Journal d'océanographie et de recherche marine
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ISSN: 2572-3103
ISSN: 2572-3103
Yahya A. M. Floos, Abdulmohsin A. Al-Sofyani
Some aspects of the physiology of the corals Seriatopora hystrix and Lobophyllia corymbosa from the Red sea are described in this paper. The two species were selected on the basis of their different responses to seasonal changes. At the study site, the lowest mean of seawater temperature is 27.42°C and 27.17°C at 5 m and 10 m depths respectively during winter, while the maximum mean of seawater temperature was 32.67°C and 31.17°C in 5 m and 10 m depths respectively during summer. The mean density of the skeleton of both species was identical at 2.5 ± 0.16 (10) g.cm-3 and 2.75 ± 0.05 (10) g.cm-3 respectively. The mean surface area (cm2g-1 skeleton) was higher in L. corymbosa 4.73 ± 2.31 (10) cm2g-1 skeleton than S. hystrix 3.58 cm2 g-1 ± 1.2 (10) cm2g-1 skeleton with no significant difference. The mean dry tissue weight g-1 skeleton in summer at 5 m depth was higher in L. corymbosa 39.6 ± 24.9 (10) mg.d.t.g-1 skeleton than S. hystrix 24.9 ± 16.4 (10) mg.d.t.g-1 skeleton and was significantly different (t-test P ≤ 0.03). While in summer at 10 m depth was higher in L. corymbosa 45.49 ± 14.00 (10) mg.d.t.g-1 skeleton than S. hystrix 24.9 ± 19.6 (10) mg.d.t.g-1 skeleton and was significantly different (t-test P ≤ 0.01). There was a significant seasonal difference in the numbers of zooxanthellae of both the species at two different depths on the basis of biomass and surface area (t-test p<0.005). L. corymbosa, had a lower number of zooxanthellae 0.05 × 105, 0.43 × 105, 0.06 × 105 and 0.46 × 105 mg-1 dry tissue weight than S. hystrix 0.19 ×105, 5.1 ×105, 0.27 × 105 and 9.59 × 105 mg-1 dry tissue weight in two season and two depths respectively. S. hystrix had higher number of zooxanthellae in 5 m depth both in summer and winter respectively (1.2 × 105, 19.09 × 105 cm-2) and in 10 m depth it was 1.6 × 105 and 25.7 × 105 cm-2 in summers and winter than the L. corymbosa. At 5 m depth, the observed zooxanthellae of L. corymbosa were 0.50 × 105 in summer and 3.51 × 105 cm-2 in winter and it was 0.58 × 105 in summer and 4.42 × 105 cm-2 in winter respectively. The mean respiration rate of whole colonies of S. hystrix was higher than that of L. corymbosa at the same depths both in summer and winter. The mean dark respiration rate decreases with increasing depths. The mean photosynthesis vs. irradiance curves of S. hystrix and L. corymbosa were plotted to the hyperbolic tangent function for summer and winter season (5 m and 10 m depths). The growth rate was linear during each period of measurement during summer, the highest mean daily skeletal growth rate of S. hystrix was 2.3 ± 1.3 (20) mg .skel.d-1 in 10 m depth and it was 1.6 ± 0.5 (21) mg .skel.d-1 at 5 m depth. Whilst during winter, the lowest was 1.9 ± 0.96 (20) mg.skel.d-1 at 10 m and also lowest (1.5 ± 0.7 (20) mg .skel. d-1) at 5 m depth. The growth rate of the two species was lower in the winter than in summer.