Coral reefs are highly productive systems which form the cornerstone of livelihoods for coastal communities around the world. In Southeast-Asia the potential sustainable economic benefits from coral reefs amount to ~US$1.1–1.6 billion per year. This economic value in terms of provisioning (e.g. fish production) has been well quantified for most coral reef systems. However, the value of regulating services — such as flood prevention — have received little attention from decision-makers. Coral reefs act as natural breakwaters, attenuating wave energy and reducing the impact of storm surges on coastlines. Globally, coral reefs reduce the annual expected damages from storms by more than US$4 billion, across ~71,000 km of coastline. Recent estimates indicate that annual damages would more than double in the absence of coral reefs, with a 69% increase in coastal flooding. Despite their importance, ~75% of coral reefs world-wide are threatened by climate change and direct human impacts such as bleaching, blast fishing, pollution and disease.
With the high value of intact coral reefs recognised, there has been a great deal of investment in the restoration or rehabilitation of coral reefs. Restoration — namely, returning a coral reef system to something near its pristine state — is highly desirable, but extremely difficult to achieve. Instead, rehabilitation is what is commonly achieved by active interventions. Rehabilitation results in a novel system, which supports the required ecosystem functions. Successful rehabilitation is complex and costly. The logistical difficulties of working in submerged environments, as well as the need for divers and boats contributes the cost. In addition, there are high material costs as rehabilitation requires the structural and functional elements of coral reefs which have been lost to be replaced. A variety of methods have been tested, but up-scaling of small projects has proven to be difficult to achieve. These range from US$50 per m2 to more than US$270 per m2.
A new study from UC Davis, published this month in Restoration Ecology demonstrates the effectiveness of a novel, low-cost (~US$25 per m2) method of coral reef restoration, based in Indonesia. The study site lies within the ‘Coral Triangle’, a roughly triangular region of the tropical marine waters of Indonesia, Malaysia, Papua New Guinea, Philippines, Solomon Islands and Timor-Leste with the highest coral diversity on earth. As is common in the tropics, these coral reefs are threatened by overexploitation, destructive fishing, coastal development, pollution, disease and climate change. The UC Davis study was conducted on coral reefs surrounding the Indonesian island of Pulau Badi. The site had been damaged by construction, blast fishing and coral mining in recent decades. Limited natural recovery had taken place at the site, leaving a rubble field interspersed with small mound corals and dead coral structures. The objective of the UC Davis study was to restore reef functions by installing hexagonal structures onto which coral fragments were attached (Figure 1).
Figure 1. Diver with spiders in restoration site. Image credit: Jordan Hollarsmith, UC Davis.
Approximately 11,000 structures, termed “spiders” (Figures 1 and 2), were deployed over ~7,000 m2 (~0.7 ha). On average, 550 spiders were deployed across 300–400m2 over a 3-day period by the study team (Figure 3). The total cost of installing 11,000 spiders was US$174,000, including materials, transporting spiders, coral attachment and installation labour. Costs could be further reduced with the participation of volunteer divers. Maintenance costs, if required to remove coral-feeding damselfish and to replace dead coral fragments during the first three months, were estimated at an additional US$3 per spider.
Figure 2. Coral fragment attached to spider. Image credit: Christine Sur, UC Davis.
Figure 3. Indonesian locals prepare spiders for installation. Image credit: Jordan Hollarsmith, UC Davis.
The deployment of spiders over 0.7 ha resulted in the recovery of coral cover across a total of 2 ha of damaged reef (Figure 4). Installation of the spiders supported a rapid increase in live coral cover at a cost of ~$25 per m2.
Christine Sur, a UC Davis graduate student at the time of the study, stated in a press release “Our study demonstrates a cost-effective, scalable method that can inform other coral reef restoration efforts aimed at reducing the global decline of these valuable and unique ecosystems.”
Figure 4. Coral growth over spider structures. Image credit: Jordan Hollarsmith, UC Davis.
From a climate change adaptation perspective, the results from the UC Davis study could be significant in informing rehabilitation efforts elsewhere in the tropics. Any successful rehabilitation intervention requires that local conditions are carefully considered, and additional protection of the area ensured. Together with these actions, the spider technique holds promise for adaptation projects along coastlines.
Image source: Press kit of images from UC Davis
Original publication: Williams et al. 2018. Large-scale coral reef rehabilitation after blast fishing in Indonesia. Restoration Ecology, https://doi.org/10.1111/rec.12866