Apply ecosystem and biodiversity concepts to the Great Barrier Reef as a case study: biophysical features, threats (bleaching, runoff, crown-of-thorns starfish), and management responses (GBRMPA, zoning, Reef 2050 Plan, Traditional Owner partnerships)

Note: This page is part of the HSC Geography 11-12 (2022) syllabus, first examined in HSC 2025. The legacy 2009 syllabus "Ecosystems at Risk" content is preserved in sibling folders.

What this dot point is asking

This dot point asks you to deploy a named, globally significant case study to integrate the rest of the focus area. The Great Barrier Reef is the natural choice: it is the world's largest coral reef system, a World Heritage Area, and the most-studied ecosystem under climate stress. You should be able to describe its biophysical features, identify the threats acting on it, and evaluate the management response across scales. The geographical concepts to lean on are interconnection (local management plus global climate), scale (reef-bommie through to ocean basin), sustainability (the long-term outlook), and change (the rapid recent shift in reef condition).

The answer

Biophysical features

The Great Barrier Reef stretches along the north-east coast of Queensland for approximately 2300 km, from near Bundaberg in the south to the Torres Strait in the north. It is the world's largest coral reef system and was inscribed on the World Heritage List in 1981. It is managed within the Great Barrier Reef Marine Park, declared under federal legislation in 1975.

Zonation

The reef shows clear cross-shelf and along-shelf zonation. From the Queensland coast outward: coastal estuaries and mangroves; inshore turbid waters; mid-shelf reefs; outer-shelf reefs at the edge of the continental shelf; and beyond the shelf the deep waters of the Coral Sea. Along the latitudinal gradient from south to north, sea-surface temperature, rainfall and adjacent catchment land use vary, producing distinct northern, central and southern sectors.

Biodiversity

The reef supports a very high marine biodiversity, including a large number of coral species, fish species, marine turtles (green, loggerhead, hawksbill, flatback, olive ridley, leatherback all use the region), dugongs, marine mammals and seabirds. Published assessments cite hundreds of coral species and well over a thousand fish species; precise counts vary in published surveys.

Coral biology

Reef-building corals are colonial cnidarians that host symbiotic algae (zooxanthellae of the genus Symbiodiniaceae) inside their tissues. The algae photosynthesise and provide most of the coral's energy in normal conditions. When sea-surface temperatures rise above a threshold sustained for too long, the algae are expelled and the coral whitens (bleaches). Bleached coral is still alive briefly and can recover if the heat stress ends quickly; sustained heat causes mortality.

Threats

Mass coral bleaching driven by ocean warming. The reef has experienced repeated mass bleaching events linked to marine heatwaves:

• 2016 (severe in the northern sector).
• 2017 (following back-to-back from 2016 in some areas).
• 2020.
• 2022 (the first bleaching event recorded during a La Nina year).
• 2024 (a further mass bleaching event reported by the Great Barrier Reef Marine Park Authority).

Coral cover varies across sectors and across surveys; published Australian Institute of Marine Science (AIMS) Long-Term Monitoring Program reports describe both losses during bleaching events and partial recovery between them. The pattern is not a smooth decline but a sequence of disturbance pulses with shorter recovery windows. Direct hard-coral-cover figures vary between sectors and across published reports.

Crown-of-thorns starfish (Acanthaster planci, COTS)

Native to the reef but undergoes periodic population outbreaks that consume coral. Outbreaks are linked in part to nutrient runoff (which boosts plankton on which COTS larvae feed) and partly to natural cycles. COTS control is a major management activity.

Runoff and water quality

Catchment land use in the Burdekin, Fitzroy, Mackay-Whitsunday, Wet Tropics and Cape York regions delivers sediment, nitrogen, phosphorus and pesticides into the reef lagoon. Sediment reduces light reaching corals; nutrients drive algae overgrowth and may boost COTS larval survival.

Other pressures

Tropical cyclones (which the reef has always experienced but which may be intensified by climate change); shipping incidents; outbreaks of coral disease; illegal fishing; coastal development.

The pattern of threat is multi-driver: climate change is the dominant emerging pressure, runoff and COTS are major local pressures, and reef resilience depends on all three being managed together.

Management responses

Great Barrier Reef Marine Park Authority (GBRMPA)

GBRMPA is the federal agency responsible for managing the Marine Park. It is jointly responsible with the Queensland state agency for management of the broader Great Barrier Reef World Heritage Area.

