Global & Australian Reef Distribution
The Indo-Pacific region.
What is the region that contains the majority of the world’s coral reefs?
Dissolved oxygen levels above ~4 mg/L.
What dissolved oxygen level is required for coral survival?
Corals first appearing over 250 million years ago.
When did corals first appear in the geological record?
A fringing reef.
What type of reef forms directly attached to a continental or island shoreline?
Aragonite.
What form of calcium carbonate makes up coral skeletons?
Between the Tropic of Cancer and the Tropic of Capricorn.
Where are most of the world’s coral reefs located in terms of latitude?
Nitrates and phosphates causing algal overgrowth.
Which nutrients cause harmful algal blooms that outcompete coral recruits?
Corals arriving in Australian waters around 500,000 years ago.
When did corals first appear in Australian waters?
An atoll.
What reef structure forms around sinking volcanic islands and encloses a lagoon?
Calcium ions (Ca²⁺) and carbonate ions (CO₃²⁻).
Which two ions combine to form calcium carbonate (CaCO₃)?
Queensland.
Which Australian state contains the majority of Australia’s coral reefs?
Reduced light availability in deeper water.
What factor limits coral growth as depth increases?
Post–Last Glacial Maximum sea-level rise beginning about 20,000 years BP.
What event began the sea-level rise that initiated modern GBR formation?
A ribbon reef.
What long, narrow reef type forms parallel to the continental shelf?
Reduced calcification at night due to low zooxanthellae activity.
Why do corals calcify more slowly at night?
Variations in temperature, turbidity, and wave exposure between locations.
What factors explain why different reef systems in Australia and WA vary greatly?
Ocean acidification reducing carbonate ion availability.
What process decreases carbonate ions needed for coral calcification?
Sea levels stabilising around 6,500 years BP.
When did sea levels stabilise enough for long-term reef development?
A coral cay formed from biogenic sand and coral rubble.
What type of island forms from accumulated coral sediments on a reef platform?
CO₂ dissolving into seawater forming carbonic acid and increasing hydrogen ions.
What process causes a drop in seawater pH and carbonate ion availability?
Declining temperature and aragonite saturation with increasing latitude.
What environmental gradients explain decreasing coral diversity moving south?
An aragonite saturation state of around Ωarag 3.0.
What is the threshold aragonite saturation point where corals struggle to calcify?
Post-glacial sea-level rise creating accommodation space for reef growth.
What environmental change allowed new coral reefs to colonise previously exposed landforms?
Wave-energy differences causing windward vs leeward zonation.
What explains the different coral communities on the windward and leeward sides of a reef?
The solubility product constant (Ksp) determining CaCO₃ stability.
What equilibrium value predicts whether calcium carbonate will dissolve or precipitate?