Heat stress from marine heat waves can create a toxic relationship between seagrasses and a hidden ecosystem of bacteria, transforming a previously beneficial co-existence between marine plants and microbes into a harmful one, a University of Sydney and UNSW study has found. Seagrasses are marine flowering plants that act as
Hannah Harrero and Stephanie Insalaco-Wyner, geographers from Florida, comment on differing methods of monitoring the resilience of seagrass meadows in Florida’s ‘Mosquito Lagoon’, following a number of extreme weather events. Florida’s Indian River Lagoon has been an ecosystem in decline going back to 2011, when harmful algal blooms led to a severe decline in
Heat stress from marine heat waves can create a toxic relationship between seagrasses and a hidden ecosystem of bacteria, transforming a previously beneficial co-existence between marine plants and microbes into a harmful one, a University of Sydney and UNSW study has found. Seagrasses are marine flowering plants that act as fish nurseries, purify water and are crucial in coastal carbon storage. Their decline is often missed until it’s too late. The role soil microbes play in land plant health and climate resilience is well known. But for marine plants like seagrass, this science has largely been overlooked. “It’s worth paying attention to what happens in seagrass habitats as marine heat waves become more common. That information could be invaluable for conservation efforts,” said lead researcher Dr. Renske Jongen, from the School of Life and Environmental Sciences. In an underwater gardening experiment, biologists found a diverse bacterial ecosystem in the soil and around seagrass roots. The bacterial ecosystem was in a delicate balance, controlling the chemistry of the soil and seagrass health. Under increased water temperature, tiny bacteria living in the sediment among seagrass roots can reduce seagrass tolerance to climate change, stunting its growth and its ability to cope with heat stress. Higher temperatures favor bacterial species known to produce hydrogen sulfide, a compound toxic to seagrass, which may stunt seagrass growth. Plants previously exposed to warmer conditions suffer more from those changes in microbes. The researchers found seagrass growing in sediments from warm areas produces 34% less biomass when the natural sediment microbes weren’t disturbed. The findings show how bacterial communities are a hidden factor in recovering and restoring seagrass. “Just as microalgal symbionts (tiny organisms that rely on sunlight as energy) are key to the health of coral reefs, bacterial symbionts nestled at the roots and sediment of seagrasses can influence whether seagrass survives or declines,” said Dr. Jongen. “Even though seagrasses may look okay at first glance, what we’ve found below ground under increased temperature tells a different story.” Just as heat waves have hit terrestrial plants, marine heat waves have thinned out once lush and widespread seagrass meadows along the Australian coast. They are mainly found in shallow coastal waters and estuaries from tropical Queensland all the way down to the cool, temperate waters of Tasmania. Microbial communities also shape marine plants’ responses to environmental stress. Heat stress isn’t only about hot water. “Increased water temperatures dramatically change the ecosystem of microbes living among the seagrass roots and how microbes co-exist,” said senior author Associate Professor Ziggy Marzinelli from the University of Sydney. “Under heat stress, the microbial communities around seagrass roots shift in ways that can harm rather than help the plant.” How decades of industrial history created a real-world climate experiment In Myuna Bay in Lake Macquarie, history has created the perfect conditions for the research team to answer the question—”what would happen to seagrasses and microbes if water temperatures increased as projected by climate change models?” Since 1984, Eraring Power Station has continually fed a plume of warm estuarine water into the lake. This has made some of the lake waters up to three degrees warmer than ambient temperature for nearly four decades, mimicking both marine heat waves and what future oceans could be like along the Eastern Australia coast by 2090. “This has inadvertently created realistic conditions for the ultimate ‘gardening experiment’—for us to test how seagrass and below ground microbe health is shaped by exposure to higher-than-normal ocean temperatures,” said Dr. Jongen. “Locals are aware of the temperature increase in the area. It also has a reputation as a popular fishing spot because the hot water attracts a lot of fish species and everything from sharks to turtles have been seen here.” The research team transplanted Zostera muelleri, a species of sea grass native to coastal areas of Australia, into the lakebed. They also extracted and analyzed DNA to find the type of bacterial communities from the sediment and sediment from the seagrass roots to find how their composition changed at different temperatures. That was when they uncovered the change in bacterial communities and especially the relative increase of bacterial species that suppressed seagrass growth. “Our study highlights the overlooked role of microbes in tipping the balance in marine environments,” said Professor Paul Gribben from the University of New South Wales. “Seagrass restoration should not just focus on selecting species that are more heat tolerant, but also look deeper, below the ground surface—and, if needed, address microbial communities before transplanting or restoring seagrass meadows.” More information: This article is republished from Phys.org Read the research paper here: Ocean warming indirectly affects seagrass performance through effects on sediment microbial communities – Jongen – New Phytologist – Wiley Online Library
