“A layer of death and decay beneath the surface of the water.”
That’s how Will Wied describes what happened in picturesque Bocas del Toro on the Caribbean coast of Panama after a dramatic drop in oxygen levels.
Wied, a Ph.D. student in the FIU Institute of Environment, was part of a collaborative group of scientists led by the Smithsonian Tropical Research Institute that witnessed and documented the devastating deoxygenation event in 2017 and recently published their findings in Nature Communications. They found half the corals in in shallower areas didn’t survive. But microbes that also live on the reef, including bacteria and viruses, responded differently, and could even provide a possible new clue for predicting future events.
“I’ve seen bleached reefs before, and this was so different. The sea urchins and the brittle stars were trying to climb up and escape. It was horrific, eye-opening and just sad to see,” Wied said.
Hypoxia occurs when oxygen levels plummet to the point of being close to zero. The 2017 Bocas del Toro event, though, was especially devastating for two reasons — how low oxygen levels dropped and how it impacted not just deeper depths, but shallower waters, as well. These factors led to two separate stories unfolding on the reef — one of death, another of resilience.
Corals at deeper depths, about 30 to 60 feet, all died. Half of the corals in shallower water also died. The corals that survived present researchers with questions that future work may be able to answer, including what sort of adaptations helped them withstand these stressful, traumatic events.
Meanwhile, the microbes living on the reef seemed to play a game of hide and seek. During the event, the team conducted water quality monitoring at more than 80 sites. When oxygen levels were lowest, the microbe community shifted and changed. Microbes not usually detected in the water when oxygen levels were normal were suddenly showing up. A month after the hypoxia event ended, those microbes returned to normal.
While there are still many unknowns, the researchers stress the importance of including deoxygenation into the overall picture when considering the threats against corals and other marine ecosystems.
“There’s still a lot we don’t know, but what we do know is that it’s important to begin to look at both deoxygenation and what these microbial communities are doing, so we can maybe use them as an indicator to predict when these hypoxia events begin and end,” Wied said. “It’s very clear they play a role, since they are coming and going with the changing oxygen levels.”
Currently, there’s very little research on how hypoxic events impact tropical habitats, but this study provides some of the first clues to begin to uncover that important question — perhaps even more urgent, since deoxygenation events are expected to become more and more common due to the impacts of the climate crisis.
Researchers hope to continue their work in Bocas del Toro, since it’s an ideal study site. The mainland coastline is primarily farmland. There isn’t adequate waste management. The water quality isn’t great and the reefs aren’t pristine. And this what makes it the most realistic, perfect example of what the future may hold for other places.