Bio accretion / mineral accretion

Bio accretion and mineral accretion are nature-based strategies for growing artificial coral reefs and restoring damaged ones. Bio accretion and mineral accretion are the processes in which minerals are accumulated from those available in seawater (primarily sodium, magnesium, calcium, potassium, chloride and sulphate) into calcium carbonate and magnesium hydroxide solids (Johra et al., 2021; Ortega, 1981; Peyrot-Clausade et al., 1995). This process can happen naturally, as hard corals accumulate minerals from the water and secrete them as calcium carbonite, which builds up over time as corals reproduce and the size of the reef grows (bio accretion) (How Coral Reefs Grow, n.d.).

Accumulation of calcium carbonate and magnesium hydroxide can also be performed through electrolysis, where a small current is passed through metal electrode structures, giving them a positive or negative charge (an anode and cathode), causing minerals available in seawater to be attracted charged structures (mineral accretion technology) (Goreau & Prong, 2017; Hilbertz, 1979). Both processes are important nature-based solutions for maintaining and improving the health of coral reefs in Te Moananui Oceania. Mineral accretion also has potential uses as construction material, with physical qualities similar to concrete, but being self-growing and able to lock up carbon as it grows (Pedersen Zari, 2018).

Biodiversity health and conservation outcomes for coral reefs can be improved through the use of mineral accretion projects, which establish structures onto which coral can be propagated (Crosby et al., 2002; Goreau, 2000). The action of electrolysis makes calcium more readily available to the coral, improving growth and health of the coral organisms. These structures can also be designed in a manner that creates habitat for other reef species. 

Bio accretion can happen in any part of the ocean but is particularly relevant to coral reefs in Te Moananui Oceania. Some urban centres in the region rely on a barrier reef for protection against the open ocean and Ocean Cities in Te Moananui Oceania often must include marine nature-based solutions into holistic urban planning (Blaschke et al., 2019).

Biorock is a mineral accretion technique developed by architect and marine scientist Wolf Hilbertz and marine biologist Tom Goreau. They discovered that running a small electrical current through seawater causes a hard shell of calcium carbonate to form on the cathode. Small pieces of natural coral can then be attached to the structure, where they achieve growth rates often five times faster than normal. Today, there are more than 60 Biorock projects around the globe, with the largest and most innovative projects located in Indonesia (Lengenheim, 2012).

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Name of NbS

 Bio accretion / mineral accretion

Type of NbS

Engineered intervention

Location

  • Urban
  • Periurban
Biorock close up, 2011. Photo by Marionpinta.

Relationship to Indigenous knowledge

Indigenous cultures in Te Moananui Oceania have deep-rooted connections to the ocean (Blaschke et al., 2019). Coral reefs play a critical role in this connection as they support the marine biodiversity upon which many communities depend. 

Indigenous knowledge encompasses an understanding of local coral species, their ecological roles, and the historical changes observed in the reef ecosystems over many generations. Indigenous people throughout Te Moananui Oceania rely on the reef ecosystems for providing food, maintaining water quality, understanding ecological indicators, and see reef systems as being essential for the creation, protection, and repair of their Islands (Crosby et al., 2002).

Climate change benefits
  • Coastal erosion
  • Storm surge
  • Ocean acidification
  • Reduced water quality
  • Sea level rise

Reefs in Te Moananui Oceania are often the first barrier between the land and the open sea, performing a critical role in wave attenuation and preventing dangerous and powerful open sea waves from reaching the shore (Goreau & Prong, 2017). In the context of climate change, ocean acidification, reduced water quality through polluted stormwat entering oceans, and sea level rise reduce the health of marine ecosystems like coral reefs (How Coral Reefs Grow, n.d.). 

Mineral accretion structures have been employed to create ‘living’ wave attenuation structures, reducing wave energy on vulnerable shorelines and preventing erosion and storm surge. 

Through knowledge of bio-accretion and the use of mineral accretion technologies, reef environments can be supported, and the ongoing effects of climate change and urbanisation on coral can be mitigated. One key way this occurs is through the development of coral nurseries using mineral accretion technology, which greatly improves coral growth due to available precipitating calcium from the seawater. Such nurseries provide living corals to seed new or repair damaged reef environments. See coral reseeding.

