Photosynthesis

Video on CORAL reefs & climate change

Catalyst: Coral Winners - ABC TV Science

GAMES to LEARN

Here are some online games about coral reefs .. which also help you learn more. 

Click on the links below:

1.
The CORAL REEF GAME - knowledge test


2.
REEF CHECK Game to learn


3.
CORAL REEF GAMES

TYPES OF CORAL

TYPES OF CORAL

There are two different types of coral: soft and hard.

• Soft corals form in the still waters of the reef ecosystem. 
  
  They look like plants as they sway in the ocean currents, and are sometimes called sea fans. 
  
  They secrete small amounts of calcium carbonate that helps them attach to the reef. 
  
  Soft coral polyps always have eight tentacles.
  
  
• Hard corals are the reef-building type. 
  
  Hard corals give a coral reef its structure. 
  
  As the coral polyps grow, they form skeletons of calcium carbonate.
  
  Various corals grow differently, and the shape of each different type is often what gives the coral its name. 
  
  It takes years for the millions of coral polyps that form a colony to build the coral reef. 
  
  Hard coral polyps can be identified by the number of tentacles they have. It is always a multiple of six. 
  
  
  ACTIVITY
  
  Draw a table to show the comparison between hard and soft corals using these headings:
  
  Features
  Polyp tentacles
  Brief description
  Include a sketc of each type of coral in your table. 
  

CORAL POLYPS

A coral reef is an offshore ridge which is composed mainly of calcium carbonate. 

It is formed from the secretions of small marine animals called coral polyps. 

Coral polyps thrive in shallow, warm, nutrient poor, tropical waters. 

These tiny animals attach themselves to objects such as rocks or existing reefs and build tiny shells of calcium carbonate around themselves. 

They sit in these shells and use their tiny tentacles to catch food. 

When coral polyps die, new coral polyps build their shells on top of the old shells of the previous generation. 

In this way the reef expands over time. Take a look at the cross section of a coral polyp below.

Diagram showing a cross section of a coral polyp. The polyp is shown sitting in its calcium carbonate shell with its  tentacles outstretched.

Coral reefs are made up of millions of individual animals called coral polyps. These give reefs their structure. One of the features of coral is the way it is able to get energy from the Sun through algae called zooxanthellae. This is one of the special relationships that exist in all reef environments.

BUILDING BLOCKS OF THE REEF

Coral polyps

The basic building blocks of the coral reef are coral polyps. Coral polyps have clear bodies and white skeletons. The calcium carbonate on coral reefs is actually the skeleton of coral polyps, or more correctly the materials left behind by coral polyps as they grow. This calcium carbonate gives the coral their shape. The polyps feed off zooplankton, tiny animals that are in reef waters. 

Up to 90 per cent of the nutrients needed by the coral polyp to grow actually come from the zooxanthellae algae that live within it.

Zooxanthellae

Zooxanthellae are algae that actually grow in the coral polyp. Algae require sunlight to grow. It is algae that give coral polyps their huge range of colours. Millions of zooxanthellae algae live within just one square centimetre of coral. *

Symbiotic relationship builds reef

Nutrients in the waters around coral reefs must be low or else the coral will die. This is unusual because coral reefs are one of the most productive environments on the planet. The way nutrients are cycled around makes coral reefs unique.

Coral polyps and the zooxanthellae have a symbiotic relationship. Each organism benefits the other—the wastes of the polyp are used by the zooxanthellae to grow, and the wastes of the zooxanthellae are used by coral polyps to grow. As zooxanthellae are plants and coral polyps are animals, it is actually the zooxanthellae that are at the base of the coral reef food web. 

CORAL & POLYPS - how coral is formed

What is Coral?
Coral is made by millions of tiny carnivorous (say: car-niv-or-us)
animals called polyps.(say: pol-lips) Carniverous means to eat meat.
Polyps live in groups called colonies.
Each polyp builds a case of limestone around itself.
Coral reefs are made of thousands of these limestone cases.

