SEASONAL VARIATIONS IN THE SKELETOGENSIS PROCESS IN SOME BRANCHING CORALS OF THE RED SEA

The seasonal variations of skeletal thickness and specific density as well as some elements; Sr, Mg, Mn, and Zn were studied in two branching coral species (Acropora humilis and Stylophora pistillata) in three sheltered, intermediate and exposed localities along the Red Sea coast under different natural and anthropogenic stresses. The two species recorded the highest average branch thickness at the lee side of Al Fanadir (12.24 mm and 11.11 mm respectively) indicated that the coral species in the exposed areas are developing well under the direct surge effects of sea currents and waves. Significant variations were recorded in the specific density of Stylophora pistillata rather than Acropora humilis in the different localities. S. pistillata at Abu Galawa locality recorded the highest density (2.30) while Al Fanadir Islands recorded the lowest one (1.21). The coral density of A. humilis was varied between 1.02 at Al-Ahyaa Bay to 1.99 at Abu Galawa indicating that the branching corals under intermediate oceanographic conditions areas have energy to construct more bulk skeletons with concentrated calcium carbonates than those in the exposed and sheltered areas. The period between autumn to spring seasons recorded the highest general trend of some metal bio-mineralization in the skeletal structure as (Mg and Zn) of the two species in the different localities. This period representing three essential stages in the coral reef growth; maturation, spawning and budding that mean the skeletogenesis process is reaching the optimum intensity in accompanying with the different stages of animal growth and might be decreased in summer due to the high temperature and salinity. The skeletogensis of the other metals (Mn and Sr) is highly influenced by the water temperature, metal saturation