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Exploring a New ‘Zone’ of Deep-Sea Coral Life Hidden in Plain Sight

A 2016 expedition near Bermuda found new species and biological communities thriving on the seabed relatively near shore. Alex Rogers, science director of the Nekton Oxford Deep Ocean Exploration Institute, says the discovery shows how little we know about marine life.

Written by Jessica Leber Published on Read time Approx. 6 minutes
Scratch the surface of the ocean, and there is often much to discover.(c) Nekton 2018

The unexplored parts of the ocean are often less remote than most people imagine. Once scientists skim beyond the shallows and move just off inhabited coasts, there’s still plenty of marine life on the planet to discover.

That was certainly the case during a 2016 mission in the northwest Atlantic Ocean, near the island of Bermuda. Scientists from more than a dozen research institutes were involved in collecting and analyzing 40,000 specimens and many hours of video as part of the Nekton Oxford Deep Ocean Exploration Institute’s XL Catlin Deep Ocean Survey. Now, they’re aiming to publish the scientific results in as many as 20 papers, including descriptions of an estimated 100 or more new species.

Alex Rogers, Nekton’s science director and a conservation biology professor at the University of Oxford, spoke with Oceans Deeply in Bermuda about some of the recently announced discoveries. This included the team’s confirmation of a new biodiversity depth “zone” of the ocean – dubbed the rariphotic, or “rare light” zone. Between 130 and 300 meters (400 and 1,000 feet) below the sea’s surface, the ocean floor harbors unique biological communities that are distinct from seabed regions just above (the mesophotic zone) and below (the bathyal zone).

Oceans Deeply: Tell us about the recent results that you’ve announced.

Alex Rogers: In 2016, we did an expedition here in Bermuda. We deployed technical divers and submersibles and looked at seabed habitats down to 300 meters in depth. We basically had transects, or survey lines, running all the way down through 15 meters down to 300 meters.

We found, first of all, confirmation that there is a new zone in the deep parts of coral reefs called, if you like, the rariphotic zone. Carole Baldwin from the Smithsonian described this zone first in March in Curacao. We found pretty much the same community between 150 to 300 meters in our case, even down to the same species. That was very exciting.

Oceans Deeply: Were you looking for it when you did these surveys?

A technical dive team deploys a seabed lab during the Bermuda survey. ((c) Nekton 2018)

Rogers: No, the data analysis kind of pulled that out when you clustered survey lines by how similar they were.

We also found lots of new species, which was lovely, particularly species of algae or seaweeds. It seems there’s a whole, almost undocumented mesophotic and rariphotic algal community that probably stretches across the Caribbean and perhaps further. People haven’t really looked at these depths much for seaweeds, and we found probably more than 40 new species.

When we looked at the feeding guilds of fish, what we found was that herbivorous fish basically stop at depths of about 60 meters, so they disappear between 60 and 90 meters. These algae seem to thrive below the depths where the grazing fish are, so it would seem there’s probably a depth refuge for these algae from grazing by fish. The nearest relatives of these algae are in Australia and New Zealand.

We also found one of the main habitats, below 150 meters, were forests of black coral and sea fans. One of those black corals was an undescribed species. These are big animals: They’re two meters or more in length. They look kind of like coiled bedsprings lining the seabed, so that was really neat. Many of the other undescribed species we’re finding essentially live on those corals or on sponges down at those depths.

Oceans Deeply: How is it that scientists didn’t know that these communities existed at this depth before?

A new coral species found during the XL Catlin Deep Ocean Survey mission to Bermuda. ((c) Nekton 2018)

Rogers: We know that black corals live to many thousands of meters, but no one had looked at Bermuda at that depth range. That habitat had been completely missed … this was a very, very poorly documented community up until now. Nobody knew it was there, nobody knew what it looked like.

Of course, Bermuda hasn’t suffered from things like bottom trawling, because all the fishing has been done either by using lines or by pot fishing or spearfishing. So these habitats are in pretty good condition, which was really nice to see.

Oceans Deeply: What does it mean to find new species of seaweed? It is a pretty common ocean plant, and yet we don’t even know the diversity there.

Rogers: You always expect to find something new, particularly in deep water, once you start looking. To find, more than 40 species – that’s a whole community that’s undescribed, and that really is surprising.

Oceans Deeply: What are you doing next?

One of a number of new algae species that have been identified from the samples. ((c) Nekton 2018)

Rogers: We are finishing working up all the Bermuda data, so we have several major papers on their way out. We did really push to get the scientific results out quickly. We had our first paper out within 12 months of the expedition finishing, and those were on the deepest records of [invasive] lionfish, which were found here in Bermuda, in the Caribbean.

We are planning for the next expedition. In January, fingers crossed, I’ll be in the Antarctic with a South African ship, the Agulhas II, on a mission funded by Ocean Infinity, a company that up to now have done a lot of work on marine archeology. So we’ll have three AUVs which we’re going to try and send under the Larsen C ice shelf to look at what lives under there.

Oceans Deeply: Another mission attempted to do that recently, right?

Rogers: Yeah, and they got stuck.

Oceans Deeply: So you might get there first.

Rogers: We’ve got our chance. But we might get stuck as well. We don’t know.

We’re also going to look for the Endurance while we’re there, Shackleton’s ship – which was crushed by the ice and sank in the Weddell Sea. It’ll be really exciting if we find that, just in terms of exploration.

Somewhere between February and April, I’ll be in the Seychelles to do a very similar mission to what was done here in Bermuda. We will be looking at habitats between 200 to 3,000 meters.

Oceans Deeply: To go back to the Bermuda work, is it just that this kind of biodiversity in these depth zones isn’t explored much at all around the world?

Tanacetipathes tanacetum, a black coral species, at 150 meters in depth. ((c) Nekton 2018)

Rogers: That’s exactly why. We also know the peak in seabed biodiversity at mid-slope depths, at depths between 1,000 and 3,000 meters. It also happens to be the zone where you see increasing human impacts. So that’s why we’re really focused on these depth zones. We’re very interested in the mesophotic and rariphotic zones because of their potentially important role in coral reef resilience.

In the Indian Ocean, there’s almost zero work being done on mesophotic coral reef ecosystems. It’s the least explored area in the world in terms of mesophotic coral reefs. We’re really excited, first of all, about the potential to establish whether those mesophotic ecosystems exist in the Indian Ocean. We’re pretty confident they do, and then [we want] to understand what biodiversity they hold, and their potential role as reef refuges, in terms of [increasing] resilience in the shallow water.

Oceans Deeply: I know corals in the Indian Ocean have suffered a lot.

Rogers: We’re working in the Chagos Archipelago at the moment, and there we’ve seen over the space of three or four years a decline in coral cover from 70 to 80 percent in places, down to 10 percent. That’s through these recent mass bleaching events. However, in some localities there, we’ve sent cameras down to 60 or 70 meters, and there’s nearly 100 percent coral cover.

Oceans Deeply: Under the areas that had bleached?

Rogers: Yes, so that’s mesophotic depths. That suggests that these mesophotic reefs are sheltered from the effects of ocean warming.

Oceans Deeply: Aside from publishing the results of the Bermuda mission, what else will you try to do with this data?

Rogers: One of the things we developed from all of our video data is a tool to help managers monitor bycatch – essentially a photographic guide to organisms that might be caught as bycatch.

We’re also going to be making policy recommendations to Bermuda. The whole idea of Nekton was really to gather ocean data to accelerate governance, talking about the results to policymakers and really informing them as to what those results mean.

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