Reef survival may depend on how far baby corals travel

Far below the ocean’s surface, the Great Barrier Reef hums with life. It is not just about colorful fish or vibrant corals. Something else is happening that we cannot see.

Tiny coral larvae drift in the currents, carried away from their parents. Some travel far and some barely move at all. Where these larvae end up can decide the fate of entire reefs.

Now, scientists from the University of Queensland have unlocked a key mystery. Their new study shows how far these baby corals can go. The research also reveals why this matters more than we ever realized.

Why some coral babies survive

Corals are under pressure. Heatwaves damage them. Storms cause destruction. Oceans keep getting more acidic. Each year, the risk becomes worse. But not all corals are affected equally. PhD candidate Zoe Meziere explained why some reefs survive better than others.

“Quantifying genetic connectivity can predict the fate of populations as more isolated reefs with lower levels of genetic variation are likely more vulnerable,” said Meziere.

When coral species spread their larvae far, they swap genetic material with distant reefs. This boosts their ability to adapt and recover. Corals that keep their offspring close face greater risks. They may struggle to bounce back after disasters.

Coral species take different paths

Meziere and her team searched for answers. They focused on two coral species found across the Great Barrier Reef, Stylophora pistillata and Pocillopora verrucosa.

The species live near each other, but their ways of reproducing could not be more different. Stylophora pistillata plays it safe. It fertilizes its eggs internally. Its larvae do not venture far. Most settle nearby, just meters from their parent colony.

Pocillopora verrucosa does the opposite. It releases eggs and sperm into the sea. Currents carry its larvae far from home.

The results surprised the researchers. Stylophora pistillata larvae traveled only 23 to 102 meters. Pocillopora verrucosa larvae journeyed as far as 52 kilometers.

Professor Cynthia Riginos noted that this is the first study to quantify how connected different coral populations are across the seascape.

Why the journey of baby corals matters

The story does not stop with distance. These differences shape the future of coral populations.

Stylophora pistillata stays close to home. It forms small, tight populations. Over time, these groups grow isolated. They lose genetic diversity. That leaves them vulnerable. Pocillopora verrucosa travels widely. It links distant populations. This mixing keeps its populations strong and diverse.

“Over time, these differences have profound evolutionary impacts with S. pistillata populations being more genetically distinctive with much lower genetic diversity and smaller population sizes than the more widely dispersing P. verrucosa,” explained Professor Riginos.

Where baby corals travel

The research team did not stop after measuring dispersal. They looked deeper into the genetic maps.

Stylophora pistillata stayed loyal to its local area. Its genetic patterns showed clear boundaries between reefs. Neighboring reefs looked genetically distinct.

Pocillopora verrucosa showed no such boundaries. Its populations mixed freely throughout the reef. From one end to another, its genetics stayed consistent.

S. pistillata’s world spanned just a few hundred meters, while P. verrucosa’s world stretched across tens of kilometers.

Coral survival and recovery

Distance is only part of the story. Gene flow also plays a big role. S. pistillata had weak gene flow. Its reefs relied mostly on themselves. This isolation put them at risk. One disaster could wipe out an entire population with no outside help.

P. verrucosa showed strong gene flow, as distant reefs shared genes often. This flow allowed for faster recovery after disasters.

This means that Pocillopora verrucosa can bounce back after bleaching far more quickly than Stylophora pistillata.

Some coral babies stay stronger

Genetic diversity matters for survival. The researchers found striking differences here too.

Stylophora pistillata had low genetic diversity. Its diversity also varied wildly between reefs. The lowest levels appeared in southern parts of the Great Barrier Reef.

Pocillopora verrucosa held onto high diversity. Its genetic richness stayed stable across all reefs. S. pistillata lives in a fragile world, and P. verrucosa thrives in a far more connected one.

Smarter conservation for corals

The research offers a clear message for coral conservation efforts. Stylophora pistillata needs focused, local protection. Efforts must center on preserving nearby populations. Without these, this species faces collapse.

Pocillopora verrucosa calls for a broader approach. Large-scale conservation networks can help maintain its natural strength.

“Dispersal and connectivity are important drivers of coral adaptation, and being able to adapt is key to having healthy coral reefs in the future,” said Meziere.

New approach to reef restoration

Coral restoration should not follow a one-size-fits-all model. Stylophora pistillata may benefit from assisted migration. Moving larvae or adult corals from healthy reefs to damaged ones could restore genetic diversity.

However, such moves must be done carefully. Forcing new genes into a delicate reef might cause new problems.

Pocillopora verrucosa already benefits from strong natural connections. Protecting these migration routes may be enough.

Each coral species has its own needs. These needs are not the same. Conservation efforts should focus on these differences.

New insights for coral conservation

Coral reefs have an uncertain future. Their survival depends on how well we understand and protect the hidden connections between them.

The study, funded by the Australian Government’s Reef Trust and the Great Barrier Reef Foundation, brings new insights to reef science.

The research makes one thing clear: not all corals are the same. Some need protection close to home, while others depend on far-reaching connections.

The study is published in the journal Science Advances.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–