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  • Thumbnail for Electrified Reefs: Enhancing Growth in a Temperate Solitary Coral Species?
    Electrified Reefs: Enhancing Growth in a Temperate Solitary Coral Species? by Barnett, Rebekah Mae

    Coral reefs provide humans with important ecosystem services including food, pharmaceuticals, and water filtration (Moberg and Folke 1999). These ecosystem services, however, are at risk from ocean acidification, coral bleaching, and other destructive anthropogenic activities. Since these ecosystem services are costly to replace and their natural ability to restore themselves has been compromised, active restoration is necessary. A promising tool for active restoration is the Biorock® method. The Biorock® method consists of running an electrode through a large metal cathode and smaller anode. The electrical current causes the precipitation of calcium carbonate onto the cathode. The cathode works as an artificial reef framework by providing a natural substrate onto which corals can grow. Claims about the effectiveness of this technology in terms of increased coral growth, reproduction, health, and diversity are spectacular (Goreau and Hilbertz 2005), but independent research is divided on the question of its effectiveness. In an attempt to help clarify the technology’s effectiveness, we conducted laboratory experiments to test the claims of growth enhancement for the electrolytic technology by exposing the temperate solitary coral Balanophyllia elegans to powered and unpowered treatments. The study focused on coral growth, but careful observations were made on other aspects of the community including presence and thickness of algal cover. Our results are not consistent with claims made about the benefits of electrolysis on coral growth. Growth between treatments was significantly different but, while claims suggest a 3 to 5-fold increase in growth (Goreau 2014), corals exposed to an electrical current grew less than control corals. The results suggest that the electric current may actually depress growth. A species-specific tolerance to electrical currents may help explain our results as well as the variation seen in other studies. In addition to variation caused by species tolerance and current level, there also seem to be overall trends of the technology being effective for warm-water corals, but ineffective or even detrimental to cold-water corals. The variation in effectiveness between warm and cold-water species is surprising given the proposed physiological mechanisms behind the benefit and suggests that photosynthesis may play an important role in determining whether or not the technology is effective. Our results suggest an ability of the electrical current to depress the growth of algae, which can positively impact photosynthesis and the corals’ ability to calcify. Algae inhibition can therefore play an important role in determining whether or not the technology is effective, but is still part of a complex interplay between current density, ion availability, algae and photosynthesis. Further study is needed to clarify these interactions and their role in determining the effectiveness of the Biorock® method.