Coral Reefs
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96 free Coral Reefs trivia questions with answers — nature quiz, new questions added Oct 2026.
10 free coral reefs trivia questions with answers. Dive deep into the colorful world of coral reefs with our engaging trivia quiz! Test your knowledge about these vital ocean ecosystems, their inhabitants, and why they matter to our planet. Whether you're a marine biology enthusiast or just curious about the underwater world, this quiz will challenge what you know.
30 of 96 questions with answers and explanations. Play the quiz
Q 01What primary mineral compound forms the rigid structure of most coral reefs?
Calcium carbonate
Calcium carbonate: polyps draw dissolved calcium from seawater and lay it down as rock beneath them, so a reef is mostly old skeleton under a thin living skin.
Q 02To which phylum of animals do corals belong?
Cnidaria
Cnidaria: corals share the phylum with jellyfish and sea anemones, and like them fire stinging cells from their tentacles to catch passing prey, mostly at night.
Q 03What is the name of the microscopic algae that live symbiotically within coral tissues?
Zooxanthellae
Zooxanthellae live inside the coral's own cells and hand over sugars made by photosynthesis, supplying up to 90% of the energy the coral needs.
Q 04Which animated film's young hero is taken from the Great Barrier Reef to a fish tank in a Sydney dentist's office?
Finding Nemo
Finding Nemo sends his father Marlin south to Sydney on the East Australian Current, a real flow of warm water that sweeps down the coast from the reef.
Q 05What term describes heat-stressed corals expelling the symbiotic algae that live in their tissues?
Coral bleaching
Coral bleaching is the loss of symbiotic algae and their pigments; the coral turns white and, if conditions do not improve, often starves.
Q 06Which broad ocean region holds the most diverse coral reefs, including the Coral Triangle?
Indo-Pacific
The Indo-Pacific holds roughly ten times as many reef-building coral species as the western Atlantic, and in 2009 six nations pledged to manage its richest corner together.
Q 07About what percentage of marine species depend on coral reefs?
25%
About 25% of marine species, including more than 4,000 kinds of fish, depend on coral reefs at some stage of life, even though reefs cover only a sliver of the ocean floor.
Q 08Atmospheric carbon dioxide dissolving into seawater directly causes which major threat to coral reefs?
Ocean acidification
Ocean acidification: dissolved carbon dioxide forms carbonic acid, which uses up the carbonate corals need, so their skeletons become harder to build and maintain.
Q 09Which Pacific climate pattern drove the 1998 ocean heatwave that killed about 16% of the world's coral reefs?
El Niño
El Niño spread unusually warm water across the tropics in 1997–98, and overheated corals cast out the algae that feed them in the first worldwide event of its kind on record.
Q 10Charles Darwin conceived his theory that atolls form around sinking volcanic islands during the voyage of which ship?
HMS Beagle
HMS Beagle was still off South America when Darwin thought the theory out, before he had seen a true coral reef; he tested it on the reefs he met later in the voyage.
Q 11In Darwin's model, what is the first reef stage, forming right against a volcanic island?
Fringing
Fringing reefs grow directly from the shore of a young volcanic island; as the island subsides a lagoon opens and the reef becomes a barrier reef, then a ring-shaped atoll once the island vanishes.
Q 12On the Great Barrier Reef, corals spawn together once a year, in the nights after which event?
A full moon
A full moon in spring or early summer is the cue: colonies release millions of egg and sperm bundles on the same nights, so that bundles from different corals can meet in open water.
Q 13The Great Barrier Reef lies off the coast of which Australian state?
Queensland
Q 21Which coral-fringed body of water is the world's northernmost tropical sea?
The Red Sea
The Red Sea is unusually salty because desert heat evaporates more water than rain and rivers return, yet about 200 kinds of soft and hard coral thrive in it.
Q 22Castle Bravo, the largest US nuclear test, was detonated in 1954 at which Pacific coral atoll?
Bikini Atoll
Bikini Atoll's Bravo blast was more than twice as strong as predicted, and its fallout sickened islanders on Rongelap and the crew of a Japanese fishing boat.