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Societal / socio-cultural benefits
  • Disaster risk reduction
  • Food security
  • Climate change adaptation

As climate change increasingly affects corals, due to ocean temperature fluctuations and changes in pH, more diverse and numerous coral growth can improve resilience to environmental stressors (Goreau, 2000). Coral reefs are crucial to the food system of many Te Moananui Oceania communities and are also important economically, as a significant component of the tourism industry for some areas.

Mineral accretion as a nature-based design strategy to build up reefs can have education and knowledge outcomes too, increasing understanding of reef ecosystems and their importance to a range of people, including local communities, funders, governmental agencies and researchers (Van Woesik & Cacciapaglia, 2018).

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Ecological and biodiversity benefits
  • Disturbance prevention
  • Habitat provision
  • Purification
  • Provision of raw materials
  • Provision of food

Disturbance, especially from human activities, can damage reef ecosystems. In addition, increasing storm severity as a result of climate change can also cause detrimental effects on reefs. Implementing mineral accretion can aid in repairing these kinds of damage, accelerating the growth of new coral (Crosby et al., 2002; Elmer, 2016). 

Coral reefs are incredibly diverse ecosystems, vital for wider ocean system health, and are breeding grounds for many marine species. Coral reefs play a role in purification, reducing the turbidity of water and providing a suitable habitat for diverse populations of reef-dwelling animals, including fish and shellfish.

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Technical requirements

Corals require correct ocean temperatures, as well as low water acidity, and low nutrient levels to grow. All of these are increasingly influenced by climate change, and human activities on land (like farming, and urban stormwater discharge) especially causing flows of nutrients into the sea.

  • The specific process used in mineral accretion electrolysis, requires a structure of metal, a power source (solar or land-based), and the ability to connect, manufacture and install these. There are numerous factors that can affect the success of these components. The metal structure which becomes the newly formed reef must be secured in place to the reef, for example with large rocks to act as weights. Connections must be securely made between the metal elements and the power source itself, and these must be insulated and the correct polarity of the circuit must also be established (if the current flows in the incorrect direction, the incorrect element will begin to accrete calcium carbonate). Coral can be ‘seeded’ by attaching small pieces of coral (ideally parts that have already broken off existing reefs or have been grown) to the new structure. 

Following establishment, mineral-accretion projects need monitoring and maintenance, to ensure functionality of electrical components. Measuring and checking coral growth and other factors for monitoring health and biodiversity outcomes must occur. Natural bio accretion taking place in living reef environments must also be maintained for healthy, natural reef growth and the myriad ecosystem services they provide.

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Issues and Barriers

Ocean acidification poses a great challenge to corals worldwide, with corals suffering substantial bleaching events where water pH becomes too low. If substantial damage occurs, this can be time-intensive and expensive or impossible to repair. Ocean exploitation, resource over-harvesting, and damaging fishing techniques are also ongoing issues in some areas. Pressures from urbanisation and intensive land use are also a growing concern, as flows of nutrients and pollutants from land-based activities can negatively impact reef ecosystems. These issues may overwhelm reef-building and coral reseeding strategies unless addressed first.

There are specific skills relating to mineral accumulation technology, and few people at this stage actively design and implement the process, so access to expert knowledge and guidance on the subject is limited.

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Opportunities

Mineral accretion presents an obvious opportunity for coral reef restoration, actively enhancing coral health and growth, and increasing reef size.  In some parts of Te Moananui Oceania, coral harvesting is still practiced, and mineral accretion projects could potentially provide an alternative source for this resource.

The technology could also be explored as an alternative building material, having similar material qualities to concrete, and shows promise in its use as self-constructing coastal protections such as wave attenuation structures (Ortega, 1981).

Financial case

Fisheries are a lifeway in Te Moananui Oceania, having particular economic significance, both for local food markets and exports. Reef environments are integral to the health and productivity of fisheries, so preventing, and mitigating damage to these ecosystems is important to preserve the economic value of this industry. Likewise, tourism makes up a large portion of some Te Moananui Oceania Economies, and coral reefs are a large tourist drawcard. Loss of coral ecosystems has numerous economic implications therefore that add to the financial case of repairing them.