Polyps

The polyp is related to the anemone, and consists of a stomach with a mouth at one end.

 The mouth is surrounded by a number of tentacles. These tentacles resemble feet, which is how they get their name: 'polyp' is a Greek word meaning 'many feet.'

The tentacles are covered with tiny stinging cells,and when a small creature brushes against the tentacles, it is killed. The prey is then brought into the polyp's stomach to be digested.

Polyps cannot move from their limestone homes. They mostly feed at night.


How do polyps reproduce?

A polyp reproduces in either of two ways:
by dividing its own body to form two polyps, or
by producing sperm and eggs 

Just after the full moon in November, eggs and sperm are released from coral polyps and float about for a few days. A small number of eggs will fertilise, hatch into larvae, and settle on the reef to begin new colonies.

Colonies grow rapidly. One polyp can become a colony of 25,000 polyps in about 3 years.









Building up a coral reefEach polyp builds a case of limestone around itself, using calcium from the water.

It is like a house, with a floor and walls. 

This remains after it has died and forms a foundation for another polyp to build a house on, putting a floor on the roof of the old one. 

When these limestone formations increase, they are called a coral reef.

In shallow water algae live in the tissues of the polyps. 

The algae use sunlight and the waste products of the polyp to make oxygen and food for the polyp. This kind of algae is called zooxanthellae. The algae need sunshine to survive, so do not live in deeper water where less sunshine filters through.

Coral reefs are the largest structures created by any group of animals in the world. They have existed on earth for over 200 million years. 

They grow in warm (18-33ºC), clear, fairly shallow water. The coral cannot grow in polluted water or water carrying soil from the land.

Coral Reefs

CORAL REEFS - General

CORAL REEF ECOSYSTEM

What is a coral reef?

A coral reef is a community of living organisms. It is made up of plants, fish, and many other creatures. Coral reefs are some of the most diverse ecosystems in the world. They are home to about 25% of all marine life!

There are sponges, sea slugs, oysters, clams, crabs, shrimp, sea worms, starfish and sea urchins, jellyfish and sea anemones; various types of fungi, sea turtles, and many species of fish. Think of them as the “rainforests of the oceans.”

Q1. Why are coral reefs called "rainforests of the oceans"?

Photo courtesy: Tony Hathcock, StockXchange.

Coral reefs have been around for millions of years. Less than 0.1% of the world’s ocean floor is covered by coral reefs. The reefs grow best in warm, shallow, clear, sunny and moving water. However, they grow very slowly—anywhere from 0.3 cm to 10 cm per year. The reefs we see today have been growing over the past 5 000 to 10 000 years.

Photo courtesy: Adam Short, StockXchange.

Coral reefs are made of tiny animals called “polyps” that stay fixed in one place and are the main structure of a reef. Polyps have a hard outer skeleton made of calcium (similar to a snail’s shell).

Each polyp is connected by living tissue to form a community. Only the top layer of a coral reef contains living polyps. As new layers of the coral reef are built, the polyps leave the lower layers.

Each polyp has a ring of tentacles shaped like a cup around a central opening. The tentacles are like long arms with tips that can sting. They are used either for defense or to capture zooplankton (small animal life) for food.

The Great Barrier Reef is the largest coral reef. It is made up of over 2 900 individual reefs and 900 islands stretching for over 2 600 kilometers off the northeast coast of Australia.

Where are coral reefs located around the world?

Photo courtesy: Wikipedia.

Why are they important? 

Coral reefs do a number of amazing things! Reefs

• Protect shorelines from big waves by absorbing wave energy
• Provide a safe place for fish to spawn (release eggs into the water)
• Provide habitats for a large variety of organisms
• Provide food (fish and shellfish) for many people living along coastlines
• Are a source of medication—some anti-cancer drugs and painkillers come from reefs
• Help in the carbon cycle
• Are a good sign of ocean water quality: Healthy reefs = Healthy water.