Cracking the genetic code of Washington’s eelgrass

Ruesink lab members collecting data on an eelgrass meadow in Willapa Bay, WA. Bryan Briones Ortiz

Eelgrass belongs to a group of plants often referred to as seagrass and forms large underwater meadows along European, North American, and Asian coasts. In the Pacific Northwest, it serves an important function in the ecosystem by binding sediments, storing carbon, and providing essential habitat for Pacific herring, juvenile salmon, and many other species. Eelgrass populations are also sensitive to a variety of human impacts related to water quality changes or direct disturbance.

Mitigation, or attempts to offset human-induced impacts, are implemented when habitats or species are disrupted. Eelgrass mitigation and restoration strategies often result in plants being transplanted to new locations where eelgrass may already be present. However, these efforts often lack information on genetic population structure in an ever-changing environment.

So, what determines if a particular mitigation attempt will be successful? It may not be as simple as moving plants out of harm’s way to a new meadow, especially if the transplanted eelgrass is genetically different from that of the receiving population.

Briones-Ortiz extracting DNA from frozen eelgrass tissue in the lab. Samuel May

“Eelgrass restoration and transplantation strategies need to be informed by genetic population structure, genetic diversity, and an understanding of local adaptation to make sure they will succeed,” said Kerry Naish, director of the Marine Biology program and professor of aquatic and fisheries sciences. Naish, along with SAFS graduate student Bryan Briones Ortiz, are part of a team of researchers at the University of Washington looking to better understand eelgrass and help advise management practices.

Working alongside Naish and Briones Ortiz is Jennifer Ruesink, a professor in the UW Department of Biology, who has been studying native Washington eelgrass (Zostera marina) for much of her career. Her research has taken her to Willapa Bay (among other sites in the region), where she is running reciprocal transplant experiments—looking at how transplanted eelgrass responds in new environments in order to identify any genetic variances.

The interdisciplinary approach to this project combines the genetics expertise from SAFS with Ruesink’s vast knowledge of eelgrass biology to develop the first comprehensive geographic map of state eelgrass population structure. These data are currently being used to describe the relationship between eelgrass population structure, phenotypic diversity, local adaptation, and resistance to environmental stressors.

Eelgrass populations sampled for genetic population structure assessment. Bryan Briones Ortiz

“We’re using DNA sequencing to find out how much population structure there is across the entire state, which we think is a lot,” said Naish. “The implication is if you get a lot of structuring in a species, then mixing them up is not necessarily a good idea because structuring within eelgrass populations implies local adaptation.” The concern is that moving eelgrass through restoration or mitigation may actually circumvent natural processes that have been going on for a very long time.

Eelgrass is measured and tagged before transplantation. Fiona Boardman

Eelgrass is a flowering plant that was at one point in its history land-based. Over time, it colonized the marine environment but retained its ability to reproduce by making flowers and seeds. In some populations, plants germinate, flower, and die every year (annual), while in others the plants make clonal branches and rarely flower (perennial). In Washington state, some of these annual and perennial populations are just 10s of meters apart. The researchers are trying to determine if a plant is annual or perennial because of the conditions at the site where it is growing or because of its genetic legacy.

The reciprocal transplant work has shown that transplanted eelgrass seeds and seedlings tend to maintain the life history phenotype of the source population, rather than shift to the life history phenotype of the original eelgrass at the transplant site, implying that the two populations are genetically different.

Learning more about Washington’s eelgrass populations can help inform successful mitigation, restoration, and conservation measures in the future.

“There’s a whole bunch of physical reasons why a particular transplant might not take: the plant’s stage of development, the time of the year, even the quality of habitat. But there might also be genetic reasons,” said Naish. “That’s what we’re trying to answer—and if there are genetic reasons, how can we inform efforts to improve transplantation.”

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