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Scrap-heaps and coral-reefs: The challenges of artificial reef restoration

Author: Jones, E. M.

During a trip to Indonesia last year, I encountered my first artificial reef. It came as a stark contrast to my previous, cossetted experiences of ‘typical’ reef ecosystems. Established 5 years prior to my visit, the artificial reef looked like the aftermath of a battlefield. I snorkeled above rows of twisted metal pylons, cinder blocks laced with chicken wire, and branching corals cable-tied to meshed bricks. This reef consisted of the hardiest corals, some barely attached to their blocks, and very low diversity of fish to tend them. Rabbit fish dominated the artificial, descending on mats of gelatinous algae in feeding frenzies. A few tiny reef fish sheltered in the branching corals, diminutive splashes of color against a backdrop of dull green and brown. I could not help but leave that artificial reef site feeling disappointed and concerned. Was this just a one-off example of a struggling restoration site, or was this one of many? What is the current state of coral reef restoration and is it working?


The primary method that gave rise to reef restoration has its origins in ship wrecks (Roberts 2012). Wrecks are popular for both recreational divers and fishers (Brickhill et al. 2005). However, wrecks are not permanent and they eventually break down into nothing (Goreau & Hilbertz 2012). Even the famous Titanic is disintegrating away and is predicted to be reduced to scattered debris soon (Salazar & Little 2017).

A shipwreck colonized by reef organisms. Obtained from:


Nevertheless, it was during the 70s and 80s that artificial reefs began receiving greater attention for recreational use (Bohnsack et al. 1985). This was due to the way fish aggregate around them, similarly to wrecks (Bohnsack et al. 1985). To this end, artificial reefs also became regarded as restoration for over-dredged areas and as mediation for heavily degraded reefs (Rinkevich 2005). However, anything from household appliances to retired military tanks are dropped into the water for restoration purposes and this method is often hit-or-miss (Outdoor Alabama 2009; Na et al. 2016). For example, the Osborne Reef restoration effort was implemented in the early 1970s for a degraded coral reef on the coast of Fort Lauderdale, Florida. Nearly 2 million rubber tires were bound together and released as an artificial reef. The tires broke free of bindings during a storm and ended up scattering along the coast. This ended up damaging the degraded reef further, resulting in the need for wide-scale tire removal which far exceeded costs for the original Osborne Reef restoration project (Cabral & Primeau 2015). While recreating a three-dimensional environment is necessary for coral reef restoration, there must be a better way forward than using such items to restore reefs.

Currently coral reef restoration has evolved to include transplants and coral attachments on a hard substrate with the hope that the coral will grow, attract other species and create a functioning environment (Bowden-Kerby 2001; Rinkevich 2005). However, attaching corals to cinder blocks is often not effective in such a complicated and sensitive marine ecosystem (Baums 2008). For example, often crustose coralline algae need to grow on a substrate which then promotes coral recruitment (Goreau & Hilbertz 2012). Likewise, some species of coral, typically branching corals, grow better than others and therefore are often the ‘go-to’ species for restoration (Lindahl 2003; Johnson et al. 2011). Success can exist in the short term due to the fast growth rates and hardy nature of branching corals (Shafir et al. 2006). However, using one type of coral may arguably result in an inferior ecosystem that is low in biodiversity and resilience (Pearson 1981).

Alternatively, a recent technological advancement in restoration has been gaining ground in the form of ‘biorocks’ (van Treeck & Schuhmacher 1999). Sending weak electrical pulses through metal domes imitates growth of coralline algae, through a method called ‘electrolysis’ can facilitate coral growth (Goreau & Hilbertz 2012). These ‘electrolysis’-based restoration projects are gaining popularity and use world-wide and has seen higher growth rates and survival of coral (Goreau & Hilbertz 2005). Therefore, perhaps it is not all bad news for coral reef restoration; there are some existing projects that have seen success. However, again, it seems to be a hit-or-miss situation with coral recruitment. Some are successful, yet some fail to restore any coral but branching species where plate and massive coral often struggle to survive (Rinkevich 2005; Johnson et al. 2011). However, the water column contains an important and often overlooked factor that has a profound effect on successful coral reef restoration; the water itself.

An electric biorock facilitating coral growth. Obtained from:

Currents have a large part to play in coral reef ecosystem function. They bring in nutrients, recruits, and they bring in offshore pollution (Connell 2007). Restoration must consider all aspects of coral reef ecosystems which might have detrimental impacts on future success (De’ath & Fabricius 2010). This is because coral reefs are susceptible to pollution as it can smother the coral, prevent photosynthesis and facilitate algal growth over the coral (Wiedenmann et al. 2013). Pollution from offshore currents has a part to play in the decline in coral cover and bleaching mortality (Glynn 1993). And this is where it comes to a stalemate. If reef restoration is to see more success, the entire ecosystem needs to be considered (Mumby & Steneck 2008). A reef may be irrevocably doomed due to the external environment, no matter how many biorocks are submerged. Therefore, this is the challenge for reef restoration, one that involves going beyond the placement of coral reef gardens.

Many studies have shown that it is not enough to place some concrete blocks and wires in the water, leave them at the degraded site and then return in five or ten years and expect to see a successful project. Restoration projects may be unsuccessful if they consist of inadequate infrastructure or if more widespread issues such as pollution and climate change degrade them anyway. It is difficult to predict what I would see if I returned to explore that restoration site twenty years from now. I want to see it succeed. Maybe it will not be the idyllic coral ecosystems I had once envisioned, but restored enough to survive. I just hope I will not see a dull world of slime-coated metal pylons like bones jutting from the sea floor where once a restoration project struggled and failed. However, there is still hope for coral reef restoration. It just deserves greater planning, careful implementation, and new technology formatted to suit coral reef ecosystems.


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