Aldabra Atoll
Country
Seychelles
Inscribed in
1982
Criteria
(vii)
(ix)
(x)
The conservation outlook for this site has been assessed as "good with some concerns" in the latest assessment cycle. Explore the Conservation Outlook Assessment for the site below. You have the option to access the summary, or the detailed assessment.
The atoll is comprised of four large coral islands which enclose a shallow lagoon; the group of islands is itself surrounded by a coral reef. Due to difficulties of access and the atoll's isolation, Aldabra has been protected from human influence and thus retains some 152,000 giant tortoises, the world's largest population of this reptile. © UNESCO
Summary
2025 Conservation Outlook
Finalised on
11 Oct 2025
Good with some concerns
Current state and trend of VALUES
Low Concern
Overall THREATS
Overall PROTECTION and MANAGEMENT
Full assessment
Description of values
Geomorphology
Criterion
(vii)
Aldabra Atoll is one of the largest coral atolls in the world (Hillary et al., 2002) and one of only two raised coral atolls worldwide to not be heavily impacted by human activities. Aldabra Atoll consists of four main islands of coral limestone separated by narrow passes and enclosing a large shallow lagoon, providing a superlative spectacle of natural phenomena (World Heritage Committee, 2010). The lagoon contains many smaller islands and the entire atoll is surrounded by an outer fringing reef (World Heritage Committee, 2010). Geomorphologic processes have produced a rugged topography, which supports a variety of habitats with a relatively rich biota for an oceanic island and a high degree of endemism (World Heritage Committee, 2010). A recent study has shown that over the past 51 years, on average Aldabra's shoreline has remained unchanged when compared to global atoll rates of change (Constance et al. 2024).
Terrestrial vegetation
Criteria
(ix)
(x)
Aldabra is an outstanding example of an oceanic island ecosystem in which evolutionary processes are active within a rich biota (World Heritage Committee, 2010). Most of the land surface comprises ancient coral reef (~125,000 years old) which has been repeatedly raised above sea level (World Heritage Committee, 2010). The size and morphological diversity of the atoll has permitted the development of a variety of discrete insular communities with a high incidence of endemicity among the constituent species (World Heritage Committee, 2010). Aldabra houses at least one currently unique, but potentially formerly widespread, habitat type, the tortoise turf. These relatively highly diverse grass-dominated areas are likely to be maintained due to the heavy grazing pressure exerted by the giant tortoises (Merton et al., 1976). Terrestrial habitats and vegetation types, have been mapped using high resolution satellite imagery. The vegetation mapping indicated no significant change in the area of Aldabra’s terrestrial vegetation (Walton, 2015), although the eradication of goats in 2012 will likely have improved grazing conditions for giant tortoises.
Freshwater and brackish pools
Criteria
(ix)
(x)
There are 20 freshwater and brackish pools on the platin surface across the Atoll, which vary from shallow depressions holding water for only a few hours; a thin lens over saline pools; to pools that are permanent throughout the wet season (Cognan & Hutson, 1971; SIF, 2016a). The largest pool is Bassin Flamant, which has a dry season diameter of about 300 m, but this and other pools increase in size during the wet season (Stoddart et al., 1971). The pools provide habitat for various algal species, crabs and fishes, and are an important source of food and water for tortoises, birds and land crabs. The habitat map includes freshwater pools as a habitat category that can be used for future monitoring (Walton, 2015). New satellite imagery is being commissioned in 2025 to map pool dynamics across seasons. Endemic red shrimps, especially on Picard Island, are found in some of the pools.
Sand beaches
Criteria
(ix)
(x)
There are 50 beaches along the outer coastline of Aldabra Atoll, predominantly on the sheltered north and south west coasts. There are also various smaller beaches within the lagoon, interspersed between the mangroves. Sandy beaches are important habitat as they provide nesting areas for green and hawksbill turtles (Mortimer et al., 2011). Sand beaches are currently in a good condition although there is some erosion occurring on parts of Aldabra’s largest beach, accumulation of marine debris is substantial in all areas but particularly on the south/east coastline, but sand deposits occurring elsewhere. Coral mortality following bleaching events may contribute to beach erosion and beaches are also susceptible to changing sea levels. Recent habitat mapping will help to assess and quantify long-term trends.
