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From storing carbon to guarding against ocean acidification, seagrass is fundamental to keeping ocean ecosystems in balance. But new research shows that seagrass meadows play another crucial, if overlooked, role: protecting shipwrecks and other underwater historical heritage.
Ancient weapons, prehistoric fishing tools, and textiles are just some of the items scientists have discovered buried beneath the protective cover of seagrass, says Oscar Serrano, a marine ecologist at Edith Cowan University in Australia. Until now, Serrano says, no one has investigated the cultural value of seagrass meadows, which “play an important role in revealing clues about the human past.”
But archaeological techniques can negatively impact seagrass meadows since excavation, sometimes with explosives, is used to access study sites.
To highlight the link between seagrass and archaeological preservation, Serrano and his colleagues compiled evidence from the literature and from consultations with archaeologists in Denmark, Australia, the United States, and around the Mediterranean. The team’s investigation revealed a clear pattern: some of the world’s best-preserved underwater archaeological sites are sealed beneath blankets of seagrass.
The scientists determined that seagrass captures floating sediment particles on its long leaves, causing a thick sediment layer to build up on the seafloor. Over time, artifacts that settle below seagrass become buried. Similar to a time capsule, this thick sediment creates a seal, leading to oxygen-free conditions that slow decomposition and keep objects intact beneath the churning ocean.
In the turquoise waters along the coast of Western Australia, seagrass meadows have played a pivotal role in the preservation of the James Matthews—a 180-year-old, 24-meter ship that is one of the best-preserved ships of its time. The James Matthews, a slave ship, traveled between Europe, Africa, Australia, and North America before sinking during a storm in 1841. When maritime archaeologists discovered the ship in 1973, a thick layer of seagrass covered its watery grave. The excavations that followed the discovery unearthed several well-preserved artifacts, including a leather shoe, a lace parasol, and an ivory chess set.
Once excavations at the site were complete, the ship was reburied to help maintain the conditions in which it was found, but the seagrass was never completely restored. When archaeologists returned to examine the shipwreck three decades later, it showed signs of decomposition. Alarmed, archaeologists covered the site with faux plastic seagrass, sandbags, and shade-cloth mats to slow its degradation. But the efforts didn’t work.
“In areas where there is little seagrass cover, organic materials such as ceramics and timber can decompose,” says Serrano. “As a result, the ship’s condition is not what it was when it was first discovered.”
Given the new appreciation of seagrass’s protective qualities, Serrano says archaeologists should adopt less invasive techniques, such as acoustic and seismic measurements, which would help maintain seagrass beds. “If archaeologists continue to use shortcuts to study these sites, such as explosives, they will be severely damaged,” says Serrano.
Some archaeologists are already using noninvasive techniques to explore underwater heritage less destructively. To learn more about the James Matthews’s past, Madeline McAllister, a maritime archaeologist at the University of Western Australia, used photographs of the site to develop an accurate 3D model of the ship. This allows for study without further excavation.
McAllister, who was not involved in the new research, says Serrano’s review highlights the importance of seagrass in preserving fragile relics. “Achieving anaerobic and low-light conditions is central to preserving cultural heritage,” she says, “but the challenge is restoring [these conditions] after excavations have taken place.”