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Carbon dioxide from industrial activities not only accumulates in the air, but has also penetrated ocean waters since the industrial revolution, increasing the acidity of the oceans by 30%. This is known to have negative impacts on marine organisms, especially those that build their skeletons with calcium.
Now, researchers have found a way to tackle this problem, using nature itself.
Researchers have long explored the idea that marine phanerogams, algae and shell beds might be able to counteract the increasing acidity of the ocean in local hot spots, but algae have remained little studied until now. That’s why an interdisciplinary team from California decided to take a closer look at their acidification mitigation potential.
“We are talking about algae forests that protect the coastal environment from ocean acidification, but under what circumstances is this true and to what extent?” Heidi Hirsh, one of the study’s authors, said in a statement. “It is important to investigate these kinds of questions before attempting to implement it as an ocean acidification mitigation strategy.”
Giant Kelp (Macrocystis pyrifera) is a key species in the coastal environment, and California’s subtidal kelp forests have some of the largest foliage in M. pyrifera in the world. It can grow remarkably fast, especially at the top of the canopy, and provide seasonal carbon storage.
California recently made it a priority for scientists to research how marine plants such as algae could serve as a refuge for marine life when the waters become acidic. In 2016, the state passed a bill commissioning scientific research into the ability of marine algae and seagrasses to locally reduce ocean acidification, which has led to several reports.
In their study, the researchers found that near the ocean’s surface, the pH of the water was slightly higher or less acidic, suggesting that algae reduce acidity. However, the effects did not extend to the ocean floor, where sensitive coldwater corals, urchins and mollusks dwell, and the greatest acidification occurred.
“It’s this very complicated story of unraveling where the benefit comes from, if there is an advantage, and evaluating it site by site, because the conditions we observe in southern Monterey Bay may not apply to other kelp forests,” Ha Hirsh said in a statement, highlighting the study’s potential limitations.
Hirsh and other team members commenced operations at Stanford’s Hopkins Marine Station, a marine laboratory in Pacific Grove, California. They collected offshore data from the facility in a 300-foot-wide kelp forest, installing pH sensors to understand chemical and physical changes in combination with water sampling.
This allowed them to distinguish patterns in seawater chemistry around the kelp forest. They observed that the water was less acidic at night than measurements made during the day. This could be due to acidic and oxygen-poor water rising throughout the day, they argue.
“It was amazing to see the pH rise overnight when we expected higher acidity as a function of algae respiration,” Hirsh said in a statement. “This was an early indicator of how important the physical environment was in driving the local biogeochemical signal.”
The researchers found an overall less acidic environment within the kelp forest than outside it. But the mitigation potential hasn’t reached those organisms on the sea floor. This means that those who live in or move in canopy are more likely to benefit from ocean acidification relief from algae, the researchers CONCLUDE.
The study was published in Scientific Reports.
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