Intertidal mudflats
Criteria
(ix)
(x)
Extensive intertidal mudflats fringe the inner edges of the lagoon on Aldabra Atoll, which have been estimated to cover a total area of 12.6 km2 (Hamylton et al., 2012). These are in good condition and apparently stable, and the populations of wading birds that use this habitat are stable (SIF, unpublished data, 2016).
Mangrove communities
Criteria
(ix)
(x)
The edge of Aldabra’s lagoon is lined with extensive mangrove forests composed of seven species (Macnae, 1971). A study showed that Aldabra’s mangrove communities have been stable and even increased slightly in the last 15 years (Constance, 2016).
Seagrass and macroalgal communities
Criteria
(ix)
(x)
Aldabra Atoll hosts large seagrass meadows both inside the lagoon and around the atoll, with the most abundant beds being found off Picard Island. A recent national seagrass mapping exercise estimates Aldabra to have 3,495 ha of seagrass.
Seagrass beds are an important functional habitat, whose roots stabilise the sediments and the leaf blades help filter water by slowing water currents and encouraging finer particulates to settle. Seagrasses are also important primary producers and critical feeding habitats for dugongs and turtles (Hamylton et al., 2012, Mortimer et al., 2011), as well as acting as nursery grounds for many species of juvenile fishes, and hunting grounds for adults. Seagrass beds appear to be stable (SIF marine monitoring programme, unpublished data, 2016).
Seagrass beds are an important functional habitat, whose roots stabilise the sediments and the leaf blades help filter water by slowing water currents and encouraging finer particulates to settle. Seagrasses are also important primary producers and critical feeding habitats for dugongs and turtles (Hamylton et al., 2012, Mortimer et al., 2011), as well as acting as nursery grounds for many species of juvenile fishes, and hunting grounds for adults. Seagrass beds appear to be stable (SIF marine monitoring programme, unpublished data, 2016).
Coral communities
Criteria
(ix)
(x)
Fringing coral reef surrounds the outer coastline of the atoll (53 km2) and covers 19.3 km2 of the shallow lagoon. The reef supports a high coral coverage and numbers of coral species, with an estimated 118 species (SIF, 2016a). During the first global coral bleaching event in 1997/1998, corals around Aldabra were subject to elevated seawater temperatures which resulted in coral mortality. During the third global coral bleaching event in 2015/2016, there was a reduction of relative hard coral cover of 52% with substantial variation across sites. By early 2022, six years post-bleaching, relative hard coral cover at these sites reached 43–107% of the pre-bleaching cover. The annual marine monitoring programme, which started in 2014 has continued to track the recovery of the reef after such disturbance events and provides updated information on the status of the reef.
Marine water quality
Criterion
(ix)
Due to the isolation of the island, there are few direct anthropogenic pressures affecting the quality of water. There is localised sewage leaching from the research base septic tank although this is low levels and believed to be insignificant (SIF, 2016a). Marine water quality is believed to be stable (SIF, unpublished data, 2016).
Aldabra giant tortoises
Criterion
(x)
Aldabra hosts the largest extant population of giant tortoises worldwide (~150,000 animals, with recent research suggesting that the popilation is higher than all former estimates; in prep). Giant tortoises of many taxa were widespread, in high densities, on islands around the world until humans arrived and exterminated them – directly, or via introduced predators (Hansen et al., 2010). Aldabra remains one of only two places in the world where giant tortoises survive (the other being Galapagos, which currently hosts a much lower density of giant tortoises per km2) and the last remaining place among the Indian Ocean islands. The tortoise population is entirely self-sustaining: all the elements of its intricate interrelationship with the natural environment are evident (World Heritage Committee, 2010). Aldabra thus emerges as the last place in the world, where the evolutionary ecology of giant tortoise – plant interactions can be studied (World Heritage Committee, 2010). Long-term monitoring data indicate that the Aldabra giant tortoise population has remained stable over the past 15 years (Turnbull et al., 2015).
