Influence of electrical fields on the performance of Acropora coral transplants on two different designs of structures

Abstract

A method for reef rehabilitation is based on mineral accretion using an electrical field to stimulate the growth and survival of transplanted coral fragments. The present study aimed to examine the impacts of exposure to an electrical field on fragments of two transplanted Acropora species. Two independently performed experimental set-ups were used to assess fragment survival and linear skeletal extension under varying electrical currents and in direct versus indirect contact to electrically charged substrate. Survival rates of transplants for A. yongei and A. pulchra were high in some treatments, but showed significantly lower survival when exposed to a high amperage, or when transplanted close to the bottom. Maximum skeletal extensions of transplants were observed in elevated controls of A. yongei (7.5±0.4 mm/month versus donor colony: 5.8±0.7 mm/month) and for A. pulchra fragments subjected to 1.67 A/m2 (6.2±0.3 mm/month versus donor colony: 8.6±0.6 mm/month). The lowest extension rates were found for A. pulchra on unelevated control boards (1.2±0.2 mm/month). At the same time, treatments exceeding current strengths of 1.67 A/m2 led to significantly smaller extension rates in both Acropora species. While a direct contact with the charged metal had a significant negative effect on growth and survival of A. yongei fragments, A. pulchra demonstrated a general tendency to smaller extension rates when exposed to an electrical current. Overall, lower extension rates of fragments indicated that A. pulchra was generally more sensitive to transplantation. Previous reports of significantly increased growth rates due to electrical stimulation could not be supported for the species examined.