Course:EOSC270/2023/Group 12- Coral Reef Restoration in French Polynesia

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Sergeant Major Fish over bleached corals on Molasses Reef. A side-by-side picture showing the visual difference between unbleached corals (left) and bleached corals (right). (Kieffer, 2014)
Example of divers help repair a damaged coral reef in Apra Harbor, Guam. (U.S. Navy, 2017)

Importance of Coral Reef Restoration

Coral reefs are found in tropical and subtropical waters and are sensitive to condition changes. As such, climate change and other global issues, many human-caused, threaten these worldwide ecosystems. Some coral reefs have not yet been significantly damaged, and restoration is best focused on those that have been.

While French Polynesia has not escaped all coral loss events, it statistically has more abundant coral. When surveyed in 2014, the French Polynesian islands averaged 58% coral cover over the 264 sites investigated[1]. Although this may not sound significant, the Great Barrier reef is down to 45% and the Caribbean Sea has less than 10% live coral coverage in some areas. Since 2014 French Polynesia has experienced several coral declines, yet the employed restoration strategies continue to rehabilitate damaged reef areas.

Local Impacts in French Polynesia

Changes in the diversity, distribution and abundance of coral reef species in French Polynesia correlate with the changing environment and climate, as well as anthropogenic interventions. French Polynesia measures 5,000,000 km², including 3500 km² of distinct archipelagos of predominantly volcanic origins and 15,000km² related lagoons with a quarter of the world’s atolls[2].

Causes and effects

Warming ocean

Rising water temperatures due to climate change have resulted in coral bleaching in the Southeast Pacific. This stresses corals' zooxanthellae symbionts, photosynthetic algae that live in coral polyps and share energy with the host coral. Warmer waters cause these algae to abandon corals, removing corals' energy source.[3][4] Research on susceptibility to the resulting colour loss (bleaching) over time has suggested the adaptability of corals to temperature regimes.[2] Furthermore, coral mortality is highest when bleaching events coincide with other environmental factors, such as cyclones, but is not significant due to bleaching alone.[5]

Crown-of-thorns starfish at the Cairns Aquarium.

Water temperatures increase cyclone frequency and subsequent long-term coastal disturbance by storm wells. Such intense weather events are not natural to coral reef ecosystems in French Polynesia and can cause damage over extended periods of time and a range of depths. Simultaneously, the increased cyclone frequency impedes timely reef regeneration. Nonetheless, asexually propagating species such as Acropora spp. have demonstrated an advantage in post-cyclone recovery.[6]

Apart from bleaching, temperature changes in sea waters could alter the dominance of species and favour detrimental predators that thrive in warmer waters.[7]

The figure indicates the disturbances events and their impact on coral reefs at Tiahura reef, Moorea Island, and French Polynesia, surveyed by Adjeroud et al.[8]. The first graph indicates the percentage of cover for coral, macroalgae and algal turf. The second graph represent the percentage of cover for the species Pocillopora, Portites, Acropora, and Montipora. Descriptions for the images on the right according to Adjeroud et. al[8]: (A) Coral dominate the healthy reef (coral cover >45%). (B) Turf algae colonized dead coral colonies following outbreaks of the coral-killing crown-of-thorns seastar Acanthaster spp. (COTS) (<5% coral cover). (C) Mostly dead and weakened coral colonies were swept away by the cyclone Oli in February 2010 (<1% coral cover). (D) Juvenile colonies of Pocillopora spp. have recolonized the substrate (∼17% coral cover).

Predator Outbreaks

Crown-of-thorn starfish (Acanthaster planci or COTS) is a carnivore of scleractinian (stony) coral tissues, whose activity is believed to be related to phytoplankton blooms.[7] The starfish feeds through extra-oral enzymatic digestion, a chemical breakdown of the coral for digestion. Crown-of-thorn starfish consume 5–6m² of coral per year per individual and may reduce the population down to 5–10% in one population outbreak. Corals of the Acropora genus are favoured by this predator, while the Porites genus is less likely to be consumed. Massive coral growth forms also see decreased predation, which may be significant in managing restoration. High-risk regions for coral are found in nutrient-rich run-off ocean waters, where crown-of-thorns starfish populations are greater.[2]

Extent

Rangiora Atoll, French Polynesia

In the late 1990s, scientists observed a drastic decrease in the Porites spp. coral reefs at Rangiora Atoll, French Polynesia,[9] which is thought to be linked with increased sea surface temperature. In 2019, similar thermal stress in the area of French Polynesia occurred, marking the most intense heatwave in the past 30 years.[10]

Tiahura Reef, Moorea Island, French Polynesia

Corals in Tiahura Reef, Moorea Island, French Polynesia experienced bleaching in 1984, 1987, 1991, 1994, 2002, 2003, and 2007, damaged by cyclones in 1992, 2010, and faced outbreaks of crown-of-thorn starfish in 1980 and 2006 that killed corals, according to locally conducted surveys.[8][11]

Coral reef coverage in this area has significantly fallen due to disturbances. In 2006 to 2010, a COTS outbreak followed by a cyclone decreased live coral cover from 49% of the area surveyed in 2005 to less than 1% in 2010.[8]

Although coral reefs' abundance has decreased due to disturbances, they demonstrate a continuous recovery trend.[8]

Coral Reef Restoration Strategies

Coral nursery bed in French Polynesia with three month old coral attached

Outplant Nurseries

The implementation of micro-fragments of "super corals" in outplant nurseries, is a primary coral reef restoration method in French Polynesia. Super corals[12] are coral species that demonstrate resistance to environmental changes, such as ocean acidification and water temperature change. Fragments of super corals are harvested and planted on nursery beds or trees in coral gardens. In French Polynesia, many of the micro-fragmentation techniques have been adapted from Dr. Bowden-Kerby's "Fiji Method", which mimics natural coral growth.[13] Coral gardens are tended to for 1–2 years, allowing the corals to grow to a stable, healthy size. The following photo shows the coral's progress at 3 months. Once grown, they are transplanted into outplant areas where reefs have experienced destruction. Outplant areas[14] can range in size but typically work within 108m² at a time.

Trees, Cookies, and Rope

Completed coral cookie tray with Elkhorn coral fragments held in place on the cement "cookie", with 50lb fishing line threaded between the holes to hold the assembly together firmly.[13]
Rope Culture of Staghorn Corals in a Coral Garden[13]

In nurseries, multiple planting strategies are used based on the ocean conditions, many of which are inexpensive. Fixed structures such as coral cookies[15] or coral trees are used in more turbulent ocean conditions to ensure that coral fragments are not lost in strong currents. Coral cookies and trees are welded/recycled substrate structures. Ropes used in coral nurseries may utilize clip attachments to prevent breakage, with smaller fragment growth possible.

Ocean Condition Monitoring

To prepare a restoration plan, in-depth research on ocean conditions is required. Equipment such as smart buoys[16] is deployed in restoration sites to collect real-time data. Environmental parameters such as water temperature, current strength, and wind shear are used to monitor the health of planted outcrops and detect future bleaching events. Data can also be used to identify super corals that can be harvested for future plantation attempts. Virtual networks like ReefOS use cameras and sensors connected to a cloud server[17] to organize data (fish population/abundance/biodiversity/water temperature) from multiple coral reef outplants. Early signs of disease or invasive species can be detected by the presence or absence of data parameters. This data can be used to identify and link certain habitat conditions that lead to increased plantation success. French Polynesian organizations have some of the highest global survival rates[14] between 60-90% depending on the outplant.

Artificial Coral Reefs

Sunken shipwreck transformed into an artificial reef in Florida

Multiple programs use artificial coral reefs to increase substrates for coral organisms and settlements for diverse species.[18] Many of these artificial reefs are shipwrecks or oil rigs[19] cleansed of toxic materials and sunken to the ocean floor. Smaller structures such as cement or PVC balls are also dumped in the ocean to increase the surface area for coral substrates. While artificial reefs can transform harmful human impacts into beneficial restoration projects, they develop slowly and can draw species away from natural reef ecosystems.[18] It is essential to monitor the ecosystem before injecting new substrate.

Mineral Accretion

Mineral accretion[20] is the use of low-voltage electric currents through seawater, which leads to the crystallization of dissolved minerals. The calcium carbonates crystallize and grow on structures as limestone, like a coral skeleton. This mimics natural coral on an expedited route, 3–5 times faster than natural growth, potentially accelerating coral restoration efforts.

