A new study has found that the very
corals responsible for establishing today's reefs are now some of the
most threatened coral species due to climate change and other man-made
stressors.
Professor John Pandolfi from the ARC Centre of
Excellence for Coral Reef Studies (Coral CoE) at the University of
Queensland (UQ) says the fast-growing, reef-building, branching
Acropora, or 'staghorn', corals are responsible for the vast amount of
modern reef growth. Although they have been around for at least 50
million years, these corals are now experiencing sharp declines in
abundance worldwide.
"Acropora became a dominant reef builder about 1.8 million years ago," Professor Pandolfi says. "And coral
reefs have been so successful ever since then due in part to its
ascendance—indeed, reefs grow most rapidly when staghorns are the
dominant reef-building corals."
The international study published today examined global
historical sea-level data, as well as global coral occurrence
data—including fossil records—dating back to more than 60 million years
ago.
The researchers found that while staghorns remained highly
successful throughout rapidly changing environmental conditions in the
past, their populations first began declining in Australia around the
time of land-use changes with European colonisation. These patterns
occur elsewhere, for example in the Caribbean Sea. More recently, these
corals have suffered declines in abundance due to bleaching and disease,
and have been almost completely wiped out across a number of reefs
throughout the world.
Yet, staghorn corals currently remain one of the most
prolific reef-builders, dominant on many reefs around the world and
across all reef habitats: reef flats, crests and slopes, submerged
reefs, and deeper reefs. They became successful because their colonies
have the highest growth rates out of all corals, paired with an ability
to regenerate when broken. Their presence is also a major factor in the
ability of reefs to keep up with sea level rise—though they are
sensitive to other environmental stresses, staghorns actually thrived
under rapid sea level changes.
Dr. Ken Johnson, from The Natural History Museum, London
explains, "These are the corals that have allowed reefs to prosper
during past intervals of rapid sea level change. But it seems as if staghorn corals will be compromised in providing this service in the future, even as we anticipate sea level rises over the next century."
The paper's lead author, Dr. Willem Renema from the
Naturalis Biodiversity Center in The Netherlands, says staghorns provide
even more benefits. "Staghorn corals contribute strongly to the
structural complexity and three-dimensionality of reefs. Therefore, they
play an important role in the ecosystem services delivered by coral
reefs. This includes coastal protection and providing habitat for
reef-associated biodiversity."
Coral reefs host more species than any other marine
environment, are crucial for healthy fish populations, and, in providing
coastal protection, they help dissipate up to 97% of incoming wave
energy. However, in the past 20 years, coral cover has diminished by as
much as 95 percent in some locations, such as the Caribbean. Coral
health is compromised by climate change and local stress such as pollution and over-fishing.
So, what would a future without staghorn corals look like?
"One need only look as far as the algal-dominated reefs of the Caribbean
to find a future in the absence of staghorn corals," Pandolfi says.
"However, there is hope. Relieving local pressures on staghorn corals—for
example, by improving water quality—helps increase their resistance to
thermal stress from climate change. So by managing local anthropogenic
stressors such as sediment runoff, dredging, and other sources of
pollution, we can insure that these corals will be at their best when
confronting global warming."
Renema et. al., 'Are coral reefs victims of their own past success?' appears in today's issue of Science Advances.
More information:
Are coral reefs victims of their own past success? Science Advances, advances.sciencemag.org/content/2/4/e1500850
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