Mineral accretion is a fairly low-cost solution that passively provides numerous benefits, requiring only minimal inputs such as electricity. It can be constructed from salvaged materials, including scrap metals and older electrical equipment like solar panels. Its benefits, which include developing coastal protection, restoring coral reefs, and producing building materials, are economically significant and help address costly environmental challenges.

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References
  • Blaschke, P., Gawler, S., Kiddle, L., Loubser, D. Pedersen Zari, M. (2019). Ocean Cities: Sustainable Urban Development for Islands. Regional Policy Guide. A Report for United Nations Economic and Social Commission for Asia and the Pacific (UNESCAP).
  • Crosby, M. P., Brighouse, G., & Pichon, M. (2002). Priorities and strategies for addressing natural and anthropogenic threats to coral reefs in Pacific Island Nations. Ocean & Coastal Management, 45(2–3), 121–137. https://doi.org/10.1016/S0964-5691(02)00051-0
  • Elmer, F. (2016). Factors Affecting Coral Recruitment and Calcium Carbonate Accretion Rates on a Central Pacific Coral Reef [Open Access Te Herenga Waka-Victoria University of Wellington]. https://doi.org/10.26686/wgtn.17057996
  • Goreau, T., J. (2000, September 2). Installation of a pilot mineral accretion coral nursery at Kimbe Bay, New Britain, Papua New Guinea. Global Coral Reef Alliance. https://globalcoral.org/_oldgcra/Installation%20of%20a%20Pilot%20Mineral%20Accretion%20Coral%20Nursery.htm
  • Goreau, T., & Prong, P. (2017). Biorock Electric Reefs Grow Back Severely Eroded Beaches in Months. Journal of Marine Science and Engineering, 5(4), 48. https://doi.org/10.3390/jmse5040048
  • Hilbertz, W. (1979). Electrodeposition of minerals in sea water: Experiments and applications. IEEE Journal of Oceanic Engineering, 4(3), 94–113. https://doi.org/10.1109/JOE.1979.1145428
  • How coral reefs grow. (n.d.). Coral Reef Alliance. Available online: https://coral.org/en/coral-reefs-101/how-coral-reefs-grow/. Date accessed 17 May, 2024.
  • Johra, H., Margheritini, L., Ivanov Antonov, Y., Meyer Frandsen, K., Enggrob Simonsen, M., Møldrup, P., & Lund Jensen, R. (2021). Thermal, moisture and mechanical properties of Seacrete: A sustainable sea-grown building material. Construction and Building Materials, 266, 121025. https://doi.org/10.1016/j.conbuildmat.2020.121025
  • Langenheim, J. (2012). Biorock giving new life to coral reefs. The Guardian, 8 June. Available online:  https://www.theguardian.com/environment/2012/jun/08/biorock-coral-reef-world-oceans-day. Date accessed 17 May, 2024.
  • Ortega, A. (1981). Basic technology: Mineral accretion for shelter. Seawater as source for building. In Mimar: Architecture in Development. (pp. 60–63). https://globalcoral.org/_oldgcra/Alvaro%20Ortega%20biorock.pdf
  • Pedersen Zari, M. (2018). Biomimetic materials for addressing climate change. In L. Martínez, O. Kharissova & B. Kharisov (Eds), Handbook of Ecomaterials. Springer, Cham. Pages 1-23.
  • Peyrot-Clausade, M., Le Campion-Alsumard, T., Hutchings, P., Le Campion, J., Payri, C., & Fontaine, M.-F. (1995). Initial bioerosion and bioaccretion on experimental substrates in high island and atoll lagoons (French Polynesia). Oceanologica Acta, 18(5), 531–541.
  • Van Woesik, R., & Cacciapaglia, C. W. (2018). Keeping up with sea-level rise: Carbonate production rates in Palau and Yap, western Pacific Ocean. PLOS ONE, 13(5), e0197077. https://doi.org/10.1371/journal.pone.0197077

Further resources