Mussels and marshes save each other from drought

As coastal ecosystems feel the heat of climate change, new research shows mussels and marsh grass form a partnership that is mutually beneficial. Their teamwork may be critical to helping them bounce back from extreme climatic events like drought.

The study shows that when mussels pile up in mounds around grass stems, they provide protection by improving water storage around the grass roots and reducing soil salinity. With the mussels’ help, marshes can recover from drought in less than a decade. Without, it can take more than century.

“It’s a story of mutual benefit between marsh grass and mussels,” says Christine Angelini, assistant professor of environmental engineering sciences at the University of Florida.

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The mussels, “protect and then accelerate the healing of drought-stricken marshes.” Saving the marshes, Angelini says, has not only environmental benefits but also economic ones.

“Marsh die-off and loss are major issues that can affect land value, fisheries, and water quality. Even if just a little bit of vegetation survives, it makes a huge difference in how quickly the marsh comes back.”

Severe droughts

The researchers became interested in the topic after three severe droughts in the Southeast over the past 17 years caused a major die-off of cordgrass, the region’s dominant, marsh-structuring plant.

Using Google Earth, researchers considered 13 sites that contained relatively large marsh areas likely to experience drought-associated grass die-offs. They selected nine that spanned a little more than 150 miles of southeastern US coastline from southern Georgia to central South Carolina at the conclusion of a severe, two-year drought in June 2012.

They found that wherever there were clusters of mussels embedded in the mud around the base of the grass stems, the grass survived; in fact, grass growing in mussel clusters had a 64 percent probability of surviving versus a 1 percent probability in areas where there were no mussels.

The researchers suspect mussels protect marsh grass during severe drought because they pave the marsh surface with their ribbed shells and attract burrowing crabs that excavate underground water storage compartments.

‘Cooperation is key’

The next step, Angelini says, is to figure out whether transplanting mussels into drought-vulnerable marshes could offer a low-cost solution for homeowners to improve the resilience of their own back yards. They are also testing whether other at-risk ecosystems—seagrass meadows or, perhaps most notably, coral reefs—may be similarly protected by keystone mutualisms.

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“More generally, this work highlights how cooperation is key for an ecosystems ability to withstand and bounce back from climate change,” says study coauthor Brian Silliman, associate professor of marine conservation Biology at Duke University. “Without cooperation, US Southeastern salt marshes would likely be in a dramatic, spiraling decline because of increasing droughts stress.”

“This is a very good example of how the diversity of life in a salt marsh promotes resilience to climate and environmental change,” says David Garrison, program director in NSF’s Division of Ocean Sciences.

Other researchers from Duke University, Swansea University, the University of Groningen, Radboud University, and the Royal Netherlands Institute for Sea Research are coauthors of the paper in Nature Communications. The National Science Foundation’s Division of Ocean Sciences and Division of Environmental Biology funded the work.

Source: University of Florida