Scientists study the effects of increasing ocean acidity on California’s marine ecosystems — by Mary Patyten, California Department of Fish & Game Research Writer
Nicole Sandoval followed the familiar dirt path past the hundred-year-old Point Cabrillo lighthouse towards the sea. Swinging her bucket full of scrub brushes, she looked like some sort of intertidal maid on her way to clean up after untidy rock crabs or turban snails. Behind the lighthouse, dark sedimentary rock veined with white calcite jutted towards the ocean from the yellow dirt embankment, running in rough peaks and shelves down to pools lined with barnacles and kelp.
Springing from rock to rock, the DFG scientific aid headed for the water’s edge, her long, chocolate-brown braid coiled in the hood of her jacket. Far from cleaning duties, Sandoval was collecting samples of young sea creatures—clams, sea urchins, abalone and mussels among them—in part, to better understand profound changes occurring in California’s nearshore waters.
Reaching a precipice, she maneuvered her way down a steep path to where two heavy, rusted chains ran into the water, mounds of epoxy cement holding the ends firmly to the rocky shelf. She pulled the few feet of corroded, reddish-brown chain out of the sea, revealing scrub brushes zip-tied to the links and a rusty brake rotor that served as an anchor. Crouching down, she severed the zip-ties with a wire cutter and placed each wet brush into a plastic bag. Taking fresh brushes from the bucket, she zip-tied them to the chain and then, standing up, heaved the chain, brushes, and anchor back into the sea.
With the wet brushes safely stowed in the bucket, Sandoval climbed back up the rocky path. Clinging to the bristles in each plastic bag, microscopic sea urchins and other young, prickly creatures swung beside her, destined for the DFG office in Fort Bragg and, ultimately, Steven Schroeter’s sea urchin research project in Santa Barbara.
The red sea urchin supports a multi-million dollar fishery off California and maintains an influential position in the nearshore ecosystem, making it nearly irresistible to fishery researchers. Schroeter, an ecologist with the Marine Science Institute at U.C. Santa Barbara, began studying the small creatures that settled onto scrub brushes in 1990, focusing on sea urchins during their early life stages, along with colleagues from U.C. Santa Barbara, Scripps Institution of Oceanography and DFG.
When first hatched, sea urchins are about the size of a period at the end of a sentence. The tiny hatchlings drift with the currents and feed on equally small plants—called phytoplankton —for about five weeks before they settle to the sea floor. Schroeter’s study documented the settlement process, funded by the commercial sea urchin fishing industry itself through a self-imposed landing tax. Naturally, urchin divers had a vested interest in finding out whether lack of nurturing habitat, or perhaps environmental trends such as El Niños or La Niñas, limited the successful settlement of young urchins. “Along the way, we collected samples of many different critters, not just urchins, preserving them for future reference,” Schroeter said.
Although his research set out to document sea urchin settlement patterns, the incidental samples of critters preserved along the way may end up stealing the show. Locked away inside the tiny shells is information that may help scientists understand the effects of ocean acidification, a newly-recognized and growing threat to marine life off the California coast and in oceans around the world.
Gauging the Threat
Underpinning this threat is a simple gas that has been part of the Earth’s atmosphere for millions of years—carbon dioxide, which has the chemical formula CO2. Plants, animals, and the Earth itself produce and consume CO2 . The ocean, with its host of plants and animals, has always taken in CO2 and other gases, and released gases as well, maintaining a sort of slowly fluctuating equilibrium. The ocean’s fluctuating CO2 content causes its pH readings—a measure of water’s acidity or alkalinity — to rise and fall slowly, as well.
At the start of the century, data from a broad spectrum of oceanographic research, from tropical coral reefs to North Pacific ice floes, was brought together by researchers to look at the effects of CO2 on the ocean. Historical data shows that ever increasing amounts of CO2 have been pumped into the atmosphere and absorbed by the ocean since the beginning of the Industrial Revolution, about two hundred years ago. This ability of the sea to absorb excess CO2 was at first hailed by scientists as a wonderful way to dispose of harmful hydrocarbons produced by the burning of fossil fuels—but closer examination has yielded sobering evidence to the contrary. Soaking up that extra CO2 has caused the ocean’s pH to shift in an extraordinary way, as confirmed by readings taken around the globe.
On average, ocean pH readings have fluctuated between 8.0 and 8.3 over the past 20 million years, in a natural rhythm established over millennia. In the same way as small changes on the Richter scale can signal large differences in earthquake intensity, small changes on the pH scale can signal large changes in acidity or alkalinity. For example, a 0.1 change in pH is a large-scale event, but considered pretty normal when spread over hundreds of thousands of years. A 0.1 shift in pH over a few hundred years, however, is unparalleled in Earth history. Yet researchers established that it has occurred and will continue at an unprecedented rate, ushering in an era of unpredictable change.