What is Mineral Accretion Technology?

Mineral Accretion Technology is a coral reef restoration technology that utilizes low voltage electricity to improve the health and growth rates of corals and other marine organisms. As electricity flows to the metal structures placed underwater, minerals, much the same as those the corals use to create their skeletons, fall out of the water and accumulate onto the structure, thus giving the technology its name. Corals growing on these electrified artificial reefs tend to grow 3-4 times faster, and survive much better during bleaching events, disease outbreaks, and other disturbances. Although invented in the 1970’s, this technology has yet to become widespread, mostly due to patent protections and high costs of installation and maintenance. However, these barriers are rapidly being overcome, as the original patent on the technology has expired, and now it is possible to develop new, open source methods that are easy to build and much less costly to install and maintain. For the first time in the 40 years since this technology has been in existence, it is finally looking like this exciting technology could become a major tool used by reef conservationists around the world.

How does it work?

Mineral accretion devices utilize a well known process called electrolysis, which is also used for other applications such as plating metals, removing rust, creating hydrogen batteries, and more. In this process, low voltage, direct current is applied to two pieces of metal that are submerged in water. At one end of the circuit, called the Anode, electrons flow from the wire into the water and causes H2O to break-up and oxygen to form. The water surrounding this area becomes quite acidic, and thus the anodes are kept small and suspended in the water. At the other end of the circuit, knowns as the Cathode, electrons flow back from the water into the metal, causing H2O to break up and release hydrogen bubbles into the water. At the Cathode, the surrounding water becomes quite alkaline, and in these conditions calcium and other minerals are no longer soluble in the water and precipitate out to accumulate onto the metal. For coral restoration, corals and other organisms are planted on the cathode, which is usually made of steel rebar and can be shaped into any design imaginable.

Hin Fai and the History of BioRockTM on Koh Tao

Our first experience with this technology was back in 2006, when we began maintaining a small pilot Biorock™ project in the vicinity of Ao Taa Chaa. The structure was constructed in 2005 as part of a community project initiated by the Koh Tao Dive Operators Club, and paid for by the island’s dive schools. The design was simply a roll of rebar mesh laid out over a reef that had experienced almost 100% mortality during the global coral bleaching event of 1998. Although small and built with a very primitive transformer, by 2007 the site hosted an amazing diversity of robust and healthy corals, some of the only hard corals in the whole bay.

Then, in 2008, dive schools joined together under the Save Koh Tao group and raised almost 1 million THB to construct the largest Biorock™ structure in the Gulf of Thailand and both a refuge for corals and marine life, and also as an alternative dive site to attempt to remove dive pressure from natural areas. This remains one of the most expensive projects we have done to date, with most of the money going to the Biorock Company, and very little going to the actual materials. Unfortunately, the site only remained electrified for two years due to the outdated technology utilized by the Biorock Company. Their ‘black box’ techniques helped to protect their patent but costed a lot of money and did not allow the users to know the status of the underwater transformer. Also, the Biorock company did not allow any users to adjust or repair the proprietary technology themselves, and instead wanted to charge a lot of money to come back and fix their own broken technology. Despite not being powered, the NHCP team visited the site every week to maintain and monitor the corals and marine life growing there. The site remained turned off until 2016, when the NHRCP, along with then Bob Sevenster removed and repaired the underwater transformer and anodes to bring the site back under power.
The site houses a vast array of coral diversity across its bars which also allows it to serve our program as a teaching aid when introducing our students to the genetic diversity of the many genera of hard coral across our island.


Robert Sevenster (a.k.a. Bob), founder of coralAID, first joined the NHRCP back in 2015 as a conservation student. With a background in electrical engineering and the drive to do good, Bob was searching for ways in which he could apply his technical expertise to help our program better protect, preserve and expand coral reefs.  After learning about the research of Professor W.H. Hilbertz and seeing first hand, the benefits and success of electrified artificial reefs here on Koh Tao, Bob set to work creating his own open source Mineral Accretion Devices (MAD).
By the end of that very first year Bob had already built and installed his first MAD in Taa Cha, which came complete with its own floating solar panel used to power the device. Since then Bob has returned to Koh Tao every year to continue to refine and perfect his designs, whilst educating and involving our students at every step in the process. The incredible success of his latest coralAID site in Ao Leuk is a testament to Bob’s hard work and plans are currently underway to continue expanding the site.
Bob’s efforts aren’t restricted to Koh Tao. Through his company coralAID, Bob plans to make the technologies he’s developing available to reef conservationists across the globe. As anthropogenic and environmental pressures continue to grow, people like Bob and technologies like the MAD will play a crucial role in the fight to save these fragile ecosystems. We’ve been incredibly fortunate to have Bob working with us, as he’s helped bring our restoration techniques into the 21st century. To read more on coralAID, visit Bob's website here: http://coral-aid.org/.

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New Heaven Reef Conservation Program