Due to the importance of preserving population genetic integrity, strategies to restore damaged coral reefs should attempt to retain the disturbed population’s allelic diversity; however, genetic diversity estimates for most coral populations are not available.
Corals are constantly threatened by a variety of anthropogenic and climatic factors. Coral reefs can be found in five different regions of India. All of them work on coral transplantation projects in various capacities. According to experts, while coral transplantation can help increase genetic diversity and population numbers, it cannot be a one-size-fits-all solution to the threats that reefs face.
Researchers hope to rejuvenate failing reefs by transplanting healthy coral as the health of coral reefs continues to deteriorate due to the stress of climate change. Unfortunately, they’ve had mixed results, with some transplanted coral dying while others taking root and flourishing.
Until now, it was unknown why some transplanted coral, known as “outplants,” thrived while others struggled or died. A new study led by USC Dornsife College of Letters, Arts, and Sciences researchers and published in the Proceedings of the National Academy of Sciences reveals the key to successful coral transplantation.
According to Carly Kenkel, Gabilan Assistant Professor of Biological Sciences at USC Dornsife and a corresponding author on the study, solving the mystery is critical to restoring dying reefs with transplanted coral. And reef conservation remains a global priority.
According to a study published in 2021, the Earth has lost half of its coral reefs since 1950. This global devastation has tragic consequences: According to the National Oceanic and Atmospheric Administration, reef ecosystems benefit a billion people and generate $3.4 billion in revenue for the US economy each year through industries such as fishing and tourism.
We didn’t know if the coral were performing poorly at some sites because the environment was poor, because the individual coral were poor performers, or because those individual corals just happened to be poor performers in that particular environment.
Carly Kenkel
Is it the one or the many?
Kenkel’s transplant research centers on the critically endangered Caribbean staghorn coral, Acropora cervicornis. Before the current study, scientists used different individual staghorn coral at various transplant sites and found some outplants fared better at some locations than others. But because they used different corals at different sites, they were unable to narrow down the reason for success or failure: Was it the environment, the coral, or a combination of both?
“We didn’t know if the coral were performing poorly at some sites because the environment was poor, because the individual coral were poor performers, or because those individual corals just happened to be poor performers in that particular environment,” said Kenkel.
To find the answer, Kenkel and Wyatt Million, formerly a Ph.D. student in Kenkel’s lab at USC Dornsife and the first author on the study, reduced the number of variables involved. They used clones of just 10 staghorn individuals and transplanted specimens of each at nine well-understood reef sites in the Florida Keys. They then tracked the outplants’ survival, growth, shape and size at each location. They found that both the coral and the environment mattered. No single clone proved strong across all environments; each site saw a different clone step up and adapt for success.
“This is very important information for reef restoration,” said Kenkel. “It means that the genetic diversity of coral transplants is going to be important for hedging our bets.” As researchers aim to restore reefs, they’ll want to use a variety of individuals to ensure at least one can adapt to the new home.
She likened the idea to investing: “Diversifying your portfolio is safer than betting big on one particular company because even if some companies lose money, others will win.” Maximizing genetic diversity – rather than looking for one standout coral to save the day, as has been the trend among researchers – is a wiser approach, she said.
“On these reefs, diversifying coral outplants is safer than betting on one ‘super coral’ to succeed. There will be winners and losers in every environment. And reefs are really dynamic; each environment can be really different from a coral’s perspective, and they’re going to be even more different as the climate continues to change.”
“Plastic coral”
The findings also mean scientists will want to focus on how adaptable individual coral can be to various environments, meaning how much an individual can change its shape, size, and other characteristics in response to changing environmental factors on the reef.
This “plasticity” could affect the chances of the long-term success of outplants over many generations as climate change continues. “We found that some coral were more plastic than others, and the most plastic coral – those that were able to grow biggest when it made sense to be big at a particular site or stay smallest when that was a benefit – were actually the ones who survived the best on average,” Kenkel said.
Study first author Wyatt Million – formerly a Ph.D. student in Kenkel’s lab and now a postdoc at Germany’s Justus Liebig University Giessen – warns that coral plasticity isn’t a substitute for addressing climate change at its roots, however. “I’d like to emphasize that adaptive plasticity is not a magic bullet for coral and cannot replace the goal of reversing the effects of climate change if we hope to ensure the ultimate persistence of coral,” he said.
What’s next?
Kenkel’s team now aims to dig deeper into what gives coral its plasticity and how it might affect future transplant efforts. “We’re going to be asking questions like, ‘Are there any downsides to a coral being more plastic?’ Maybe it doesn’t show up in their lifetime — maybe it affects their offspring or their ability to produce offspring,” Kenkel said.
They’ll also study how coral plasticity impacts the function of the whole reef as well as what’s happening at a cellular and molecular level to enable the coral to grow, an avenue Million finds particularly interesting. “Perhaps the most pertinent next steps include identifying the genetic basis of this plasticity and whether it belongs to the animal host or the algal symbiont,” he said.
Coral have microscopic algae living within them in a relationship known as “symbiosis.” The algae provide the coral with food and other benefits in exchange for nutrients and a safe place to live. Understanding the genetics of both organisms will help scientists predict how a coral’s plasticity might evolve over generations with changing climate conditions.
