Seagrass can only be restored in calm waters. This principle has confined global restoration efforts to protected bays and harbors for decades. But a research team at the Scripps Institution of Oceanography has now challenged that assumption on Catalina Island, California: a new seagrass meadow on the open, wave-exposed Pacific coast survived and reached the density of natural reference stands within two years.
What seagrass does and why so much is missing
Seagrass meadows cover less than 0.1 percent of the global seafloor but account for between 10 and 18 percent of all ocean carbon uptake. Their sediment stores between 8.3 and 23.1 petagram of organic carbon, or 8.3 to 23.1 billion tons. If these stands continue to degrade, conservation organizations estimate climate damages worth over $200 billion could result as stored carbon escapes into the atmosphere.
Seagrass meadows also serve as nurseries for juvenile fish and crustaceans, act as natural water filters, and provide food for sea turtles and manatees. Since the early 1900s, roughly 29 percent of all seagrass meadows globally have disappeared. The annual loss rate stands at 1.5 percent and has accelerated in recent decades. Main causes include shipping traffic, coastal development, and rising water temperatures.
The core restoration challenge was long practical in nature: seagrass requires clear water, sufficient light, and a stable seafloor. In wave-exposed coastal sections, transplants have typically been lost. This is why restoration projects worldwide have focused on calm bays and shallow zones in harbors.
Catalina Island: How the transplantation succeeded
The team, led by Rilee D. Sanders, collected Zostera marina, the Pacific coast's native seagrass species, from an established population in Ripper's Cove on Catalina Island and transplanted it in 2022 to the exposed Button Shell site. What researchers call an open coast is precisely defined: unlike protected bays and harbor areas typical for restoration, such a section faces the Pacific directly, with stronger wave action and changing currents. Two methods were used, individual shoots and bundles of multiple shoots. Before transplanting, the team measured light conditions, oxygen levels, and water temperature at both sites to ensure comparable biophysical conditions.
The results after two years: the new meadow counted 244 shoots per square meter. Natural reference beds nearby reached 306 shoots per square meter, a difference that was statistically insignificant. Time-lapse camera footage and diver observations showed that fish communities after one year were indistinguishable from those in natural seagrass meadows. Visits by the endangered Green Sea Turtle (Chelonia mydas) were also documented. The restored area covered roughly 0.18 hectares, with transplanted areas expanding approximately 150 square meters in the first year and another 560 square meters in the second.
How other countries restore seagrass
The world's largest seagrass restoration project has been underway since 1999 on the U.S. East Coast. The Virginia Institute of Marine Science and The Nature Conservancy rely on seed sowing rather than transplantation: volunteers collect mature seed heads, seeds are processed and dispersed in autumn. The result now encompasses around 3,612 hectares of restored seagrass in Virginia's coastal lagoons, roughly 20,000 times larger than the Catalina study. Yet these meadows too are located in protected bays, not on the open sea.
Several smaller projects run in Europe. The largest British effort to date began in Cornwall: the goal is 10 hectares of new seagrass in Falmouth Bay. Off the Llŷn Peninsula in Wales, five million seeds are being sown, also targeting 10 hectares by 2026. A British trial in 2025 reported 97 percent survival rate for transplanted shoots and a four-fold increase in colonized seafloor area within six months. All these projects rely on protected marine sections.
What open-coast restoration means for the field
The significance of the Catalina study lies not in its scale. At 0.18 hectares, the new meadow is globally tiny. It lies in proof of principle: seagrass can grow and thrive in wave-exposed coastal sections under the right conditions.
For global restoration practice, that opens new possibilities. Coastal sections once considered unsuitable now merit consideration if researchers pre-assess critical biophysical conditions. The research team emphasizes the importance of site selection based on measured light and temperature conditions, as well as spatial proximity to the donor population. Whether this principle is transferable to other coastlines worldwide depends on how many sites have similar conditions and whether suitable seagrass populations exist nearby.
Three conditions, the research team noted, are decisive: light and temperature must be comparable at donor and target sites, the seafloor must remain stable despite wave stress, and a suitable donor population must exist in spatial proximity. For seagrass research, Catalina Island is proof of concept. Whether it becomes the foundation for large-scale restoration of exposed coasts will be determined by the projects that follow.