Categories: Post

Under the Sea: The Invisible Changes to Ocean Life

At a long-term monitoring site at Tatoosh Island in northern Washington, researchers noticed an unexpected trend in their pH data. “We thought maybe it was a mistake,” recalls Dr. Cathy Pfister, an ecology and conservation scientist. “But after lots of checking and double-checking…it became really clear. Ocean pH was declining at our long-term study site.”

Ocean pH is a measurement of how acidic or how basic seawater is on a scale from 0 to 14. A pH of 7 is neutral, with values below 7 being acidic and levels above 7 being basic. As the ocean absorbs carbon dioxide from fossil fuel emissions, its average pH drops, becoming more acidic. The shift is subtle, and while invisible to most people, it has profound effects on marine life. Ocean acidification is exactly what it sounds like: excess carbon dioxide from the atmosphere dissolving into the ocean, lowering its pH. “It makes it more difficult for organisms that need carbonate ions to build shells or skeletons,” Pfister explained. “And many biological processes—from how fish smell to how organisms interact—are closely tied to pH.”

Organisms like coral and shellfish use calcium carbonate to build their shells and skeletons. But as the water becomes more acidic, it becomes more difficult for these organisms to build and maintain their structures. And because of this, one of the clearest indicators of the changing ocean comes from a surprisingly humble source: mussel shells. Over decades, mussel shells collected from Tatoosh Island have been thinning and becoming more structurally unsound. “These carbonate structures have recorded the increasing CO₂,” Pfister notes. “They’re the first ones interacting with ocean acidification.” Similar patterns are observed in coralline algae, which form crusts that can live for decades. Together, these organisms are essentially a living archive of environmental change.

But the consequences are not just biological. Some shellfish farmers, noticing declining water quality, have relocated their operations to regions with higher alkalinity (water’s ability to neutralize acids, making the water more stable). So, shellfish farmers are moving to areas where the water will be better protected from changes in pH levels. “That strikes me as just a huge indicator,” Pfister commented. “It’s affecting economic opportunity in coastal areas and the food sources that many of us depend upon.” Even for those far from the coast, ocean acidification is tied to global ecosystems and economies.

Yet, there are reasons for hope. Many nearshore organisms naturally experience fluctuations in pH and temperature, giving them some built-in ability to adapt. “They may have the genetic background to cope with changes,” Pfister said. Meaning that these organisms may be able to slowly adapt to changes in pH levels, finding ways to live in more acidic waters. Long-lived species face a harder road, but the potential for adaptation exists. Just as importantly, public awareness is growing. “People are noticing these changes, and hopefully that continues to build an ethic of reversing change.”

For Pfister, the deeper message is about persistence. “We must be relentless in documenting what’s going on, collecting the data, and trying to understand it,” she emphasized. Archival sources, from museum specimens to decades-old photographs, are equally essential for understanding how ecosystems have changed over time. Long-term records, including those made possible through decades of collaboration with the Makah Tribal Council and Makah Cultural and Research Center on Tatoosh Island, are crucial for understanding how ecosystems shift over time.

After 37 years working at Tatoosh Island, Pfister reflected on the privilege of such a sustained study. “I honor that as an exceptional opportunity. I’m still learning, so I don’t feel like I have any grand conclusions. But these observations show that persistence, curiosity, and long-term commitment are vital for understanding our changing oceans.” The island itself is demanding, “it can be difficult to get to, to live there, and to get back off,” but it remains an invaluable natural laboratory for understanding how species respond to change.

Through mussels, algae, and years of careful observation, the ocean is telling a story—one of rapid change, resilience, and the urgent need for continued attention. It’s a story that connects the microscopic chemistry of shells to global ecosystems and human livelihoods alike, reminding us how closely tied we are to the shifting chemistry of the ocean.

If you want to learn more: