A report released today from the Australian Institute of Marine Science on the effects of Category 5 Cyclone Hamish, which, in March this year, chewed its way along 500 kilometres of the Great Barrier Reef (fortunately missing Magnetic Island) and caused damage to the reefs, which could take 15 years or more to restore themselves, brings again into focus the vulnerability of Magnetic Island to these storms, which the International Panel on Climate Change predicts will increase in both frequency and intensity.

While some Magnetic Islanders can remember the massive impact of Category 4 Cyclone Althea on Christmas Day 1971, when it was reported that 90 percent of the houses in Picnic Bay, 60 percent in Nelly and 40 percent in Arcadia were wiped out, we can only imagine the unbelievable damage of a Cat 5 cyclone on people, buildings and infrastructure.

But for the Island's surrounding coral reefs, which support so much of the marine life and beauty of Magnetic, and is such a major part of Magnetic's appeal as a tourist destination, we should also be deeply concerned.

AIMS' Dr Hugh Sweatman told Magnetic Times, “Inshore reefs (as occur around Magnetic Island) are not so well cemented as offshore reefs in general and would be more susceptible.”

Dr Sweatman admits that reef damage is very variable and depends on the path of the cyclone and how particular reefs are exposed to wave action. "But reefs which are not usually affected by trade winds and not used to wave action from them can be home to fairly delicate corals which are not so well concreted.”

According to Dr Sweatman, reefs which are rarely exposed to north westerly winds, for instance, may encounter such forces in a cyclone and be ill-equipped to survive the onslaught.

The Great Barrier Reef was severely buffeted by Severe Tropical Cyclone Hamish, which roared down a substantial part of the reef system, causing widespread though variable damage and in some places reducing coral cover from 70 per cent to 10 per cent.

In a wild 16 hours or so between 8 and 9 March, Hamish made its presence felt on the GBR, leaving a legacy that, according to AIMS, could take up to 15 years to overcome.  Bureau of Meteorology reef weather stations recorded wind speeds of over 200km per hour as the eye of the cyclone passed over about a quarter of the length of the GBR.

AIMS deployed two research teams soon after the cyclone hit to assess the damage caused.  Preliminary results of those surveys are being made available publicly today.

While the GBR regularly experiences cyclones, TC Hamish was unusual in that it ran along the coast instead of crossing on to land quickly.  This meant that about 25 per cent of the length of the GBR was directly in the path of the destructive force of a Category 5 cyclone.

Hamish moved from the Coral Sea on to the Great Barrier Reef on 8 March 2009 and tracked south parallel to the coast, downgrading from Category 5 to 4 during its passage along the reef.  Most cyclones track fairly directly from the Coral Sea to the coast and so only relatively small areas of the GBR are affected.  By running parallel to the coast for about 500km, Hamish damaged much more of the GBR than most recent cyclones.

AIMS surveyed 24 reefs in late March and April.  The teams found that many were damaged, but the extent of damage varied greatly between reefs and also within different parts of individual reefs.

“The damage was patchy,” Dr Ray Berkelmans said.  “The exposed faces of reefs lost most of their coral, but surprisingly delicate corals survived where a curve in the reef gave some shelter or where one reef was protected by a neighbouring reef..  We found the greatest damage on reefs not sheltered by other reefs that were close to the eye of the cyclone.”
 
“The type of damage also depended on the distance from the cyclone track and the type of coral community present,” he said. “Reefs within 30km of the cyclone eye sustained most damage, with around half of the 500 reefs in this area exposed to destructive waves and suffering significant damage.”
 
Damage ranged from “exfoliation”, where the reef matrix was removed along with all that grew on it, leaving bare limestone, to “scouring” that essentially stripped all living tissue from living corals, to coral breakage in which massive coral heads as well as more delicate branching corals broke off.
 
“The most damaged areas of reef had forests of green slime, spectacular but ephemeral blooms of green algae, suggesting a pulse of nutrients had been released into the ecosystem,” Dr Sweatman said. The source of these additional nutrients has now become an interesting research question.
 
Most damage was sustained from the surface down to eight metres, but on some reefs it extended down to 15m.  Loss of coral cover was variable, dropping from 35-70 per cent to 10-15 per cent. 
 
Based on past experience with similar reefs, the researchers estimate that coral should recover in eight to 15 years, if there are no further major disturbances such as cyclones or coral bleaching or declines in water quality which might reduce the resilience of these reefs.
 
Dr David Wachenfeld from the Great Barrier Reef Marine Park Authority said the summer of extreme weather earlier this year that brought a triple whammy of pressures to the Great Barrier Reef is a stark reminder of the potential impacts of climate change.
 
"We saw stifling heat, heavy rainfall causing significant flooding, and destructive winds from cyclone Hamish, all compounding to have a hard hitting impact on the Great Barrier Reef."
 
"The research results from the AIMS surveys continue to remind us of the remarkable nature of this extraordinary ecosystem and the importance of ensuring that it is as healthy as possible to withstand the impacts of more extreme weather events in the future."
 
"The Great Barrier Reef continues to provide one of the world's most outstanding visitor experiences for tourists and is highly valued and critically important to the industries and communities that depend on it for both their lifestyles and livelihoods,” Dr Wachenfeld said.

Photo: Eric Matson, AIMS