QCAA Marine Science The reef and beyond

Both barrier and fringing reefs have a reef crest, which is the highest point of the reef where wave action is typically strongest.

Both types of reefs can have reef flats of varying widths; a narrow reef flat is not the distinguishing feature of a barrier reef.

Both barrier and fringing reefs have a reef front (or fore-reef) that slopes down into deeper water, so this does not differentiate the two.

Incorrect. Spawning refers to the release of eggs and sperm into the water column for fertilization, which occurs before larvae are even formed.

Incorrect. While site selection involves larvae exploring and choosing a suitable location, settlement is the actual physical process of attaching to the reef structure.

Incorrect. Larval dispersion is the process of ocean currents transporting free-swimming larvae to new areas, which occurs prior to their attachment.

Incorrect. Atolls are ring-shaped reefs that typically form around subsiding oceanic volcanoes, not continental islands.

Incorrect. A coral cay is a small, sandy island formed by sediment deposition on top of a reef, rather than a reef structure attached to a continental island.

Incorrect. Platform reefs are isolated, flat-topped reefs that grow on the continental shelf, but unlike fringing reefs, they are not directly attached to the shoreline.

Sodium combining with carbonate forms sodium carbonate ($Na_2CO_3$), which is highly soluble in ocean water and does not form solid skeletal structures.

Chloride ions ($Cl^-$) and carbonate ions ($CO_3^{2-}$) are both negatively charged anions, meaning they repel each other and do not combine to form a compound.

Hydrogen ions ($H^+$) combining with carbonate forms bicarbonate ($HCO_3^-$). An excess of hydrogen ions actually causes ocean acidification, which dissolves coral skeletons rather than building them.

While predation affects population sizes and community dynamics, physical habitat complexity is a much stronger predictor of overall species richness and biodiversity.

Light availability is critical for the photosynthetic algae living inside corals, but it is not the primary direct driver of fish biodiversity compared to the physical structure of the reef.

Although dissolved oxygen ($O_2$) is essential for survival, reef waters are typically well-oxygenated, making it less of a limiting factor for biodiversity than habitat complexity.

While corals use their mouth to ingest food, it is not the structure responsible for stinging or disabling prey.

Although tentacles are used to grab and pull prey toward the mouth, the actual disabling is done by microscopic stinging cells located on the tentacles.

Zooxanthellae are symbiotic algae that live inside coral tissues and provide energy through photosynthesis, not structures used for hunting.

Continental drift operates on a geological timescale of millions of years, meaning tectonic movement over the past 20,000 years was too minimal to be the primary driver of change.

The Triassic extinction event occurred approximately 200 million years ago, which is vastly outside the 20,000-year timeframe specified in the question.

As the Earth emerged from the last ice age over the past 20,000 years, global sea surface temperatures have generally increased, rather than decreased.

Hard corals belong to the order Scleractinia, whereas Alcyonacea specifically refers to soft corals.

Hermatypic refers to reef-building corals that produce hard calcareous skeletons, a characteristic that soft corals (Alcyonacea) lack.

Soft corals (Alcyonacea) lack the rigid calcium carbonate skeletons necessary to be primary reef-forming organisms.

Sediment run-off reduces water clarity and can smother corals, which hinders coral recovery and often provides a competitive advantage to algae.

Severe weather events cause physical damage to coral reefs, creating more open space for fast-growing algae to colonize and accelerating a phase shift.

Sea cucumbers are primarily detritivores that feed on decaying organic matter in the sediment, not the macroalgae that compete directly with corals for space.