Continued cathodic operation in coral restoration: Are calcification benefits generalizable?

Electrochemically induced mineral accretion has been proposed as a way to support coral transplantation and accelerate coral growth. At a submerged cathode, reduction reactions raise local pH and can produce a mineral coating, but the same system changes substrate condition, corrosion, attachment, and seawater chemistry. This review asks whether keeping a mineral-coated cathodic structure connected to external power (“continued externally powered cathodic operation”) improves scleractinian coral calcification or skeletal growth beyond coating effects. Experimental reports are classified by the biological outcome, measured and weighted by comparator directness and treatment-level replication. Quantitative pooling was inappropriate because outcomes, exposure conditions, experimental units, and controls were incompatible. The strongest direct calcification experiment reported a 43% increase for 5-mm Pseudodiploria clivosa microfragments within a measured elevated-pH boundary layer, but no significant benefit for 15-mm conspecifics or for 50-mm Acropora cervicornis. The closest field comparison of continued power with power removal after coating found no consistent scleractinian geometric-growth advantage and reported adverse bleaching or tissue outcomes in some taxa during a heatwave. Other field studies produced positive, null, or negative extension and planar-growth results, but most did not isolate continued power from substrate, attachment, corrosion protection, structure or site, and several failed to replicate at the powered-structure level. The evidence therefore supports a conditional local mechanism, not a general restoration benefit: continued cathodic operation can enhance coral-produced calcification when living tissue remains within a favorable electrochemical boundary layer, but current experiments do not establish that keeping mineral-accreted field structures powered generally adds a skeletal-growth benefit. Generalization is limited principally by fragment height relative to the boundary layer, flow, exposure duration, taxonomic and morphological coverage, non-equivalent controls, indirect growth proxies and insufficient treatment-level replication.