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Some Sea Creatures May Already Be Dissolving in Our Acidifying Oceans

A new study finds that tiny animals that build their skeletons from minerals such as magnesium could dissolve in conditions that already exist off the coast of California.

By Kate Wheeling


Evactinopora bryozoan

found in Jefferson County, Missouri. (Photo: Wikimedia Commons)

Since the industrial age began in the late 18th century, the pH level at the oceans’ surface has fallen by an average of 0.1. While that may not sound like a lot, that increased acidity, when combined with warming temperatures, could spell trouble for tiny, kelp-dwelling sea creatures known as bryozoans, a new study shows.

Bryozoans assemble via budding into coral-like colonies of genetically identical units, building their skeletons out of calcite minerals. The exact mineral make-up of their skeletons can vary based on factors like temperature or available food. But research shows that the more magnesium the bryozoans incorporate into their skeletons, the more likely it is those structures will dissolve as the pH of seawater increases.

In order to understand how the bryozoans will fare as the pH of the ocean continues to drop—and it’s expected to fall as much as 0.4 pH units by the end of the century as the oceans continue to suck carbon dioxide out of the atmosphere—researchers at the University of California–Davis and UC–Berkeley looked at how one species grew in the lab as they fiddled with temperature, mineral availability, and food accessibility.

The team collected colonies of Jellyella tuberculata, a bryozoan species that lives in intertidal zones in warm waters around the globe, that were living on blades of red algae in Dillon Beach, California. They then raised the colonies in the lab for six months under varying conditions. The team found that, when they turned up the heat, the tiny creatures used more magnesium in their skeletons, which then rapidly dissolved when the team upped the acidity. The colonies tried to expand by adding on newly budded units, but that growth didn’t outpace the dissolution of existing buds.

The most troubling element of this finding: The conditions to which the researchers exposed the lab-grown colonies exist already off the coast of California. In the spring and summer, the ocean’s natural circulation patterns bring deep water—already low in pH and rich in carbon dioxide—up to the surface. That natural upwelling, coupled with the warming of California’s coasts that’s already occurring, means that bryozoans and other species that build skeletons the same way (like sea stars or sea urchins) may already be threatened.