Barriers to Methods

Microfragmentation of Orbicella faveolata, a species of slow-growing, massive stony coral, is more effective than larger fragments where predation of these corals is lower than 40%.[21] Below this threshold of predation, such "super corals" can generate ten times more tissue than traditionally used larger fragments.[21] As such, micro-fragmentation of super corals may not be an effective means of restoration in areas where predation events are frequent.

Artificial reefs' deployment has been publicly popular; however, evidence supporting this method as effective is incomplete.[18] While successful sometimes, deploying artificial reefs too close to natural reefs can negatively affect their natural neighbours. Natural reefs' inhabitants, for example, may leave to inhabit an artificial reef, thus damaging their previous ecosystem,[18] and even when successful, artificial reefs develop slowly.

Mineral accretion has not yet been used in French Polynesia but has seen application elsewhere. Nevertheless, like artificial reefs, mineral accretion requires further research as their long-term survival is uncertain. As an adequate solution to coral reef destruction, mineral accretion must remain stable long-term.

Restoration efforts must be carefully planned to avoid inadvertently causing further damage, especially when threats to a reef continue. Ecological roles must be studied prior to implementation to prevent major changes in community composition, as they may be caused by the introduction of a donor coral that could cause a rise in grazing activity.[18] Rapid responses to restore coral reefs may be unsuccessful and harmful, indicating that careful study should begin as soon as possible.

Community-Based Conservation in French Polynesia

In many Oceanic communities, including those of French Polynesia, coral reefs are a source of food, entertainment, spiritual identity, and economic prosperity.

Example of GEF/SGP Divers working in a coral farm at Indonesia. (GEF, 2016)

Indigenous Management

The Act of Rahui, or "temporary ban", is sometimes employed by the traditional management to place restrictions on resources and territories such as tools and reef lagoon. Having legal force under French Polynesia’s environmental code since 2016, Rahui has proven to work for effective lagoon conservation in Tahiti.[22] [23] Furthermore, in July 2021 the Government of Polynesia announced the transfer of management powers to the local communities as part of the new Coral Reef Protection Plan.[24]

Local Organizations: Coral Gardeners

Coral Gardeners[25] is a local NGO working on coral reef restoration. The team of divers assesses reef areas through drone mapping, transects, species distribution diversity, coral state, and predators and communicates with the local nation to develop a reef restoration plan, as well as educate the population on reef fragmentation and nursing. The organization receives worldwide funding through an "Adopt a Coral" initiative and partners with tourist organizations such as Windstar cruises[26] to involve visitors in restoration action and funding.

Raising awareness in communities by reef environments allows for continued support in coral reef protection. Educating the younger and older generations on sustainability practices that can sustain reef restoration is vital. Social impact organizations such as the Coral Gardeners have begun workshops within local communities identifying negative impacts on coral reefs and what they can do to make positive changes. Furthermore, awareness can be a global endeavour as well. Marine researchers can teach new methods to coral nurseries so that more organizations can be involved in monitoring/planting coral reefs in various locations. Increased awareness further protects pre-existing reefs and outplants.

Global Impact: Similarities and Differences with French Polynesia

Globally, coral reefs are subject to a number of environmental stressors that cause degradation. Corals depend on zooxanthellae, an ectosymbiotic photosynthetic organism that provide food to the host. Pollution, photoinhibition, extreme low tides,[27] and disease[28] put stress on these algae symbiotes, causing them to leave and starve the coral. Moreover, ocean acidification stunts the growth of corals by slowing the growth of their calcium carbonate skeleton.[29]

Common Impacts of Coral Reef Decline on an Ecosystem

Loss of Biodiversity
This diagram displays schematically the effect of wave reduction by coastal habitats, including coral reefs on the far right side of the diagram.[30]

Coral reefs play significant roles in sustaining and balancing various aspects of marine ecosystems by providing key habitats for their symbionts and reef-associated fauna. The loss of coral diversity negatively affects reef fish diversity, as the alteration in preferred coral species leads to loss of shelter, reproduction sites, microhabitat requirements and other environmental conditions these fish communities require.[31][32]

Loss of Shoreline Protection

Coral reefs are natural wave breakers[30] that absorb an average of 97% of the wave energy in coastal areas.[33] The decrease in the abundance of coral reefs would reduce the buffer zone for the coastal areas. As a result, shoreline positions are often altered and retreated, along with coastal erosions when the shore experiences strong waves and circulation.[34] With sea levels rising and extreme weather conditions induced by climate change, coastal habitats face greater risks of flooding and tidal wave damage at the shorelines with the loss of coastal coral reefs.

