In a cold room at Temple University, in landlocked Philadelphia, finger-size fragments of coral bathe in four small tanks of seawater. The white skeletons look dead or bleached — but they are not. Healthy animals reside within these hard bodies. Some wave their tentacles from holes in the gnarled stems, like flowers at a mermaid’s wedding.
Getting here was not easy. They were clipped from reefs a thousand feet down in the Gulf of Mexico, and then housed inside a special refrigerated van which traveled by ship before an overnight delivery to the lab. When the van broke down, some stayed in a chilled cattle trough. They were even packed into Mason jars on ice. Not all the jars made it, but the corals did.
Before today, they were kept for nearly a year in another tank designed to mimic the conditions of their home environment. A refrigerated room maintains their water at 46.4 degrees, while pumps deliver carbon dioxide, acidifying the water to levels most other sea creatures won’t tolerate. To prevent stress, the corals are strictly monitored by students who hand-feed them with pipettes, like mother birds tending to their babies.
Alexis Weinnig, a graduate student in the lab who has ushered the corals on their journey, said they are happy today but happier in their home tank, then apologizes for making them sound so human.
“We get really invested in them,” said Weinnig. “And then we kill them.”
Humans are pretty good at killing corals. Over the past 30 years, overfishing, pollution and climate change have knocked out about half the shallow water reefs on the planet.
But much less is known about how humans are influencing reefs in the deep sea, where slow-growing cold-water corals may make up two-thirds of all coral species. Add the threats of offshore drilling and trawling, and deep-sea corals may be just as threatened as shallow water corals.
The tentacled niblets being studied in this cold room are Lophelia pertusa. These widely abundant “super corals” build huge reefs in cold waters around the world, as deep as 3,280 feet below the surface. They support as much biodiversity as tropical reefs and are home to brittle stars, octopuses, sharks, crabs and fish.
Erik Cordes, a deep-sea ecologist who leads the lab at Temple, has found that Lophelia are better at withstanding industrial and climatic stressors than other deep sea corals, and in some places more than others. Populations in the Gulf of Mexico survive life at the edge of some of the harshest conditions, near natural methane seeps and in slightly warmer temperatures with lower oxygen concentrations and higher acidity levels. They may adapt to changes, too.
But Cordes and Weinnig want to know just how much Lophelia can take.
The survivors of today’s death match will be candidates for unprecedented efforts to restore deep-sea environments affected by the Deepwater Horizon oil spill in 2010.
Their results will also help inform future efforts to conserve vast areas of the deep sea.
“Lophelia is sort of our lab rat,” said Cordes. It is charismatic, survives in extreme conditions and yet could die from even the slightest changes.
“Now that we understand something about how it responds to climate change, we want to know how does it respond to oil spills, and how will it respond to future oil spills under climate change?”
The largest marine oil spill in history
When the Deepwater Horizon drilling platform exploded in the Gulf of Mexico in 2010, hundreds of millions of gallons of oil and gas gushed from its well nearly 5,000 feet below the surface. About 5 percent of it wound up on the seafloor.
To break down the oil faster, 700,000 gallons of a chemical dispersant were injected right above the wellhead. This industrial detergent, before only used at the surface, broke up the oil — and made it more toxic.
The explosion and its aftermath killed 11 people, shut down fisheries and decimated coastal and marine ecosystems, including deep water corals, which were found dead or dying miles from the well.
Since 2010, Cordes and other scientists have been working to understand the role that hydrocarbons from the accident and natural gas seeps play in coral reefs and other deep sea ecosystems.
To find out if climatic changes making their way to the deep could break Lophelia’s coping abilities, Weinnig has been exposing corals to various combinations of stressors — elevated temperature and pH, oil and dispersant — and monitoring the animals’ response and recovery.
In today’s experiment, six different types of Lophelia from the Gulf of Mexico, which are expected to respond differently to the stressors, will face oil, dispersant and a combination of the two.
Back in the cold room, Weinnig begins by jotting down the corals’ health scores (all healthy) and noting the normal pH and temperature of the water.
Then she selects fragments of coral from each tank, flash-freezing them one by one in a billowing vat of liquid nitrogen kept in the hallway. She will do this at every step, which will help her assess the health of the coral in response to changes in their environment over time.
Back in the cold room are three beakers containing seawater mixed with the same oil and dispersant released in the Deepwater Horizon spill. The corals appear translucent until Weinnig adds them to a set of exposure tanks.
The tank that gets the oil acquires a sheen and highway-esque scent. The dispersant tank clouds up.
She removes the remaining corals from their clean tanks and places them into the exposure tanks and waits.
In 24 hours, she will assess the effect of each exposure. Then she will place the remaining corals into recovery tanks with clean water to see how they fare in the days to come — because in the real ocean, some corals can bounce back.
By extracting ribonucleic acid or RNA from the flash-frozen samples, she will be able to see what genes are turning on and off and compare differences between the types of coral. This will give her molecular snapshots of the least and most resilient Lophelia strains.
“We’re trying to find what makes it super,” said Cordes. “You can’t just look at them and tell. They’re not wearing little capes.”
But to see which corals are definitely not super, it only takes a couple hours: In the dispersant exposure tank, a few fragments are already spitting out their guts (or filaments). Some make excess mucus, like humans when they are sick.
Nothing special seems to be happening in the oil, dispersal, control or combination tanks, which reflects what Weinnig has been finding throughout these exposure experiments.
She has found that regardless of temperature or acidity, dispersant makes Lophelia very sick. These corals can recover from exposure after just 24 hours in regular temperatures, but struggle or get worse if temperatures are elevated.
The other stressors, including increased acidity, do not seem to bother the corals too much, alone or combined. Some corals even seem to investigate the oil with their tentacles. As sick as the corals got in any condition, only two fragments died — and that was in a tank with elevated temperatures and dispersant.
This suggests that while Lophelia may be able to recover from an oil spill and cleanup under current climate conditions, coping with an environmental accident in a warmer ocean of the future may be too much for even this super coral to handle. Less toxic dispersants that exist but aren’t widely used may reduce stress on the corals in the case of a future disaster.
“Most species can handle one stressor or a couple of stressors,” said Cordes, “but when you really start piling on like that, it makes it tough — just like people.”
The risks of rejection
The next step for the gulf is restoration — something new in the deep sea.
The lab and its collaborators are considering collecting the Lophelia strain that proves strongest in these experiments from still healthy populations in the wild. They could then propagate it in the lab and transplant it to build new reefs where old ones were lost. Further down the line, using gene editing to make stronger corals is also a possibility.
But restoration by super coral is not so simple, said Ruth Gates, a marine ecologist at the Hawaii Institute for Marine Biology. “The reality is we don’t know whether it will work, shallow or deep,” she said.
Gates’ lab is using assisted evolution to develop corals that can keep up with rapidly warming shallow waters. This restoration approach means finding the strongest individuals and breeding them, but also training them to get used to certain stressors or strengthening the supportive microbes, like algae, living in their tissues.
Every reef ecosystem is a little different: Certain problems require corals with certain superpowers. Gates says restoration of deep water reefs threatened by drilling will be a challenge, because poorly understood reef ecosystems are difficult and costly to access.
“But it’s all about survival of the fittest in the long run, so leveraging the fittest individuals for this restoration makes sense,” she said. “Will these approaches work? I don’t think we know until we try and assess the evidence.”