Ocean Life Quiz
Whale sharks, coral polyps, anglerfish and sea turtles: 15 questions from the reef to the deep sea.
What is the largest species of fish in the world?
Got a hunch? Pick the answer that feels right.
Whale shark
Whale sharks can grow to around 12 metres (40 feet) or more, yet they are gentle filter feeders that cruise slowly through tropical seas scooping up plankton and small fish.
Each whale shark carries a unique pattern of white spots, which researchers photograph and match using software adapted from star mapping.
Which fish is famous for living safely among the stinging tentacles of sea anemones?
Got a hunch? Pick the answer that feels right.
Clownfish
Clownfish are coated in a mucus layer that stops the anemone's stinging cells from firing, so they can shelter among the tentacles while predators keep their distance.
All clownfish are born male, and the largest fish in a group changes sex to become the dominant female.
How many arms does a typical starfish have?
Got a hunch? Pick the answer that feels right.
Five
Most starfish, or sea stars, have five arms arranged around a central disc, a pattern called pentaradial symmetry, although some species carry 20 or more.
A starfish can regrow a lost arm, and in some species a single severed arm can regrow an entire new animal.
What is the largest coral reef system in the world?
Got a hunch? Pick the answer that feels right.
Great Barrier Reef
The Great Barrier Reef stretches for about 2,300 km (1,400 miles) along the coast of Queensland, Australia, and it is made up of nearly 3,000 individual reefs.
The reef is so large that it can be seen from space, and it was listed as a UNESCO World Heritage Site in 1981.
What do baleen whales such as the blue whale mainly feed on?
Got a hunch? Pick the answer that feels right.
Krill
Baleen whales gulp huge mouthfuls of water and strain out krill, tiny shrimp-like crustaceans, through the comb-like baleen plates that hang from their upper jaws.
A single blue whale can eat around 16 tonnes of krill in a day during the summer feeding season.
Coral reefs are built by tiny animals called what?
Got a hunch? Pick the answer that feels right.
Polyps
Each coral is a colony of thousands of tiny polyps, soft-bodied relatives of jellyfish, which secrete calcium carbonate skeletons that slowly build up into reefs over thousands of years.
Most reef-building corals feed at night, extending their tentacles to catch plankton drifting past in the dark.
The orca, or killer whale, is actually the largest member of which family of marine mammals?
Got a hunch? Pick the answer that feels right.
Dolphins
Despite its name, the orca is the largest species of oceanic dolphin, with males reaching about 9 metres (30 feet) and hunting in coordinated family pods.
Orcas have no natural predators and have been recorded hunting great white sharks, often targeting the sharks' livers.
In which fish does the male carry the fertilised eggs in a pouch until they hatch?
Got a hunch? Pick the answer that feels right.
Seahorse
The female seahorse deposits her eggs in a pouch on the male's belly, where he fertilises and carries them for several weeks before giving birth to hundreds of tiny fry.
Seahorses are poor swimmers and curl their tails around seagrass and coral to avoid being swept away by currents.
What is the largest species of sea turtle?
Got a hunch? Pick the answer that feels right.
Leatherback turtle
Leatherback turtles can exceed 1.8 metres (6 feet) in length and weigh over 500 kg (1,100 lb), and unlike other sea turtles they have a leathery, ridged back instead of a hard shell.
Leatherbacks can dive deeper than 1,000 metres (3,300 feet) and feed almost entirely on jellyfish, which is why floating plastic bags are so dangerous to them.
Which marine mammal floats on its back and uses a rock to crack open shellfish?
Got a hunch? Pick the answer that feels right.
Sea otter
Sea otters keep a favourite stone in a pouch of loose skin under a foreleg and hammer clams, mussels and sea urchins against it while floating on their backs.
Sea otters have the densest fur of any animal, up to a million hairs per square inch, because they have no blubber to keep them warm.
Which deep sea fish attracts prey with a glowing lure dangling from its head?
Got a hunch? Pick the answer that feels right.
Anglerfish
Female deep sea anglerfish carry a modified fin ray tipped with light-producing bacteria, dangling it in front of their enormous jaws to draw curious prey in the darkness.
In some anglerfish species the tiny male bites onto the female and fuses with her body, living as a permanent sperm-producing parasite.
