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Coral Reef Ecosystems Guide

Corals occupy less than 0.1% of the earth's surface. Yet, the four different types of coral reefs provide habitats for more than one million fish species and other animals.

This section explains the most pressing problems faced by vulnerable corals with a list of easy ways to help protect and conserve coral reef environments.

Ecology & Biodiversity of Coral Formations

There are two different types of coral, hard stony corals (e.g. staghorn coral) and soft corals (e.g. sea whips).

The biodiverse marine ecosystems created by corals are a habitat for:

Reef producing coral are called hermatypic corals. These reef builders are invertebrate animals that have a rigid calcium carbonate skeleton.

Healthy coral reefs are important for several reasons. They provide food, income (e.g. scuba diving tourism), and coastal protection for more than half a billion people living in coastal regions around the world.

Pro Tip: We often get asked... What is coral, plant or animal? Another segment explains what corals are made of, how these tiny colonial organisms create colourful reef structures, and the difference between hard and soft corals (hermatypic vs. ahermatypic).

4 Types of Coral Reef Formations

When marine biologists and scientists use words related to sea life, they tend to list four different classifications of coral reef structures.


Usually circular or ring-shaped, atolls are small, low lying islands that have a coral rim encircling a lagoon. Often, they are in the middle of the sea and far away from land, such as the Great Blue Hole in Belize, Central America.

Barrier Reefs

For the most part, a barrier reef (e.g. the GBR in Australia) tends to run parallel to the coastline, often separated by a deep or wide lagoon.

Coral Reef Formations: The Importance of Reef Producing CoralsThe shallowest parts of some barrier reefs are visible at the surface of water. This feature often creates a navigational barrier for large ships.

Fringing Reefs

A fringing reef is one that grows quite close to a coastline, especially at the outer edge of islands and continents.

Narrow and shallow lagoons often separate them from the shoreline. The most common type of coral reef is fringing reefs.

Patch Reefs

A patch reef is a small coral reef ecoregion growing upwards - often in isolation - from an open bottom of an island platform or continental shelf. The best place to find a patch reef is between a fringing reef and a barrier reef. They vary in size, but rarely break the surface of the water.

Different Types of Hard Corals

Acropora Millepora

The best place to find these branching stony corals is the western Indo-Pacific, at depths between two and twelve metres (6 to 40 feet).

Yet, the geographical range of Acropora millepora is broad. It exists in the shallow reef flats near the east coast of Africa, Egyptian Red Sea, as far north as Japan, and around the southern shorelines of Indonesia, and Australia.

Characteristics and Colouring

It is a small colonial species with short, cylindrical branches that tend to grow in patches or clumps. Their radial skeletal cups (called corallites) are uniform with scaly lower rims.

Acropora millepora is a colourful species of coral. In general, its branches are dark green with orange tips, or sometimes pink, blue, or green.

Conservation Status

The general destruction of coral reef formations worldwide is the biggest threat to the long term survival of Acropora millepora.

They are quite abundant in some shallow water locations. But, this particular species is susceptible to (all):

Important: The IUCN Red List of Threatened Species assessed Acropora millepora in January 2008. They recorded the species as being Near Threatened (NT) and the population trend is "decreasing".

Acropora Tenuis

Artichoke Coral

Elkorn Coral

Several global factors (e.g. climate change) threaten the survival of most corals located in shallow tropical reefs and lagoons because it interrupts the symbiotic relationship they have with algae.

This section contains detailed facts and interesting information about elkhorn coral, and the significance of healthy "bush-like" coral species for fish families and other reef organisms.

Golfball Coral

Great Star Coral

Lattice Table Coral

Leaf Plate Montipora

Lettuce Coral

Lobe Coral

Mountainous Star Coral

Pillar Coral

Porites Lutea

Porites coral, of the genus scleractinia (meaning stony coral), is also known as finger coral (scientific name Porites compressa), boulder coral, and sometimes hump coral.

This finger-like characterisation and morphology is typical of the Porites species that create colonial rings of corals (microatoll formations) and large sturdy habitats for Spirobranchus giganteus.

Staghorn Coral

Several global factors (e.g. climate change) threaten the survival of most corals located in shallow tropical reefs and lagoons because it interrupts the symbiotic relationship they have with algae.

This segment contains detailed facts and information about staghorn coral, and the significance of healthy "bush-like" coral species for fish families and other reef organisms.