Landbirds
Criterion
(x)
The property is a significant natural habitat for birds, with three endemic landbird species, including two extant species (Aldabra drongo and Aldabra fody) and one species presumed extinct (Aldabra Brush Warbler). The Aldabra fody was only recently confirmed as a separate species by SIF staff (Van de Crommenacker et al., 2015a). There are another ten distinct subspecies of landbird, amongst which is the White-throated rail, the last remaining flightless bird of the western Indian Ocean. Long term monitoring of seven landbird species found populations to be either increasing (6 species) or stable (1 species, the Aldabra drongo) between 2002 and 2014, showing an overall stable trend (Van de Crommenacker, 2015b). The Aldabra rail has expanded its re-introduced population size on Picard island to greater than the predicted carrying capacity on the island (Sur et al., 2013b). A planned eradication of rats and cats on the islands would significantly increase populations for this and other bird species on Aldabra.
Other terrestrial fauna
Criterion
(x)
There is rich aquatic insect fauna on Aldabra Atoll in comparison with other island groups, due to the high variability in chemical and biological conditions of the freshwater pools (SIF, 2016a). There are 11 species of land crabs on Aldabra Island, including three types of hermit crabs (SIF, 2016a). Aldabra’s coconut crab (Birgus latro) population was monitored twice monthly since between 2006–2016, and although there are seasonal changes in abundance, the population is stable (Appoo et al, 2021). There are three known species of lizards on Aldabra Atoll; a skink (Cryptoblepharus boutonii), and two gecko species (Hemidactylus mercatorius, LC and Phelsuma abbotti LC), the latter being endemic to Aldabra Atoll. The population status is understood to be stable (SIF, 2016a). Bats are the only mammals native to Aldabra Atoll and there are four species, three of which are endemic to the atoll. There is no trend data available for other terrestrial species (SIF, unpublished data, 2016).
Sea and shorebirds
Criterion
(x)
There are vast waterbird colonies including the second largest frigatebird colony in the world and one of the world's only two oceanic flamingo populations (World Heritage Committee, 2010). Aldabra also contains a population of the endangered Madagascar Pond-heron (Bunbury, 2014), which is in decline in most other parts of its range. Monitoring shows that the population of seabirds are stable or increasing. The annual frigatebird census indicates stable or increasing numbers of both species (with substantial year-to year fluctuation) with 6,000 pairs of lesser frigatebird (Fregata ariel) and, 4,000 pairs of great frigatebird (Fregata minor) (Šúr et al., 2013a). Tropicbird nest monitoring shows no decline in numbers of nest activity between 2009–2016, although nesting success is among the lowest recorded for the species (Burt et al. 2021). A red-footed boobie census in 2022/23 indicates a population of 22,628 breeding pairs (SIF, internal report) . Wading bird populations are seasonal but stable (SIF, unpublished data, 2016).
Marine turtles
Criterion
(x)
Aldabra is a highly significant breeding ground for green turtles (Chelonia mydas, EN) and it also hosts a small population of breeding hawksbill turtles (Eretmochelys imbricata, CR) (World Heritage Committee, 2010). While green turtles tend to nest on the sand beaches on the outer edges of the atoll, critically endangered hawksbill turtles nest primarily on beaches inside the lagoon (SIF, 2016a). The atoll is also an important feeding ground for both species and for occasional loggerhead turtle (Caretta caretta, VU), which occur in the area but do not breed on the atoll. Aldabra Atoll is the largest rookery in the western Indian Ocean for green turtles. Published data to 2008 showed a 500-800% increase in nesting green turtles over a 40-year period (Mortimer et al., 2011). Numbers of green turtles have continued to increase since then (Pritchard et al., 2022).
