Porites sp.

Lore & Background

Porites corals are found in reefs throughout the world, with a dominant presence on the Pandora platform of the Great Barrier Reef. Potts et al. (1985) identified seven dominant species there, and the oldest of six colonies was approximately 700 years old, growing at 10.3 mm per year. Representatives occur in both the Indo-Pacific and Caribbean basins. Meyer and Schultz (1985) demonstrated that P. furcata has a mutualistic relationship with schools of French and white grunts (Haemulon flavolineatum and H. plumierii), which provide ammonium, nitrates, and phosphorus compounds, leading to higher growth rates and nitrogen composition in coral heads with resting grunts.

In the aquarium trade, Porites specimens are sometimes available but difficult to keep due to strict water quality, lighting, and dietary requirements. Many collected specimens have Christmas tree worms (Spirobranchus giganteus) boring into them, and are sold as 'christmas tree worm rocks' or 'christmas tree worm coral.' In paleoclimatology, Porites corals are accurate recorders of past marine surface conditions; oxygen isotopic composition of their aragonitic skeleton indicates sea-surface temperature and the precipitation/evaporation balance, aiding reconstruction of past climates and patterns like the El-Nino Southern Oscillation and the Intertropical Convergence Zone.

Physiologically, some Porites species show high halotolerance. In the Gulf of Thailand, P. lutea tolerates daily tidal shifts of 10-30‰ salinity. Moberg et al. (1997) found that when salinity declines, symbiotic zooxanthellae decrease photosynthesis as the coral contracts its polyps, and the coral temporarily switches to heterotrophy, consuming brine shrimp and other zooplankton. Growth rates can be determined from annual rings; P. astreoides grows about 3.67 mm/year, calcifies at 0.55 g/cm2/year, and increases density at 1.69 g/cm3/year. Meyer and Schultz (1985) reported seasonal variation, with P. furcata's growth peaking between May and August.

Reader's Guide

Porites corals hold significance in multiple fields. In paleoclimatology, they serve as precise recorders of past sea-surface temperature and the oxygen isotopic composition of seawater, which reflects the precipitation/evaporation balance. This allows reconstruction of large-scale climate patterns such as the El-Nino Southern Oscillation, the Intertropical Convergence Zone, and the mean state of the climate system. Their growth rates, determined from annual skeletal rings, provide additional temporal data; for example, P. astreoides grows approximately 3.67 mm per year. Ecologically, Porites is a dominant taxon on the Pandora platform of the Great Barrier Reef, where the oldest colony was about 700 years old. The mutualistic relationship between P. furcata and grunts demonstrates nutrient exchange that enhances coral growth. In the aquarium trade, Porites specimens are challenging to maintain but are valued when hosting Christmas tree worms. Threats include predation, climate change, and anthropogenic pollution; increased temperature and copper slow P. cylindrica's production and reduce zooxanthellae photosynthesis. Larvae are vulnerable to competition from other corals and predation from sea urchins, and mortality increases after strong storms. The genus's wide distribution across Indo-Pacific and Caribbean basins underscores its ecological importance.

Did You Know?

• Porites corals are also called finger coral or hump coral due to their finger-like morphology.
• The oldest Porites colony on the Pandora platform was approximately 700 years old, growing at 10.3 mm per year.
• P. furcata has a mutualistic relationship with French and white grunts, which provide it with ammonium, nitrates, and phosphorus compounds.
• In the Gulf of Thailand, P. lutea tolerates daily salinity shifts of 10-30‰.