Stanford Scientists Reveal How Human-Generated Carbon Dioxide Could Reshape Oceans

Something strange is taking place in the blue waters off the rocky cliffs of Ischia, Italy. There, streams of gas-filled volcanic bubbles rising up to the surface are drastically altering life around them by turning the seawater acidic. Stanford scientists examining species existing near these gassy vents have learned what is required to survive in acidic waters, thereby providing a preview of what oceans in the future might look like as they become more acidic.

Their findings, reported in the December 11^th issue of Nature Communications, suggest that ocean acidification triggered by human-caused carbon dioxide emissions could have a greater impact than formerly thought.

When an organism’s environment becomes more acidic, it can dramatically impact not only that species, but the overall ecosystem’s resilience, function, and stability. These transformations ultimately impact people, especially our food chains.

Fiorenza Micheli, Study Lead Author and Professor of Biology, Stanford University.

A natural laboratory

A majority of ocean acidification studies thus far have been conducted in laboratories, making it difficult to measure how whole ecosystems made up of multiple, interacting species would be impacted. The real-life laboratory gave scientists a chance to inspect dozens of species, from sea urchins to marine snails that reside in areas of different acidity along Ischia’s volcanic carbon dioxide vents. Besides exploring how species diversity varied with acidification, they examined species traits, such as diet and growth that impact how well the ecosystem does. For instance, sea snails were smaller in more acidic water, as their shells take more time to grow and are thinner and more fragile. These detrimental effects on sea snails, a chief food for animals higher up in the food chain, may impact fish populations.

Overall, the scientists learned that the active venting zones with the most acidic waters were inhabited not only by the least number of species, but also the lowest number of “functional diversity”—the range of ecosystem-support services or roles that each species can offer.

“Studying the natural carbon dioxide vents in Ischia allowed us to unravel which traits from different species, like snail shell strength, were more vulnerable to ocean acidification. These results illuminate how oceans will function under different acidification scenarios in the future,” said lead author Nuria Teixidó, a marine biologist from Stazione Zoologica Anton Dohrn in Italy, who was a visiting researcher at Stanford during the study.

The acidification in the waters of Ischia caused the displacement of long-lived species, such as corals, that provide a habitat for other species—a process already repeatedly witnessed on reefs globally. The scientists also discovered that high levels of carbon dioxide and more acidity suited species with short lifespans and fast turnover as they are the only species that can endure in these environmental conditions. This alteration could result in further diversity loss and instability in the oceans, as biodiversity tends to boost an ecosystem’s stability.

A broader application

Localized case studies such as Ischia can offer insight on how future global environmental conditions may impact ocean life. More than losing biodiversity, ocean acidification will jeopardize food security for millions of people who rely on seafood, together with tourism and other ocean-related economies.

The effects of ocean acidification on whole ecosystems and their functioning are still poorly understood. In Ischia, we have gained new insights into what future oceans will look like and what key services, like food production and coastal production, will be lost when there is more carbon dioxide in the water.

Fiorenza Micheli, Study Lead Author and Professor of Biology, Stanford University.

Micheli is the David and Lucile Packard Professor in Marine Sciences at Stanford’s School of Humanities and Sciences and is also a senior fellow at the Stanford Woods Institute for the Environment and co-director of the Stanford Center for Ocean Solutions. Other co-authors are from Villa Dohrn Benthic Ecology Center of the Stazione Zoologica Anton Dohrn, University of Perpignan, University of California, Santa Cruz, University of Montpellier and Centre d’Estudis Avançats de Blanes-CSIC.

The research was sponsored by National Geographic Society, the Total Foundation, a Maire Curie Cofund and by a Marie Sklodowska-Curie Global Fellowship.

Stanford researchers studying species living near underwater volcanic vents have learned what it takes to survive in acidic waters. (credit:Pietro Sorvino and Pasquale Vassallo)