Assessing the damage 2009

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After Cyclone Hamish.

In March 2009, Category 5 Tropical Cyclone Hamish passed directly over the southern central section of the Great Barrier Reef in a rare alongshore path with potential to damage a large portion of reefs in the Marine Park.

Hamish formed in the Coral Sea about 300km offshore from the Princess Charlotte Bay area in the northern Great Barrier Reef on 5 March 2009. For three days it travelled parallel to the GBR before it crossed onto the reef near the Whitsundays as a Category 5 cyclone.

Over the next three days it moved through the middle of the western, mid and eastern Swains reefs with wind speeds up to 280km per hour.

Soon after the passage of the cyclone, AIMS deployed two teams to assess the damage on 26 reefs, at a total of 61 sites. The teams found that most reef damage was sustained within 30km of the cyclone eye track. Within this area, damage was often severe on several sides of the reef. However, even on severely damaged reefs, pockets of untouched reef often remained. Scouring (tissue stripped off coral), coral breakage and macro-algal blooms were the most common type of impact.

Although many cyclones have had an impact on the GBR over the years, this one was notable for the size of the area that was affected (over 500km or 25 per cent of the Great Barrier Reef).

One observation reported by the first voyages to reach the affected region was the presence of spectacular but ephemeral blooms of filamentous algae, indicating massive enrichment of the ecosystem. The source of these additional nutrients has now become an interesting research question.