Porites

Porites is a genus of stony coral; they are SPS (Small Polyp Stony) corals. They are characterised by a finger-like morphology. Members of this genus have widely spaced calices, a well-developed wall reticulum and are bilaterally symmetrical. Porites, particularly Porites lutea, often form microatolls. Corals of the genus Porites also often serve as hosts for Christmas tree worms (Spirobranchus giganteus). Specimens of Porites are sometimes available for purchase in the aquarium trade. Due to the strict water quality, lighting and dietary requirements, keeping Porites in captivity is very difficult. Most Porites that are collected have Christmas tree worms (Spirobranchus giganteus) that bore into the coral, serving as additional aesthetic livestock. These particular Porites specimens are called 'christmas tree worm rocks' or 'christmas tree worm coral'. Porites corals have been shown to be accurate and precise recorders of past marine surface conditions. Measurements of the oxygen isotopic composition of the aragonitic skeleton of coral specimens indicate the sea-surface temperature conditions and the oxygen isotopic composition of the seawater at the time of growth. The oxygen isotopic composition of seawater can indicate the precipitation/evaporation balance because oxygen atoms of the more abundant mass 16 will preferentially evaporate before the more rare mass 18 oxygen. The relationship between temperature, precipitation, and the oxygen isotopic composition of Porites corals is important for reconstructing past climates, and associated large-scale patterns such as the El-Nino Southern Oscillation, the Intertropical Convergence Zone, and the mean state of the climate system. Corals in the genus Porites are found in reefs throughout the world. It is a dominant taxon on the Pandora platform of the Great Barrier Reef. Potts et al. (1985) identified 7 dominant species: P. lobata, P. solida, P. lutea, P. australiensis, P. mayeri, P. murrayensis, and P. anae. The oldest of six colonies in this reef was approximately 700 years old, and was estimated to be growing at 10.3 mm per year. Meyer and Schultz (1985) demonstrated that P. furcata has a mutualistic relationship with the schools of French and White Grunts (Haemulon flaviolineatum and H. plumieri) that rest in their heads during the day. The fish provide it with ammonium, nitrates, and phosphorus compounds. Coral heads with resting grunts experience significantly higher growth rates and nitrogen composition than those without. Representatives of this genus are found in both the Indo-Pacific and Caribbean basins. Some species in this genus demonstrate high levels of halotolerance. In the Gulf of Thailand P. lutea tolerates daily tidal shifts of 10-30‰ salinity. Moberg et al. (1997) determined that when the salinity declines, the symbiotic zooxanthellae decrease their photosynthesis rate as the coral contracts its polyps to protect them. The corals maintain their metabolic rate by temporarily switching to heterotrophy, consuming prey such as brine shrimp and other zooplankton.