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Coral reefs retreat from equatorial waters and establish new reefs in more temperate regions, according to a new study published in the journal Progress series in marine ecology. The researchers found that the number of young corals on tropical reefs had decreased by 85% – and doubled over subtropical reefs – over the last four decades.
"Climate change seems to be redistributing coral reefs, in the same way that it is modifying many other marine species," said Nichole Price, principal investigator at the Bigelow Laboratory for Ocean Sciences and lead author of the paper. "The trend is clear in this trend, but we do not yet know if the new reefs can withstand the incredible diversity of tropical systems."
As climate change warms the ocean, subtropical environments become more favorable to corals than equatorial waters where they have traditionally thrived. This allows the drifting coral larvae to settle and grow in new areas. These subtropical reefs could serve as a refuge for other species facing climate change and provide new opportunities for protecting these emerging ecosystems.
Researchers believe that only certain types of coral are able to reach these new locations, depending on how far microscopic larvae can swim and drift on the currents before depletion. The exact composition of most new reefs is currently unknown because of the cost of collecting data on genetic diversity and species.
"We are witnessing the transition of ecosystems to new species mixes that have never coexisted, and we do not know yet how long it will take for these systems to reach equilibrium. "said Satoshi Mitarai, an associate professor at the Okinawa Institute of Graduate Science and Technology University an author of the study. "The lines really start to fade over what is a native species and the time when ecosystems are functioning or are breaking down."
New coral reefs develop when the larvae settle on a suitable seabed away from the reef where they originate. The research team examined latitudes up to 35 degrees north and south of the equator and found that coral reef movement was perfectly reflected on both sides. The document assesses where and when "refugee corals" could settle in the future – potentially bringing new resources and opportunities such as fishing and tourism.
The researchers, an international group of 17 institutions from 6 countries, compiled a global database of studies dating back to 1974, when record keeping began. They hope that other scientists will enrich the database, making it more and more complete and useful for other research questions.
"The findings of this article underscore the importance of true long-term studies documenting change in coral reef communities," said Peter Edmunds, a professor at the University of California at Northridge and author of the paper. "The trends we have identified in this analysis are exceptionally difficult to detect, but it is of utmost importance to understand the evolution of the reefs over the next decades as the coral reef crisis unfolds. the international community will have to intensify its efforts to combine and synthesize its results as we have been able to accomplish with this study ".
Coral reefs are closely interconnected systems, and it is the interaction between species that allows them to function well. It is unclear what other species, such as coralline algae that facilitate the survival of vulnerable coral larvae, are also developing in new areas or how successful young corals can be without them. Price wants to study the relationships and species diversity in the new reefs to understand the dynamics of these evolving ecosystems.
"There are still a lot of questions about which species do and do not come to these new places, and we do not know the fate of these young corals in the longer term," 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."
Some of the research that inspired this study was conducted on the Moorea Coral Reef long-term ecological research site of the National Science Foundation, near French Polynesia, one of the country's 28 long-term research sites. and the whole world.
"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."
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