Written by Matthew Tietbohl
Recent research reveals new techniques to improve coral restoration practices. These novel processes may assist in our ability to effectively outplant corals on degraded reefs.
Over the last 50 years, the average coral cover around the world has declined by a staggering 50-75% (Jackson et al. 2014; Hughes et al. 2018). Climate change induced ocean warming, increased coastal sediment and nutrient runoff, destructive fishing practices, and various other stressors have caused coral reef phase shifts in many places around the world. Reef benthos once dominated by living, habitat-forming hard corals are now outcompeted by fast-growing, weedy organisms that do not contribute to the overall complex nature of a coral reef, like sponges or algae (Loh et al. 2015). Declines in coral cover result in poor reef complexity that negatively impact the diversity of fishes and invertebrates, which rely on the complex mesh of corals for food and shelter. Not only does the loss of live coral create difficulties for organisms living on reefs, but it can also create problems for people who are reliant on coral reefs as a source of food or income (Moberg & Folke 1999).
The destruction of coral reef ecosystems can be a highly depressing subject, but there is hope on the horizon. Though coral cover has declined around the world, there are organizations working to actively restore degraded reefs through coral farming and restoration. Coral farming often involves removing fragments of corals from the wild and growing them in aquaria or on structures in the ocean. Once they have reached a certain size, they are moved out to a degraded reef and cemented into place. The goals are generally to replace corals that have perished, increase the density of rare species to help ensure successful reproduction, and provide the complex habitat that many species rely on after out-planted corals grow. If these corals survive and reproduce, then their offspring may be able to help repopulate degraded habitats. There are other ways to restore coral populations, such as artificial breeding, with restoration groups around the globe utilizing different combinations of techniques to maximize their success. Coral restoration is a highly complex process, as hard corals tend to grow slowly, and branching corals are particularly sensitive to mechanical damage such as storms or even hungry predators. Any technical advantage that can aid coral survival or speed up the restoration process is crucial! Lots of research is happening around the world to improve this process, but two recent publications have found simple ways to help improve the effectiveness of coral restoration!
One recent study conducted by Alejandro Tagliafico et al. (2018), has found a simple method to help coral fragments better attach to the substrate, and it involves cementing the fragment upside down. In laboratory experiments with the popular aquarium species known as horn coral (Hydnophora rigida), the authors found that simply flipping over coral fragments and allowing them to grow upside-down significantly improved their ability to attach to the substrate. Inverted-grown corals fully attached to the substrate, glass stoppers in this case, about 10 days faster than corals grown right-side up and with a higher proportion of coral fragments cementing to the substrate overall (Figure 1). When corals were fed more, the difference between cementing methods was increasingly clear. Though it remains to be seen how this will scale with more realistic substrates and environmental conditions, this study shows how simple interventions can be used to help improve coral attachment, which is important for helping out-planted corals survive rough ocean conditions.
Another study by Page et al. (2018) has explored another effective way to improve our ability to restore reefs. This recent research has explored a way to improve the ability to out-plant massive stony corals. Out-planting massive corals as part of a restoration project is difficult because they grow so slowly, and consequently they take a long time to cover a reef and build structure. But researchers from the Mote Marine Laboratory have found a new way to help improve the speed massive corals to re-cover reefs. The process of micro-fragmenting involves breaking massive coral colonies into tiny fragments and then planting them out together on a reef. These fragments from the same colony then grow together to recover more area of reef than if they were left to grow alone (Figure 2). This research was first published in 2015 (Forsman et al. 2015). However, the 2018 study reports on long-term findings from out-planting these corals. Observations over 2 years comparing micro-fragmented corals to large single colonies showed that micro-fragmenting can increase the coverage of massive corals by up to 6.5 times what a large fragment will grow over the same time. The long-term nature of this study is great because it shows this technique maintains effectiveness over time. Improved ability to out-plant massive corals matters because a lot of coral restoration focuses on fast-growing, weedy species that have more complex, branching growth forms. This focus on few species can lower the diversity of out-planted reefs, and often these species are less resilient to warming waters than massive corals Page et al. (2018) point out. By demonstrating the technique of micro-fragmenting as a way to speed up the process of coral reef regrowth, this technique appears to have serious potential for assisting in coral restoration projects.
The two studies discussed here demonstrate different ways we can help to restore coral reef habitats by out-planting coral fragments. Upside-down growth and micro-fragmentation can help speed up the process of attachment for fragments and may help their long-term survival. However, there are several caveats of these studies that should be addressed. Laboratory experiments do not always transfer to the field very well, and upside-down growth trials should be conducted in natural environments with a variety of species and substrates to better match field conditions. Scientists working with micro-fragmenting acknowledge the need for more research into how this process may affect calcification and reproductive output among other factors. They also acknowledge that smaller coral fragments are more susceptible to predation, so micro-fragmenting projects need to keep this in mind, especially when working in areas with low coral cover where predators may concentrate feeding on the out-planted fragments. Cages can be used to keep hungry predators at bay, but also make coral fragments subject to rapid algae overgrowth which can be more harmful than some predators (Ceccarelli et al. 2019). Disease can also be a problem, especially when damaging coral tissue, which opens an avenue for potential diseases to enter; investigating the immune systems of micro-fragmented corals could help us understand if they actually are able to avoid disease any better than larger colonies. But despite these potential limitations, both projects take key steps in the right direction to better understanding how we can help improve the restoration process. Many groups conducting coral restoration are reliant on volunteers as well, so if you are eager to get involved in coral restoration, check out and support these groups that are working to save coral reefs around the world!
Literature Cited:
Ceccarelli DM, Loffler Z, Bourne DG, Al Moajil-Cole GS, Boström-Einarsson L, et al. 2018.
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Forsman ZH, Page CA, Toonen RJ, Vaughan D. 2015. Growing coral larger and faster: micro
colony-fusion as a strategy for accelerating coral cover. PeerJ. 3:e1313
Hughes TP, Anderson KD, Connolly SR, Heron SF, Kerry JT, et al. 2018. Spatial and temporal
patterns of mass bleaching of corals in the Anthropocene. Science. 359: 80–83.
Jackson J, Donavan M, Cramer K, Lam V, eds. 2014. Satus and Trends of Caribbean Coral Reefs: 1970–2012. Gland, Switz.: Coral Reef Monit. Netw.
Loh T, McMurray SE, Henkel TP, Vicente J, Pawlik JR. 2015. Indirect effects of overfishing on Caribbean reefs: sponges overgrow reef-building corals. PeerJ. 3:e901
Moberg F, Folke C. 1999. Ecological goods and services of coral reef ecosystems. Ecological Economics. 29: 215-233.
Page CA, Muller EM, Vaughan DE. 2018. Microfragmenting for the successful restoration of slow growing massive corals. Ecological Engineering. 123: 86-94.
Tagliafico A, Rangel S, Christidis L, Kelaher BP. 2018. A potential method for improving coral self-attachment. Restoration Ecology. 26,2: 1082-1090.
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