The collaboration between Salk Institute and UC San Diego is synthesizing light, awareness and optimism for local seagrass ecosystems.

Waving with the currents in La Jolla’s Underwater Park is a littoral lawn of seagrasses, ecosystems of environmental benefits that are often as unseen by the public as the marine life they hide.

However, a new discovery by a collaboration of La Jolla researchers from Salk Institute and UC San Diego’s Scripps Institution of Oceanography of a hybrid seagrass growing in Mission Bay might mean hope for these dwindling meadows that protect the coast.

The study, published in Nature Oct 29, details how the hybrid seagrass demonstrates low-light tolerance, which may lead to more genomically-informed approaches to coastal restoration and more awareness for the importance of eelgrass.

Seagrasses in La Jolla

Flo Li, @flowing_zen_nature

There are a few types of seagrasses in La Jolla; the most prevalent, highly visible being the phyllospadix, or surfgrass, commonly seen in La Jolla’s tide pools.

This is the closest relative to eelgrass, the subject of the recent study. Two species of eelgrass are found locally: the shallow-water Zostera marina and its deeper-water cousin, Zostera pacifica, which is La Jolla’s eelgrass version and only grows in Southern California.

Malia Moore/Bradley Moore, Scripps Institution of Oceanography

Right under the half-mile buoy in La Jolla Cove, in fact, lies a bed of Zostera pacifica that forms an important study site for Scripps Institution of Oceanography researchers, according to the study’s first author, Malia Moore, a PhD candidate at SIO.

The restoration problem

Flo Li

These eelgrass meadows are under constant threat; though restoration efforts occur all over California and globally, they’re only successful around 50% of the time, Moore said.

“That’s not great odds.”

One reason efforts often fail: light limitation. Seagrass needs light to thrive.

Whether due to coastal runoff, which makes the water cloudy, or dredging and replanting, which removes sediment and makes the water deeper and darker, low light conditions mean less photosynthesis, which means less seagrass.

Why it matters

Flo Li

Seagrass is a crucial micro environment that “fulfills a very parallel function with kelp,” Moore said, albeit in different places.

“Seagrass is the kelp of the bay,” she added. “If seagrass isn’t there, there’s no three-dimensional environment for fish to live in. It’s just sand.”

Much of the fish off La Jolla spend the first part of their lives in the eelgrass, which serves as a nursery habitat for many foraged fish species that are at the bottom of the food chain for larger fish.

Flo Li

“When you step off our coast, whether you’re at The Cove or Windansea,” Moore said, “and you’re going fishing and you’re seeing fish, there’s a direct link back to the eelgrass beds in the bays.”

Further, seagrass ecosystems are natural carbon sinks, Moore said, creating biomass and contributing to carbon drawdown, or the pull of carbon dioxide from the air for storage in the ground.

Touching grass: A solution emerges

In the waters of San Diego’s Mission Bay, a new hybrid seagrass has begun to grow naturally, a cross between the shallow-water Zostera marina and the deepwater Zostera pacifica.

Hybrid species can often “respond to different stressors, just in a more robust way,” said Moore, who located the hybrid and examined it on a dive, noting the thicker leaves and other identifying characteristics.

The Mission Bay seagrass meadows are “constantly being restored,” Moore said, replanted when San Diego dredges the bay to reshape its islands. 

This particular hybrid seems to have occurred when the two Zostera species were replanted next to each other.

“You can think of it as an ecological ‘whoopsies,’” Moore said, “but it turned into something potentially cool.”

Pichaya Lertvilai, Scripps Institution of Oceanography

Moore, who is advised by the study’s senior author, SIO adjunct and Salk professor Todd Michael, PhD, took a sample of the eelgrass back to the lab, where she and her team sequenced its genome to confirm its hybrid status. 

The researchers then placed the hybrid and the bay-native Zostera marina in a tank at SIO to recreate the marine environment. 

“We got it all comfy and then we put it in the dark,” Moore said, “in severe shade for five days,” looking to compare how both grasses responded to the stress. 

The team discovered the hybrid eelgrass continued photosynthesizing, she said. “It had very little light, but it kept making food.”

The findings are an indication of adaptability to stressful situations, Moore emphasized. The next step is to test the results in the wild.

“Salk is really interested in harnessing plants in order to contribute to carbon sequestration and ameliorating climate change,” Moore said. 

“Our study is motivating the restoration community,” she added.

The hope is for greener pastures underwater, with more of these essential marine meadows being grounded in adaptable endurance.