News / Feature Articles / Electricity and the Reef, A Shocking Way to Repair Coral Ecosystems PART 2 (06/28/10)

Electricity and the Reef, A Shocking Way to Repair Coral Ecosystems PART 2



WARNING: Do not mix electricity and water. Doing so will lead to serious injury or death. The following article is in no way a recommendation to attempt the scientific endeavors described herein.



by Charles J. Hanley III

The Set-Up

Electrochemical reef construction (ERCON) uses solar energy and relatively unobtrusive constituent parts to create an electrolytic cell within localized regions of the ocean. Basically, a small array of photo-electric cells, otherwise known as a solar panel, keeps a battery charged. The battery, in turn, provides a direct current of low amperage to the electrodes. Both the solar panels and the battery are housed in a buoy on the surface, while the electrodes are anchored to the bottom. The circuit is then completed by the electrolyte soup that is seawater. In order to make an electric cell work, each electrode must be made of a different metal. In the case of ERCON, the metals used are steel and titanium, as cathode and anode respectively. For the cathode, a steel mesh is connected to a pyramid-, tent-, or Quonset hut-shaped cage. Above or adjacent to the cathode, an anode is created from titanium mesh mounted to PVC tubing. To be precise, it should be noted that there may be multiple anodes and cathodes, so long as the electrical field is evenly disbursed.

Once in place, electricity is applied to the circuit. It can be used at a constant rate, pulsed, or be activated intermittently. Interestingly, accretion occurs dramatically fast at first, but the rate slows once a significant amount of material has precipitated onto the cathode. Essentially, the rock that is formed acts to insulate the cathode from direct contact with the seawater, an effect that also protects the steel wire from corrosion. Typically, the current need only be active for the initial 4-6 months of the artificial reefs life. By that time, the colonization process is well
under way. Because the accretionary material significantly prolongs the life of the
steel cathode, electricity can be reapplied in the future in the event the new reef is
damaged somehow. Doing so helps to repair a damaged electric reef in a
quick and efficient manner.



The Benefits of Electrochemical Accretion

By building artificial reefs using electrochemical accretion, a variety of benefits are conferred to coral recruits and fragments (the scientific word for which is, oddly enough, nubbin). There are also definitive biological benefits to using this technique, as compared to previous methods of artificial reef construction.

The primary benefit of electrochemical accretion is that it can rapidly create new substrate, which becomes seeded with life at an equally rapid rate. Past restoration attempts have met with highly mixed results, but there does seem to be a pattern to the results. The primary approach has been to insert an object into the environment and let fouling organisms colonize it on their own. In many cases, several years pass before anything resembling coral growth takes hold. Often, the subsequent community that develops does not reflect endemic diversity of the surrounding waters. Differing substrate materials and porosity, potentially in conduction with leached toxins, are presumed to select for particular organisms. Such selection obviously leads to a disproportionate number of said organisms, while others are under-represented. Accordingly, communities develop unnaturally, if at all. Additionally, coral nubbins are less likely to survive transplantation to these types of reefs because they are slow to securely attach themselves.

The rapid reattachment of coral nubbins has been demonstrated to be a critical factor for their ultimate survivability. There are two main reasons that reattachment is so important. First, SPS corals that are securely attached to a stable substrate grow better. If the coral senses that it is not well-stabilized, it will expend much metabolic energy laying down aragonite at its base. When this happens, the coral is not spending as much energy on fighting pathogens and axial growth. The second main reason that electrolysis works to enhance the success of coral transplantation is because the elevated alkalinity at the cathode enables the rapid precipitation of new skeletal material. Since the skeleton of a scleractinian coral is external to its tissues, the electrolysis happens without needing a contribution from the coral itself. However, the increased alkalinity may actually enhance the corals metabolism as well, leading to a growth spurt. The new material also seals the wound caused by fragmentation, thereby preventing pathogens and parasites from gaining an advantage over the corals immune defenses.

Fragmentation and transplantation are not the only way that electric reefs gain new life. When larval organisms join a community, they are referred to as recruits. These recruits are the product of sexual reproduction, and their importance to a populations genetic diversity cannot be understated. Whereas coral nubbins are clones of a parent colony, recruits each possess their own unique combination of genes. After the initial accretionary phaseonce the electricity is turned offa film of bacteria and cyanobacteria develops on the substrate. This colonization happens within hours of the end of the electrical current. RNA sequencing conducted at 72 hours post-current has shown that as much as 51% of the bio film may be Cnidarian in origin. The assumption is that the microbes that grow in the first few hours somehow influence the ability of Cnidarians to gain a foothold, though the mechanism by which this occurs in unclear.

Another advantage to electrochemical reef restoration is that the shape and size of the reef can be more precisely controlled. This control is an important factor because it has been proven that greater vertical dimensionality (relative to footprint size) has a profound influence on colonization rate. In addition, the use of flexible steel mesh enables the construction of more variegated surfaces. In other words, it can be folded into wavy patterns that have more surface area and present the opportunity for very small micro-habitats to develop. Such micro-habitats vary slightly in light levels and water flow. They also may act to reduce the impact of grazing animals.

Unfortunately, there are only a few coral species that have been intensively studied under electrolytic conditions. Not surprising, the data is not as complete as it needs to be. In some studies, available coral nubbins were restricted to those that had been collected after a ship had run aground and smashed parent colonies. Some of these animals were severely stressed and/or injured. In many cases, injured nubbins placed on a cathode or within an electrical field exhibited more growth than uninjured conspecifics that were transplanted in the absence of electricity. I located references to 25 different coral species, mostly acroporids, which have been found to grow better under these circumstances. At the same time, at least 3 species, Stylophora pistillata, Acropora formosa and A. nobilis, are believed to be unsuitable for electrolytic growth. One study showed that A. pulchra grows on a cathode, but does far better when simply placed within an electrical field. By comparison, A. yongei exhibited the best growth while in an electrical field but its highest mortality rates when placed on a cathode.





On the Way, PART 3

Part 3 concludes this multi-part feature by discussing some of the metabolic benefits electrochemical accretion offers to corals.



Works Cited:

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Photo Credits:

Kwok, R., L.D. Groot, and D. Fleschler. Global Coral Reef Alliance. Sun Sentinel: AP. 2009.