References

  1. ↑ Purkis, Samuel; Dempsey, Alexandra; Carlton, Renée D. (2017). "French Polynesia: Global Reef Expedition Final Report". Khaled bin Sultan Living Oceans Foundation. 1: 1–84.
  2. ↑ 2.0 2.1 2.2 Penin, Lucie (2012). "Response of coral assemblages to thermal stress: are bleaching intensity and spatial patterns consistent between events?". Environmental Monitoring and Assessment.
  3. ↑ Baird, Andrew (November 19, 2008). "Coral Bleaching: The Role of the Host". Trends in Ecology & Evolution. 24: 16–20 – via Trends in Ecology & Evolution.
  4. ↑ Douglas, A.E. (April 2003). "Coral Bleaching––How and Why?". Marine Pollution Bulletin. 46: 385–392 – via Science Direct.
  5. ↑ Lamy, T (2015). "Three decades of recurrent declines and recoveries in corals belie ongoing change in fish assemblages".
  6. ↑ Bambridge, Tamatoa. "Society-based solutions to coral reef threats in french pacific territories". Science Direct.
  7. ↑ 7.0 7.1 Uthicke, S (2015). "Climate change as an unexpected co-factor promoting coral eating seastar (Acanthaster planci) outbreaks". Scopus.
  8. ↑ 8.0 8.1 8.2 8.3 8.4 Adjeroud, M., Kayal, M., Iborra-Cantonnet, C., Vercelloni, J., Bosserelle, P., Liao, V., Chancerelle, Y., Claudet, J., & Penin, L. (2018). Recovery of coral assemblages despite acute and recurrent disturbances on a South Central Pacific reef. Scientific Reports, 8(1), 9680. https://doi.org/10.1038/s41598-018-27891-3
  9. ↑ Mumby, P., Chisholm, J., Edwards, A., Clark, C., Roark, E., Andrefouet, S., & Jaubert, J. (2001). Unprecedented bleaching-induced mortality in Porites spp. At Rangiroa Atoll, French Polynesia. Marine Biology, 139(1), 183–189. https://doi.org/10.1007/s002270100575
  10. ↑ Speare, K. E., Adam, T. C., Winslow, E. M., Lenihan, H. S., & Burkepile, D. E. (2022). Size-dependent mortality of corals during marine heatwave erodes recovery capacity of a coral reef. Global Change Biology, 28(4), 1342–1358. https://doi.org/10.1111/gcb.16000
  11. ↑ Berumen, M. L., & Pratchett, M. S. (2006). Recovery without resilience: Persistent disturbance and long-term shifts in the structure of fish and coral communities at Tiahura Reef, Moorea. Coral Reefs, 25(4), 647–653. https://doi.org/10.1007/s00338-006-0145-2
  12. ↑ Camp, Emma F.; Schoepf, Verena; Suggett, David J. (March 2018). "How can "Super Corals" facilitate global coral reef survival under rapid environmental and climatic change?". Global Change Biology. 24: 2755–2757 – via Wiley Online Library.
  13. ↑ 13.0 13.1 13.2 Bowden-Kerby, Austin (2001). [file:///home/chronos/u-ae450fb82040fd1682a67dbc5913f566eba69648/MyFiles/Downloads/University%20Year%203/TERM%202/EOSC%20270/Wiki%20Project/lowtechaustinbowdenkerby.pdf "Low-tech coral reef restoration methods modeled after natural fragmentation processes"] Check |url= value (help) (PDF). Bulletin of Marine Science. 69: 915–931.
  14. ↑ 14.0 14.1 Bayraktarov, Elisa; Stewart-Sinclair, Phoebe J.; Brisbane, Shantala (May 2019). "Motivations, success, and cost of coral reef restoration". Restoration Ecology. 27: 981–991 – via Wiley Online Library.
  15. ↑ Bowden-Kerby, Austin; Carne, Lisa (July 2012). "Thermal tolerance as a factor in Caribbean Acropora Restoration" (PDF). Proceedings of the 12th international coral reef symposium. 1: 1–5 – via ARC Centre of Excellence for Coral Reef Studies Townsville.
  16. ↑ Bernicot, Titouan (2021). "Impact Report 2021" (PDF). Coral Gardeners. Retrieved February 2023. Check date values in: |access-date= (help)
