The effect of zooxanthellae availability on the rates of skeletal growth in the Red Sea coral Acropora hemprichii

Abstract

Zooxanthellae density affects growth rate of Acropora hemprichii at reef flat and 10m depth, where the correlations were significantly moderate at reef flat (r=0.461 &P<0.01) and significantly high at 10m depth (r=0.636 &P=0.424). While non interactive effects were obtained at 20 and 25m depth, where the correlations were non significant (r=0.346 &P<0.19 and r=0.103 &P<0.706, respectively). Either zooxanthellae density, hosted by A. hemprichii, or growth rate was decreased with depth increase. Zooxanthellae density at reef flat (1.55±0.303×106cells/cm2) was twice higher than at 25m depth (0.706±0.253×106cells/cm2). However, growth rate at reef flat was approximately three times higher than 25m depth (0.013±0.0024mm/day). The maximum growth rate (0.0335mm/day) and zooxanthellae density (1.32×106cells/cm2) were recorded during summer season, and the minimum growth rate (0.01769mm/day) and zooxanthellae density (0.931106cells/cm2) were recorded during autumn.