The Seychelles’ coral reefs are one of the world’s most beautiful and fragile ecosystems on the planet.
But scientists have now discovered a ‘coral highway’ that could be crucial in helping these stunning natural wonders survive.
Despite being spread over more than 1.4 million square kilometers, scientists discovered that corals from remote reefs are actually genetically related.
Researchers from the University of Oxford say this is the first evidence of an extensive network of ocean currents that helped transport coral larvae from reef to reef.
The findings come shortly after experts warned that coral reefs in the Great Barrier Reef are in ‘grave danger’ amid the worst bleaching event on record.
The remote reefs of the Seychelles (photo) are among the most beautiful but most fragile ecosystems in the world
Researchers have discovered a ‘coral highway’ of ocean currents that transports coral larvae from reef to reef and could be key to helping the Seychelles’ reefs survive
Using genetic analyzes on coral samples from 19 different locations like this one, the researchers found that the scattered reefs had a strong genetic link
With help from the Seychelles government and local reef management organizations, the researchers collected coral samples from 19 different locations.
Using genetic analysis, the researchers found a striking degree of similarity between the different coral populations.
This was an unexpected result, as previous ocean simulations had suggested that only limited connectivity should exist between the outer and inner islands.
However, using a more detailed ocean model, the researchers found that the patterns of genetic connection closely matched the patterns of ocean currents.
This suggests that when coral larvae spawn, they can be transported many thousands of kilometers before finding a new reef to settle and grow.
Dr. April Burt, lead author of the study, said: ‘This discovery is very important because a key factor in coral reef recovery is the supply of larvae.’
The researchers found that coral spawned on remote Aldabara had spread westward to the east coast of Africa via the East African Coastal Current.
From there, the coral would be carried so far north along the coast that some would eventually reach the South Equatorial Countercurrent, which would carry them back east towards the Inner Islands of the Seychelles.
As this diagram shows, ocean currents can carry coral larvae from the remote Aldabra Atoll west toward Africa before traveling north and back east to reach the Inner Islands.
These maps show the distance between the different reefs of the Seychelles
The researchers believe this discovery could be vital for the future conservation of the Seychelles’ coral reefs.
The Seychelles’ reefs have already been devastated by massive bleaching events where changes in temperature or light kill large amounts of coral.
In 1998, a particularly devastating event killed 90 percent of living corals.
In their paper, published in Scientific Reports, the researchers write: ‘The prospects for long-term survival are bleak, with bleaching predicted to become an annual event within the next 15 to 40 years.’
However, the outer islands of the Seychelles appear to be less affected by bleach, suggesting that more bleach-resistant species may live here.
If these species can travel to the Inner Islands via the Coral Superhighway, they may be able to replenish at least part of the reef.
But while long-distance travel is possible, the researchers suggest the coral moves mainly by ‘stepping stone dispersal’, jumping from reef to reef.
Coral bleaching events have caused massive damage to the population of reefs like this one on Aldabra Atoll, but some more resistant species have survived
The researchers believe the highway could transport bleach-resistant coral from one reef to another
This means that choosing the right reefs to protect can ensure that a link exists between the bleach-resistant populations and the more vulnerable reefs.
Dr. Burt says: ‘Although corals around the world have declined alarmingly due to climate change and a number of other factors, actions can be taken on a local and national scale to improve the health and resilience of the reef.
‘These actions can be more effective if we better understand the connectivity between coral reefs, for example by prioritizing conservation efforts around coral reefs that act as important sources of larvae to support the resilience of regional reefs.’
The researchers now hope that their discovery of the coral highway can help the Seychelles government and environmental groups focus their efforts more effectively.
Maintaining the right reefs allows coral larvae to travel from one place to another, using reefs like these in the Seychelles as stepping stones.
Dr. Noam Vogt-Vincent, who led the modeling, said: ‘These simulations also allow us to investigate how regular these connectivity patterns are over time, as a regular supply of larvae will be essential for reef recovery in the face of climate change.’
These efforts will be especially critical in the coming years, as rising ocean temperatures threaten to lead to massive bleaching events.
This year, studies suggest that the El Niño weather event could lead to unprecedented high temperatures.
Under a moderate El Niño, global average surface temperatures will be between 1.03 and 1.10 °C above average, while a strong event will increase temperatures by 1.9 to 2.16 °F (1.06 to 1.20 °C) will increase. above that average.
Professor Lindsay Turnbull, senior author of the paper, added: ‘The world is once again watching as El Niño devastates coral reefs in the Indian Ocean.
‘Now we know which reefs will be crucial for coral recovery, but we cannot pause in our commitment to reducing greenhouse gas emissions and halting climate change.’