That’s the latest startling evidence to emerge from research into the likely fate of reefs under climate change and rising sea levels, at the ARC Centre of Excellence for Coral Reef Studies (CoECRS).
“We’ve known for a while that having a lot of sediment in the water is bad for corals and can smother them. What we didn’t realize is how permanent this state of affairs can become, to the point where it may prevent the corals ever re-establishing,” says Professor David Bellwood of CoECRS and James Cook University.
The killer blow for a degraded coral reef is a thick mat of sand and weeds that shrouds the rocky surfaces on which the corals would normally grow, preventing them from re-establishing. This gritty algal ‘turf’ has shown itself to be remarkably hardy and, once in place, makes it almost impossible for the corals to return.
If sea levels rise, then the smothered reef ‘drowns’ and never recovers, Prof, Bellwood says. “We know this from geological history, at the time of previous sea level rises. The reason we are doing the work is to see whether or not coral reefs will be able to keep up with rising sea levels under climate change.”
But Prof. Bellwood and colleague Dr Chris Fulton from the Australian National University have also uncovered a remarkable link in the chain which explains why the algal turf can win in its ‘turf war’ with the corals.
When the water is thick with sediment and it settles on the seaweeds, herbivorous reef fish turn up their noses at the gritty food, much as humans disdain a sandwich that has been dropped on a sandy beach.
“Remarkably we found that when there is little sediment around and plenty of fish, the fish ‘mowed’ the weeds very fast, eating two thirds of their length in about 4 hours. This action by fish in keeping the algal turf down gives the corals a chance to re-establish” said Dr Fulton.
“But if there is a lot of sediment in the water, the fish go off their feed, the weeds grow, more sand settles – and the murky shroud that smothers the reef becomes more stable, often permanent. Then, when sea levels rise, the reef drowns.”
Prof. Bellwood says that in many cases the sediment is generated naturally by the reef itself, particles are swept into its back lagoon and then stirred up by wind, tide and wave to settle on the turf-covered flats. “In those cases it is almost like the reef defecating onto itself,” he adds.
In other cases the sediment is released from the land, often as a result of human activity such as farming, grazing, land clearing or construction.
In either case, if there is enough sediment in the water to settle on the seaweed, it turns the weed-eating fish off their meal. “We’re not entirely sure why this is - it may be that the sediment acts as an antacid and gives the fish indigestion by preventing their stomach acids digesting their food. Or it may simply be that fish, like people, don’t appreciate a mouthful of sand and mud.”
There is not a lot that humans can do to disrupt the natural processes that cause reefs to smother under stable algal turfs, then drown as sea levels rise, Prof. Bellwood says.
However, he adds, there is plenty we can do to reduce our own impact on the process by checking the flow of erosion off the land onto coral reefs, and by ensuring that populations of weed-eating fish are maintained at levels high enough to control the weeds - and give the corals an even chance of making a comeback.
Professor David Bellwood, CoECRS and JCU, 07 4781 4447 or 0419 422 815
Dr Chris Fulton, ANU, 02 6125 9892 or 0419 797 500
Jenny Lappin, CoECRS, + 61-(0)7 4781 4222
Jim O’Brien, James Cook University Media Office, 61-(0)7 4781 4822
Martyn Pearce, ANU Communications Office, 02 6125 5575 or 0416 249 245
Associated publication: Bellwood, D.R. and C.J. Fulton (2008) Sediment-mediated suppression of herbivory on coral reefs: Decreasing resilience to rising sea-levels and climate change? Limnology and Oceanography 53: 2695-2701.
David Bellwood | Source: EurekAlert!
Further information: www.jcu.edu.au
More articles from Ecology, The Environment and Conservation:
Turning wet biomass waste into high-value products
04.12.2013 | ttz Bremerhaven
Study shows reforestation in Lower Mississippi Valley reduces sediment
03.12.2013 | USDA Forest Service ‑ Southern Research Station
Quantum entanglement, a perplexing phenomenon of quantum mechanics that Albert Einstein once referred to as “spooky action at a distance,” could be even spookier than Einstein perceived.
Physicists at the University of Washington and Stony Brook University in New York believe the phenomenon might be intrinsically linked with wormholes, hypothetical features of space-time that in popular science fiction can provide a much-faster-than-light shortcut from one part of the universe to another.
But here’s the catch: One couldn’t actually ...
A star is formed when a large cloud of gas and dust condenses and eventually becomes so dense that it collapses into a ball of gas, where the pressure heats the matter, creating a glowing gas ball – a star is born.
New research from the Niels Bohr Institute, among others, shows that a young, newly formed star in the Milky Way had such an explosive growth, that it was initially about 100 times brighter than it is now. The results are published in the scientific journal, Astrophysical Journal Letters.
The young ...
EPFL scientists have shown how to achieve a dramatic increase in the capacity of optical fibers; Their simple, innovative solution reduces the amount of space required between the pulses of light that transport data
Optical fibers carry data in the form of pulses of light over distances of thousands of miles at amazing speeds. They are one of the glories of modern telecommunications technology.
However, their capacity is limited, because the pulses of light need to be lined up one after the other in ...
NASA's Hurricane and Severe Storms Sentinel airborne mission known as HS3 wrapped up for the 2013 Atlantic Ocean hurricane season at the end of September, and had several highlights. HS3 will return to NASA’s Wallops Flight Facility in Wallops Island, Va., for the 2014 Atlantic hurricane season.
During the 2013 mission, two unmanned Global Hawks flew from Wallops for the first time. The mission highlights included studying the Saharan Air Layer, following the genesis of a tropical storm, finding a unique hybrid core or center circulation in a redeveloped storm, obtaining measurements on the strongest side of ...
Nanosponges that soak up a dangerous pore-forming toxin produced by MRSA (methicillin-resistant Staphylococcus aureus) could serve as a safe and effective vaccine against this toxin.
This "nanosponge vaccine" enabled the immune systems of mice to block the adverse effects of the alpha-haemolysin toxin from MRSA—both within the bloodstream and on the skin. Nanoengineers from the University of California, San Diego described the safety and efficacy of this nanosponge vaccine in the December 1 issue of ...
04.12.2013 | Health and Medicine
04.12.2013 | Materials Sciences
04.12.2013 | Ecology, The Environment and Conservation
04.12.2013 | Event News
12.11.2013 | Event News
29.10.2013 | Event News