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Friday, February 23, 2024

An international study conducted by UC Davis, other research institutions sheds light on genetic history of eelgrass

The health of eelgrass communities, a marine plant forest in the Pacific and Atlantic oceans, are of concern due to the changing global climate


By YASH RATHI — science@theaggie.org 


On Aug. 1, a new collaborative study between UC Davis and other research institutions was published in the Proceedings of the National Academy of Sciences journal (PNAS). Researchers worked with a community of species called eelgrass, which is a marine plant at the bottom of many coastal food webs specifically found on the North Atlantic and Pacific coasts. 

According to the study, eelgrass is commonly found in shallow water and in the tropical regions of Baja California, reaching as far as Alaska. This species not only provides food and shelter to marine organisms found in that area but also provides a plethora of services to humans, which include absorbing carbon from the water, protecting coastlines from storms and reducing harmful bacteria in the oceans. 

“Here, we explore how the growth form and associated community of the coastal foundation species eelgrass (Zostera marina) are shaped by current environmental conditions and a complex history of evolution and dispersal,” the study reads. “Eelgrass inhabits shallow marine waters across the Northern Hemisphere, from warm temperate regions to the Arctic in both the Atlantic and Pacific oceans.”

However, researchers have seen a sudden disappearance of eelgrass from many areas due to the rising temperatures in oceans. A very recent example is seen in Portugal’s southern region, where the eelgrass is moving toward the north to colder water. The Atlantic species has less genetic diversity than the Pacific species, which makes it more difficult to adapt to this sudden change in the temperature of the water. 

Jay Stachowicz, Ph.D. is a co-author on the study and a professor in the Department of Evolution and Ecology at UC Davis. He highlighted the importance of the diversity that is evidently lost in the Atlantic species. 

“Diversity is like having different tools in your tool belt,” Stachowicz said. “And if all you’ve got is a hammer, you can put in nails, but that’s about it. But if you have a full complement of tools, each tool can be used to do different jobs more efficiently.”

Through analysis of genetic data, Stachowicz and his collaborators discovered eelgrass’s ancient genetic history, which helped them to determine its size, placement, structure and potential organisms that lived among them in the past. Specifically, the genetic data pointed out how eelgrass survived multiple periods of climate change. 

About half a million years ago, eelgrass started its journey to the Atlantic from the Pacific. However, not even half of the organisms could make it to the Atlantic. Further, due to the Pleistocene Epoch, a time during which multiple ice ages occurred, not even 20% of the plant species survived. 

The surviving eelgrass population found in that region has some signatures left in its DNA due to this long-lasting struggle during its migration. One of these differences is a vivid genetic difference in the grasses in the Pacific and Atlantic, according to researchers. 

Emmett Duffy, Ph.D., who is the lead author of the study and a marine biologist from the Smithsonian Environmental Research Center, provided further insight into the migration of eelgrass. 

“The ancient legacy of this Pleistocene migration and bottleneck of eelgrass [or decrease in its population size] into the Atlantic has had consequences for the structure of the ecosystem 10,000 years later,” Duffy said.

The researchers were concerned about this sudden disappearance of eelgrass and its health. Therefore, they created a global network called Zostera Experimental Network, or ZEN, which comes from the eelgrass’ scientific name Zostera Marina. With this network, the researchers hoped to unite scientists worldwide who study eelgrass to develop a clearer global picture of the species’ health. 

Studying the eelgrass community at 50 different sites across the Atlantic and Pacific, the researchers conducted 20 sample plots per site and came up with 1,000 total eelgrass plots to make inferences. The team collected data including the species’ sizes and the nutrition available to them. 

The most common difference observed in the two regional species of eelgrass was a difference in height. The Pacific coast variant presented like an underwater forest that was three to six feet tall. On the other hand, the Atlantic species were more like meadows that rarely reached the height of three feet. 

Further, while only genetics played a very important role in the Pacific species’ survival and growth, the Atlantic species’ was influenced by both environmental and genetic factors. 

Jeanine Olsen, Ph.D., is a co-author on the study and an emeritus professor at the University of Groningen in the Netherlands. She talked about the sudden decrease in eelgrass population from rising pollution over the past decade. 

“I don’t think that we’re going to lose [eelgrass] in the sense of an extinction,” Olsen said. “It’s not going to be like that. It’s got lots of tricks up its sleeve. Climate warming by itself is probably not the primary threat to eelgrass. Pollution from cities and farms, which can cloud the water and lead to harmful algal blooms, also endangers seagrasses. That said, the vast array of environments eelgrass can survive in testifies to its hardiness.” 


Written by: Yash Rathi — science@theaggie.org