Coral Reef Ecosystems

What Is a Coral Reef Ecosystem?

Word of the Week

Zooxanthellae

Zooxanthellae are microscopic algae found in some Cnidarians (corals, jellyfish, etc.). They provide the animal with energy through photosynthesis.


Corals typically grow in shallow, sunlight water where zooxanthellae can photosynthesize.

Species Spotlight

Elkhorn Coral

Acropora palmata

Elkhorn coral lives in the warm, tropical waters of the Caribbean. It is called elkhorn coral because the branches look like elk antlers. The cracks and crevices between the branches make great hiding spots for small animals. If one of its branches falls off, it can grow into a new coral. 


Like most coral species, elkhorn coral lives in shallow, sunlit water. It relies on microscopic algae called zooxanthellae for energy. The zooxanthellae live inside the coral polyps. Using photosynthesis, the zooxanthellae use the sun's energy to produce sugar (energy) for the polyps. Elkhorn coral gets most of its energy from the zooxanthellae. However, they also get energy from catching and eating small prey using stinging tentacles. 


Elkhorn coral uses this energy to build their hard skeleton. Like all hard corals, their skeletons are made of calcium carbonate. Snails and clam shells are also made of calcium carbonate. Elkhorn coral is one of the fastest-growing coral species. It can grow up to 5 inches per year. Some ancient elkhorn coral colonies can reach 12 feet wide!


Unfortunately, elkhorn coral is in danger. More than 90% of elkhorn corals have disappeared in the last 50 years. Like most coral, elkhorn coral faces threats like disease and pollution. However, their greatest threat is warming ocean water due to climate change. Corals struggle to survive in water that is too warm. You can help save elkhorn coral and other coral species by reducing your impact on climate change.

Learn More

Brain Blast

Research different coral species. Make a list of 5 coral species that are named for their appearance (for example, how elkhorn coral is shaped like an elk's antlers).

Conservation Corner

Heat Resistant Coral

Why does it matter if corals disappear? 


For many reasons! Coral reefs…

  1. Are home to ¼ of all ocean life
  2. Protect coastlines from storms like hurricanes
  3. Provide food (fish) to people
  4. Create businesses (like owning a scuba shop) in local communities


More than 500 million people depend on coral reefs for food, money, and storm protection. 

Unfortunately, coral reefs are in danger. The ocean has warmed due to climate change. Most corals and the zooxanthellae (algae) they depend on cannot survive in warm waters. Fortunately, scientists created a plan to make sure coral reefs do not disappear.


The first step is figuring out which corals can survive in warm water. Scientists breed and grow these heat-resistant corals in aquariums and other safe areas. Then, they transplant the corals to the ocean to continue growing on the reef. The reefs have a better chance of surviving with heat-resistant corals.


Restoring coral populations on reefs all around the world takes a lot of time and support! You can help organizations like the…

…by adopting a coral, purchasing swag, or making donations. 

Coral Reef Lingo

Match each word to its definition.

Ocean Organization Printable

Coral Reef Vs. Kelp Forest Challenge

Comparing & Contrasting

*To complete this challenge, you will also need to complete the Coral Reef Adventure*

Glossary

Abiotic

A part of an ecosystem that is nonliving.

Biodiversity

 Describing the variety of living organisms in one place.

Biotic

A living organism.

Calcium Carbonate

 Hard, chalky substance that makes up the hard outer structure of corals, snails, oysters, and other ocean invertebrates.

Climate Change

A change in global weather patterns as a result of greenhouse gases in the atmosphere.

Cnidarian

Group of invertebrates including corals, jellyfish, and sea anemones.

Coral

Animals related to jellyfish and sea anemones comprised of tiny polyps working together to support the colony.

Coral Bleaching

The process of corals turning white as they die.

Coral Reef

Diverse ecosystem made of individual corals growing close to each other.

Ecosystem

An area of the planet filled with living and nonliving things that interact.

Habitat

An area where a plant or animal lives.

Invertebrate

An animal that has no bones.

Nematocyst

Stinging cell found in the tentacles of corals and their relatives.

Ocean

A very large saltwater ecosystem that covers more than 70% of the planet.

Photosynthesis

The process used by plants and algae to change energy from the sun into sugar (energy) for the organism.

Polyp

Small animal with stinging tentacles found in corals and other cnidarians.

Shelter

A space where animals go for protection.

Tropical

Describing the warm, rainy region near the equator.

Zooxanthellae

Microscopic algae found in some Cnidarians (corals, jellyfish, etc.). They provide the animal with energy through photosynthesis.

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