Branching dynamics of transplanted colonies of the threatened coral Acropora cervicornis: Morphogenesis, complexity, and modeling

Abstract

Acropora cervicornis is a threatened Caribbean coral that depends on branch fragmentation to proliferate. Understanding the patterns of branch formation is, therefore, essential for the development of management and conservation initiatives. This study describes branch morphogenesis in 100 colony fragments that were transplanted to two reefs in Puerto Rico that differ in light intensity. Four morphometric variables were measured for one year: internode length, branch growth rate, the number of ramifying branches (mother branches; MB), and the number of branches produced (daughter branches; DB). Branching complexity was also evaluated using two indices: the Horton-Strahler bifurcation ratio (Rb) and the Carrillo-Mendoza branching index (CM-BI). A simple discrete model was constructed to estimate the number of harvestable branches over time. No spatial difference was observed when comparing the development of the primary branches, as the mean internode lengths, the mean extension rates, and the mean number of branches produced did not differ statistically between sites. Likewise, internode lengths in secondary branches did not vary significantly between sites. In contrast, the mean branching and growth rates of secondary branches differed statistically between the two study locations. Significant spatial differences were also observed when comparing the total number of MB and the total number of DB but not for the ratio of DB to MB. The CM-BI was more appropriate than the Rb in describing the branching structure of A. cervicornis. The model provided a good fit to the observed branching dynamics; demonstrating its usefulness as a tool for predicting branch productivity of this species. The implications for restoration activities are discussed.