Suitability of mineral accretion as a rehabilitation method for cold-water coral reefs

Extensive areas of the cold-water scleractinian Lophelia pertusa have been damaged due to the impact of bottom-trawling and natural recovery is slow or absent. Here we evaluate a method for coral reef rehabilitation intended to enhance coral transplant survival and growth, i.e. mineral accretion by electrolysis in seawater. Electrolysis in seawater produces a semi-natural substrate in the form of aragonite (CaCO 3). The method has been used in coral reef rehabilitation programmes in tropical coral habitats but has so far not been tested in temperate deep-water habitats. A controlled laboratory experiment was performed to test the effect of the substrate per se and different levels of applied current densities (0.00–2.19 A m −2), including galvanic elements (Fe|Zn), on coral fragments attached to the cathodes. The studied responses were; growth rate, budding frequency, mortality, and general health status (degree of polyp activity). We found that the budding frequency differed significantly between treatments, with higher frequencies in low current density treatments. Significant differences were also found in the frequency distribution of calices displaying a growth of ≥ 2 mm yr −1, with higher frequencies in the lowest applied current density (LI), controls, and galvanic elements. Growth rates were slightly higher in LI, although non-significant. Zero mortality was observed in the control group as well as in LI. The degree of polyp activity was not affected by the treatments. These results are in part congruent with earlier studies and the method is found suitable for L. pertusa. The positive effects were mainly restricted to the lowest applied current density treatment (0.06 A m −2). The optimal current density level is hereby found to be considerably lower than levels used in previous studies and provide new guidelines for what levels to use in rehabilitation programmes with this method.