REPORT Differential physiological responses of two congeneric scleractinian corals to mineral accretion and an electric field E. M. Borell • S. B. C. Romatzki • S. C. A. Ferse Received: 2 April 2009 / Accepted: 26 October 2009 / Published online: 12 November 2009 Ó Springer-Verlag 2009 Abstract Despite increasing popularity of ‘electric’ reefs as a means for reef restoration, there is a distinct lack of quantitative evidence supporting the alleged benefits of this method. This study investigated the effects of an electric field versus an electric field in combination with a cathode on coral growth (skeletal extension) rates, coral survival, zooxanthella densities, chlorophyll a (chl a) concentrations, and chlorophyll fluorescence of Acropora pulchra and A. yongei. Coral transplants were grown for 4 months under three treatment conditions: (1) on an iron cathode, (2) on bamboo inside an electric field, or (3) on bamboo in the absence of an electric field. Contrary to predictions, coral growth rates of both species were highest inside the electric field and not on the cathode. Except for chl a concentra- tions, the cathode had a significant adverse effect on all measured variables for A. yongei but not for A. pulchra. Treatment had no effect on the survival of A. pulchra, while mortality rates of A. yongei were significantly higher in the presence of mineral accretion compared to the electric field and control. A. yongei on the cathode featured low zoo- xanthella densities, depressed electron transport rates (rETR) and maximum quantum yield (F v /F m ), and reduced growth. By contrast, treatment had no effect on the fluo- rescence characteristics of A. pulchra, and zooxanthella densities were highest for corals on the cathode, coincident with high growth rates relative to the control. Overall, the data indicate that the proposed benefits of the mineral accretion technology to meet important objectives of reef rehabilitation with regard to colony growth and survival should be considered with caution. Keywords Acropora pulchra Á A. yongei Á Cathode Á Chlorophyll fluorescence Á Growth Á Mortality Introduction Burgeoning anthropogenic and natural disturbances, sepa- rately or in synergy, are causing coral reef degradation worldwide (Bellwood et al. 2004). In recognition of the fact that many destroyed coral reefs often do not recover naturally, the scientific discipline of reef restoration has drawn much attention over the past two decades (Rinke- vich 2005). Various restoration methods aimed at improving live coral cover, biodiversity, and topographical complexity have been proposed to date, including the construction of artificial reefs (Clark 2002; Zimmer 2006). The interacting effects between artificial substrates, the ecology of transplanted organisms, and the environment into which they are placed, however, are still poorly understood, and transplantation efforts frequently yield high mortality and low growth (skeletal extension) rates of transplanted coral fragments (Clark 2002; Rinkevich 2005). Firm attachment of coral transplants is a prerequisite for high survival rates, as securely fixed corals are likely to recover faster from the stress of transplantation and may allocate more energy to lesion repair and subsequent growth (Lindahl 1998; Ammar et al. 2000). The mineral accretion technology described by Hilbertz (1992) has been Communicated by Biology Editor Dr. Clay Cook E. M. Borell (&) Á S. B. C. Romatzki Á S. C. A. Ferse Leibniz Center for Tropical Marine Ecology (ZMT), Fahrenheitstr. 6, 28359 Bremen, Germany e-mail: estherborell@yahoo.co.uk Present Address: E. M. Borell The Interuniversity Institute for Marine Sciences (IUI), P.O.B. 469, 88103 Eilat, Israel 123 Coral Reefs (2010) 29:191–200 DOI 10.1007/s00338-009-0564-y