New research reveals genetic insights key to eelgrass restoration efforts

April 14, 2025

A Washington Sea Grant-funded study shows that nature, not just nurture, explains whether eelgrass flowers

Graduate researcher Bryan Briones Ortiz stands in an eelgrass meadow.

Graduate student researcher Bryan Briones Ortiz stands in an eelgrass meadow. Photo courtesy of the research team.

Native Washington eelgrass (Zostera marina) is in trouble. Due to declines in some areas of the Salish Sea and Pacific coast over the last 20 years, restoring eelgrass – and the crucial habitat and ecosystem services it provides – is a high priority for Washington state.

Restoring eelgrass meadows often looks like simply taking eelgrass from one location and replanting it in another. But for resource managers looking to maximize the impact of these efforts, many questions remain unanswered. Will eelgrass taken from one meadow really survive in another area? How similar or different are Washington’s eelgrass meadows from one another?

A study funded by Washington Sea Grant (WSG) seems to have revealed a piece of the puzzle. Led by Kerry Naish of the University of Washington’s (UW) School of Aquatic and Fishery Sciences, Jennifer Ruesink of UW Biology, and doctoral student Bryan Briones Ortiz, research published last month in Molecular Ecology provides the first evidence that the life history strategies of eelgrass are genetically determined.

Though it grows underwater, in many ways, eelgrass is similar to terrestrial plants. Each eelgrass plant can have one of two types of life cycles, annual or perennial. Annual plants complete their entire life cycle in one year, while perennial plants return to flower over multiple years.

“Annual eelgrass is reported in the literature, but it only lasts from April when it germinates to September when it senesces after flowering. No one had applied modern genetic techniques to evaluate its relationship to the more common perennial form,” explains Ruesink. “Here in Washington we had an opportunity to compare the life histories because they’re found close together in some of our larger coastal bays.”

It was believed that these life history strategies were based not on genetic differences but on the environment the plant happened to be in, and that the annuals were cued to flower by the more extreme environments they occupied.

The new findings say differently. The research team first applied genetic analyses to eelgrass collected from 16 sites to describe extensive population structure around Washington state. In the next part of the study, seedlings from annual and perennial plants were taken from their locations of origin – only a few hundred meters apart – and swapped. Instead of the plants adopting new life history strategies, as may have been expected from the previous hypotheses, the plants kept the ones they had. The researchers found that the two life history strategies are genetically distinguishable, and that the plants were more closely related to each other than to more distant eelgrass elsewhere in the state.

“Finding that life history types in eelgrass are genetically determined in Willapa Bay raises exciting questions about whether the same holds true in other regions where annual and perennial forms co-occur – and whether similar genetic pathways shape this diversity across the species’ range,” notes Briones Ortiz.

The findings have important implications for ongoing restoration work in Washington. Because eelgrass populations tend to be more genetically distinct at greater distances, managers will need to be careful in selecting an appropriate source for restoration projects. Further, annual genotypes may enable populations to resist seasonal stressors and can be added to the options that managers may want to favor.

Questions raised in part by this project are driving a follow-up study: the researchers are characterizing the genotypes, phenotypes and environments of distinct eelgrass populations that could serve as a source of plants for use in restoration efforts, and are evaluating the performance of the various plants at restoration sites. WSG selected this follow-on project for two years of funding; the second year of this work will continue once funds from NOAA are released to WSG.

“The success of eelgrass restoration depends on many practical issues, such as whether to use seeds or plants, what method to use, and where to plant,” says Naish. “We’ve now learned that we need to take into account where source plants come from – and what life history type they are.”

Which eelgrass plants should managers use in restoration projects? With the results of this research, the answer is one step closer.