Coral restoration
An article by Paul Marks in New Scientist describes what sounds like interesting work by Baruch Rinkevich and colleagues on coral gardening (Intensive care heals damaged reefs). But the article doesn't refer to other projects to cultivate coral world wide which have had varying degrees of success.
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Intensive care heals damaged coral reefs
09 July 2006
From New Scientist Print Edition.
Paul Marks
TERMS like "triage" and "transplant" are usually the stuff of hospital emergency rooms. Now the same phrases are turning up in an entirely different context as conservationists struggle to repair the damage done by human neglect and natural disasters to coral reefs, some of the oldest and most diverse ecosystems on Earth.
Great swathes of the world's reefs are in a desperate state after years of damage, and marine conservationists are fighting to provide the necessary intensive care. One approach they are taking to repair and rebuild them is to send down divers to literally glue the damaged reefs back together, using coral nurtured in large underwater nurseries.
Reefs are under attack from all sides as human-inflicted damage amplifies natural wear and tear. Hurricanes and tsunamis can cause injuries that may take decades for a reef to repair naturally. Meanwhile, destructive fishing practices, pollution, ships running aground and climate change pose an even more serious threat.
A report issued by the UN Environment Programme in April this year warned that 30 per cent of the world's coral reefs are either already dead or seriously damaged. The scale of human impact on coral reefs was further highlighted late last month when scientists in the US and Australia found fossil evidence that reefs have suffered more during the past 30 years than over the preceding 220,000 (New Scientist, 24 June, p 16).
After decades of neglect and misuse, however, restoration technologies are starting to make a difference. Before, a shipwreck on a reef caused irreparable damage. Now at least some of that damage can be repaired.
"In the last 10 years, we have had eight major ship groundings on reefs in Florida, including giant bulk carriers loaded with cement and a nuclear submarine," says Walter Jaap of the Florida Marine Research Institute in St Petersburg (see "Accident victim nursed back to health"). "After each, we immediately undertake a triage effort on the reef to assess the damage to the habitat. We then salvage what we can of the viable living coral. We often rescue up to 500 colonies, varying in size from a fist to a metre across."
These colonies are made up of living coral polyps - funnel-shaped organisms that build reefs by constructing a protective skeleton of calcium carbonate. Divers can graft the rescued polyps back onto the reef base using hydraulic cement or epoxy putty; the acidity of the adhesive can be adjusted to ensure it does not harm the polyps.
Areas irreparably gouged by ships can be filled with concrete hemispheres a metre across and shot through with large holes. These "reef balls" form a scaffold that the surviving colonies can be glued onto. Where reefs are too severely damaged to be repaired this way, whole artificial reefs can be constructed from concrete blocks, reef balls or even old car tyres.
Underwater gardens
This still leaves the problem of acquiring sufficient quantities of viable coral polyps. Harvesting corals from other reefs tends to "abuse and inflict trauma on the donor reefs", says Baruch Rinkevich of Israel's National Institute of Oceanography. So inspired by successful forestry practices, Rinkevich, his colleague Shai Shafir and partners from the European Union's Reefref project are developing ways to set up subsea "nurseries" of young coral.
“Coral relies on a healthy broth of natural nutrients in the surrounding water”
Polyps rely on a healthy broth of natural nutrients in the surrounding water and are highly sensitive to temperature and salinity changes, which makes it difficult to grow coral in the lab. "Corals grown in captivity don't look right - the size of branches and the branching patterns are all wrong," Rinkevich says. "We need to grow coral in its proper environment if it is to thrive."
To test the idea of underwater coral gardening, Rinkevich and colleagues set up 10-metre-square horizontal nets 6 metres beneath the surface of the Red Sea near Eilat, Israel. The nets were held from below by metal wires anchored to the sea floor and supported from above by buoys. More than 6800 cuttings, otherwise known as "nubbins", were collected from 11 species of local coral and nurtured in trays placed on the nets. After 10 months, more than 90 per cent of them were still alive.
Natural water flow supplied the corals with much more of the plankton that they feed on than would have been available in captivity, Rinkevich says, and as the nets sway with the waves the motion dislodges harmful debris and sediment. The technique is economical to operate too, as only two divers were needed to run the entire operation.
Now Rinkevich and colleagues are stringing up scores of underwater coral nurseries close to ailing reefs in Thailand, Singapore, the Philippines, Israel and Jamaica. Divers take cuttings from local coral and glue them to trays measuring 80 by 60 centimetres, sticking each nubbin to one of about 100 posts dotted across the tray's surface.
The corals are thriving in their natural environment and also feed back into it. Rinkevich likens this to the way trees in a nursery attract birds and insects. "With coral, we hope to do the same by growing them alongside the vertebrates, invertebrates and fish they will live with in the wild." Once mature enough, the corals can then be cemented back onto the base of a natural reef.
Rinkevich's efforts will go some way towards rescuing and rehabilitating many coral reefs harmed by shipwrecks and other mechanical damage. However, a more serious threat may be still to come. Human-induced climate change is altering ocean temperatures and salinity, while CO2 emissions are increasing the acidity of the oceans.
The symbiotic relationship with photosynthetic algae called zooxanthellae that corals rely on makes them extremely sensitive to temperature and salinity changes. The algae, which lend coral its vivid colour, provide energy through photosynthesis in exchange for nitrogen and carbon dioxide from the coral. But just a few degrees outside their preferred temperature range of about 20 to 30 °C, and a few per cent outside a 34 to 37 per cent salinity range, and the algae are forced off the polyps, leaving the coral "bleached" and so short of energy that they may die.
In 2002, when Australia's Great Barrier Reef was hit hard by unseasonable warming, 95 per cent of its coral was adversely affected, and around 3 per cent of it died off completely. Though David Wachenfeld, a director of the Great Barrier Reef Marine Park Authority in Townsville, Queensland, describes this as the "worst ever recorded bleaching event", the reef got off lightly: its sheer size has meant much of it has been able to recover after conditions returned to normal, with surviving coral repopulating damaged areas. Prolonged ocean warming may make recovery harder in the future.
Measures to control climate change are crucial for coral's future, as CO2 is acidifying the oceans, warns Ken Collins, an oceanographer at the University of Southampton in the UK: "If we are not careful, we are likely to see acid oceans that simply dissolve the reefs in 50 to 100 years' time."
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