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Learning to live
without oxygen

September 5, 2019

Bocas del Toro
Text by Leila Nilipour, STRI

In Bocas del Toro’s Caribbean waters in Panama, a STRI postdoctoral fellow asks how marine life responds to low oxygen levels and higher temperatures in the ocean

Inside a white container next to the Smithsonian Tropical Research Institute’s (STRI) dock at the Bocas del Toro research station, Noelle Lucey is raising ostracods. These tiny crustaceans, about the size of a tomato seed, live in tanks where they are exposed to different conditions. Some spend their days in warm water with little oxygen; others, in warm water with sufficient oxygen. The lucky ones live at adequate temperature and oxygen levels.

What the STRI postdoctoral fellow hopes to find out with her experiment is how these marine organisms adapt to climate change conditions, such as higher temperatures and reduced oxygen levels in the ocean. Since they have a short life span and reproduce quickly, she can observe how they adapt from one generation to the next.

Noelle’s ostracods were collected from three different sites around the bay. Therefore, some are more sensitive than others to changes in temperature and oxygen. Those from Tranquilo Bay –where the ocean is in better condition because it isn’t near human activity– died during the first month of the experiment and failed to reproduce. The ostracods collected in Solarte and in the area near the STRI laboratory, close to the local town and tourist attractions, showed more resistance. The marine conditions at these sites are less ideal and the organisms that inhabit them have likely adapted.

“Now I am exposing their babies to different conditions. I want to see how the descendants of ostracods who managed to adapt to stressful conditions fare,” Noelle explains.

At the back of the container, sea urchins take part in a similar experiment. They are being exposed to conditions simulating those of a heat wave in the ocean. And as the water temperature increases, its ability to retain oxygen molecules is reduced, so in addition to being hot, the urchins might need to hold their breath.

And urchins have a curious attribute. When they are exposed to critical oxygen levels, they can change their metabolism from aerobic –which requires oxygen to produce energy– to anaerobic, which does not require it.

“Heat waves may be associated with oxygen depletion for a number of reasons, so urchins may need to hold their breath to survive one of these events. But how long can they hold their breath?” the scientist wonders.

In a spin-off of this experiment, Noelle is trying to resolve this question. She exposed the urchins to temperatures mimicking a marine heat wave and dropped the oxygen levels. They were left at their critical oxygen levels for an hour, and then returned to normal conditions to see how many survived. She repeated this process at additional time increments, until reaching 12 hours, the point where only half survived. This allowed her to determine how long urchins can really resist with anaerobic metabolism.

“I love keeping things alive. However, these types of survival studies provide conclusive evidence of how impacted marine life will be. And I try to make sure that the levels of exposure I subject them to are very realistic, like temperatures that are already occurring in the marine environment,” she points out. “I believe that this increases the power of the experiments, and makes the sacrifice worth it.

The important thing about Noelle’s research is that it combines the temperature increases with the lack of oxygen, two conditions occurring simultaneously in tropical oceans, but that are usually studied separately. To understand what really happens at sea, it is necessary to study them concurrently.

“The amount of oxygen deficient sites is growing considerably, due to the temperature increases everywhere. I have been monitoring how long and frequent these hypoxic events are and I want to look at how quickly invertebrate communities can recover after they occur,” she explains.

And they will adapt, but will they adapt at the pace that the environment is changing? Unlike the species that inhabit temperate oceans, those in the tropics may be much more susceptible, because they are more sensitive to fluctuations in temperature. Since Noelle started working in Bocas, for example, she has witnessed entire ecosystems completely wiped out.

 “While my work emphasizes the severity of ocean change, I like to think about how it can help inform change in simpler terms. For example, coastal hypoxia can often be partially mediated just by reducing water pollution locally,” Noelle concludes. “This type of action should be a relatively easy thing to do on the short-term, and it can help to protect marine communities by giving them just a little more time to adapt to the combination of changes coming their way.”

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