Free QCE Marine Science Flashcard Review
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Between which approximate latitudes are most hermatypic coral reefs found?
Roughly between 30° N and 30° S, in shallow tropical seas. Beyond these latitudes winter water is too cold for reef accretion.
Why are coral reefs scarce on the western coasts of continents?
Cold boundary currents and upwelling make the water cooler and richer in nutrients, conditions that suit algae and plankton rather than reef-building corals.
How does coral diversity change with latitude along the Great Barrier Reef?
It generally declines towards the south as winter temperatures fall, so southern reefs have fewer species than northern reefs.
Why are inshore GBR reefs often dominated by sediment-tolerant corals and macroalgae?
They receive river flood plumes carrying sediment, fresh water and nutrients, which reduce light and favour algae over light-dependent hard corals.
What are outer-shelf reefs like compared with inshore reefs?
They are bathed in clear, low-nutrient oceanic water with stable salinity, so light-dependent hard corals grow well and water quality is rarely limiting.
What temperature range suits hermatypic corals?
About 18–30 °C, with most growth in roughly 23–29 °C; they live close to their upper limit, so small rises cause stress.
Why do hermatypic corals need low nitrate and phosphate levels?
High nutrients favour fast-growing macroalgae and phytoplankton, which shade, smother and outcompete corals.
Why are reef-building corals limited to shallow water?
Their zooxanthellae need light for photosynthesis, so reef building occurs mainly within the photic zone, typically shallower than about 50 m.
How does salinity limit coral distribution?
Corals are stenohaline and do best near full oceanic salinity (about 35 ppt); fresh flood water near river mouths can stress or kill them.
Why does aragonite saturation matter for reef distribution?
Corals build aragonite skeletons; warm tropical surface water is highly supersaturated with aragonite, so calcification is easier there than in cold water.
Why do coral larvae need a hard substrate?
Planulae must attach to stable, clean rock or dead skeleton to metamorphose; soft mud and sand shift and smother recruits.
How long have corals existed in the geological record?
For more than 250 million years, although corals have been present in Australian waters for only about 500 000 years.
What was sea level like about 20 000 years BP?
About 120 m lower than today, during the last glacial period, so most of the Queensland continental shelf was dry land.
When did sea level stabilise near its present level?
About 6500 years BP; modern GBR reef tops grew up to this stable sea level on older reef foundations.
Why is the modern Great Barrier Reef described as geologically young?
Its living surface has grown only since the shelf flooded after the last glacial period, mostly in the last 6500–9000 years, on top of older reef platforms.
Fringing reef
A reef that grows directly along a coastline or island shore, with little or no lagoon between it and the land.
Platform reef
A flat-topped reef that grows upward from the continental shelf, away from the coast; it may develop a shallow lagoon and a coral cay.
Ribbon reef
A long, narrow reef along the edge of the continental shelf, such as those along the northern GBR outer edge.
Atoll
A ring-shaped reef around a central lagoon, formed when a fringing reef keeps growing upward as a volcanic island subsides.
Coral cay
A low island of sand and rubble built on a reef flat by waves and currents, sometimes stabilised by vegetation.