Heat wave kills seagrass resulting in major CO2 emissions

In 2010, an unprecedented marine heat wave in Western Australia drove water temperatures up by 2 to 4 degrees Celsius for over two months. Researchers discovered that the loss of seagrass meadows at Shark Bay, which is one of the largest seagrass ecosystems on the planet, resulted in major carbon dioxide emissions.

Ultimately, seagrass loss at Shark Bay led to 9 million metric tons of carbon dioxide emissions over the three years following the heat wave. This amount is roughly equivalent to driving 1.6 million cars for a year or the annual carbon dioxide output of 800,000 homes.

“The widespread losses in the summer of 2010/11 were unprecedented,” said first author Ariane Arias-Ortiz. “The net loss of seagrass extent was accompanied by a dramatic shift in seagrass cover. What remained was sparser with ‘dense’ seagrass areas that had declined from 72 percent in 2002 to 46 percent in 2014.”

The researchers used satellite imagery from the Department of Biodiversity, Conservation and Attractions of Western Australia and soil samples from 50 sites to estimate the potential carbon dioxide emissions.

Professor Carlos M. Duarte is a professor at King Abdullah University of Science and Technology and the lead author of the study.

“This decrease is significant because seagrass meadows rank among the most intense CO2 sinks in the biosphere, giving them the name ‘Blue Carbon ecosystems.’ They take up and store CO2 in their soils and biomass through biosequestration. The carbon that is locked in the soils may remain there for millennia if seagrass ecosystems, which offer physical protection to these stocks, remain intact,” explained Duarte.

Study co-author Dr. Oscar Serrano added: “When you have an event such as the losses at Shark Bay, not only do you lose the benefits of CO2 uptake by seagrasses but also any carbon sequestered by the seagrasses is released back into the atmosphere as CO2 when the seagrasses decompose.”

Arias-Ortiz pointed out that climate change is predicted to increase the frequency of extreme weather events. Now that these carbon stores have been compromised, she said, it further stresses “the importance of reducing greenhouse gas emissions and implementing management actions to avoid adverse feedback on the climate system.”

The study is published in the journal Nature Climate Change.

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By Chrissy Sexton, Earth.com Staff Writer
Image Credit: Oscar Serrano