Marine mammals
Criterion
(x)
Aldabra hosts various species of marine mammals at different times throughout the year, which include humpback whales and dugong. Aldabra’s dugong population is the only one remaining in Seychelles, and one of the few remaining in the western Indian Ocean region. The dugong population appears to be larger than initially thought, with at least 23 individual animals counted in a 2022/23 survey of the lagoon (SIF, unpublished data, 2024). Several observations of female dugongs with juveniles in Aldabra’s lagoon suggest that the site plays an important regional role as a dugong breeding/nursery area (SIF Newsletter August 2016).
Fishes
Criterion
(x)
The coral reef surrounding Aldabra host a wealth of marine life with exceptionally high abundances of reef associated fishes and pelagic species, including many threatened species of bony fishes and elasmobranchs. The marine monitoring programme, which started in 2014 introduced the use of Baited Remote Underwater Videos (BRUVs). The BRUVs have since been used to record fish community composition and abundances around the atoll. The cameras have detected high abundances of threatened shark species, such as hammerheads, and giant groupers. Results of the monitoring programmes indicate that fish populations are exceptionally high in comparison to other locations within Seychelles and the wider region. This was also confirmed by National Geographic Pristine Seas team expedition in 2015, which estimated fish biomass in the near shore waters surrounding Aldabra to be 5 tonnes per hectare, more than ten times the fish biomass found in the Seychelles inner islands (Pristine Seas, 2015).
Marine invertebrates (other)
Criterion
(x)
The coral reef surrounding Aldabra host a wealth of marine life with high abundances of other types of marine invertebrates (e.g., echinoderms, gastropods, crustaceans). There is limited information available to date and further in-depth research is required.
Assessment information
Several of the invasive species that previously threatened Aldabra's unique flora and fauna have been eradicated in recent years. Feral goats were removed in 2012, two invasive bird species were eradicated in 2016 and the island is almost free from sisal, the main invasive plant species. Efforts are also underway to assess the feasibility of eradicating both cats and rats from the atoll. The neighbouring island of Assumption was also declared free from the invasive bird species, reducing the likelihood of imminent reintroduction. However, cats and rats are present on other islands in the Seychelles and the construction of a luxury resort on Assumption will once again increase the likelihood of arrival of other invasive species, despite the best efforts of a biosecurity plan for Aldabra. Marine litter remains one of the main ongoing challenges, as it does with many locations. Marine litter is being addressed through regular clean-ups on Aldabra's more accessible sand beaches. The rubbish accumulating on more remote inaccessible beaches remains a concern. Efforts to address the threat of illegal fishing will be assisted by the increase in the marine boundary and efforts of the coast guard. The results of terrestrial and marine monitoring programmes and analyses of archive datasets, such as seawater temperature and rainfall data, are revealing that changes have already occurred on the atoll. With the efforts that have been invested in tackling the invasive species and other threats climate related threats are becoming more prominent as the main threats to Aldabra's terrestrial and marine ecosystems and flora and fauna.
Invasive Non-Native/ Alien Species
(Invasive mammal species)
Invasive/problematic species
Felis catus
Rattus sp.
Inside site
, Throughout(>50%)
Outside site
Cats and rats are the two remaining invasive mammal species that currently pose the greatest threat to Aldabra after the feral goats were successfully eradicated in 2012 (Bunbury et al., 2018). Cats and rats are highly invasive species and problematic on tropical islands around the world. Research into rat abundances and impacts on Aldabra (Harper et al., 2015; Harper & Bunbury, 2015) found particularly high abundances of rats in the mangrove habitats, where they grow larger, survive for longer, have larger litters and longer breeding seasons compared to rats in other habitats (scrub and coastal habitats). Rats are having impacts on seabirds, landbirds, small reptiles, plants, invertebrates and turtle and tortoise nests through egg predation. Research into cats on Aldabra found that they are not particularly abundant but their main prey is turtle hatchlings, rats, small reptiles and invertebrates. The cats that are found on the largest island of Aldabra, Grand Terre, may be responsible for the absence of frigatebirds on that part of the atoll, and their presence prevents the reintroduction of Aldabra rails, which would improve the prospects for this species. The eradication of these two species remains a priority and a world class eradication feasibility assessment commenced in 2023. The results of the rat ecology research indicates that eradication will be particularly challenging due to the high abundance of this species in mangrove habitats. A comprehensive biosecurity plan for Aldabra has been developed and implemented. Biosecurity measures will help support all ongoing eradication programmes and prevent other new species, such as the myna bird, yellow crazy ant, and African land snail, known to be invasive elsewhere in Seychelles, from being introduced to Aldabra.
