Corals move away from stifling tropics – and establish new reefs

Number of young corals in the equatorial reefs decreased by about 85% more than the last four decades, new research shows. At the same time, their prevalence in subtropical reefs has doubled. While this undeniably poses a significant risk to the survival of the equatorial reefs, the good news is that this change could help conserve both corals and other species that live in the reefs – all of which are threatened by climate change.

reefing

"Climate change seems to redistribute coral reefs, in much the same way that it is altering many other marine species," said Nichole Price, lead author of the study and principal investigator at Bigelow's laboratory for marine sciences. the sea. "The clarity of this trend is staggering, but we do not yet know if the new reefs can withstand the incredible diversity of tropical systems."

In today's warmer oceans, subtropical areas are more comfortable for corals than equatorial areas. The drifting coral larvae are beginning to settle in areas that have never been home to corals before. New coral reefs begin to develop when the larvae find a piece of seabed far from the reef where they originated.

However, the team believes that only certain types of coral are able to reach these new comfortable areas, depending on how long their larvae can swim or drift on the currents before they run out of fat (of which they have a sufficient amount limited). As such, the exact composition of these subtropical reefs is still unknown (because it is difficult, slow and expensive to collect data on genetic diversity and species).

"There are still so many questions about which species do and do not arrive in these new places, and we do not know the fate of these young corals in the longer term yet," said Price. "The changes we see in coral reef ecosystems are staggering and we have to work hard to document how these systems work and what we can do to save them before it's too late."

The team began by compiling a global database of studies until 1974, when accounting began. They then examined tropical and subtropical reefs at altitudes up to 35 degrees north and south of the equator. The transition from older to more recent reefs is perfectly reflected on both sides of the equator, they report. On the basis of these results, the team also mapped areas "refugee corals" are likely to settle in the future. This is particularly interesting because the coral reefs bring immense resources and opportunities at communities that can access it.

However, the team also noted that it's not just corals that make a reef – they are highly complex ecosystems of interconnected species and can function properly only when these species live and mix. For example, coral (symbiotic) algae are necessary for the survival of coral larvae once settled in a new area, but it is unclear if these algae are also appearing in these new areas. At the same time, it is unclear how the new reefs will be in the absence of these algae.

The team plans to expand its research to understand the diversity and relationships between species in these new reefs.

"We are witnessing the transition of ecosystems to new mixtures of species that have never coexisted, and we do not know how long it will take for these systems to reach equilibrium," said Satoshi Mitarai, Associate Professor. at the Okinawa Institute of Science and Technology Graduate University. an author of the study. "The lines really start to fade over what is a native species and when ecosystems are functioning or are breaking down."

"This report addresses the important question of whether warming waters have resulted in an increase in coral populations," said David Garrison, Program Director at the Division of Marine Science at the National Science Foundation, which funded the research. "That this offers hope for the sustainability of coral reefs requires more research and monitoring."

The document "Global Biogeography of Coral Recruitment: Tropical Decline and Subtropical Increase" was published in the journal Progress series in marine ecology.