As climate change-driven ocean acidification and higher ocean temperatures continue to threaten various marine animals, some species are beginning to evolve in order to adapt to warmer, more acidic conditions. But does this evolution come at a price? A recent experiment from the University of Vermont, in collaboration with the University of Connecticut, the GEOMAR Helmholtz Center for Ocean Research in Germany, and the University of Colorado, Boulder, focuses on this question.

This March 2022 study analyzed how one copepod (a small crustacean species), Acartia tonsa, will likely evolve in order to adapt to warmer ocean temperatures and higher levels of carbon dioxide. However, these copepods’ resilience to climate change comes hand in hand with increased vulnerability to other stresses such as limited food sources.

Background Information: What is Ocean Acidification?

Full Study: Loss of transcriptional plasticity but sustained adaptive capacity after adaptation to global change conditions in a marine copepod (Brennan et al. 2022)

How Copepods Adapt to Ocean Acidification

acartia tonsa - ocean animals adapt ocean acidification — *Acartia Tonsa*
*Source:* *UC Davis*

Scientists from the University of Vermont conducted a laboratory experiment to understand the effects of ocean acidification on copepods, a group of small crustacean species that serve as a food source for many marine species. Copepods also act as an important biological control agent against mosquitos carrying human diseases.

Researchers artificially evolved 23 generations of Acartia tonsa, a copepod species, in order to study the effects of ocean acidification on copepod reproductive success. The results reveal that copepods can adapt fairly quickly to a warmer, acidified ocean ecosystem, but that this rapid evolution decreases the species’ genetic flexibility, which leads to increased vulnerability to other stresses.

Finding One: Copepods have the ability to quickly adapt to ocean acidification due to high genetic flexibility.

Copepods have the ability to become sexually mature and reproduce in just four to six weeks, making them a helpful organism to help scientists study evolution over shorter periods of time. This study utilizes copepods’ ability to reproduce and create new generations in a short period of time to analyze the effect of ocean acidification and warming on the health and reproductive success of twenty-three generations of copepods.
Scientists created an ecosystem that simulates future ocean conditions under climate change. They exposed thousands of copepods in multiple generations to the acidic environment and tracked their health and reproductive ability.
The study found that copepods showed resistance to ocean acidification and continued to thrive throughout twenty-three generations. This is due to copepods’ plasticity (genetic flexibility), or the ability to manipulate their genes, allowing them to adapt to environmental changes. This includes but is not limited to:
- Ability to adapt to increasing temperatures in their environment
- Ability to grow skeletons in an acidified environment
- Ability to generate additional energy in order to adapt to the stress caused by ocean acidification.
- Although the results provide optimism for the future of copepod populations, the next experiment demonstrates the cost of this generational adaptability to copepods’ health and reproduction.

Finding Two: Rapid evolution in order to evolve to ocean acidification decreases copepods’ ability to adapt to other environmental stressors in the future.

After twenty-three generations of copepods living in an acidified environment, scientists reintroduced some of the copepods in the less acidic environment – the current acidity level of the ocean today. The new generations of copepods that were reintroduced to this less acidic environment did re-adapt to these new conditions – but with lowered ability to respond to other kinds of stressors like a limited food supply.
The researchers explained that, in an effort to adapt quickly to acidified conditions, the copepods lost genetic flexibility (known as “phenotypic plasticity”), their ability to genetically adapt to different environmental conditions.
The copepods genetically adapted to high acidity conditions, which left them all with similar genetic makeup. This left them less able to adapt to new stressors, such as a lowered food supply. Copepods in the lower-acidity environment their ancestors had come from had smaller populations and were generally less healthy.

The scientists concluded that, while there is hope for copepods and other ocean animals to adapt to increased ocean acidity and warming ocean, there may be hidden costs for those species as a result of rapid evolution.

scientist with copepods - ocean animals adapt acidification — Professor Dr. Melissa Pespeni of the University of Vermont during the copepod experiment.
(Source: © Joshua Brown/Geomar)

Sources:

Brennan et al. “Loss of transcriptional plasticity but sustained adaptive capacity after adaptation to global change conditions in a marine copepod.” Nature, March 3, 2022, DOI: 10.1038/s41467-022-28742-6.

“Ocean life may adapt to climate change, but with hidden costs.” Science Daily, March 22, 2022. https://www.sciencedaily.com/releases/2022/03/220322150905.htm.