Deep-sea Expedition Documents Coral Diversity

A sea star and sea fan photographed during the deep-sea expedition.

In the pitch black of the ocean’s depths, the only light comes from the bioluminescence of strange deep sea creatures and from the large strobes on the outside of our small yellow submarine. It is cramped inside the steel spheres of the sub, and pretty chilly as the surrounding waters at this depth are barely 50° Fahrenheit (10° Celsius). Claustrophobics are not advised to take up deep-sea diving!

As part of a deep-sea expedition led by NOAA’s Center for Coastal Environmental Health and Biomolecular Research in collaboration with Conservation International, Harte Research Institute at Texas A&M, Roatan Institute of Deepsea Exploration and the Smithsonian Institution, we are exploring deep waters in the southern part of the Mesoamerican Reef off the Honduran Island of Roatan. Here Karl Stanley, a submarine enthusiast and pilot, operates a three-person submarine he spent 15 months building in a warehouse in Oklahoma. This submarine is the primary research platform for the Deep Corals and Associated Species and Taxonomy and Ecology (DeepCAST) Expeditions. This trip marks the second in a series of explorations that began in August 2010.

During six research dives to 2,000 feet [610 meters], we observed amazing marine life with exotic names such as siphonophores, pyrosomes, gorgonians and slitshells.

Among our discoveries, we documented:

  • The first live observation of the reef-building deep-sea coral Lophelia pertusa on the Mesoamerican Reef.
  • Record number of slitshells — rare deep-sea mollusks whose delicate shells can bring in over a thousand dollars each among collectors.
  • Large concentrations of very large, very old deep-sea gorgonian corals.
  • Octocoral diversity rivaling — and possibly exceeding — other known sites in the Gulf of Mexico.
  • Numerous species of animals that live in association with corals, including sea stars, urchins, crabs and fish. Some have a narrow habitat range and live only on one or a few coral species.

Feather stars and a squat lobster photographed on the deep-sea expedition.

The expedition is unique in that it used a land-based, low-cost submarine to observe and collect deep-sea marine life. In total we collected 18 biological specimens and DNA samples that will aid species identification and help resolve taxonomic questions, 20 hours of HD video, 1,200 still images and 10 hours of water chemistry data. This vast data set will dramatically increase our understanding of deep-sea waters around the Mesoamerican Reef, the second largest reef on the planet.

Many of the species we saw are also found elsewhere in the West Atlantic, so what we learn about natural recovery of damaged corals can help us better understand how deep-sea corals in other places may respond to human impacts, including last year’s large oil spill in the Gulf of Mexico.

The deep sea is the largest place on Earth where life occurs, yet despite its remoteness, it is not immune to human impact. Our expedition found disturbing evidence of the human toll on this sensitive marine ecosystem, including trash and discarded fishing gear. Efforts to protect the ocean are concentrated in shallow coastal waters; if we want to maintain ocean health, it is clear we need to expand conservation to deeper waters.

Sebastian Troeng is the vice president of CI’s Global Marine division.


  1. Tom says

    Hi Sebastian, first of all, life as a deep sea researcher sounds like a lot of fun. I’m jealous.

    Second, since the deep sea mollusks are rare, and their shells are valuable, is their survival compromised?

  2. Sebastian Troeng says

    Hi Tom,

    Diving deep is very exciting indeed and gives you a totally new perspective on how most of the planet looks and what life in the deep and dark is like.

    The conservation status of species can be found on the IUCN Red List ( As far as I know the conservation status of deep sea slitshells have not yet been evaluated. It shows how little we know about deep sea life. It was very encouraging to see relatively large numbers of slitshells during our dives in Honduras. Given how remote and difficult to access their habitats are, my guess is that they are not yet threatened by overexploitation.


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