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Just like the land heat waves we are familiar with, Marine heatwave Currently Exacerbated by climate change. These extreme warm water events Some of the most devastating impacts Climate change now poses a major threat to marine life.
Coral Reef The ocean is home to a quarter of all life, and is also the most vulnerableThis is a scary situation because many people Dependence on coral reefs For their survival and livelihood.
As climate change pushes corals beyond their limits, a key question is Why do different corals have different sensitivities? To warm waters.
in our New research Scientific progressIn a new study, we examined the genes of hundreds of corals during the 2015-16 El Niño heatwave. Our results suggest that heatwaves have hidden effects on the genetic makeup of reef-building corals. Understanding this could help scientists increase the resilience of coral reefs to future heatwaves.
Pushing corals out of their comfort zone
Coral is Highly adaptable to temperature The temperature of local waters was even 1 degree Celsius higher than normal, forcing them to leave their comfort zone.
The water temperature is abnormally warm Damage to important relationships Interactions between stony corals (reef builders) and their symbiotic partners (microscopic algae that provide food for the corals). This can lead to coral bleaching and, in many cases, death.
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The tropical heatwave at our research site, Kiritimati (Christmas Island), in the central Pacific, lasted a world record 10 months. This caused widespread coral bleaching, providing an opportunity to determine why some corals died while others survived.
Cryptic diversity of widespread coral species
We focused on the widespread lobed coral (Porites). This species is one of the most heat tolerant corals, although Almost 90% of coral cover lost On Kiritimati, more than half of the leaf corals survived.
In fact, some Porites The colonies did not fade at all.
Why?
Using genomic tools, we identified three different types of Porites These lineages may represent different species that are indistinguishable to the naked eye but are genetically distinct.
This biodiversity is called “Cryptid diversity” or “hidden diversity”. Although cryptic diversity is widespread in corals, its ecological significance remains unclear.
Marine heat waves threaten hidden diversity
We found a genetic lineage Porites Highly sensitive to heat waves: only 15% of coral colonies survived, compared with 50-60% for other lineages. Thus, even among corals widely considered to be resilient, heat waves can have hidden impacts, threatening diversity that is invisible to the naked eye.
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If future marine heatwaves continue to have similar impacts, eventually sensitive genotypes like these could be wiped out completely, reducing the genetic diversity of coral reefs.
Because cryptic lineages and hybridization between species can provide Potential pathways for future adaptationIn contrast, loss of genetic diversity could limit future adaptation to a changing environment, making an already serious problem even more severe.
Forced to break up
So why Porites How do the various lineages on Kiritimati differ in their survival?
One hypothesis is that they have symbiotic partners that differ in their sensitivity to heat. Using metabarcoding, a technique that attempts to identify all the organisms in a coral’s tissue, we determined which symbionts were partnered with which corals before, during, and after the heatwave.
we discover Porites Before the heat wave, people of different descent had different partnerships. Porites Species transmission through symbionts Generation after generation So these relationships may have occurred over many generations.
(Julia K. Baum), Author provided
However, by the end of the heat wave, Porites The unique algal partners were nearly wiped out. Survivors from all lineages had similar symbionts, suggesting that the special relationship between the partners was lost under extreme temperatures.
As a result, not only are cryptic coral lineages threatened with local extinction, but their special symbiotic relationships are also being forcibly disrupted.
Impact on protecting coral reefs
Due to climate change and other threats, we are currently experiencing Biodiversity crisisOur findings highlight that the impact of this crisis goes beyond what we can see.
Cryptic species often occupy Unique ecological niche and plays a specific role in the ecosystemUncovering these hidden differences could enhance our understanding of how ecosystems work. But the worry is that we may be losing this critical diversity before we discover it.
Continued research into cryptic diversity may be critical to building climate-resilient ecosystems. Recovery MethodsFor example, it could help coral reefs better tolerate future climate warming.
finally, Greenhouse gas emissions must be reduced rapidly to curb global warmingWhile targeted efforts to protect coral reefs against climate change may buy limited time, the heatwave currently sweeping the world’s oceans underscores that ocean temperatures are too hot for corals and that we need to act quickly to mitigate the damage.
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