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Corals

Coral Biology

What are corals?

Corals are animals (Cnidaria, class Anthozoa) that live in symbiosis with photosynthetic algae called zooxanthellae (Symbiodinium sp.). Zooxanthellae:

  • They live inside the coral tissue
  • They perform photosynthesis → they provide up to 90% of the coral's energy
  • They give the coral its color

Coral Bleaching

When a coral is stressed (high temperature, intense light, pollution), it expels its zooxanthellae → loses its color → has no photosynthetic energy → and may die.

Types of Corals by Requirements

SPS (Small Polyp Stony) — Small-polyp stony coral

  • Examples: Acropora, Montipora, Pocillopora, Stylophora
  • High light, high current
  • Highly sensitive to parameters (NO3 <5, PO4 <0.05)
  • For Advanced Aquarists

LPS (Large Polyp Stony) — Large-polyp stony coral

  • Examples: Favia, Acanthastrea, Hammer, Blastomussa, Goniopora, Trachyphyllia
  • Moderate light and electricity
  • More tolerant of fluctuations
  • Good for beginners in choir singing

Soft Corals

  • Examples: Zoanthus, Palythoa, Sarcophyton, Xenia, Clavularia
  • Very tolerant, without a calcareous skeleton
  • They do not require such strict Ca/Alk monitoring
  • Perfect for beginners in sailing

Calcification

SPS and LPS corals form aragonite (CaCO₃) skeletons. They require:

  • Calcium: 380–450 ppm
  • Alkalinity: 8–12 dKH
  • Magnesium: 1200–1400 ppm (important to prevent Ca and KH from precipitating)