SL Pre-class: B4.1.5— Conditions required for coral reef ...

Which factor best explains why reef-building corals are rarely found below 50 meters in depth?

• Deeper waters have fewer dissolved nutrients available for coral polyps to consume.

• Light penetration decreases with depth, limiting photosynthesis by zooxanthellae.

• Greater water pressure at depth makes it harder for polyps to secrete calcium carbonate.

• Cold water temperatures at depth inhibit coral reproduction and larval dispersal.

Why does excessive turbidity from human activities threaten coral survival?

• It warms surface waters, triggering mass bleaching and coral mortality events.

• It raises salinity levels beyond the tolerance range of most reef-building corals.

• It reduces sunlight penetration, limiting zooxanthellae photosynthesis and energy supply.

• It decreases pH levels, leading to faster ocean acidification near coastal reefs.

Which scenario would most likely result in coral bleaching?

• A temporary drop in pH that increases carbonate ion availability for coral skeletons.

• Prolonged exposure to temperatures above 29°C causing corals to expel zooxanthellae.

• A rapid increase in freshwater inflow that raises salinity levels above 42 ppt.

• Short-term shading from suspended sediments followed by a return to clear water.

Why does stable salinity matter for coral reef ecosystems?

• Corals rely on fluctuating salt levels to trigger seasonal mass spawning events.

• Changing salt levels enhance the camouflage strategies of reef fish and octopuses.

• Salinity stability allows corals to maintain osmotic balance and efficient ion exchange.

• High variability in salinity increases carbonate ions needed for skeleton formation.

What is the main consequence of ocean acidification on coral reefs?

• It reduces carbonate ions, weakening skeleton formation and reef stability.

• It accelerates coral growth by increasing dissolved carbon dioxide availability.

• It raises salinity levels, making reefs more resilient to freshwater runoffs.

• It lowers water clarity, preventing zooxanthellae from performing photosynthesis.

Which adaptation best supports survival in the highly competitive reef environment?

• Symbiosis with algae, where corals receive glucose while providing protection.

• Protective shells that prevent ocean acidification from affecting reef organisms.

• Reproductive strategies that reduce dependence on photosynthesis for survival.

• Camouflage that increases salinity tolerance in regions affected by freshwater runoff.

What makes the Abrolhos Bank an especially important reef system to conserve?

• It is the largest reef in the South Atlantic and hosts species unique to Brazil.

• It survives in waters deeper than 50 meters, showing resilience to low light.

• It contains the largest coral reef biodiversity anywhere in the South Atlantic.

• It is the world’s first UNESCO World Heritage reef site, recognized internationally.

How does international cooperation contribute to reef protection?

• It reduces salinity fluctuations by establishing artificial barriers near rivers.

• It facilitates knowledge-sharing and joint conservation policies across nations.

• It directly lowers sea surface temperatures during periods of marine heatwaves.

• It eliminates turbidity by banning all construction near tropical coastlines.

Which human activity is most directly linked to increased sedimentation that harms corals?

• Coastal deforestation and construction that raise turbidity in shallow waters.

• Overfishing of herbivorous fish that alters ecological balance in reef systems.

• Greenhouse gas emissions that accelerate ocean warming and acidification.

• International tourism that increases recreational diving on fragile reefs.

If ocean acidification continues to lower seawater pH, which of the following ecological outcomes is most likely, and why?

• Coral reefs will expand because more CO₂ will enhance zooxanthellae photosynthesis.

• Corals will migrate to deeper waters where pH is more stable and light is limited.

• Fish biodiversity will increase because weakened corals provide more open space.

• Reef growth will slow as reduced carbonate ions weaken coral skeleton formation.