Coral Reefs, Atolls & Bleaching

These flashcards encompass various aspects of coral reefs, their formation, biodiversity, and environmental impacts, aimed at high-level understanding for UPSC exam preparation.

Why are coral polyps restricted to latitudes between 25°N and 25°S?

They require warm, stable, shallow tropical waters with specific salinity and temperature ranges.

How do submarine platforms support coral reef development?

They provide hard substrates in shallow waters ideal for coral polyp attachment and growth.

Why are coral reefs largely absent along the western margins of continents?

Cold ocean currents lower water temperature below thresholds suitable for coral growth.

How does the depth of water (45–55 m) influence the vertical zonation of coral species?

Sunlight availability decreases with depth, limiting coral biodiversity.

Why do coral reefs grow more on the seaward side compared to the landward side?

Seaward side has better light penetration, nutrient-rich plankton inflow, and cleaner water.

Why are corals unable to survive in waters with high turbidity?

Turbid waters reduce sunlight penetration, hampering photosynthesis of symbiotic algae.

How does salinity range influence coral reef formation?

Corals require a narrow salinity range (27–40 ppt); deviations stress polyps.

Why are coral reefs often used as indicators of global climate change?

Their narrow ecological tolerance makes them sensitive to temperature, pH, and sea level changes.

Which regions globally are classified as coral triangle and why?

Indonesia, Philippines, Malaysia, and nearby areas; due to warm stable waters and shallow seafloor.

Why is reef growth faster on windward sides of islands?

Wave action brings oxygen and plankton, promoting faster polyp activity.

What differentiates fringing reefs from barrier reefs?

Fringing reefs form close to shore without a lagoon; barrier reefs are separated by lagoons.

How do atolls form from subsiding volcanic islands?

Fringing reefs evolve into barrier reefs and then atolls as the island sinks.

Why is Darwin’s theory of atoll formation geologically significant?

It links biological coral growth with tectonic subsidence, explaining atoll evolution.

What is the difference between patch reefs and platform reefs?

Patch reefs are small isolated formations; platform reefs are large, flat-topped structures.

Why are coral knolls ecologically distinct?

They are mound-like reef structures hosting unique species due to isolated vertical growth.

How does temperature-induced bleaching differ from acidification-related coral stress?

Bleaching expels zooxanthellae due to heat; acidification slows calcification.

Why is coral bleaching considered reversible in early stages?

If stressors subside, polyps can regain zooxanthellae and restore activity.

How do mass bleaching events signal broader climatic disruptions?

They coincide with marine heatwaves and rising SSTs.

Why are deep-water corals less susceptible to bleaching?

They live beyond photic zones and rely less on photosynthesis.

Why does coral mortality accelerate after repeated bleaching episodes?

Energy reserves deplete, immune responses weaken, and algal overgrowth occurs.

What role do zooxanthellae play in coral reef productivity?

They photosynthesize within coral tissues, supplying energy for calcium carbonate secretion.

How do reef ecosystems maintain high biodiversity despite low nutrient waters?

Efficient recycling of nutrients and niche specialization allow complex food webs.

Why are herbivorous fish vital for coral reef health?

They control algal growth, allowing corals to thrive.

How do coral reefs act as natural breakwaters?

Their structures dissipate wave energy, protecting coastlines.

How does mutualism between coral polyps and zooxanthellae enhance calcification?

Photosynthesis removes CO2, favoring calcium carbonate deposition.

Identify three major coral reef regions in the world.

1. Great Barrier Reef, 2. Coral Triangle, 3. Mesoamerican Reef.

Which country is outside the tropical coral reef belt: Maldives, Kenya, Peru, or Fiji?

Peru, due to cold Humboldt Current.

Arrange these by declining coral biodiversity: Coral Triangle, Red Sea, Caribbean, Hawaii.

Coral Triangle > Red Sea > Caribbean > Hawaii.

Which latitudinal range supports maximum coral reef distribution?

Between 30°N and 30°S.

Why is the Andaman & Nicobar region richer in coral diversity than Lakshadweep Islands?

It spans different reef types and hosts deeper waters.

How does destructive fishing damage coral reefs?

Techniques like blast fishing physically shatter corals and poison marine life.

Why is sunscreen considered a threat to coral health?

Chemicals disrupt polyp development and increase bleaching susceptibility.

How does coastal tourism contribute to coral reef degradation?

Anchor damage, trampling, and wastewater discharge harm coral structures.

Why are Marine Protected Areas (MPAs) effective in reef conservation?

They regulate fishing, tourism, and pollution, allowing coral recovery.

What is coral gardening and how does it support restoration?

It involves growing coral fragments in nurseries and transplanting them to degraded reefs.

How does ocean acidification affect aragonite saturation levels?

It lowers aragonite levels, reducing availability of carbonate ions.

Why are mesophotic coral ecosystems gaining attention in conservation?

They occur at depths possibly acting as refuges during surface bleaching.

How does ENSO variability influence coral health?

El Niño raises SST and weakens currents, intensifying bleaching stress.

What is the Reef Check Program and its role in monitoring reefs?

It’s a global citizen science initiative tracking reef health.

Why is coral calcification considered a proxy for past oceanic pH?

Growth rings reflect historical carbonate ion levels.

Why do ocean gyres influence coral reef distribution?

Western boundary currents carry warm waters poleward, creating ideal conditions.

How does sediment runoff from deforested areas affect coral reef ecosystems?

Sediment blocks sunlight, clogs polyps, and promotes algae blooms.

Why are branching corals more vulnerable to wave action than massive corals?

Their delicate structures are easily broken by currents.

How does reef accretion rate relate to sea level rise adaptation?

If coral growth keeps pace with rising sea levels, reefs maintain necessary light exposure.

Why are reef flats considered biologically productive zones?

They host high sunlight, shallow depths, and diverse marine life.

How does volcanic island subsidence contribute to atoll ring formation?

As the island sinks, fringing reefs grow upward, encircling a lagoon.

Why are coral reefs absent in the eastern Pacific despite warm temperatures?

Cold upwelling inhibits coral development.

How does symbiont shuffling help coral reefs adapt to warming oceans?

Corals may expel heat-sensitive zooxanthellae and acquire tolerant strains.

Why is ocean stratification a threat to coral reef ecosystems?

It reduces vertical nutrient mixing, starving surface waters of essential nutrients.

How do artificial reefs support coral regeneration?

They offer stable substrates for coral settlement and mimic natural functions.