Yellow Pencil Coral

Different Types of Soft Corals

Black Coral

Bubble Coral

Dead Man's Fingers

There is a colonial species of soft coral with branching, finger-like encrustations (lobes) that resemble the fingers of an upturned human hand.

This segment contains facts about dead man's fingers coral, and why this epifaunal sea creature thrives around the United Kingdom coastlines.

Organ Pipe Coral

Sarcophyton Ehrenbergi

Sea Fingers

Sea Pen (Pennatulacea)

Toadstool Leather Coral

Wire Coral

Frequently Asked Questions about Coral

All corals are (or were) living organisms. They are not simply mineral rock! Put another way, a coral reef is a colonial collection of marine organisms that are either alive or dead.

What are Corals Made Of?

Most of the six thousand different coral species thrive best in warm, shallow, coastal waters. But, you can also find corals deep down in the darkness of open oceans.

In fact, corals are marine invertebrate animals that form huge underwater structures. Coral reefs provide sheltered habitats and food sources for 25% of fishes worldwide.

What are Porites?

A porite has an exceptionally sluggish growth rate. In fact, some porites coral species (e.g. Porites lutea) grow less than one (1) centimetre per year.

But, the tall giants of seven or eight metres high rank among the oldest and most established of all earth life forms.

What are Reef-Producing Coral Called?

Understanding how tiny polyp structures produce fabulous coral reef gardens is often misunderstood and underestimated.

What Do Artificial Reefs Do?

They are becoming popular in many diving destinations around the world and the reasons for creating an artificial reef vary in different oceans and environments.

What Causes Coral Bleaching?

Simply put, coral bleaching is a process that causes coral to lose its normal pale brown or dark grey colour and appears white instead.

Even though the inexperienced diver may admire the apparent snow-like environment, it is a sign that the coral is distressed.

Why Do Corals Get Disease?

You don't need to be a scuba diver to learn that healthy coral is less common nowadays. Find out how the different types of coral diseases are caused by various pathogens, fungi, and bacteria.

10 Steps to Save Coral Reefs

Join the actions of concerned individuals by discovering some of the most pressing problems facing these vulnerable environments. Then, you can also help to protect and conserve them.

The Project AWARE course is informative and interesting. It's also a great way to make a difference, and you don't even need to get scuba qualified.

Here's the deal:

You can make a positive impact against global Earth climate change, ocean acidification, coral bleaching, and other world threats to our oceans by helping to preserve coral reef formations.

Collectively, following these simple steps below "will" make a difference. The daily actions of everyone are effective!

  1. Educating the public of the seriousness is imperative. People need to learn, read about, and take action against marine pollution. The more information you learn, the better the actions, with more success directly impacting conservation. Saving the Earth is everyone's responsibility.
  2. Not everyone lives near coral reef formations. However, if you plan a vacation accordingly, it's a great opportunity to visit a local marine park. Volunteer organisations would benefit from your inclusion of their surveys and clean-ups.
  3. Take steps to lower your carbon footprint. Planting trees helps to reduce run-off and reverse global warming. Walking or using public transport helps to reduce pollution. Driving cars and industry emit fossil fuels, which increases coral bleaching.
  4. Coral reefs are precious. Although they portray a rocky appearance, corals are delicate animals. If you go diving or snorkeling, do it responsibly, using appropriate anchoring techniques and do not touch the reef.
  5. Plan to eat sustainable seafood. Seafood Watch produces a pocket guide that highlights seriously overfished species such as bluefin tuna, blue marlin, Atlantic cod, salmon, sea bass, and others.
  6. Fertiliser products eventually run into the seas, polluting the water, and harming coral reefs and marine animals. Try to use organic fertilisers that are eco-friendly, to reduce the impact on our water systems.
  7. Using water conservatively creates less waste-water. Dispose trash and litter properly. When garbage ends up in the sea, it is extremely harmful for marine life animals.
  8. You can contact your local governmental representatives and petition them to increase their activities against marine pollution. Peaceful demonstrations are increasingly changing the way that governments act.
  9. It makes sense to support "eco and reef-friendly" businesses and organisations. So-called "Green" scuba diving business operatives actively engage in conservation activities and sustainable practices. You can learn more about these establishments from the National Green Pages.
  10. Scuba divers and water enthusiasts are ambassadors for the underwater world. Spread the message that coral reef formations need our help.

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