Hannah Harrero and Stephanie Insalaco-Wyner, geographers from Florida, comment on differing methods of monitoring the resilience of seagrass meadows in Florida’s ‘Mosquito Lagoon’, following a number of extreme weather events. Florida’s Indian River Lagoon has been an ecosystem in decline going back to 2011, when harmful algal blooms led to a severe decline in seagrass, the foundational component of shallow coastal ecosystems. Seagrass meadows stabilize sediments, improve water clarity and provide critical habitat and forage for species ranging from invertebrates to sea turtles and manatees. Seagrass also generates a significant amount of economic activity in the state of Florida. The loss of seagrass in the Indian River Lagoon System undermined fisheries, tourism and wildlife, ultimately leading to the starvation of more than 1,200 manatees from 2020-25, peaking in 2021-22. Mosquito Lagoon is part of the Indian River Lagoon system that spans 28 miles (45 kilometers), running from Cape Canaveral in the south up to Ponce Inlet in the north. As in the rest of the lagoon system, years of nutrient pollution and recurring algal blooms had diminished seagrass cover to nearly zero by the early 2020s. By most accounts, Mosquito Lagoon had crossed a critical ecological tipping point. In the fall of 2022, hurricanes Ian and Nicole struck Florida’s east coast within six weeks of one another, bringing intense rainfall, storm surges and coastal erosion. In the immediate aftermath, seagrass declined even further. But a few months later, in the spring of 2023, seagrass began to return. Satellite imagery revealed rapid and widespread regrowth. Hannah and I are geographers who study environmental change. Our research documents this unexpected recovery and examines what it may reveal about ecosystem resilience in heavily degraded coastal systems. One of us, Hannah Herrero, is a Volusia County native who grew up around the lagoon. She returned to her hometown at the outset of the COVID-19 pandemic. It was there that some local guides and fishermen she’d known for years suggested that our team should use satellite imagery to look at the state of collapse in the lagoon. The study we designed as a result used satellite imagery and machine learning, a type of artificial intelligence that uses advanced algorithms to learn and predict patterns, to track seagrass dynamics in Mosquito Lagoon before, during and after the storms. This approach allowed us to observe change at a scale and frequency that is difficult to achieve using only traditional field survey methods. Florida Manatee Tracking seagrass from space Monitoring seagrass coverage “the old-fashioned way” involves going into the lagoon and laying out transects, straight lines that cut through a landscape, so standard observations could be recorded. We would then have to boat or wade all along those lines to measure seagrass extent and locations and create digital maps manually to show where it is present. As you can imagine, this is a time-intensive process that’s limited by how far you can boat or swim in a day, and by financial resources. So we decided to use satellite imagery instead. This method is not without its own challenges—water turbidity, or cloudiness, seasonal variability and the patchy nature of vegetation that grows on the bottom of the lagoon all make it difficult to observe seagrass growth directly on the imagery. To address this challenge, our study used imagery from NASA’s Harmonized Landsat–Sentinel program, which combines data from multiple satellites into a consistent record of photos of the same areas taken frequently over time. We analyzed imagery collected between September 2022 and January 2024, focusing on periods before and immediately after the hurricanes and throughout the subsequent recovery. We applied a type of machine learning model called Random Forest to classify each image into seagrass and nonseagrass categories. The machine learning algorithm is informed by training samples collected in the field, but once the model has learned the signature of seagrass, it is able to then apply the classification model to the rest of the lagoon and across time with limited human input. We can then validate this classification. Heading into the field First, we had to train the model using hundreds of GPS points collected in the field over multiple seasons. This step helps to ensure that satellite classifications align with on-the-ground conditions and are accurately interpreting the images. Over several weeks during the summers of 2020 through 2023, our team spent many hours navigating Mosquito Lagoon in a small skiff designed for shallow depths, recording seagrass presence. It wasn’t always easy — Florida summers are intensely hot and humid, and Mosquito Lagoon definitely lived up to its name. But we got to see a wide variety of wildlife, including manatees, dolphins, sea turtles and alligators. And occasionally, on lucky days, we even spotted a roseate spoonbill or reddish egret. Our experience in the field highlighted why this system matters: Mosquito Lagoon is a remarkably vibrant place, teeming with wildlife. These long days on the lagoon, surrounded by its biodiversity and immersed in its unique sense of place, are what anchor the remote sensing data to on-the-ground ecological conditions and make the resulting models credible. The authors wade into Mosquito Lagoon to track seagrass growth as they train their AI model. Captain William B. Wolfson, Grassroots Guide Service, New Smyrna Beach, FL What we found Our analysis reveals three distinct phases of seagrass coverage. First, seagrass declined sharply following hurricanes Ian and Nicole. By December 2022 and early 2023, satellite imagery showed virtually no detectable seagrass across the lagoon. Then, in March 2023, we identified a statistically significant shift. Seagrass began to reappear, initially in small, scattered patches. Finally, during late spring and summer 2023, seagrass expanded rapidly. By July 2023, it covered more than 20% of the lagoon—levels not observed in more than a decade. Coverage then declined again during the winter of 2023–24, as expected based on seasonal growth cycles. But even our last observation, completed in January 2024, showed seagrass covering 4.3% of the lagoon, substantially higher than pre-recovery levels during the winter season. In spring 2026, seagrass in Mosquito Lagoon has remained at stable levels. Although it still experiences fluctuations due to algal blooms, seasonality and other changes in the ecosystem, we have not seen a
