Ten questions on the ocean and its inhabitants, each linking the creature to the conditions it lives in.
The ocean is a set of extreme environments arranged by depth, and its inhabitants make far more sense once that is clear. This quiz covers the basins, the forces producing tides and currents, and the animals from the surface down to the deepest trench. It includes reefs, which occupy a tiny fraction of the seabed and support a quarter of marine species. The explanations tie each adaptation to the pressure, light or temperature it answers.
Every question in this quiz is listed below with its correct answer and the reasoning behind it. Play first if you would rather not see the answers — or read through as a study sheet.
Play it insteadAnswer: A. The Mariana Trench
Why: The Challenger Deep in the Mariana Trench reaches nearly 11 kilometres down. Everest would fit inside it with more than a kilometre to spare.
Answer: C. The Moon
Why: The Moon dominates, with the Sun contributing roughly half as much. When they align, the combined pull produces the larger spring tides.
Answer: B. Coral polyps
Why: Polyps are small animals that secrete hard calcium carbonate skeletons. They depend on algae living inside their tissue, which is why bleaching is so damaging.
Answer: A. The whale shark
Why: Whale sharks reach around 12 metres and feed on plankton. The blue whale is larger but is a mammal, not a fish.
Answer: A. Wind and differences in water density
Why: Surface currents are pushed largely by prevailing winds, while deeper circulation is driven by differences in temperature and salinity. The two systems together move heat around the planet.
Answer: A. Salt content
Why: Salinity describes dissolved salts in seawater, averaging around 35 parts per thousand. It varies with evaporation, rainfall and river inflow.
Answer: C. The Arctic
Why: The Arctic Ocean is both the smallest and the shallowest. Much of it is covered by sea ice that varies sharply with the season.
Answer: C. Organisms that drift with the currents
Why: Plankton includes both plant-like and animal forms, defined by drifting rather than swimming against currents. Phytoplankton produce a large share of the world's oxygen.
Answer: A. A mammal
Why: Dolphins are warm-blooded, breathe air and nurse their young. Their resemblance to fish is convergent evolution rather than shared ancestry.
Answer: B. It increases steadily with depth
Why: Pressure rises by roughly one atmosphere every ten metres. This is the main engineering constraint on deep-sea exploration.
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