--- title: Coral reef builders: polyps, bleaching, sand from parrotfish and giant clams — a lesson of Mova's school · trees and pragmatics description: «Coral reef builders: polyps, bleaching, sand from parrotfish and giant clams», a lesson of the biology course of Mova's primary school, sentence by sentence with dependency trees and pragmatics. It begins: A coral feels like stone, but it is a city of tiny animals called polyps, each like a little --- [Mova](https://md.mova.elamur.ai/free/en/) · [this page in HTML](https://mova.elamur.ai/free/en/corpora/school/biology/172-coral-reef-builders-polyps-bleaching-sand-from-parrotfish-and-giant-clams/) [home](https://md.mova.elamur.ai/free/en/) / [corpora](https://md.mova.elamur.ai/free/en/corpora/) / [school](https://md.mova.elamur.ai/free/en/corpora/school/) / [Biology](https://md.mova.elamur.ai/free/en/corpora/school/biology/) / Coral reef builders: polyps, bleaching… # Coral reef builders: polyps, bleaching, sand from parrotfish and giant clams Lesson 172 of the biology course of Mova's primary school: 14 sentences, each with its syntax tree and pragmatics. The lessons are written for Mova, and their agreed trees are part of Mova corpus 0.4 (CC BY-SA 4.0). How Mova does on its tests: [the lesson at school](https://md.mova.elamur.ai/free/en/school-run/biology/172-coral-reef-builders-polyps-bleaching-sand-from-parrotfish-and-giant-clams/). - [0](https://md.mova.elamur.ai/free/en/corpora/school/biology/172-coral-reef-builders-polyps-bleaching-sand-from-parrotfish-and-giant-clams/0/) — A coral feels like stone, but it is a city of tiny animals called polyps, each like a little sea anemone, and each builds a cup of limestone around itself; millions of cups stacked over thousands of years make a reef. - [1](https://md.mova.elamur.ai/free/en/corpora/school/biology/172-coral-reef-builders-polyps-bleaching-sand-from-parrotfish-and-giant-clams/1/) — Inside the polyps live tiny algae that make food from sunlight and share it, which is why reefs need clear, shallow, sunny water, and why a reef in poor blue water is full of life, like an oasis in a desert. - [2](https://md.mova.elamur.ai/free/en/corpora/school/biology/172-coral-reef-builders-polyps-bleaching-sand-from-parrotfish-and-giant-clams/2/) — If the water gets too hot, the corals push their algae out and turn white like bone; this is bleaching, and if the heat lasts too long the coral starves. - [3](https://md.mova.elamur.ai/free/en/corpora/school/biology/172-coral-reef-builders-polyps-bleaching-sand-from-parrotfish-and-giant-clams/3/) — Walk on a white tropical beach and much of the sand under your feet may have passed through a parrotfish, which crunches coral with its beak and poops out fine sand. - [4](https://md.mova.elamur.ai/free/en/corpora/school/biology/172-coral-reef-builders-polyps-bleaching-sand-from-parrotfish-and-giant-clams/4/) — Corals are animals, not plants or rocks: colonies of tiny polyps that build hard skeletons of limestone and at night stretch out tentacles to catch tiny food. - [5](https://md.mova.elamur.ai/free/en/corpora/school/biology/172-coral-reef-builders-polyps-bleaching-sand-from-parrotfish-and-giant-clams/5/) — Coral reefs grow in warm, clear, shallow water, where the tiny algae living inside the polyps get enough sunlight to make food. - [6](https://md.mova.elamur.ai/free/en/corpora/school/biology/172-coral-reef-builders-polyps-bleaching-sand-from-parrotfish-and-giant-clams/6/) — When water gets too warm, corals push out their algae and turn white, which is called bleaching; big bleaching events have hit the Great Barrier Reef many times since 1998. - [7](https://md.mova.elamur.ai/free/en/corpora/school/biology/172-coral-reef-builders-polyps-bleaching-sand-from-parrotfish-and-giant-clams/7/) — Parrotfish bite algae off coral with beak-like teeth and grind up bits of coral; one big parrotfish can make hundreds of kilos of sand a year. - [9](https://md.mova.elamur.ai/free/en/corpora/school/biology/172-coral-reef-builders-polyps-bleaching-sand-from-parrotfish-and-giant-clams/9/) — The giant clam is the biggest clam in the world and can weigh more than two hundred kilos; the story of giant clams trapping divers' legs is a myth, because they close slowly and usually not fully. - [10](https://md.mova.elamur.ai/free/en/corpora/school/biology/172-coral-reef-builders-polyps-bleaching-sand-from-parrotfish-and-giant-clams/10/) — On a few nights a year many corals release tiny pink bundles of eggs and sperm into the water at the same time, like an underwater snowstorm. - [11](https://md.mova.elamur.ai/free/en/corpora/school/biology/172-coral-reef-builders-polyps-bleaching-sand-from-parrotfish-and-giant-clams/11/) — The Great Barrier Reef off Australia is the largest coral reef system on Earth, made of thousands of separate reefs. - [12](https://md.mova.elamur.ai/free/en/corpora/school/biology/172-coral-reef-builders-polyps-bleaching-sand-from-parrotfish-and-giant-clams/12/) — People say the Great Barrier Reef is the only living thing you can see from space, but it is made of countless living things, and astronauts can see cities and roads too. - [14](https://md.mova.elamur.ai/free/en/corpora/school/biology/172-coral-reef-builders-polyps-bleaching-sand-from-parrotfish-and-giant-clams/14/) — Coral reefs cover less than one percent of the ocean floor but are home to a huge share of sea life, and they protect coasts from waves like natural walls. - [15](https://md.mova.elamur.ai/free/en/corpora/school/biology/172-coral-reef-builders-polyps-bleaching-sand-from-parrotfish-and-giant-clams/15/) — Not all corals live in warm water: some reefs grow in cold, dark water deep down, for example off Norway, and some are thousands of years old. - ← previous: [The Southern Ocean: blue whales, colossal squid and life under the ice](https://md.mova.elamur.ai/free/en/corpora/school/biology/171-the-southern-ocean-blue-whales-colossal-squid-and-life-under-the-ice/) - next →: [Coral reef partners and tricksters: clownfish, cleaners, mimics and puffers](https://md.mova.elamur.ai/free/en/corpora/school/biology/173-coral-reef-partners-and-tricksters-clownfish-cleaners-mimics-and-puffers/) - ↑ back to [Biology](https://md.mova.elamur.ai/free/en/corpora/school/biology/)