Mussels act as ecosystem engineers to keep coasts healthy

"Small and innocuous animals that live within an ecosystem can play a critical role in helping coastal systems persist in the face of climate change," says Sinéad Crotty. (Credit: brian lawrence ellwood/Flickr)

The humble mussel and other faunal organisms often play an underappreciated yet important role in protecting and building coastal ecosystems, according to a new study.

“As sea levels rise, coastal ecosystems have to adapt and evolve to changing conditions,” says lead author Sinéad Crotty, associate director of science at the Carbon Containment Lab at the Yale University School of the Environment.

“This study shows that small and innocuous animals that live within an ecosystem can play a critical role in helping coastal systems persist in the face of climate change.”

Mussels (Geukensia demissa) serve as “ecosystem engineers”—organisms that directly or indirectly drive habitat construction and control the availability of resources to other organisms, according to the study in Nature Communications.

Mussels are considered indicators of water quality, helping to keep streams and rivers clean by absorbing heavy metals and filtering harmful silt and particulates as they feed and breathe in aquatic ecosystems. Their shells also provide habitat and nesting sites for insects, small fish, and plants.

In addition to these valuable characteristics, mussels also deposit large volumes of material on marsh surfaces through their feeding process. This contribution of sediment helps marshes grow through a process called accretion, which is the natural action of sand, soil, or silt washing up to the land from the seashore or river.

For the study, researchers focused on 750,000 acres of expansive salt marsh systems in the US along the coastal area known as the South Atlantic Bight, a region stretching over 150 miles from Cape Fear, North Carolina to Cape Canaveral, Florida and examined research on a variety of fauna including crabs, lugworms, and ghost shrimp.

Field research for the study included surveys of mussel cover across the South Atlantic Bight. The researchers took more detailed field measurements on Sapelo Island, a barrier island off the coast of central Georgia.

In addition to measurements taken across seasons and tidal phases, the researchers deployed three experiments designed to test mussels’ impact on accretion from small, local scales to whole landscape scales. The largest experiment involved moving over 200,000 mussels by hand from one landscape to another and measuring changes to the marsh elevation over three years.

“We found that, in reality, the effects of mussels are far greater than predicted by the models, and occur at large, landscape scales,” Crotty says.

Similar trends are likely to occur with other fauna engineers, such as bioturbating crabs or worms, the authors note. Including these ecosystem engineers in future modeling and ecosystem management will be important as sea levels continue to rise, the study’s authors say.

“This study can help us think through how we prioritize certain marsh areas for protection,” Crotty says. “Given that mussels are disproportionately important in driving accretion and other ecosystem functions, we should prioritize their protection, or outplanting, as a means to promoting all of their associated benefits.”

The study provides important data on salt marshes and climate change, says coauthor Tjeerd J. Bouma, senior scientist at the Royal Netherlands Institute for Sea Research.

“The present study provides new insight into the mechanisms by which coastal ecosystems that are highly valuable for flood defense, such as salt marshes, can cope with sea-level rise,” he says.

Additional coauthors are from the University of Florida, the Royal Netherlands Institute for Sea Research, and Utrecht University.

Source: Ken Best for Yale University