A predator’s role in storing carbon

Publication specs

Title: Predators help protect carbon stocks in blue carbon ecosystems

Authors: Trisha B. Atwood, Rod M. Connolly, Euan G. Ritchie, Catherine E. Lovelock, Michael R. Heithaus, Graeme C. Hays, James W. Fourqurean, Peter I. Macreadie

Journal: Nature Climate Change

Year: 2015

When you think about carbon (C) storage in an ecosystem, you may think about a lush tropical forest sucking up carbon dioxide from the atmosphere. What isn’t considered as often is coastal marine ecosystems, which take up C 40 times faster than tropical forests. An estimated 25 billion tons of C is buried in vegetated coastal habitats like seagrass meadows, mangroves, and salt marshes, making them the most C rich environments in the world. Degrading these “blue carbon ecosystems” releases C into our atmosphere, fueling climate change. But did you know that losing predators like sharks within these environments also indirectly leads to the release of C?

One example of this comes from Western Australia where sharks influence how often herbivores like dugongs and sea turtles feed in a given time period. These grazers like to eat in places where there are very few tiger sharks waiting to attack them. In habitats where sharks are present, they spend more time watching their backs. This means that less seagrass is being consumed, and in some cases is only being cropped. In the areas where sharks are present and there are fewer grazers, the seagrasses are mostly slow growing species, which promotes the storage of C since it is not breaking down quickly. In other words, where the abundance and behavior of herbivores are being controlled by predators, growth of vegetation is enhanced, which leads to increased storage of C.

Scientists don’t know the total global area affected by the loss of predators. However, if only 1% of the vegetated coastal areas were to be affected, about 460 million tons of C would be released, equivalent to the emissions from 97 million cars. In order to protect these blue carbon ecosystems, balanced conservation efforts will need to occur where the habitat, predators, and herbivores are protected together.

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