Coral bleaching occurs when corals expel which symbiotic algae living in their tissues?
Got a hunch? Pick the answer that feels right.
Zooxanthellae
Zooxanthellae are microscopic algae that live inside coral polyps, providing most of their food through photosynthesis and their colour. When heat-stressed corals expel them, the white skeleton shows through.
A bleached coral is not dead, and it can recover if conditions improve within a few weeks before it starves.
Which ocean zone begins at about 1,000 metres (3,300 feet) down, where sunlight no longer reaches at all?
Got a hunch? Pick the answer that feels right.
Midnight zone
The midnight zone, or bathypelagic zone, runs from about 1,000 to 4,000 metres, is permanently dark and near freezing, and its animals rely on bioluminescence to find mates and prey.
The twilight zone above it still receives a faint glow, which is why so many of its residents have huge upward-facing eyes.
Animals living around deep sea hydrothermal vents depend on bacteria that make energy from which chemical?
Got a hunch? Pick the answer that feels right.
Hydrogen sulfide
Vent bacteria use chemosynthesis, drawing energy from hydrogen sulfide in the mineral-rich water, and they support giant tube worms, clams and shrimp in total darkness.
Hydrothermal vents were first discovered in 1977 near the Galápagos Islands, surprising scientists who expected the deep sea floor to be almost lifeless.
Which shark is thought to be the longest-lived vertebrate on Earth, possibly reaching 400 years?
Got a hunch? Pick the answer that feels right.
Greenland shark
A 2016 study in the journal Science used radiocarbon dating of eye lenses to estimate that one Greenland shark was about 392 years old, making the species the longest-lived known vertebrate.
Greenland sharks grow only about 1 cm a year and are thought not to reach maturity until around 150 years of age.
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All Science quizzes →About the Ocean Life Quiz
The ocean covers more than 70 percent of our planet and hides its strangest residents. The whale shark is a fish the size of a bus that eats plankton, the Greenland shark may live for 400 years, and the glowing lure of the anglerfish hangs in water so deep that no sunlight ever reaches it.
These 15 questions start with marine animals everyone recognises, from clownfish and starfish to orcas and sea turtles, before diving into coral reef biology and the chemistry of deep sea vents. It suits nature documentary fans, young marine biologists and anyone who wants to feel smart the next time the conversation turns to the sea.
You will find 15 multiple choice questions here, each with four options. Difficulty: Medium. Most people finish in about 6 minutes, and every answer comes with a short explanation and one extra fact worth keeping.
How to play
Read the question and pick one of the four answers. The correct answer is revealed straight away with a short explanation, then press Next question to keep going. At the end you get your score out of 15 and a full review of your round. Play again any time and the questions arrive in a fresh order. There is no timer and no account.
Good to know before you play
What is the biggest fish in the ocean?
The whale shark is the largest fish alive, reaching around 12 metres (40 feet), and despite its size it feeds on plankton and tiny fish.
What causes coral bleaching?
Stressed corals, usually in water that is too warm, expel the colourful algae living inside them, leaving the white skeleton visible and the coral at risk of starving.
Does this ocean life quiz include deep sea questions?
Yes. The later questions cover sea otters, ocean zones, anglerfish and hydrothermal vents, with an easy start on reef and coastal animals.
Answer key: all 15 questions with explanations
- What is the largest species of fish in the world?
Whale shark Whale sharks can grow to around 12 metres (40 feet) or more, yet they are gentle filter feeders that cruise slowly through tropical seas scooping up plankton and small fish. Each whale shark carries a unique pattern of white spots, which researchers photograph and match using software adapted from star mapping. - Which fish is famous for living safely among the stinging tentacles of sea anemones?
Clownfish Clownfish are coated in a mucus layer that stops the anemone's stinging cells from firing, so they can shelter among the tentacles while predators keep their distance. All clownfish are born male, and the largest fish in a group changes sex to become the dominant female. - How many arms does a typical starfish have?
Five Most starfish, or sea stars, have five arms arranged around a central disc, a pattern called pentaradial symmetry, although some species carry 20 or more. A starfish can regrow a lost arm, and in some species a single severed arm can regrow an entire new animal. - What is the largest coral reef system in the world?
