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Coral restoration efforts could be dramatically improved with technologies that support the survival and growth of baby corals, suggests a new study.

Findings showed that two novel devices, the Underwater Zooplankton Enhancement Light Array (UZELA) and 3D printed artificial settlement modules, could together boost the population of a species of coral native to Hawaii.

In a previous study led by researchers at The Ohio State University, scientists found that UZELA successfully attracted nearby zooplankton, microscopic organisms that coral feed on. That study found that the light greatly enhanced local zooplankton density and increased the feeding rates of adult coral. In this one, they found that combining the light with 3D printed housing modules could double survivorship and quadruple the growth of baby corals, which are called recruits.

Coral reefs are vital drivers of the marine ecosystem. Yet as rising global temperatures and acidifying oceans threaten their food sources, many coral reefs are now experiencing severe population declines. Typically, these losses would be recovered slowly via a process called coral recruitment, where adult coral colonies reproduce by releasing small larvae to recolonize the reef.

But juvenile corals often die before they can become larger colonies, creating a population bottleneck that nature can't always overcome alone, said Shannon Dixon, lead author of the study and a graduate student in earth sciences at Ohio State.

"Coral recruitment is super important for reef persistence throughout time," she said. "Just like how trees drop seeds to create new trees, the life cycle of coral is very similar."

While this process also acts as a way for coral to cope with environmentally stressful events like heat stress or cyclones, some reefs, like the Florida Keys, experience little to no coral recruitment, so human intervention is needed to ensure the reef continues to thrive, said Dixon.

Now, as the first team to exhibit a combined technology method for coral recovery, the researchers in this study reveal that the presence of UZELA and the complex settlement modules could reduce the time coral need to complete this vulnerable "baby" phase of their lives, while accelerating the timeline for establishing genetically diverse coral populations. More importantly, by exposing coral recruits to higher concentrations of zooplankton, these tools worked to double coral survivorship and quadruple their growth.

"Making reefs more habitable for coral recruits is extremely important," said Dixon. "If we can create the ideal living conditions for struggling coral reefs, we'll see more survivorship, higher biodiversity, and more reefs in geographical locations than we would see without these tools."

The study was recently published in the journal

On the quest to help coral offspring survive a harrowing early life, scientists used UZELA in tandem with three types of artificial ceramic settlement modules.

Of the 30 modules used in this experiment, 10 had flat surfaces, 10 were smooth domes, and 10 were spiral domes. Half of the modules of each type were coupled with UZELA to concentrate zooplankton, while the other half did not have UZELA as a control. Researchers had theorized that certain domes would be better for the survival and growth of the coral because of their complexity, which turned out to be true.

After six months on the reef, no corals on the flat surface survived, but some had on both the smooth and spiral domes. However, those that grew with UZELA on the smooth and spiral dome settlement modules survived at twice the rate of those that didn't have UZELA.

Unsurprisingly, these findings are consistent with the idea that coral larvae tend to avoid horizontal surfaces, preferring to settle in a structure's minute crevices, said Dixon.

At the end of the experiment, all surviving coral recruits appeared healthy, suggesting the tools this team used are extremely adept at improving coral feeding. This result is great news during a time when global coral mortality is reaching record highs, said Andrea Grottoli, senior co-author of the study and a professor in earth sciences at Ohio State, but it is especially meaningful for baby corals, as they usually require lots of high-quality nutrition to prosper.

"This outcome is directly applicable to what we might expect survivorship and growth to look like on other reefs using these technologies," she said. "It just goes to show how a little goes a long way when you give coral a little more to eat."

UZELA is currently patent pending in three countries, including the United States. This work illustrates how effectively the project could be scaled up for use in active coral restoration programs, potentially making both local and worldwide conservation efforts faster and far more effective. But there's only so much that man-made gadgets can do for the coral community, said Grottoli.

"Technological interventions like UZELA and the settlement modules will help some corals survive in some places, sometimes," she said. "But with all technologies, there are real costs and real efforts associated with them."

One of the most important keys to bridging the current coral survivorship gap may be to determine the impact this study's devices will have on multiyear coral recruit survivorship, maturation and reproduction, which the team plans to investigate.

"This project highlights how wonderfully you can combine technological interventions that you didn't necessarily see fitting together, but push the envelope to solve problems in new multidisciplinary ways," said Dixon. "Research like this allows us to embrace the collaborative nature of science to make the environment better for coral."

Co-authors include Ann Marie Hulver and Jacob Welter from Ohio State, Hendrikje Jorissen, Robert J. Toonen, and Joshua S. Madin from the University of Hawaiʻi, and the R3D Consortium.