  17. ↑ Ditria, Ellen M.; Buelow, Christina; Gonzalez-Rivero, Manuel; Connelly, Rod (July 2022). "Artificial intelligence and automated monitoring for assisting conservation of marine ecosystems: A perspective". Frontiers in Marine Science. 9: 1–14 – via frontiers.
  18. ↑ 18.0 18.1 18.2 18.3 18.4 Abelson, Avigdor (2006). "Artifical reefs vs. coral transplantation as restoration tools for mitigating coral reef deterioration: benefits, concerns, and proposed guidelines". Bulletin of Marine Science. 78: 151–159.
  19. ↑ Hazelwood, Emma; Sparks, Amber (2015). "Rig to Reef- Blue Latitudes". Blue Latitudes. Retrieved February 2023. Check date values in: |access-date= (help)
  20. ↑ Goreau, Thomas; Trench, Robert Kent (2013). Innovative Methods of Marine Ecosystem Restoration. Boca Raton, FL: CRC Press. pp. 35–45. ISBN 978-1-4665-5773-4.
  21. ↑ 21.0 21.1 Page, Christopher; Erinn, Muller; Vaughan, David (November 2018). "Microfragmenting for the successful restoration of slow growing massive corals". Ecological Engineering. 123: 86–94 – via Elsevier Science Direct.
  22. ↑ "Tahiti Lagoon Rescued by Tradition".
  23. ↑ "Rahui Supporting Traditional Resource Management With Contemporary Conservation in French Polynesia".
  24. ↑ "French Polynesia Announces Coral Reef Protection Plan At Ocean Conference".
  25. ↑ "Coral Gardeners".
  26. ↑ "WINDSTAR CRUISES' NEW PARTNERSHIP TO PROTECT CORAL REEFS IN FRENCH POLYNESIA".
  27. ↑ Anthony, K.R. (March 6, 2007). "Coral Mortality Following Extreme Low Tides and High Solar Radiation". Marine Biology. 151: 1623–1631 – via SpringerLink.
  28. ↑ Rosenberg, Eugene (November 13, 2008). "The Role of Microorganisms in Coral Bleaching". The ISME Journal. 3: 139–146.
  29. ↑ Anthony, K.R. (Novermber 11, 2008). "Ocean Acidification Causes Bleaching and Productivity Loss in Coral Reef Builders". Proceedings of the National Academy of Sciences. 105: 17442–17446 – via PNAS. Check date values in: |date= (help)
  30. ↑ 30.0 30.1 Narayan, S., Beck, M. W., Reguero, B. G., Losada, I. J., van Wesenbeeck, B., Pontee, N., Sanchirico, J. N., Ingram, J. C., Lange, G.-M., & Burks-Copes, K. A. (2016). The Effectiveness, Costs and Coastal Protection Benefits of Natural and Nature-Based Defences. PLOS ONE, 11(5), e0154735. https://doi.org/10.1371/journal.pone.0154735
  31. ↑ Komyakova, V., Munday, P. L., & Jones, G. P. (2013). Relative Importance of Coral Cover, Habitat Complexity and Diversity in Determining the Structure of Reef Fish Communities. PLOS ONE, 8(12), e83178. https://doi.org/10.1371/journal.pone.0083178
  32. ↑ Komyakova, V., Jones, G. P., & Munday, P. L. (2018). Strong effects of coral species on the diversity and structure of reef fish communities: A multi-scale analysis. PLOS ONE, 13(8), e0202206. https://doi.org/10.1371/journal.pone.0202206
  33. ↑ Ferrario, F., Beck, M. W., Storlazzi, C. D., Micheli, F., Shepard, C. C., & Airoldi, L. (2014). The effectiveness of coral reefs for coastal hazard risk reduction and adaptation. Nature Communications, 5(1), 3794. https://doi.org/10.1038/ncomms4794
  34. ↑ Reguero, B. G., Beck, M. W., Agostini, V. N., Kramer, P., & Hancock, B. (2018). Coral reefs for coastal protection: A new methodological approach and engineering case study in Grenada. Journal of Environmental Management, 210, 146–161. https://doi.org/10.1016/j.jenvman.2018.01.024
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