Great Barrier Reef The Great Barrier Reef stretches for about 2,300 km (1,400 miles) along the coast of Queensland, Australia, and it is made up of nearly 3,000 individual reefs. The reef is so large that it can be seen from space, and it was listed as a UNESCO World Heritage Site in 1981. - What do baleen whales such as the blue whale mainly feed on?
Krill Baleen whales gulp huge mouthfuls of water and strain out krill, tiny shrimp-like crustaceans, through the comb-like baleen plates that hang from their upper jaws. A single blue whale can eat around 16 tonnes of krill in a day during the summer feeding season. - Coral reefs are built by tiny animals called what?
Polyps Each coral is a colony of thousands of tiny polyps, soft-bodied relatives of jellyfish, which secrete calcium carbonate skeletons that slowly build up into reefs over thousands of years. Most reef-building corals feed at night, extending their tentacles to catch plankton drifting past in the dark. - The orca, or killer whale, is actually the largest member of which family of marine mammals?
Dolphins Despite its name, the orca is the largest species of oceanic dolphin, with males reaching about 9 metres (30 feet) and hunting in coordinated family pods. Orcas have no natural predators and have been recorded hunting great white sharks, often targeting the sharks' livers. - In which fish does the male carry the fertilised eggs in a pouch until they hatch?
Seahorse The female seahorse deposits her eggs in a pouch on the male's belly, where he fertilises and carries them for several weeks before giving birth to hundreds of tiny fry. Seahorses are poor swimmers and curl their tails around seagrass and coral to avoid being swept away by currents. - What is the largest species of sea turtle?
Leatherback turtle Leatherback turtles can exceed 1.8 metres (6 feet) in length and weigh over 500 kg (1,100 lb), and unlike other sea turtles they have a leathery, ridged back instead of a hard shell. Leatherbacks can dive deeper than 1,000 metres (3,300 feet) and feed almost entirely on jellyfish, which is why floating plastic bags are so dangerous to them. - Which marine mammal floats on its back and uses a rock to crack open shellfish?
Sea otter Sea otters keep a favourite stone in a pouch of loose skin under a foreleg and hammer clams, mussels and sea urchins against it while floating on their backs. Sea otters have the densest fur of any animal, up to a million hairs per square inch, because they have no blubber to keep them warm. - Which deep sea fish attracts prey with a glowing lure dangling from its head?
Anglerfish Female deep sea anglerfish carry a modified fin ray tipped with light-producing bacteria, dangling it in front of their enormous jaws to draw curious prey in the darkness. In some anglerfish species the tiny male bites onto the female and fuses with her body, living as a permanent sperm-producing parasite. - Coral bleaching occurs when corals expel which symbiotic algae living in their tissues?
Zooxanthellae Zooxanthellae are microscopic algae that live inside coral polyps, providing most of their food through photosynthesis and their colour. When heat-stressed corals expel them, the white skeleton shows through. A bleached coral is not dead, and it can recover if conditions improve within a few weeks before it starves. - Which ocean zone begins at about 1,000 metres (3,300 feet) down, where sunlight no longer reaches at all?
Midnight zone The midnight zone, or bathypelagic zone, runs from about 1,000 to 4,000 metres, is permanently dark and near freezing, and its animals rely on bioluminescence to find mates and prey. The twilight zone above it still receives a faint glow, which is why so many of its residents have huge upward-facing eyes. - Animals living around deep sea hydrothermal vents depend on bacteria that make energy from which chemical?
Hydrogen sulfide Vent bacteria use chemosynthesis, drawing energy from hydrogen sulfide in the mineral-rich water, and they support giant tube worms, clams and shrimp in total darkness. Hydrothermal vents were first discovered in 1977 near the Galápagos Islands, surprising scientists who expected the deep sea floor to be almost lifeless. - Which shark is thought to be the longest-lived vertebrate on Earth, possibly reaching 400 years?
Greenland shark A 2016 study in the journal Science used radiocarbon dating of eye lenses to estimate that one Greenland shark was about 392 years old, making the species the longest-lived known vertebrate. Greenland sharks grow only about 1 cm a year and are thought not to reach maturity until around 150 years of age.
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