Modeling the Power of Eelgrass in Coos Bay

According to a study conducted in Coos Bay, Oregon, eelgrass could be a valuable ally in the fight against ocean acidification. Scientists from the universities of Washington and Oregon, the South Slough Reserve, and Confederated Tribes of Coos, Lower Umpqua, and Siuslaw Indians combined real-world data with existing models to build a detailed biophysical model of the Coos Bay Estuary—one that shows what happens when eelgrass disappears or spreads. The study was funded by the Oregon Ocean Science Trust.

“Unusually low oxygen, or hypoxia, and ocean acidification are threats for Coos Bay and many coastal waters nationwide; we were interested in the capacity of eelgrass to moderate these conditions,” says Caitlin Magel, coastal ecologist at the University of Washington and project lead. “The model tells us that eelgrass can help reduce water’s acidity, which is important for fish, oysters, and other marine life, but the eelgrass and oxygen relationships were more dynamic, resulting in mixed results for hypoxia mitigation.”

That nuance is critical for scientists and communities who want to make strategic investments in eelgrass conservation and restoration, that, for example, supports shellfish farms or protects fish habitat.

“In the new model of Coos Bay, areas with more eelgrass tended to have less acidic water—especially during the summer and in specific locations,” says Alicia Helms, the Reserve’s estuarine monitoring coordinator and study co-author. “While water quality improvements were variable, in some places the differences could be meaningful for shellfish survival and the communities that depend on them.”

Found in shallow, salty waters along U.S. coasts, eelgrass is a true ecosystem all-star. It creates essential habitat for culturally significant and commercially valuable fish, traps sediment and slows erosion to help keep water clean, and captures and stores carbon. Through photosynthesis, it also absorbs carbon dioxide and releases oxygen—making it a potential buffer against harmful acidification and low oxygen, particularly for vulnerable, shell-building species like crabs, oysters, and clams.

This project was informed by the Reserve’s System-Wide Monitoring Program, which has tracked water quality and weather conditions for three decades and eelgrass health in Coos Bay for over two decades. This high-quality local data set helped this research team build a model that reflects the real conditions of Coos Bay—and gives resource managers a new tool to plan for the future. The model shows where eelgrass is most effective at improving water quality, helping decision-makers focus protection and restoration efforts where they’ll have the biggest impact.

The research team collects data at three monitoring sites in the Coos Bay Estuary: (from left to right) Valino Island, Barview, and Collver Point.

“This study is a great reminder of how important it is to have consistent, high-quality monitoring data to meet the many, complex challenges facing coastal communities today,” says Rebecca Roth, executive director of the National Estuarine Research Reserve Association. “Thanks to the South Slough Reserve and its partners, we now have a better understanding of how eelgrass can support water quality and resilience in Coos Bay, and potentially other parts of the country.”