Characteristics of Acropora divaricata and Acropora nobilis on different transplantation depths based on growth rate and zooxanthellae density

Coral reefs are aquatic ecosystems with the highest biodiversity and a complex structure of interconnections between invertebrates and photosynthetic dinoflagellates. While coral reefs have many ecological and economic functions, the condition keeps declining due to many factors. One of the efforts made to improve the condition is transplantation activities. We transplanted two species of Acropora, namely A. divaricata and A. nobilis using the PVC rack method in water depths of 5, 10 and 15 m. This study was conducted from January to October 2018. The growth rate and zooxanthellae densities from each depth were analyzed using ANOVA and Tukey's studentized rang statistical analysis (HSD) to determine the best treatment. The growth of both species showed significant differences (P< 0.05). The highest growth rates of A. divaricata and A. nobilis were obtained at 5 m depth of 0.539±0.7 and 0.500±0.16 (mean±SD) cm month-1, and the lowest growth at 15 m depth was 0.21 ±0.02 and 0.162±0.14 (mean±SD) cm month-1. Zooxanthellae density also showed differences at each depth. The highest zooxanthellae density of A. divaricata and A. nobilis at 5 m depth was 1.372±0.25 × 106 (mean±SD) cells cm-2 and 0.603±0.455 × 106 (mean±SD) cells cm-2, respectively. Pearson correlation analysis showed that the correlation between growth and zooxanthellae densities on A. divaricata was highly significant (r2 = 0.331 and p< 0.01). Meanwhile, it was not significant at A. nobilis (r2 = 0.011 and p > 0.05). The highest growth rate and zooxanthellae densities were found at a lower depth and decreased with the increasing depth. The correlation between growth rate and zooxanthellae densities is positive, despite different values according to species.