Coral Reef Habitats & Zones

Coral Reef Habitats & Reef Zones

• Corals are animals, specifically in the Kingdom Animalia, Phylum Cnidaria, Class Anthozoa. They are related to jellyfish and sea anemones.
• Over 800 known species of reef-building coral exist worldwide. Many other species of soft corals and deep-sea corals also exist.
• Coral reefs cover less than 0.015% of the ocean but harbor more than one-quarter of ocean biodiversity. No other ecosystem occupies such a small area with so many life forms.
• Coral reefs are often called the "rainforest" of the sea because they're incredibly diverse and complex.
• Reefs are the largest geological features built by organisms.
• Coral growth needs specific conditions: salt water, clear water, shallow water, and warm water (above 20°C/68°F). Ideal temperature for coral growth is 21-29°C (70-85°F). Water above 30-35°C (86-90°F) is harmful to corals.

Types of Reef Systems

• Fringing Reefs:

  • Most common type.
  • Grow in a narrow band along the shore.
  • Vulnerable to sediment, freshwater runoff, and human disturbance.

• Barrier Reefs:

  • Separated from the shoreline by a lagoon.
  • Lagoons are protected from waves and currents.
  • Patch reefs are often found in the lagoon.
  • Example: The Great Barrier Reef (2000 km/1200 miles) along the NE coast of Australia.

• Atolls:

  • Ring of reef with a steep outer slope.
  • Encloses a central, shallow lagoon.
  • Found far from land primarily in the tropical Indian and Western Pacific Oceans.
  • Atolls begin as fringing reefs and grow on sediment as islands sink.
  • Original volcanic island rock is found deep below the lagoon.

Reef Zones

• Outer slope: Good for coral growth.
• Buttress zone: Heavy wave action, only the densest corals survive.
• Algae ridge: Coralline algae withstand waves.
• Reef flat: Often exposed at low tide, with a good variety of corals.
• Leeward islands: Densest coral due to lack of waves.

Coral Adaptations & Interactions

• Corals rely on symbiosis (a close relationship between two different species) with zooxanthellae (a type of algae).
• Zooxanthellae perform photosynthesis, providing food for the coral. In return, the coral provides protection for the algae and supplies waste products like carbon dioxide, nitrates, and phosphates.
• Intense competition exists for space, light, and nutrients among reef organisms.
• Habitat stratification in reefs helps various species survive.
• Reef fish are often brightly colored for mate identification, or for camouflage.

Factors Influencing Coral Reefs

• Some animals (e.g., crown-of-thorn starfish, parrotfish) eat coral, contributing to bioerosion (coral erosion due to living organisms).
• Natural disasters such as hurricanes and seasonal patterns can improve the reefs by reducing overcrowding.