea. We could be on the cusp,” said DeVogelaere. While a lot of mystery surrounds deep-sea corals there is one thing that certainly shines through the depths of the darkness – the corals themselves. DeVogelaere views the protection of corals under the basic understanding of respecting nature, “We have this precious planet to take care of and everything in it is valuable. We’ve been given this gift and we are stewards of corals for future generations.”

Marisa Ferreira is a science communication intern with NOAA’s Monterey Bay National Marine Sanctuary.