Coral reefs are among the most diverse and productive ecosystems on Earth, but they are also under threat from rising ocean temperatures and other stressors caused by climate change.
Some corals, however, may have a secret weapon to survive the heat: their symbiotic algae.
The role of symbionts in coral health and resilience
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Corals are animals that form colonies of tiny polyps, each with a mouth and tentacles.
They also host microscopic algae called zooxanthellae, which live inside their cells and provide them with nutrients and oxygen through photosynthesis. In exchange, the corals give the algae a safe home and access to sunlight.
This symbiotic relationship is essential for the growth and survival of corals, but it is also sensitive to environmental changes.
When the water temperature rises above a certain threshold, the corals may expel the algae, causing them to lose their color and become bleached.
Bleached corals are more vulnerable to disease, starvation, and death.
However, not all corals and algae are equally susceptible to heat stress. Some corals may have more heat-tolerant symbionts, which can help them cope with warmer waters and recover faster from bleaching events.
Scientists are studying how these symbionts affect the corals' physiology, genetics, and ecology, and whether they can be used to enhance the resilience of coral reefs.
The potential and challenges of assisted evolution for coral conservation
One of the ways that scientists are trying to help corals adapt to climate change is through assisted evolution, which involves accelerating the natural processes of selection, adaptation, and acclimation.
For example, scientists may selectively breed corals with heat-tolerant symbionts, or expose them to warmer conditions in the lab or in the field, to enhance their thermal tolerance and performance.
Some studies have shown promising results from these approaches.
For instance, a study published in Global Change Biology found that adult fragments of a coral species can better tolerate bleaching and recover faster when treated with tougher heat-evolved symbionts.
Another study published in PLOS Genetics found that a staghorn coral species, a key reef builder, has enough genetic diversity to survive for another 100 to 250 years, depending on the rate of warming.
However, there are also many challenges and uncertainties associated with assisted evolution.
For example, scientists need to consider the ecological and evolutionary consequences of introducing novel or modified corals and symbionts into natural reefs, such as the potential impacts on biodiversity, competition, and disease.
Scientists also need to evaluate the effectiveness and feasibility of scaling up these interventions to restore large areas of degraded reefs.
Moreover, assisted evolution is not a silver bullet for coral conservation. It can only buy some time for corals to cope with the current and near-future levels of warming, but it cannot prevent the long-term effects of climate change, such as ocean acidification, sea level rise, and storm frequency and intensity.
Therefore, assisted evolution needs to be complemented by other strategies, such as reducing greenhouse gas emissions, protecting marine habitats, and managing local threats, such as pollution, overfishing, and invasive species.
