Quick questions on Great Barrier Reef case study: HSC Geography Ecosystems at Risk

Reef-building corals are colonial animals (polyps) hosting symbiotic algae (zooxanthellae) in their tissues. The algae photosynthesise, supplying around 90 percent of the coral's energy. Corals in turn secrete calcium carbonate skeletons that build the reef structure over thousands of years.

Bleaching occurs when corals expel their zooxanthellae under thermal stress. Without the algae, corals lose colour and most energy supply. Prolonged bleaching causes coral death.

Catchment land use delivers around 14 Mt of sediment, 50,000 t of nitrogen, and 4,200 t of phosphorus annually. Sugar cane (north QLD), grazing (Burdekin), and bananas (Wet Tropics) are the dominant sources. The 2019 Townsville flood deposited a major mud plume on inshore reefs.

Acanthaster planci. A native species that has population outbreaks linked to nutrient enrichment. A single starfish can eat its body area in coral per day. Outbreaks have caused around 42 percent of recent coral loss according to AIMS.

Strong cyclones cause direct damage. Yasi (2011, Cat 5) damaged 17 percent of the reef. Debbie (2017, Cat 4) caused widespread coral damage to central reefs. Climate change is projected to reduce cyclone frequency but increase intensity.

Although 33 percent of the marine park is no-take zone, illegal fishing and historical overfishing have reduced large predatory fish populations on inshore reefs.

Ocean temperature has risen around 1 degree C in the GBR region since pre-industrial. Marine heatwaves are around five times more frequent than 1900. Ocean acidification has lowered pH by 0.1 units, reducing coral calcification rates by an estimated 11 percent since 1990.

The current zoning plan divides the marine park into multiple use zones: - No-take zones (green zones). 33 percent of the marine park; no fishing or extraction. - Habitat protection zones. Restrict bottom trawling. - Conservation park zones. Limit certain commercial fishing. - General use zones. Most fishing and tourism activity.

Released 2015, refreshed 2021. Coordinates Australian and Queensland Government actions. $3 billion in committed funding through 2030 across 35 actions including:

Reef 2050 Water Quality Improvement Plan targets 60 percent nitrogen reduction and 25 percent sediment reduction by 2025 (against 2009 baseline). Many catchments are not on track. The Great Barrier Reef Foundation's reef rescue programs work with sugar cane and grazing operators.

The Crown-of-thorns Starfish Control Program (around $80 million committed) deploys teams of divers killing starfish with injection at high-value reefs. Has reduced COTS damage on protected reefs.

The most important management response in principle but the slowest in practical effect. Australia's 2022 Climate Change Act locks in 43 percent emissions reduction by 2030 and net zero by 2050. Without globally coordinated reductions, sea temperature will continue to rise and bleaching events will continue.

Over 70 Sea Country Indigenous Land Use Agreements are in place. Traditional Owner partnerships in monitoring (Indigenous Rangers), reef restoration, and policy.

Australian Institute of Marine Science (AIMS) operates research programs in: - Coral seeding. Producing larvae in laboratories and releasing onto degraded reefs. - Selective breeding. Selecting heat-tolerant coral genotypes. - Coral cooling. Marine cloud brightening experiments. - Larval restoration. Boosting larval supply on small reefs.