Coral reefs are in trouble. Physical destruction from dredging and coastal development, pollution, climate change, and ocean acidification have all contributed to the decline of coral reefs around the world, according to the Environmental Protection Agency.
Despite these challenges, corals have shown some signs of hope and different genes in theses resilient animals can potentially protect one another from diseases. A new study published this week in the journal Scientific Reports finds that disease-resistant corals can help “rescue” corals that are more vulnerable to disease, under the right living arrangement
A team from the University of California, Davis, the University of Florida, and the University of South Florida monitored a disease outbreak at a coral nursery at Little Cayman in the Caribbean. They found that corals of the same genetic makeup, or genotype, grown together are often more vulnerable to disease than the ones that grow among a mixture of different genotypes.
“We saw that some corals were more resistant to disease just by being around other corals that were particularly resistant,” said lead author Anya Brown, an assistant professor at the UC Davis Bodega Marine Laboratory, in a statement. “Proximity to these resistant genotypes helped buffer the susceptible corals from the effects of the disease.”
The study also found that some of the more vulnerable corals can be “rescued” and helped along by resistant genotypes.
In 2019, an outbreak of white band disease spread through the Central Caribbean Marine Institute’s coral nursery in Little Cayman. White band disease is a devastating bacterial disease that can completely destroy coral tissue in Caribbean staghorn coral (A. cervicornis) as well as elkhorn coral (Acropora palmata). The nonprofit organization worked with the study’s academic authors to monitor the nursery’s population of endangered A. cervicornis.
Coral fragments in the nursery were attached to plastic PVC frames before the outbreak. Coral from a single donor colony was housed in some frames, while others had corals from multiple donor colonies with a mixture of genotypes.
The team tracked the presence of the disease in 650 fragments of coral for five months and found that the corals living on the frames with a variety of genotypes were “substantially” more resistant to white band disease.
These stronger disease-resistant coral can help protect the more vulnerable ones similar to how mass vaccination works to protect groups of humans. Vaccinated people who are resistant to a specific disease create a barrier that weakens the disease’s ability to move among the population and onto the next susceptible person. This is sometimes called herd immunity.
The importance of genetic diversity for disease resistance is also seen in farming. Monocrops, or where the same crop is planted in the same place every year, tend to be more susceptible to disease than diverse systems where the crops are more mixed.
This study suggests a similar dynamic is at play among the ocean’s coral reefs and provides some evidence that genetic diversity can help reduce disease transmission among corals. It also demonstrates the importance of considering how corals are arranged in nurseries and reef restoration projects to prevent the spread of diseases like white band disease.
“I hope people working with coral nurseries use this as a springboard to see how this influences the spread of disease,” Brown said. “Nurseries that intentionally arrange corals with mixtures of genotypes can help corals vulnerable to disease thrive. This can help build coral resilience by repopulating reefs with a diverse genetic mixture of corals.”