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Coral Reef Ecology

← Builds on Marine and Estuary Ecosystems

Terms you will need

  • coral reefA coral reef is an underwater ecosystem made of colonies of coral polyps that create hard carbonate exoskeletons. These structures support a wide variety of marine life and are often called the 'rainforests of the sea' because of their biodiversity.
  • zooxanthellaeZooxanthellae are microscopic algae that live inside coral polyps. They provide the coral with nutrients through photosynthesis, which helps the coral grow and gives it its color.
  • hermatypic coralHermatypic coral is a type of coral that builds reefs by creating hard calcium carbonate skeletons. These corals are essential for forming the structure of coral reefs.
  • coral bleachingCoral bleaching is when corals turn white because they lose the algae (zooxanthellae) that live inside them. This happens when the corals are stressed, often due to high water temperatures, and it can lead to the death of the coral.
  • hard coralHard coral is a type of coral that creates a hard, calcium carbonate skeleton. These corals are the main builders of coral reefs and provide structure for many marine species.
  • soft coralSoft coral is a type of coral that does not create a hard skeleton. Instead, it has a flexible, soft structure and is often found in areas with strong water currents.

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Coral reefs are underwater ecosystems built by reef-building corals, which form colonies held together by calcium carbonate. These structures, often called the rainforests of the sea, support an extraordinary diversity of marine life, providing habitat for at least 25% of all marine species despite occupying less than 0 1% of the ocean's surface. Found in warm, shallow, clear, and agitated tropical waters, coral reefs are among the most productive and complex ecosystems on Earth. They deliver essential ecosystem services, including shoreline protection, fisheries, and tourism, with an estimated annual global economic value ranging from $30–375 billion to as high as $9 9 trillion. However, coral reefs are highly sensitive to environmental changes and have declined by 50% since 1950 due to threats like rising ocean temperatures, pollution, overfishing, and ocean acidification. Understanding coral reef ecology is crucial for protecting these vital ecosystems and the countless species and human communities that depend on them.

Figures (4)

Yellow-brown zooxanthellae
Cross section of the mantle tissue of a giant clam showing the symbiotic protozoa
A ciliate with green zoochlorellae living inside it endosymbiotically
Diagram of radiolarian containing zooxanthellae (z)

Coral reefs are formed by colonies of coral polyps that secrete calcium carbonate to build their skeletons. These polyps live in a symbiotic relationship with microscopic algae called zooxanthellae, which provide the corals with nutrients through photosynthesis. This partnership allows corals to grow and form the complex structures of reefs.

The most common types of coral reefs are fringing reefs, barrier reefs, and atolls. Fringing reefs are attached to the shore and are the most common type. Barrier reefs are separated from the mainland by a deep lagoon and are much rarer.

Atolls are ring-shaped reefs that form around submerged volcanic islands. These different reef types develop based on the movement of the Earth's crust and changes in sea level over time. Coral reefs are found in tropical and subtropical waters, typically between 30° N and 30° S of the equator.

They thrive in warm, shallow waters with plenty of sunlight, which is essential for the photosynthesis of their symbiotic algae. When water temperatures rise too high, corals can expel their zooxanthellae, leading to a condition called coral bleaching. Without their algae, corals lose their color and become more vulnerable to disease and death.

Protecting coral reefs involves reducing pollution, overfishing, and climate change impacts. Conservation efforts include establishing marine protected areas, restoring damaged reefs, and promoting sustainable fishing practices. These actions are essential for preserving the biodiversity and ecological functions of coral reefs for future generations.

Key Points

  • A coral reef is an underwater ecosystem characterized by reef-building corals.
  • Zooxanthellae are microscopic algae (dinoflagellates) of the genus Symbiodinium that live within the tissues of coral polyps and provide organic nutrients through photosynthesis.
  • Coral bleaching is the process where corals become white due to loss of symbiotic algae and photosynthetic pigments.
  • Hard coral refers to corals that secrete hard carbonate exoskeletons that support and protect the coral.

Terms

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