Seasons in Coral Reefs: Eternal Summer with Subtle Rhythms

Coral reefs don't have seasons in the temperate sense—no winter dormancy, no autumn leaf fall. They exist in the tropical and subtropical zones where two things are remarkably constant:

• Water Temperature: 23–29°C (73–84°F) year-round. Variation is typically <2°C annually.
• Day Length: Near 12 hours year-round (within 1–2 hours of equator).

So, No Seasons at All?

Not no variation—just not the four-season model. Reefs experience:

Wet vs. Dry Season (Monsoonal Regions)

• Increased runoff → lower salinity, higher turbidity, nutrient pulses.
• Can trigger coral spawning (often tied to lunar cycles after monsoon onset).
• Cyclone/hurricane season (physical damage, cooling).

Temperature Micro-Seasons

• Slight warm/cool periods can cue mass spawning events (e.g., Great Barrier Reef: November–December).
• Even 1–2°C anomalies (marine heatwaves) cause bleaching—now the dominant "seasonal" threat.

Biological Rhythms

• Spawning synchrony (lunar + thermal cues).
• Fish recruitment pulses.
• Predator migrations (e.g., whale sharks, mantas following plankton).

In essence: reefs live in perpetual growing season. The "seasons" are biological events, not climatic shifts. Climate change is now imposing a new, deadly season: bleaching season.