Ancient Ice Age Legacy Shapes How Seagrasses Respond To Today's Environmental Threats | Smithsonian Institution

Evolution in casting a longer shadow than previously thought, scientists report in a new paper published the week of Aug. Proceedings of the National Academy of Sciences. Smithsonian scientists and colleagues looked at eelgrass communities—the basis of many coastal marine food webs along the north Atlantic and Pacific coasts—and found that their ancient genetic history can play a more powerful role than the current environment in determining their size, structure, and who they are. live in it. And this could have implications for how well eelgrass adapts to threats like climate change.

About half a million years ago, when the world was warmer, some eelgrass plants made the arduous journey from their homes in the Pacific to the Atlantic. Not all plants are hardy enough to travel across the North Pole. For those who succeeded, a series of ice ages during the Pleistocene Epoch further influenced how far they could spread. That millennial struggle left a lasting imprint in their DNA: Even today, eelgrass populations in the Atlantic are far less genetically diverse than those in the Pacific.

However, in the classic “nature versus nurture” debate, scientists were surprised to find that genetic inheritance was sometimes more instrumental in shaping modern eelgrass communities than today’s environment.

“We already knew that there was a great genetic split between the oceans, but I don’t think any of us ever dreamed that it would be more important than environmental conditions,” said Emmett Duffy, marine biologist at the Smithsonian Environmental Research Center and lead author of the report. . “It was a big surprise for everyone.”

Eelgrass in Hot Spring

Eelgrass is one of the most widespread shallow water plants in the world. Its range extends from semi-tropical areas such as Baja California to Alaska and the Arctic. In addition to providing food and habitat for many underwater animals, eelgrass offers many services to humans. It protects coastlines from storms, absorbs carbon and can even reduce harmful bacteria in the water.

But in most of the places where it grows, eelgrass is the dominant—or only—existing seagrass species. That makes its survival very important for humans and the animals that live there. And lower genetic diversity in the Atlantic could make it harder for some populations to adapt to sudden changes.

“Diversity is like having different tools in your tool belt,” says Jay Stachowicz, co-author and ecologist at the University of California, Davis. “And if you only have a hammer, you can put nails in, but that’s about it. But if you have a complete set of tools, each tool can be used to do a different job more efficiently.”

Ecologists have seen eelgrass disappear from some areas as the water warms up. In Portugal, the southernmost place in Europe, eelgrass begins to retreat and move further north, into colder waters.

“I don’t think that we will lose [eelgrass] in the sense of extinction,” said co-author Jeanine Olsen, a professor emeritus at the University of Groningen in the Netherlands. “It won’t be like that. It’s got a lot of tricks up its sleeve. “But local extinctions, he said, will occur in some places. That could put areas that depend on their local eelgrass in trouble.

Achieving a More ZEN World View

Recognizing the urgent need to understand—and conserve—eelgrass around the world, Duffy and his colleagues came together to form a global network called ZEN. The name stands for Zostera Experimental Network, a nod to the eelgrass’ scientific name, Zostera marina. The idea is to bring together seagrass scientists around the world, conducting the same experiments and surveys, to get a coordinated global picture of seagrass health.

For the new study, the team studied eelgrass communities at 50 sites in the Atlantic and Pacific. With 20 sample plots per site, the team obtained data from 1,000 eelgrass plots.

First, they collected basic data on eelgrass: size, shape, total biomass, and the variety of animals and algae that live in and around them. Then they collected genetic data on all eelgrass populations. They also measured several environmental variables at each location: temperature, salt water and nutrient availability, to name just a few.

Ultimately, they hope to discover what shapes the eelgrass community more: environment or genetics?

After running a series of models, they found a number of differences between Atlantic and Pacific eelgrass ecosystems—differences that closely align with genetic differences from the Pleistocene migration and subsequent ice age.

While Pacific eelgrass often grows in “forest” that regularly exceeds 3 feet and sometimes reaches more than twice its height, the Atlantic hosts more small “grasslands” that rarely come close to that height. Genetic differences are also consistent with the total eel biomass. In the Atlantic, evolutionary genetics and the environment today play an equally strong role in eelgrass biomass. In the Pacific, genetics has the upper hand.

These impacts also flow to other parts of the ecosystem. When it comes to small animals that live on eelgrass, such as invertebrates, genetic signatures from the Pleistocene again play a stronger role than the environment in the Pacific—while both play an equally strong role in the Atlantic.

“The ancient legacy of the Pleistocene migration and eelgrass congestion into the Atlantic had consequences for the structure of the ecosystem 10,000 years later,” said Duffy. “Probably more than 10,000.”

Preserving the Future

That ancient genetics can play such a powerful role—sometimes more powerful than the environment—has some ecologists worry about whether eelgrass can adapt to more rapid changes.

“Climate warming—by itself—may not be a major threat to eelgrass,” Olsen said. Pollution from cities and agriculture, which can cloud water and lead to the development of harmful algae, also harms seagrasses. That said, the variety of environments eelgrass can survive in is a testament to its hardiness.

“I’m hopeful because our results illustrate long-term resilience to repeated large changes in thermal tolerance and a wide range of eelgrass habitats in about half of the Northern Hemisphere,” Olsen said. “With the genomic resources now available for eelgrass, we began to analyze functional changes in genes and their regulation in real time. This is very interesting.”

To protect existing eelgrass beds, maintaining current diversity is a good first step. In places that have lost eels, restoration offers some hope. Several success stories already exist, such as on the east coast of Virginia. But many restoration efforts have had only limited success. As Stachowicz points out, this raises additional questions.

“Should you recover seagrass using plants from the local environment, or should you think about the future and try plants with genetics that are more suitable for future environmental conditions?” He asked. “Or should you hedge your bets?” Maintaining or increasing genetic diversity could be the best way to provide seagrass populations with the diverse tools needed to survive in an uncertain future.

The study will be available on the journal’s website upon publication. For photos or to talk to the author, contact Kristen Goodhue at goodhuek@si.edu.

# # #

SI-262-2022

#Ancient #Ice #Age #Legacy #Shapes #Seagrasses #Respond #Todays #Environmental #Threats #Smithsonian #Institution