Coral Behavior: Feeding, Reproduction, Growth, and Defense

1. Feeding Strategies

• Symbiotic Photosynthesis: Most reef-building corals host zooxanthellae (dinoflagellate algae) in their tissues. The algae provide up to 90% of the coral's energy (glucose, glycerol, amino acids) via photosynthesis.
• Heterotrophic Capture: Polyps extend tentacles armed with nematocysts (stinging cells) to capture zooplankton, small fish, and organic particles—mostly at night.

2. Reproduction

• Sexual (Broadcast Spawning): Synchronized mass release of gametes (eggs/sperm) into water column → external fertilization → planula larvae → settlement → new colony. Often tied to lunar cycles and temperature.
• Asexual: Budding (new polyp forms on parent) and fragmentation (broken pieces reattach and grow). Allows rapid colony expansion and recovery.

3. Growth & Colony Formation

• Colonies = thousands of genetically identical polyps connected by living tissue (coenosarc) and a shared calcium carbonate skeleton.
• Growth forms: branching, massive, plating, encrusting. Rates vary: branching ~10–20 cm/yr; massive ~0.5–2 cm/yr.

4. Defense Mechanisms

• Nematocysts: Stinging cells deter predators (e.g., parrotfish, crown-of-thorns starfish) and competitors.
• Mucus: Traps sediment, pathogens; some contains antimicrobial compounds.
• Chemical Warfare: Allelopathic compounds inhibit neighboring coral/algal growth.
• Zooxanthellae: Provide UV-protective pigments (mycosporine-like amino acids).

5. Environmental Sensitivity

Corals are sentinels of ocean health. Stressors—temperature spikes (>1–2°C above summer max), high light, acidification, pollution—cause bleaching (zooxanthellae expulsion). Prolonged stress leads to mortality. Understanding these behaviors is critical for reef conservation and restoration.