Carbon dioxide from industrial activities doesn't just accumulate in the air, it has also seeped into ocean waters since the industrial revolution, boosting ocean acidity by 30%. This is known to have negative impacts on marine organisms, especially those that build their skeletons out of calcium.
Now, researchers have found a way to tackle this problem -- using nature itself.
Researchers have long been exploring the idea that seagrasses, kelps, and shell beds might be able to counteract the rising ocean acidity in local hot spots, but kelp has remained understudied until now. That’s why an interdisciplinary team from California decided to take a closer look at their acidification mitigation potential.
"We talk about kelp forests protecting the coastal environment from ocean acidification, but under what circumstances is that true and to what extent?" Heidi Hirsh, one of the authors of the study, said in a statement. "These kinds of questions are important to investigate before trying to implement this as an ocean acidification mitigation strategy."
Giant kelp (Macrocystis pyrifera) is a critical foundation species in the coastal environment, and California subtidal kelp forests have some of the most extensive surface canopies of M. pyrifera in the world. It can grow remarkably fast, especially in the upper canopy, and provide seasonal carbon storage.
California has recently made it a priority for scientists to research how sea plants such as kelp might serve as refuges for marine wildlife as waters acidify. In 2016, the state passed a bill commissioning scientific research on the ability of kelp and seagrasses to reduce ocean acidification locally, which has led to different reports.
In their study, the researchers found that near the ocean's surface, the water's pH was slightly higher, or less acidic, which suggests kelp reduces acidity. Nevertheless, the effects didn’t extend to the ocean floor, where sensitive cold-water corals, urchins, and shellfish dwell, and the most acidification has occurred.
"It's this very complicated story of disentangling where the benefit is coming from—if there is a benefit—and assessing it on a site-by-site basis, because the conditions that we observe in southern Monterey Bay may not apply to other kelp forests," Hirsh said in a statement, highlighting the potential limitations of the study.
Hirsh and the other members of the team set up operations at Stanford's Hopkins Marine Station, a marine laboratory in Pacific Grove, California. They gathered data offshore from the facility in a 300-foot-wide kelp forest, installing pH sensors to understand chemical and physical changes in conjunction with water sampling.
This allowed them to distinguish patterns in the seawater chemistry around the kelp forest. They observed that the water was less acidic at night compared to measurements taken during the day. This could be due to the upwelling of acidic, low oxygen water during the day, they argue in their conclusions.
"It was wild to see the pH climb during the night when we were expecting increased acidity as a function of kelp respiration," Hirsh said in a statement. "That was an early indicator of how important the physical environment was for driving the local biogeochemical signal."
The researchers found an overall less acidic environment within the kelp forest compared to outside of it. But the mitigation potential didn’t reach those organisms on the seafloor. This means those that live in the canopy or move into it are more likely to benefit from the kelp’s ocean acidification relief, the researchers CONCLUDE.
The study was published in the journal Scientific Reports.