Corals in the deep ocean

In the International Year of the Reef in Trinidad and Tobago, Dr Diva Amon brings us the corals of the deep. Dr Amon is a deep-sea biologist who has explored the deep ocean in Antarctica, the Atlantic, the Pacific and the Caribbean. Her research focuses on what lives in our world’s deep ocean and how we are impacting life down there. You can find out more @divaamon on Twitter and her website https://divaamon.com/

Did you know that most species of coral are actually found in waters so deep that sunlight cannot reach them? Yes, that’s right, contrary to what most of us have been taught, the majority of corals do not live in tropical waters surrounded by colourful fish and bathed in sunlight. In fact, most are found in waters deeper than 50 metres around the world, even in our frigid polar seas.

Deepwater corals include many of the same groups seen on shallow reefs, such as stony branching corals, cup corals, octocorals and black corals. There are already over 3000 species known, with many more yet to be discovered. They come in a variety of colours and shapes, from yellow, orange, red, and purple, to branching, fan-shaped, feather-shaped, and even spirals!

As the coral species in the deep sea live out of the reach of sunlight, they lack the symbiotic algae (zooxanthellae) found in shallow species that are crucial for their survival. Instead they suspension feed, using the tentacles on their polyps to catch food particles floating by in the current. Amazingly, in areas with stronger currents, deep-sea corals can be spotted all oriented in  the direction of the current in order to create a path of least resistance while also making a quick meal of anything passing by.

Iridigorgia – My favourite deep-sea coral, the striking Iridigorgia magnaspiralis, spotted in the Gulf of Mexico by the NOAA Ship Okeanos Explorer earlier this year. Image courtesy of the NOAA Office of Ocean Exploration and Research.

Deep-sea corals are also incredibly important! As shallow-water coral reefs are known to be hotspots of biodiversity, deepwater corals provide complex 3-dimensional structures for many invertebrates (snails, crabs, shrimp, amphipods, ctenophores, barnacles, brittle stars, sea stars, sea urchins, crinoids, etc.) and fishes to attach to, hide within and even feed on. Some deepwater genera, such as Lophelia and Madrepora, can even form huge calcareous reefs, stretching up to 35 metres above the seafloor, supporting levels of diversity that parallel shallow-water reefs.

Black coral – A rare image of a black coral observed in the deep waters off Trinidad and Tobago. This species was observed in 2014 by the EV Nautilus. Image courtesy of the Ocean Exploration Trust.

Deep-sea corals are extremely slow growing and many can also be very long-lived. Some species can even live to hundreds or thousands of years old. One black coral, Leiopathes glaberrima, collected from off Hawaii, is known to be one of the oldest marine organisms at a record 4265 (±44) years. That means it was alive at the same time as woolly mammoths, the Trojan War, the Crusades, the colonization of the Caribbean by Europeans, all the way up to present time. While this is incredible, these characteristics have big implications for conservation. Corals are especially vulnerable to human impacts like fishing, mining and oil and gas extraction, which are increasing in the deep ocean given our insatiable appetite for resources. Climate change and ocean acidification are also increasing threats. To compound this issue, deep-sea corals are not well-known and poorly understood.

Here in Trinidad and Tobago, we know very little about the deep-sea corals that inhabit our waters. A recent study conducted using the limited imagery collected by the EV Nautilus in 2014 identified 11 species, some of which were previously unknown in our waters. Understanding our deep-sea corals here in Trinidad and Tobago is a crucial step in managing our seas. Trinidad and Tobago must gain more information about what lives in our deep sea to ensure that we make informed decisions about how best to use it. I’m sure that with further exploration, more deep-sea coral discoveries await us, not only in Trinidad and Tobago but also regionally and globally! So while we are celebrating the International Year of the Reef worldwide this year, it’s important that we remember that there are reefs in the dark depths of the world’s oceans too!

Lophelia – Reef-building coral such as Lophelia pertusa, provide 3-D structure for many other species to live on, within and under. These were spotted at 500 metres depth in the Gulf of Mexico. Image courtesy of Lophelia II Reefs, Rigs, and Wrecks Expeditions, NOAA-OER and BOEM.

Want the chance to see some deep-sea corals? Check out the live deep-sea video stream from the NOAA Ship Okeanos Explorer every day (weather permitting) from ~8am to 4pm from 12th June to 2nd July on https://oceanexplorer.noaa.gov/livestreams/welcome.html. You can also find the live video stream on NOAA Ocean Explorer Facebook and YouTube.