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Unexpected coral adaptations challenge conservation plans

A recent study from USC Dornsife has revealed some unexpected details about the effects of global warming on corals. According to the research, the adaptations of a common Caribbean coral could have significant implications for our approach to conserving these vital marine ecosystems.

Mountainous star coral

The study was focused on the mountainous star coral, Orbicella faveolata, a species frequent in Caribbean waters. The goal was to determine whether coral populations that had endured increased temperatures could pass this heat resilience to their progeny. 

“Orbicella faveolata, commonly known as the mountainous star coral, is a dominant reef-building species in the Caribbean, but populations have suffered sharp declines since the 1980s due to repeated bleaching and disease-driven mortality,” wrote the researchers.

“Prior research has shown that inshore adult O. faveolata populations in the Florida Keys are able to maintain high coral cover and recover from bleaching faster than their offshore counterparts. However, whether this origin-specific variation in thermal resistance is heritable remains unclear.”

Heat-tolerant corals 

The popular assumption among scientists has been that heat-tolerant coral parents would produce offspring with similar adaptations for heat resistance.

However, Professor Carly Kenkel and her team discovered a contradiction. They found that the offspring of a population less acclimated to heat showed better resilience when subjected to higher temperatures compared to those from a heat-tolerant lineage.

“The study findings have significant implications for how we think about saving coral reefs,” said Professor Kenkel. “It’s not as simple as just breeding more heat-tolerant corals.”

How the research was conducted 

For the investigation, the scientists collected gametes (reproductive cells) from coral reefs in two distinct sites in the Florida Keys. They then crossbred the corals in controlled conditions, and exposed the larvae to elevated temperatures.

The team also examined the genes of these corals to detect signs of stress under heightened temperature conditions.

Study limitations

The results of the study suggest that the ability of coral offspring to withstand heat may be determined by a range of factors. This includes the frequency with which their parent corals may have bleached or faced other environmental challenges.

However, it is important to note that this research was focused on a single coral species. Other coral species might respond differently, and the study’s controlled lab setting does not capture the myriad factors that impact coral reefs in natural habitats.

Future research 

The scientists plan to delve deeper into coral adaptation mechanisms, factoring in their historical experiences and interactions with other organisms, as well as the overall health of the reef system.

Professor Kenkel noted that coral rescue may require a more comprehensive approach. “Instead of focusing solely on breeding more heat-tolerant corals, we might need to consider other factors affecting coral survival and more diverse interventions.” 

Study implications 

“The documented resilience of adult corals to recurrent heat stress and bleaching in environments with high and variable temperatures may come with highly consequential trade-offs,” wrote the researchers.

“In this study, we show that larvae from a site that routinely experiences and recovers from heat-induced bleaching significantly underperformed relative to larvae from a cooler, less variable reef site.” 

“The unexpected outcome that more thermally tolerant O. faveolata produced poorer quality offspring challenges the prevailing paradigm that breeding vulnerable populations with thermally tolerant individuals can contribute to genetic rescue.”

The research is published in the journal Global Change Biology.

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