New research reveals a
dramatic rebalancing of young corals from tropical to subtropical waters during
the last 40 years
July 9, 2019
Bigelow Laboratory for Ocean
Sciences
Coral reefs are retreating
from equatorial waters and establishing new reefs in more temperate regions,
according to new research. The researchers found that the number of young
corals on tropical reefs has declined by 85 percent -- and doubled on subtropical
reefs -- during the last four decades.
Coral reefs are retreating
from equatorial waters and establishing new reefs in more temperate regions,
according to new research in the journal Marine Ecology Progress Series.
The researchers found that the number of young corals on tropical reefs has
declined by 85 percent -- and doubled on subtropical reefs -- during the last
four decades.
"Climate change seems to
be redistributing coral reefs, the same way it is shifting many other marine
species," said Nichole Price, a senior research scientist at Bigelow
Laboratory for Ocean Sciences and lead author of the paper. "The clarity
in this trend is stunning, but we don't yet know whether the new reefs can
support the incredible diversity of tropical systems."
As climate change warms the
ocean, subtropical environments are becoming more favorable for corals than the
equatorial waters where they traditionally thrived. This is allowing drifting
coral larvae to settle and grow in new regions. These subtropical reefs could
provide refuge for other species challenged by climate change and new
opportunities to protect these fledgling ecosystems.
The researchers believe that
only certain types of coral are able to reach these new locations, based on how
far the microscopic larvae can swim and drift on currents before they run out
of their limited fat stores. The exact composition of most new reefs is
currently unknown, due to the expense of collecting genetic and species
diversity data.
"We are seeing ecosystems
transition to new blends of species that have never coexisted, and it's not yet
clear how long it takes for these systems to reach equilibrium," said
Satoshi Mitarai, an associate professor at Okinawa Institute of Science and
Technology Graduate University and an author of the study. "The lines are
really starting to blur about what a native species is, and when ecosystems are
functioning or falling apart."
New coral reefs grow when
larvae settle on suitable seafloor away from the reef where they originated.
The research team examined latitudes up to 35 degrees north and south of the
equator, and found that the shift of coral reefs is perfectly mirrored on
either side. The paper 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 from 17 institutions in 6 countries, compiled a global
database of studies dating back to 1974, when record-keeping began. They hope
that other scientists will add to the database, making it increasingly
comprehensive and useful to other research questions.
"The results of this
paper highlight the importance of truly long-term studies documenting change in
coral reef communities," said Peter Edmunds, a professor at the University
of California Northridge and author of the paper. "The trends we
identified in this analysis are exceptionally difficult to detect, yet of the
greatest importance in understanding how reefs will change in the coming
decades. As the coral reef crisis deepens, the international community will
need to intensify efforts to combine and synthesize results as we have been
able to accomplish with this study."
Coral reefs are intricately
interconnected systems, and it is the interplay between species that enables
their healthy functioning. It is unclear which other species, such as coralline
algae that facilitate the survival of vulnerable coral larvae, are also
expanding into new areas ¬- or how successful young corals can be without them.
Price wants to investigate the relationships and diversity of species in new
reefs to understand the dynamics of these evolving ecosystems.
"So many questions remain
about which species are and are not making it to these new locations, and we
don't yet know the fate of these young corals over longer time frames,"
Price said. "The changes we are seeing in coral reef ecosystems are
mind-boggling, and we need to work hard to document how these systems work and
learn what we can do to save them before it's too late."
Some of the research that
informed this study was conducted at the National Science Foundation's Moorea
Coral Reef Long-Term Ecological Research site near French Polynesia, one of 28
such long-term research sites across the country and around the globe.
"This report addresses
the important question of whether warming waters have resulted in increases in
coral populations," says David Garrison, a program director in the
National Science Foundation's Division of Ocean Sciences, which funded the
research. "Whether this offers hope for the sustainability of coral reefs
requires more research and monitoring."
Story Source:
Materials provided
by Bigelow Laboratory
for Ocean Sciences. Note: Content may be edited for style and length.
Journal Reference:
NN Price, S Muko, L Legendre,
R Steneck, MJH van Oppen, R Albright, P Ang Jr, RC Carpenter, APY Chui, TY Fan,
RD Gates, S Harii, H Kitano, H Kurihara, S Mitarai, JL Padilla-Gamiño, K Sakai,
G Suzuki, PJ Edmunds. Global biogeography of coral recruitment: tropical
decline and subtropical increase. Marine Ecology Progress Series, 2019;
621: 1 DOI: 10.3354/meps12980
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