Course:CONS200/2025WT2/Restoration of Coral Reefs in the Chagos Archipelago

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Background

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Deterioration of the Chagos Archipelago coral reefs has been occurring for decades due to over-fishing, the invasive crown-of-thorn starfish (Acanthaster planci), environmental degradation such as pollution and natural events such as hurricanes and heat waves.

Coral reefs are the ecosystems most susceptible to anthropogenic activities (Hughes et al., 2017). As water temperatures increase so does the frequency of coral bleaching (Heron et al., 2016). Compared to ocean temperatures 125 years ago (post dawn of the industrial revolution) oceans now are hotter and are continuing their trend of heating up (Yao & Wang, 2022). Additionally, marine heatwaves are continuing to become more common; without drastic intervention, our world's waters could likely enter into a permanent state of marine heatwave (Yao & Wang, 2022).

The first mass bleach event that the Chagos Archipelago experienced was in 1998. This and subsequent events were a result of ocean warming. Contrary to the belief that the environment of remote islands would suffer less, remote islands experienced equivalent or worse environmental deterioration from the 1998 ocean warming event. The Archipelago coral recovery was unusually long due to the lack of algae growth following the 1998 warming event. Due to the lack of algae growth the bare rock was uncolonised by macro-organisms for approximately 3 years. Coral mortality in the Archipelago’s reached a depth of 30m on seaward slopes, with the mortality of certain coral species reaching even deeper. The coral cover of the Chagos Archipelagos islands ranged from 50-95% before the coral bleaching and reduced to an average of 12% following the bleaching event. In shallow areas between 0-5m then coral cover average even reached 0% (Harris. A, Sheppard. A, 2008).

Current Remedial Actions

There have been island restoration efforts which began when Chagos was still a British territory (Moolna, n.d.). There have been lots of restoration efforts, some are more human involved while some have a more holistic approach. One of the strategies include reducing rat populations. By restoring abandoned coconut plantations and eliminating rats, a more natural, seabird-driven ecosystem will be able to regenerate (Healthy Islands, Healthy Reefs | Chagos Conservation Trust, n.d.). This will lead to healthier islands and coral reefs while providing a sanctuary for native species like the iconic coconut crab and red-footed booby (Healthy Islands, Healthy Reefs | Chagos Conservation Trust, n.d.). In 2018 scientists discovered there is a direct correlation between island seabird populations and key reef health indicators, such as herbivorous fish populations (Healthy Islands, Healthy Reefs | Chagos Conservation Trust, n.d.). Seabirds rely on the ocean for food, and their droppings naturally fertilize the corals around the islands they live on (Healthy Islands, Healthy Reefs | Chagos Conservation Trust, n.d.). However, when rats are introduced, this relationship is disrupted as they reduce seabird populations by consuming eggs and chicks and damage native plants (Healthy Islands, Healthy Reefs | Chagos Conservation Trust, n.d.). Researchers discovered that seabird densities and nitrogen deposition rates are 760 and 251 times greater, respectively, on islands free from rats (Healthy Islands, Healthy Reefs | Chagos Conservation Trust, n.d.). The reefs around these rat-free islands also show higher fish biomass and coral reef productivity, suggesting these factors may help increase resilience to coral bleaching (Healthy Islands, Healthy Reefs | Chagos Conservation Trust, n.d.). These findings highlight the crucial role that rat eradication and seabird restoration play in maintaining the health of both island ecosystems and coral reefs, underscoring the need for continued and holistic conservation efforts.There is current a restoration effort called The Barton Point Native Hardwood Restoration Project is the management and removal of non-native vegetation is essential as the coconut palm is the predominant introduced species on many, if not all, of the islands and atolls (Jeffery, 2014). This species should be controlled through selective cutting to encourage the regeneration of native plant life (Jeffery, 2014). Coconut palms pose three main challenges. First, their fronds block sunlight from reaching the ground, and fallen fronds accumulate, preventing the regeneration of other species (Jeffery, 2014). Second, coconut palms offer shelter and food for rats, a pest that was unintentionally introduced to the islands by humans (Jeffery, 2014). Third, replacing coconut palms with native hardwoods would create additional nesting sites for the red-footed booby, whose colony in the Barton Point Reserve is now the largest in the Indian Ocean and one of the largest in the world (Jeffery, 2014). The Restoration Project involved removing coconut palms, clearing coconuts from the ground to prevent reseeding, and replanting hardwoods (Jeffery, 2014). In 2011, it was reported that the team was pleased to see how quickly the natural recovery of native forest occurred once the coconuts were removed (Jeffery, 2014).

