Coral Growth and Skeletal Density Relationships in Some Branching Corals of the Red Sea, Egypt

Abstract

The coral reefs at the exposed zones are exhibited to strong wave action, renewable water masses, clear seawater and small temperature variations, however, in the sheltered zones they exposed to high turbidity, high temperature variations and protected from the surge waves and currents. In situ measurements of seasonal and annual growth rates and the branch thicknesses using Varner Caliber and the laboratory measurements of skeletal densities using Archimedes’s Principle were done in four branching coral species growing in the exposed and sheltered zones of Hurghada and Hamrawin at the northern Red Sea. Acropora humilis recorded the highest seasonal and annual growth rates at all zones; 0.68±0.02, 0.76±0.03, 0.66±0.03 and 0.69±0.02mm/month and 7.25±0.20, 7.96±0.33, 7.10±0.11 and 7.34±0.14mm/yr respectively. Pocillopora damicornis recorded the highest averages of skeletal density at the different zones of Hurghada and Hamrawin; 2.04±0.35, 1.64±0.26, 2.64±0.66 and 1.96±0.18gm/cm³ respectively and the highest averages of the branch thicknesses at the exposed and sheltered zones of Hurghada (1.66±0.42cm², 1.51±0.30cm²) while, A. humilis recorded the highest average of the branch thicknesses at the exposed and sheltered zones of Hamrawin (1.49±0.16cm², 1.14±0.08cm²). A. humilis was the fastest growing species in the worm season at the exposing and sheltered zones of Hurghada and Hamrawin, while P. damicornis was the slowest growing species because of it tends to form thick and dense branches. The oceanographic and local conditions as; temperature variations, aragonite saturation, turbidity, effects of surge waves and light intensity are responsible about the differences in the skeletal parameters of the studied species.

Keywords: Branching corals – Growth rates - Skeletal density – Branch thicknesses – exposed and sheltered zones.