Tiny But Vital Organism Can Adapt To Climate Change With ‘Hidden Costs’

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A recent study shows that the tiny copepod crustacean is the ocean equivalent of a canary in a coal mine. New research demonstrates that these ‘sea cows’ may be able to evolve to adapt to climate change – but this could come at the cost of their resilience, a recent Nature Communication suggests a study. More importantly, any change in their health affects the food chain.

How the copepod copes

When simulating future climate change conditions in a laboratory, namely higher temperatures and oceanic carbon dioxide concentrations, scientists found that zooplankton can adapt to warmer and more intense conditions. acid the water. This is because individuals that could not tolerate the higher temperatures and levels of acidification died. After a few generations, the better-equipped survivors were able to reproduce at a normal rate.

But it made them less able to survive other stressors, like a shortage of the phytoplankton they eat. Copepods reproduce every 20 days, allowing researchers to observe how nearly two dozen generations have adapted to climate change. At first, their reproductive levels went down a bit, but they were back on track after a few generations, says study co-author Melissa Pespeni, a biologist at the University of Vermont. But when the 21st generation was placed in colder waters, their breeding levels plummeted.

“They lose a lot. They expend their genetic currency, as you will, because they adapt at the expense of their ability to tolerate anything else the environment then throws at them,” she says. “Yes, there is adaptability, but there are hidden costs.”

The noble copepods, along with all life on Earth, have faced a particularly difficult decade: the past eight years have been the warmest on record since record-keeping began in 1880, reports NASA Earth Observatory. Earth’s temperature in 2021 tied 2018 as the sixth warmest year on record, according to analysis by NASA and the National Oceanic and Atmospheric Administration (NOAA). If, after a warm year, the temperature drops the following year, the copepod population could suffer negative consequences, says Reid Brennan, co-lead author of the copepod study and a marine evolutionary biologist at the German Center. GEOMAR Helmholtz for ocean research.

Supply chain issues

Copepods occupy an important place at the bottom of the food chain: they feed on algae and are eaten by fish, including salmon, tuna and cod. Besides the oceans, they live in almost all marine and freshwater habitats.

Since climate-changing conditions in the lab replicate real-life settings, Pespeni says, the loss of their genetic flexibility means they’re more susceptible to population crashes. These would impact the entire food chain, she says. Larger creatures, like fish and lobsters, she says, are able to move away from warmer waters, but tiny copepods (which measure up to 2 millimeters) cannot.

Pespeni and his team studied a herbivorous species of copepods, a population that grows with algal blooms. Jellyfish and larger fish then eat them, linking the plants and their nutrients, essentially, to the fish. “So if you give up in the middle of this food web, you’re missing a vital link between the grassroots and upper-level consumers,” Brennan says. “If we have a reduction in zooplankton, then we have a reduction in fish; it has implications for the food we eat, for the general functioning of the ecosystem in the oceans, for the sequestration of carbon in the oceans, and so on.

The scientists focused on a species of copepod called Acartia tonsa, although the fish also eat other species of copepods, as well as other types of zooplankton. Different species of copepods have varying tolerances for salinity levels, temperatures, and hypoxia, or reduced ocean oxygen levels, Brennan says. So there is hope that if the populations of some species of copepods crash, others might survive. Various zooplankton have different nutritional compositions, and fish fare better or worse depending on the type of zooplankton they eat, he says.

Another scientist involved in the study, Hans Dam, a biological oceanographer at the University of Connecticut, says he was surprised at how quickly the species transformed. “They adapt very quickly and get to the point where they can’t improve any more, but they don’t go back to where they were before they hit these stressors,” he says. “That means there is no free lunch with climate change. There is always a price to pay. »

So if we could somehow slow climate change and get warming waters and ocean acidification back to normal parameters, he says, populations that have genetically evolved to adapt to climate change may no longer be able to do so – just as those in the experiment have failed. thrive when returned to cooler, less acidic water.

Species have historically evolved and adapted to changing conditions, but these changes have generally occurred more gradually than in recent decades. Ultimately, the climate is warming so quickly that nature can’t keep up, warns Dam. “This idea that nature takes care of things is true; it happened in the past. Things are adjusting,” he says. “The problem is that the process took many, many millions of years: what took millions of years to happen is now happening in less than a century – nature cannot adapt so quickly.”

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