Flood plumes and cyclone Yasi combined to affect large sections of coral reefs in the Great Barrier Reef Marine Park.
Approximately six per cent of the reef area in the Marine Park suffered severe damage, with broken corals reported across an area exceeding 89,000 square kilometres.
The most severe damage was confined to the area between Cairns and Townsville, sparing the key tourism areas off Cairns and Airlie Beach from major impacts.
In contrast, the impacts of flood plumes were generally confined to shallow areas of inshore coral reefs near major rivers, such as those in the Keppel Bay region.
Our report Impacts of tropical cyclone Yasi on the Great Barrier Reef details survey results of the spatial extent and severity of physical damage.
The Coral Reef Fin Fishery is vulnerable to the effects of severe tropical cyclones, as coral trout live in shallow coral reefs which are most at risk of cyclone damage.
Commercial fishers reported there was a significant and sustained decrease in the catch rates of coral trout from shallow waters (less than 20 metres deep). Underwater surveys indicated this was due to fish 'going off the bite', rather than a decrease in fish abundance.
Seagrass can be vulnerable to the effects of reduced light during long periods of exposure to flood plumes, as this can inhibit photosynthesis needed for growth.
Significant losses of seagrass meadows occurred in 2010–11 in the path of tropical cyclone Yasi.
There were also broader scale losses in meadows exposed to flooding.
Islands are highly exposed to the destructive forces of cyclones.
Aerial photographic surveys of islands revealed a number of cays disappeared or altered shape and size after the 2011 cyclone. Several new rubble cays also appeared.
Dugongs and turtles
The floods and cyclones of 2010–11 led to unprecedented losses of dugongs and green turtles within the Great Barrier Reef region due to the toll they took on seagrass, the animals’ main food source.
About twice as many marine turtles were found stranded on Queensland beaches in that year compared to previous years, and the number of strandings remained high in 2012.
At the end of 2011, there were 187 dugong strandings, compared with 73 for 2010, 48 for 2009 and 36 for 2008 over the same period of time.
There were also 1460 reports of turtle strandings (including 288 alive), compared with 821 in 2010, 931 in 2009 and 799 in 2008 over the same period of time.
In response to the dugong and turtle strandings, we implemented measures to minimise impacts on these animals.
This included identifying hotspots for net-related deaths from incidental capture in Bowling Green Bay (near Townsville) and near the Boyne River at Gladstone, and working with the Queensland Government and commercial fishermen to identify ways to manage impacts.
This led to regulations being implemented in late 2011 to modify netting practices in Bowling Green Bay, and the Queensland Government’s introduction of temporary changes to netting practices in the Boyne River.
Many industries and communities also took action to help the Reef recover. As a result of increases in dugong and turtle deaths, a number of Traditional Owner groups voluntarily reduced traditional hunting activities in affected areas.
The marine aquarium collection industry also placed a voluntary moratorium on collecting sensitive species in affected reef locations. In addition, aquarium collectors played a key role in assessing impacts from flood plumes in the southern parts of the Great Barrier Reef.
The Coral Reef Fin Fish Fishery also identified strategies to improve the ecological, economic and social resilience of the fishery after extreme weather events.