A Mediterranean Window into Acidification's Future

Like the makers of the rough-hewn medieval buildings above water on the Italian island of Ischia, the marine life underwater has had to learn how to make do with what the environment has given it.

The vents that are part of the same volcanic plumbing network as Mt. Vesuvius infuse the ocean waters around the island with high levels of carbon dioxide. Because excess levels of CO₂ make seawater more acidic, the island has drawn the attention of oceanographers. Several groups have recently visited the island to witness what life over large expanses of ocean could look like by the end of the century as the pH of the oceans drops.

Acidification has emerged in recent years as one of the most dangerous potential risks of anthropogenic climate change, though its gradual pace also makes it a subtle one. Of the CO₂ added to the atmosphere, the oceans take up about 30 percent, attenuating the effects of climate change at the cost of altering seawater chemistry. Much of the added carbon in the water converts to carbonic acid.

From a historical norm around 8.2, the pH in many ocean regions could drop to 7.8 by 2100, many researchers believe. This could have major effects on calcifying organisms such as coral or many shelled invertebrates, though detailed information remains scarce.

Scripps Assistant Professor Todd Martz is a leading developer of the instruments other researchers need to observe ocean acidification trends. Martz joined a team of Stanford University scientists that found that the total amount of life around the island vents was comparable to norms in the Mediterranean Sea but its diversity was drastically diminished, with only a few species of invertebrates existing there in abundance. The scientists published their findings in the journal Proceedings of the National Academy of Sciences.

“One of the most exciting aspects of my role as a sensor developer is the inter-disciplinary collaboration with ecologists and biologists interested in using sensor technology,” Martz said.  “Each unique project comes with a mutual sharing of information and we both get to learn new things along the way.”

Other researchers for whom Martz has built instrumentation include his own colleagues at Scripps. Lisa Levin, a biological oceanographer, and graduate student Christina Tanner also chose Ischia as a study site, in order to rear larvae in waters with naturally low pH. The team limited their examination to two species of sea urchins.

When they exposed sea urchin larvae to seawater with mean pH levels ranging from 8.0 to 7.2, they found that the most acidic water did not kill them off but did stunt their growth. In some cases, the larvae even shrank. These changes are likely to affect the larvae’s ability to swim and feed.

“Yet in the context of ocean acidification, urchin larvae were not sensitive to pH levels expected in the near future,” said Tanner. “This is important because the successful development of early life stages is critical for the persistence of urchin populations.”

The pH sensor Martz built for the Stanford researchers is one of nearly 50 he has supplied to various research groups. Martz continues work to create sensors that can measure other parameters of the CO₂ system such as the total amount of dissolved carbon dioxide in seawater. The pH of seawater alone, he noted, only tells part of the story.

Tanner’s dissertation work continues to examine low pH and its effects on sea urchin and other larvae closer to home, in the La Jolla kelp forest. She plans to use new facilities that control pH and oxygen levels currently being constructed by Scripps marine chemist Andrew Dickson and his student Emily Bockmon.