The Zoning Plan

The Marine Park is divided into a multiple-use zoning plan, first introduced in 1981 and most recently substantially revised in 2003-2004 (the 2003 Representative Areas Program). Zones include general use, habitat protection, conservation park, no-take marine national park (green zones), preservation zones, and special-purpose zones. The 2003-2004 rezoning substantially increased the share of the Marine Park in highly protected (no-take) zones. Zoning is an in-situ conservation tool that manages local pressures (fishing, anchoring, dredging) but cannot address ocean warming.

The Reef 2050 Long-Term Sustainability Plan

The Reef 2050 Plan is a joint Australian and Queensland Government plan for the future of the reef, first released in 2015 and updated subsequently. It sets goals and actions across themes including ecosystem health, biodiversity, heritage, water quality, community, economic benefits and governance.

Reef 2050 Water Quality Improvement Plan

A subordinate plan focused on reducing sediment, nutrient and pesticide runoff from agricultural catchments through grazing land management, sugar-cane best practice, and revegetation. Progress is independently reported and is uneven across pollutants and catchments.

Crown-of-thorns control program

A targeted COTS culling and monitoring program operates on priority reefs.

Traditional Owner partnerships

Traditional Owners have connections to the Great Barrier Reef extending over many thousands of years. Sea Country Plans developed with Traditional Owner groups (including Gunggandji, Yirrganydji, Wuthathi, Mandubarra and many others) inform management. GBRMPA's Traditional Use of Marine Resources Agreements (TUMRAs) recognise and support Traditional Owner use and management of sea country. Indigenous Rangers contribute to monitoring, COTS control and turtle-and-dugong management.

The limits of local management

The dominant emerging driver, ocean warming, is global. No local management action can prevent ocean heatwaves; reducing the rate of warming requires global greenhouse-gas mitigation under the UNFCCC and Paris Agreement. Strong evaluations note this asymmetry: GBRMPA can build reef resilience by managing local pressures, but cannot fix the dominant pressure.

How this case integrates the focus area

The Great Barrier Reef demonstrates almost every concept in the focus area at once: it is a biotic-abiotic system; it supports very high biodiversity; it provides all four ecosystem service categories (provisioning fisheries, regulating coastal protection, cultural tourism and Indigenous heritage, supporting habitat for marine life); it faces the full HIPPO suite plus climate change; it is managed through in-situ protected-area zoning, restoration, Traditional Owner partnerships and global frameworks (World Heritage, Convention on Biological Diversity). It is the most comprehensive Australian case study available for the focus area.

Examples in context

Example 1. The 2016-2017 back-to-back bleaching. The northern sector of the Great Barrier Reef experienced severe bleaching in early 2016, with high coral mortality in the most heat-stressed reefs. The 2017 event followed without a full recovery window, producing a cumulative impact across consecutive years. Subsequent bleaching events in 2020, 2022 and 2024 reduced the average recovery time between disturbances. The case demonstrates the geographical concept of change at decadal scale and the limits of local management in the face of repeated heat stress.

Example 2. Traditional Use of Marine Resources Agreements (TUMRAs). TUMRAs are formal agreements between Traditional Owner groups and GBRMPA that recognise Traditional Owner rights to access and use sea country in accordance with cultural practice while contributing to conservation outcomes. Examples include TUMRAs covering dugong and turtle harvest, monitoring and management. The case demonstrates the interconnection concept (cultural, ecological and management dimensions in one instrument) and the application of Indigenous land and sea management within a federally administered protected-area framework.

Try this

Q1. Describe the biophysical features of the Great Barrier Reef and identify its current World Heritage status. [4 marks]

• Cue. Approximately 2300 km along Queensland coast; cross-shelf zonation (coastal, inshore, mid-shelf, outer-shelf); coral-zooxanthellae symbiosis; high biodiversity. World Heritage-listed 1981; managed under the Great Barrier Reef Marine Park (federal, 1975).

Q2. Analyse the major threats to the Great Barrier Reef, identifying which threats are local and which are global in scale. [6 marks]

• Cue. Local: COTS outbreaks, runoff, coastal development. Global: ocean warming driving mass bleaching (2016, 2017, 2020, 2022, 2024). Interaction: local pressures reduce resilience to global warming pulses. Use the scale concept explicitly.

Q3. Evaluate the effectiveness of management strategies for the Great Barrier Reef, with reference to GBRMPA, the Reef 2050 Plan, Traditional Owner partnerships, and global climate agreements. [8 marks]

• Cue. Local strengths: zoning plan, COTS control, water-quality plan, TUMRAs, Ranger programs. Limits: climate change is global and not addressable through reef-specific management; runoff reductions are uneven across catchments. Reach a calibrated judgement; reference scale, interconnection and sustainability as geographical concepts.