Warm Waters Disrupt Seagrasses’ Microbial Environment

Renske Jongen, an ecologist at the University of Sydney, calls seagrass ecosystems the “tropical rainforests” of the ocean. These underwater flowering plants offer habitats to marine life, protect coastlines from damage, and, like rainforests, store enormous amounts of carbon.

They’re also under threat from pollution, development, and warming ocean waters, which stress plants and slow growth rates. Seagrass populations have been declining globally for nearly a century, and recent estimates suggest 7% of seagrasses are lost worldwide each year.

A new study published in New Phytologist shows that warming waters may affect a microscopic aspect of the seagrass ecosystem, too: the microbes that live in their sediments. The new insight can inform efforts to restore seagrasses, the authors write.

Seagrasses are “getting attacked from both sides,” said Jongen, the lead author of the new study. Warming water stresses the plants themselves, while “something changes in the sediment that makes them grow worse.”

Sediments and Seagrass

To test how microbial communities affect seagrass growth under warming temperatures, Jongen and the research team transplanted seagrasses and their sediment from both warm and cool areas of Lake Macquarie, a coastal saltwater lake in New South Wales, Australia, into an artificially warmed part of the lake. The artificially warmed part of the lake has received intermittent plumes of heated water from a nearby power plant since 1984, leading to a consistent temperature increase of 1°C–3°C (1.8°F–5.7°F) compared with the rest of the lake.

For half of the seagrasses, the team also used an autoclave, an instrument that uses steam to sterilize materials, to kill most of the microbes in their associated sediment before transplanting them to the experimental garden. “By looking at how plants respond with and without their microbes, you can get an idea for whether [those microbes] help or harm the plant under certain environments,” Jongen said.

The plants were then left to grow for 28 days before the team measured how they’d fared.

The warm-origin seagrasses in their original, warm-origin sediments with microbes intact grew the slowest once they were in the artificially heated waters, producing 35% less aboveground biomass than their counterparts whose sediment microbial communities had been killed. That result suggests that the microbial community in warmed sediment contributes to seagrass stress, the authors wrote.

“These plants, in general, do not like sediments that have been exposed to warmer temperatures,” Jongen said. She was surprised that the plants that came from the warm areas had the worst outcomes but hypothesizes that perhaps these plants were already too stressed from warm waters to deal with the changes to sediment bacterial communities that occurred after they were transplanted into the even warmer part of the lake.

“It’s just like us, for example: When we don’t sleep or we’ve had a stressful week, then we get sick more easily,” she said.

Jongen said more research is needed to say for sure why warmed sediment seems to change microbial communities in a way that harms seagrasses. But research has shown that some microbes in ocean sediment produce sulfide, which can be toxic to seagrasses if it accumulates, especially if those seagrasses are already stressed. Warmer conditions may allow these sulfide-producing microbes to grow more quickly, harming the plants.

The new research highlights the “context dependency of host-microbe interactions,” said Karolina Zabinski, a marine ecologist at the University of California, Davis, who was not involved in the new study. Previous research by Zabinski and others also showed that seagrass growth depends on their associated sediment microbiome.

Restoration Lessons

The new study “serves as a great springboard” for both academics seeking to understand seagrass-microbe interactions and practitioners working on seagrass restoration in the field, Zabinski said.

For academic researchers, the paper raises exciting questions about how the microbial communities present in the sediment actually function, she said. Though the study identified the types of microbes in the seagrasses’ sediments, it didn’t evaluate the abilities of those microbes, which genes they possess or express, or how those microbes interacted with each other. “What are their actual genes, and what are they doing?” Zabinski asked.

For seagrass restoration practitioners, the study could offer new methods to try to improve restoration success. Some projects, for example, aim to take plants from warmer environments and transplant them to seagrass ecosystems that will face warming stress in the future as the climate changes. “It seems pretty intuitive that maybe those plants will have the traits or the genetics to respond to that warming,” said Randall Hughes, a marine ecologist at Northeastern University in Boston who was not involved in the new study. But the study’s results highlight “that intuition is not always reliable.”

“Certainly, having experimental studies like this helps us think about those restoration efforts in a more informed way,” she said. “When plants don’t do well, we can’t just assume it’s inherent to the plants—we have to remember it could be driven by the microbes that they’re interacting with.”

Jongen hopes to continue studying related questions about how seagrasses respond to warming waters. In particular, she’d like to investigate how long changes to the sediment microbial community last and whether those changes reverse once a marine heat wave subsides.

Ultimately, the answers to these questions will help scientists better predict where seagrasses are in danger and how they might be helped. “If we lose the seagrasses, we don’t only lose the seagrasses, we lose all the other benefits that they provide,” Jongen said. “I think they deserve a little bit more attention.”

—Grace van Deelen (@gvd.bsky.social), Staff Writer

Citation: van Deelen, G. (2026), Warm waters disrupt seagrasses’ microbial environment, Eos, 107, https://doi.org/10.1029/2026EO260166. Published on 22 May 2026.

Text © 2026. The authors. CC BY-NC-ND 3.0
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