Evaluating the survival and growth rate of Acropora digitifera in wild and mesocosm systems

Abstract

The growing interest in coral culture for restoration and biotechnological applications has prompted researchers to improve their understanding of coral culture, with a focus on ex-situ production. This study aimed to understand the performance of common hard coral, Acropora digitifera by examining their survival and growth at Pulau Bidong (in-situ) and in a mesocosm system (ex-situ). First, three branches were tagged from each of eight A. digitifera colonies (n = 24). Mortality and linear extension rate were recorded monthly, from July - November 2018. Meanwhile, five branches from each tagged colony were brought back to a mesocosm set up at the hatchery in the Institute of Tropical Aquaculture (AKUATROP), Universiti Malaysia Terengganu (UMT) for the ex-situ experiment. All coral nubbins (n=40) were then divided into two coral size groups: small (<5cm) and large (>5cm). After four months, small nubbins showed 100% survivorship, while large nubbins survived for only two months. In contrast, 67% of wild colonies remained alive. However, nubbins in mesocosm extent with almost 2-folds slower (0.091 + 0.027 mm day-1) than those in the wild (0.166 + 0.033 mm day-1). Coral nubbins in mesocosm form a basal self-attachment “disc” at the bottom. This suggests that fragmented corals invest more energy in self-stabilization, especially in the early stage of transplantation, which affects their linear growth. This study demonstrates the different demographic traits for corals in both the environments.