Tyler Phelps: Twilight Zone Ecosystems

By: Alan Throop & Tyler Phelps

[graphics & photos: from program or as noted, download the PDF for additional photos]

At the January General Mt, Tyler Phelps from the California Academy of Sciences gave an intriguing program on his exploration of Deep Reefs, also called  “The Twilight Zone”.  While working on his MS in Ichthyology from San Francisco State, he is part of the unique team at Cal Academy that supports their Hopes for Reefs Initiative, aimed at understanding and developing ways to protect the coral reefs of the world.

Photo 1: Twilight Zone presentation slide by Tyler Phelps.

From their website: “Nearly 75% of the world’s coral reefs are currently threatened by the combined impacts of overfishing, habitat destruction, water pollution, and climate change. Though coral reefs provide human societies with vital goods and services worth an estimated several hundred billion dollars per year, very little is known about shallow reefs’ deeper counterparts [i.e., Deep Reefs] —the species they shelter, the threats they face, or the refuge they’ve been thought to provide.” Scientist have/had hoped that these deep reefs are suffering less damage than the shallow reefs and that they might therefore – if there is sufficient species overlaps between the shallow and deep reefs – provide a place of refuge for species that are being decimated at the shallower depths. These two questions – relative damage and species overlap – are the focus of their research. At the same time, their exploration has turned up many new species.

As the figure above shows, shallow reefs above about 200’ depths are well-studied; while suffering damage, the ecosystems are at least fairly well understood. The “Very-Deep Reefs”, below say 500’ depths, have been studied in recent years, but are the deep-water (“cold-water”) corals are thought to function differently as an ecosystem (e.g., perhaps not photosynthesis-based) [https://en.wikipedia.org/wiki/Deep-water_coral] and would therefore likely not share overlapping species or serve as a refuge for shallow species.

The unique contribution of the Cal Academy team is to study Deep Reefs at depths in the range of 250’ to 500’. Tyler pointed that shallow reefs above about 200’ can be explored easily using conventional SCUBA and are fairly well studied.  The Very-Deep Reefs are studied by submersibles only and – as Tyler pointed out – are very expensive to operate.  Coral reefs in the range of 200’ – 500’ depths are still accessible to divers on SCUBA (with special training), still operate as a photosynthesis-based ecosystem,  and thus still hold/held the potential for good species overlap and refuge for shallow reef species. Prior to the Cal Academy initiative, these depths had not been extensive evaluated by scientists for species overlap or damage.

Photo 2: Exhibit at Cal Academy on their research in the Twilight Zone.

Diving to these “Twilight Zone” depths requires special skills, equipment, and great planning. Tyler discussed the basic issues and risks of both Nitrogen Narcosis and Oxygen Toxicity that drives the need from a standard air or enriched air (EAN) for certain applications.   These issues typically drive a diver to the use of Tri-Mix for deep-diving, where a 10/70 mix of 10% Oxygen, 70% Helium, and 20% Nitrogen can minimize these risks. But the cost for the mixed-gas is about $300 per dive … and there are 4 divers on each dive. This drives them to the use of rebreathers for their twilight dives, where the cost of the gas is only $30 per dive. Of course, they still have bailout tanks, scooters, lights, sample containers, etc …. Deep diving is an equipment-intensive business (like SCUBA in general, as we all know)! Tyler’s takeaway: “Teach your kids technical diving … and they’ll never have enough money to buy drugs”. There is an exhibit at Cal Academy on their research in the Twilight Zone with an example of a suited diver (photo 2) … but Tyler said that they actually carry more equipment than the exhibit shows!

These deep dives obviously require long decompression times. For only 5-20 minutes of bottom-time at their maximum depth, they required 3-6 hours of decompression. As they progress to the surface during the deco ascent, however, they can continue to do surveys and sampling on the progressively-shallower depths. In many cases, they are on walls, so that they need to be careful to maintain their depth while continuing to do science.  During these long dive times, the divers need to both eat and drink fresh water.  Photo 3 (see PDF) shows examples of them doing that.

Photo 5a: Guam reef at 30 feet.

Photo 5b: Guam reef at 350 feet.

The Deep Reef team has studied a number of sites so far, including the Philippines, Palau, Guam, Brazil, and several others (see photo 4 in PDF). Tyler showed two videos of their dives, showing the content of the deep reefs, their equipment, and survey methods as well as how they gather specimens. PHOTO 5a & 5b shows a shallow 30’ and deep 400’ reef  in Guam. In this location the shallow reefs are almost lifeless  due to human impact, while the deep reefs look more vibrant (in this particular location). But as the insert shows, even here there is human-generated debris. Also, there is a surprising good level of light in these clear-water sites at these depths.

Photo 7a: Photo by Luiz Rocha.

In their surveys, they use a technique much like Reef Check: they run a 20-meter tape and then follow the line, counting and recording species within a given distance of the line (see photo 6 in PDF). They also collect specimens to compare with those in the shallow reefs, to study the species overlap question. Tyler discussed the variety of new species that they have discovered in this new range of depths. They have discovered 12 new species so far, that have been described and published, and have 9 other pending publications (photo 7a & photo 7b in PDF)

To bring these fish safely to the surface, their team has developed what Tyler calls a “fish decompression chamber” (see photo 8 in PDF)  The fish are captured by net and then placed in the chamber.  As the divers do their ascent, at some point they seal the chamber at that depth. On the boat, they transfer them to another larger pressurized chamber that can be oxygenated; it then takes about 2 days to fully decompress to atmospheric pressure. In fact, his team has developed deco tables for fish!  As a result of their work, many of these deep-coral reef species can be exhibited in the Cal Academy aquarium. In fact, they currently have 5 undescribed species on display in the aquarium!

Their work so far has produced perhaps-unexpected results regarding the questions that they were trying to answer:  First, the deep reefs in this range are, in general, quite vibrant and preserve a lot of their own bio-diversity. However, they are being affected by both human debris and silting from human-produced runoff as well as from hurricanes.  But – second issue –  they observe very little overlap in species of the shallow and the deep reefs. This seems to indicate that the deep reefs can’t really serve as a refuge for the shallow-reef species.  However, their research shows that the unique biodiversity of these deep reefs and species need protection just as the shallow reefs do.

During Q&A, Tyler said that they plan to return to these sites about every 3 years to monitor their condition and rates of deterioration.  He said that the temperature at depth can vary widely. In Guam, the surface and 300’ temperatures are about 86o F and 82o, respectively, while in Brazil they might be 79o and 51o, respectively. So the thermal protection needs to change accordingly. He was asked if they are doing work off our west coast, and he said no, that MBARI (Monterey Bay Aquarium Research Institute) is studying the deep canyons, but no one has tried to look for or study reefs in the 200’-500’ range. Tyler said that their have been technical divers that have explored these zones but they remain poorly studied in the scientific literature.

We thank Tyler for presenting such an interesting program. He is now writing his master’s thesis on the ichthyology of this work and we wish him the very best in his future career.

Editor’s note, for your interest on deep dives: