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January 24, 2023

Coastal Defenders: Protecting the Nation’s Coasts with Natural Solutions

Maddison Harman, a marine biologist, shows a coral sample in APL’s NAMI facility.

Maddison Harman, a marine biologist, shows a coral sample in APL’s NAMI facility.

Credit: Johns Hopkins APL

Coral fragments housed in APL’s NAMI facility.

Coral fragments housed in APL’s NAMI facility.

Credit: Johns Hopkins APL

Forty percent of the nation’s population, $9 trillion in contributions to the U.S. economy every year and 1,700 Department of Defense-managed military installations — that’s what is vested on the 95,471 miles of United States shoreline. Experts predict that within the next 30 years, the sea level along the U.S. coastline will rise an average of 10-12 inches and cause a profound shift in coastal flooding. At risk is much of the infrastructure, communities, resources and ecosystems on which our nation relies.

Recognizing the need to safeguard America’s coastlines and the value natural structures play in their protection, researchers at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, are finding ways to use materials science to support coral reef growth and restoration.

“Coral and oyster reefs, mangroves and seagrasses are all essential to attenuate large waves and storm surge,” explained Marisa Hughes, assistant program manager for the Biological and Chemical Sciences Program in APL’s Research and Exploratory Development Department (REDD). “These structures slow waves down and hold on to the ground to reduce erosion. As we adjust to live in a world impacted by climate change, we need to think about innovative ways to handle this additional threat.”

A Call to Action

Hughes is the founder and co-leader of the APL Climate Network, a Laboratory-wide initiative addressing the national and global challenges resulting from climate change. Part of that role involves incubating new research in understanding, mitigating and adapting to the rapidly changing environment. When Hughes launched a small internal challenge several years ago, Jenny Boothby, a biomaterials engineer in REDD’s Multifunctional Materials and Nanostructures Group, began to brainstorm.

“I have a background in biomedical engineering and remembered reading a paper about using coral skeletons as bone tissue implants,” Boothby recalled. “I just sat with that idea for a minute and thought, ‘What if we reverse that process?’ It’s common practice to build ceramic scaffolds for bone tissue; maybe we could do that for corals too.”

Boothby teamed up with the Lab’s marine science researchers, including Maddison Harman, a marine biologist, on internally funded projects to explore coral scaffolds. The group utilized tools and technologies within APL’s NAMI facility, a 3,000-square-foot, first-of-its-kind laboratory dedicated to unique maritime biology research, that houses aquariums sized from 10 to 1,000 gallons and the capability to make its own seawater.

Strategic Partnerships

The team’s work evolved into a collaboration with University of Miami researchers on the Defense Advanced Research Projects Agency’s (DARPA) Reefense program. The aim is to develop novel hybrid biological and engineered reef-mimicking structures to mitigate wave and storm damage, and reduce the ecological impact of current coastal protection measures.

“We’re developing hydrogels that are adhesive to underwater structures, so we can take the coral larvae when they've spawned, encapsulate them in that gel and apply the larvae directly on these artificial underwater structures,” Boothby explained. This method allows researchers to spatially control the larvae, provide them with sufficient nutrients and encourage them to grow down into the coral’s protective substrate.

The hope is that this process will lead to high survival rates, but that’s no easy task. Predators, increasing water temperatures and pollution all hinder the growth of these coastal defenders.

“Imagine trying to replant a forest, but a huge percentage of the trees you plant die without extremely active care and are continuously threatened by wildfires, underbrush growth or being chopped down,” Hughes said.

Not only is the attrition rate extremely high for new corals, but they develop very slowly, growing just tenths of a centimeter per year for certain species and taking up to 10,000 years to grow a reef from a group of larvae. But, Boothby said, once fragile larvae successfully establish themselves, they become self-sustaining. The task is tall, but healthy coral reefs are a natural and evolving solution to many threats, and could be for years to come.

“Corals build skeletons out of calcium carbonate, and they continue to build those skeletons over their life span, which is thousands of years for some of them,” said Boothby. “As they grow, the corals extend their skeletons toward the sunlight, so even as the sea water level rises, the corals will rise with it to remain close to the sunlight, and concrete can’t do that.”

Boothby is referring to human-made seawalls and bulkheads, structures that attempt to control erosion but degrade over time and are costly to maintain and build. Where corals will grow to meet the rise of sea levels for hundreds of years, seawalls are typically destroyed by waves in half a century.

The collaboration with the University of Miami, titled X-REEFS, is one of three projects funded through DARPA’s Reefense program and focuses on finding solutions for coral reefs in the Atlantic Ocean. X-REEFS researchers are currently working on the development of a model organism called Hydractinia that has similar behavior and larval stages to coral. The Hydractinia will prove useful for researchers when they can’t get their hands on real coral larvae between larvae spawns that only occur once a year. “We’ll put the Hydractinia larvae into a variety of polymers and encapsulate them, and see if they can survive and navigate to the underlying surface,” Boothby said.

The goal is that the findings from those trials will lead to further and faster developments to support coral growth in the ocean.

Cross-Laboratory Coastal Resilience Efforts

Utilizing materials science to help coral reefs grow is just one tool APL is developing as part of its larger coastal resilience toolkit. From arctic sea ice modeling to tracking carbon emissions, Laboratory researchers are leaning on the varied strengths and capabilities of sectors and departments across APL to make sustainable contributions that address national security and global challenges resulting from climate change.

“If we’re going to see how coral and oyster reefs mitigate erosion, we’re going to have to see how those waves move, and then how they change when they react with these natural structures,” Hughes said.

To do that, they’ve been working with researchers from APL’s Sea Control Mission Area and using APL’s Hydrodynamics Research Laboratory, home to a hydrodynamic tank that emulates ocean behaviors and dynamics.

“Our teammates across the Lab have been looking at modeling and modifying what hurricanes look like and what their impacts are under different conditions,” noted Hughes. “We’ve been working closely with the marine biologists in the NAMI lab to help us grow mangroves and oysters and see how they respond to our studies. It’s been fulfilling to see so many of the Laboratory’s strengths work together toward these common research goals to understand the planet.”

Just as Hughes’ initial challenge began turning wheels in Boothby’s mind to grow corals, the projects she’s working on today are already spurring future innovation with robotics and artificial intelligence applications.

“There are so many different ways we can take this research and not only make it applicable, but make it automated in the field,” Boothby said. “We’re consistently monitoring what the government is hoping to achieve and how we can best respond to those calls for action.”

Media contact: Katie Kerrigan, 240-761-9046,

The Applied Physics Laboratory, a not-for-profit division of The Johns Hopkins University, meets critical national challenges through the innovative application of science and technology. For more information, visit

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