Q 23Australia's Ningaloo Reef is famous for seasonal visits from which giant fish?
Whale sharks
Queensland's rivers wash farm run-off onto the reef in tropical floods, one of its main threats, because the reef hugs some 2,300 km of the state's coast.
Q 14Which explorer's ship ran aground on the Great Barrier Reef in June 1770, needing seven weeks of repairs?
James Cook
James Cook's crew heaved the ship's guns overboard to float Endeavour off the coral, patched the hole with a sail, then beached her near today's Cooktown.
Q 15Which nation, independent only since 2002, is the smallest of the six Coral Triangle countries?
Timor-Leste
Timor-Leste chose independence in a UN-supervised referendum in 1999; its waters lie in a region that holds 76% of the world's reef-building coral species.
Q 16The Belize Barrier Reef is a section of which larger reef system, shared by four countries?
Mesoamerican
The Mesoamerican Barrier Reef runs from Mexico's Yucatán to Honduras; Belize's stretch came off UNESCO's danger list in 2018 after the country curbed offshore oil activity.
Q 17Which explorer's 1971 expedition to Belize's Great Blue Hole made it famous?
Jacques Cousteau
Jacques Cousteau's team brought up stalactites from its drowned caves, showing the hole formed on dry land long ago, before the ocean rose and flooded it.
Q 18How does the crown-of-thorns starfish feed on living coral?
By everting its stomach over the coral
By everting its stomach over the coral: the starfish pushes its stomach out through its mouth, digests the living tissue externally, and leaves a white scar of bare skeleton.
Q 19Which reef fish grinds up coral, digests the edible parts and excretes the rest as sand that builds beaches?
Parrotfish
Parrotfish excrete the ground-up rock as sand that builds beaches and islands; many also sleep in a mucus cocoon, which experiments show keeps blood-sucking parasites off.
Q 20In a clownfish group, what happens when the dominant female disappears?
The breeding male changes sex
The breeding male changes sex into the new female, and the largest non-breeding juvenile matures into the breeding male; clownfish are protandrous hermaphrodites in a strict size-based hierarchy.
Whale sharks, the largest fish alive, gather at Ningaloo from March to August to filter plankton, and are so docile that visitors snorkel alongside them.
Q 24Raja Ampat, home to about 75% of the world's known hard coral species, is in which country?
Indonesia
Indonesia: Raja Ampat sits where the Indian and Pacific oceans meet, so currents carry its coral and fish larvae outwards to reseed reefs across the region.
Q 25Tubbataha Reefs Natural Park, a World Heritage atoll reef in the Sulu Sea, belongs to which country?
Philippines
Philippines: when the US Navy minesweeper Guardian ran aground there in 2013, it was cut up and removed in pieces, and Washington paid about $2 million for the damage.
Q 26The continental United States' only living barrier reef lies a few miles seaward of which island chain?
The Florida Keys
The Florida Keys are themselves old reef: the upper and middle islands are the exposed top of a fossil coral reef, with today's living reef growing just offshore.
Q 27Røst Reef, one of the largest cold-water coral reefs ever found, lies off which country's Lofoten Islands?
Norway
Norway: the reef grows in cold darkness 300 to 400 m down, so its Lophelia corals catch drifting food instead of relying on sunlit algae as tropical reef builders do.
Q 28Fire coral, whose sting burns divers, is really a closer relative of which animal than of true corals?
Hydra
Hydra and fire coral are both hydrozoans: fire coral's hair-fine stinging polyps reach out through pores in its skeleton, and a brush against them brings burning pain that can last for days.
Q 29Which reef coral forms rounded boulders covered in a maze of winding grooves?
Brain coral
Brain coral feeds mainly at night, stretching its tentacles out to catch drifting animals and pulling them back in by day.
Q 30Which disease drove the Caribbean staghorn coral's collapse and its critically endangered listing?
White-band disease
White-band disease strips living tissue from the branches in a band that creeps from base to tip; it destroyed most Caribbean staghorn coral and left the species critically endangered.