The Path Forward

In order to prevent the Chagos Archipelago coral reef's continued decline in ecosystem biodiversity (Sheppard et al., 2020; Williamson et al., 2024), and to assure its continued existence and recovery, stressors such as the increasing ocean temperature, invasive species, and overfishing must be dealt with (Sheppard et al., 2012).

Research Directions

As one of the world's largest Marine Protected Areas (MPAs), the Chagos Archipelago area is valuable to researchers who want to better understand how climate change affects the area. What's special about it being a large MPA is that there is significantly less direct human impact from sources like pollution.

Potential areas for research include but are not limited to:

• Clarifying the trophic roles of herbivorous and detritivorous reef fishes (Samoilys et al., 2018; McDevitt-Irwin et al., 2024).
  • By clarifying these roles we can better understand reef resilience to climate change and fishing.
  • There are key species that drive the differences in fish assemblages, which describes an ecosystems abundance and richness. Among these species are surgeonfish who graze on epilithic algae and keeping algal growth in balance. Additionally there is the parrot fish who grazes on the nutrients held within a coral's calcareous matrix. Together, these herbivorous fish play an important role in keeping levels of macroalgae down (Samoilys et al., 2018).
• Reef ecosystem and trophic interactions.
• Reef resilience factors.
• Global trends and impacts.
  • By recognizing current trends and their impacts, we can begin to model future trends and their impacts, giving us the opportunity to pre-emptively mitigate damages or anticipate the consequences.
  • There is some evidence to support the idea that the role of fishes on reef recovery does not vary with human impact (McDevitt-Irwin et al., 2024). This is not to say that anthropogenic activities don't carry detrimental consequences to marine life and the planet as a whole, because they certainly do (Rockström, 2009). Instead of mitigating direct human impacts on coral reefs it's possible that effort would be better spent by focusing more on supporting fish species if the aim is promoting the recovery of reef ecosystems.
  • In a 2022 study by Yao & Wang, they model how marine heatwaves are seeing an increased number of total days and average duration over the year, while marine cold-spells are seeing the opposite trend. Both sides of marine extreme weather are detrimental for
• _____

Technical Solutions

1) Continued environmental monitoring:

2) Promoting herbivorous fish species:

• Evidence supports the hypothesis that in large MPA's herbivores' role in keeping the growth of algae in check is especially important during the recovery periods of coral (McDevitt-Irwin et al., 2024). These fishes were found to significantly promote crustose coralline algae (CCA) as well as decreasing macroalgae populations. CCAs are important due to their role as food source in substrate for species of limpets and other intertidal herbivores (Maneveldt et al., 2006).

3) Promoting reef structural complexity:

• Reefs that had a high structural complexity as well as the fast growing table coral Acropora spp. saw a 3x faster recovery in carbonate production (Lange et al., 2022). This is important in order for the reef to return to a positive carbonate budget. Carbonate is an important mineral for marine life across the globe, it plays a structural role for the shells and bodies of lots of marine life like corals and shells (Environmental Protection Agency, 2024).

4) Climate Mitigation - Technology:

Economic Solutions

• Reducing illegal fishing
• Reducing anthropogenic marine debris/pollution
• Climate mitigation - Economic

Cultural Solutions

• Climate mitigation - Cultural

Conclusion

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References

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Moolna, A. (n.d.). Chagos Islands: how to ensure their coral reefs aren’t damaged as they return to Mauritius. The Conversation. https://theconversation.com/chagos-islands-how-to-ensure-their-coral-reefs-arent-damaged-as-they-return-to-mauritius-240610#:~:text=Island%20restoration%20efforts%20that%20began,UK%20and%20other%20regional%20partners.

Healthy Islands, Healthy Reefs | Chagos Conservation Trust. (n.d.). https://chagos-trust.org/our-work/healthyislands#:~:text=By%20managing%20the%20abandoned%20coconut,crab%20and%20red%2Dfooted%20booby.

Jeffery, L. R. (2014). Ecological restoration in a cultural landscape: conservationist and Chagossian approaches to controlling the ‘coconut chaos’ on the Chagos Archipelago. Human Ecology, 42(6), 999–1006. https://doi.org/10.1007/s10745-014-9696-y

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