Water-borne & other effluent Pollution
(Sewage and waste water)
Inside site
, Localised(<5%)
Due to the isolation of the atoll, there are few direct anthropogenic pressures affecting marine water quality. There is likely localised sewage leaching from the research base septic tank into near shore waters, although this is believed to be insignificant (SIF, 2016a). There is a risk that the amount of waste water being released into the marine environment from visiting boats may increase if more tourist boats were to visit the atoll, therefore, strict regulations are enforced.
Invasive Non-Native/ Alien Species
(Invasive sponge)
Inside site
, Scattered(5-15%)
In 2012, during Aldabra’s outer reef mapping project, an encrusting sponge identified as Terpios hoshinota was observed at high densities on the coral reefs around the atoll (R. Klaus, pers. obs). This sponge has caused massive and rapid coral mortality in other parts of the world. T. hoshinota grows rapidly and widely and can outcompete hard corals. It also releases compounds that are toxic to other reef organisms. Once the sponge has colonized an area of the reef it can last for over a decade, dominating the reef bottom and preventing the recruitment of juvenile corals. The cause of these ’outbreaks’ is still unknown, although pollution, coastal development and other human activities such as boats and shipping have been implicated. A monitoring programme for this species was started, and surveys are ongoing (State Party of Seychelles, 2021).
Recreational Activities
(Anchor damage)
Inside site
, Localised(<5%)
Tourism has been gradually increasing at Aldabra, as such a designated anchoring area for boats and ships was implemented in the 2016 management plan. This is the only site where anchoring is currently allowed within the MPA. Dive and snorkel operations conducted by tourist vessels are supervised by SIF staff to enforce anchoring and other reserve regulations.
Invasive Non-Native/ Alien Species
(Invasive plant species)
Invasive/problematic species
Agave sisalana
Casuarina equisetifolia
Catharanthus roseus
Inside site
, Widespread(15-50%)
Outside site
There are several plant species on Aldabra that are known to be invasive, including: sisal (Agave sisalana), Casuarina (Casuarina equisetifolia), and herbs such as the Madagascar periwinkle (Catharanthus roseus) and the porterweed (Stachytarpheta jamaicensis). The latter two species are able to dominate low ground vegetation and are not grazed by tortoises. Casuarina is highly invasive in many places, and is believed to have been planted and now thought to be invading Ile Picard and Middle Camp on Ile Malabar. A sisal eradication programme was started in 2014 with Sisal thought to have been eradicated by 2017, however, a small area of regrowth has occurred on Picard and is currently (in 2025) under treatment. Further research is needed to assess the magnitude of impacts of the other introduced plant species and decide on control/eradication efforts.
Fishing, Harvesting & Controlling Aquatic Species
(Illegal fishing)
Inside site
, Localised(<5%)
Outside site
No fishing is permitted around Aldabra apart from in the specified subsistence fishing zones, which can only be fished by SIF staff to feed the staff on the research base (SIF, 2016a). Surveillance and enforcement of the marine environment of Aldabra is a challenge given the remote location and large area that needs to be patrolled and there have previously been reports of poaching. In 2015, five illegal fishing vessels entered the Aldabra Reserve and extracted over 1 tonne of fish in just one week (State Party of Seychelles, 2021). While all five boats were caught and dealt with by the Seychelles authorities, the illegal extraction was a big drain on resources and demonstrated how vulnerable Aldabra is to illegal activities. Poaching activities seem to be increasing and the SIF have signed an MOU with the Seychelles Coastguard, who will assist in surveillance and enforcement of Aldabra.
Subsistence fishing for Aldabra residents was previously unrestricted, but since 201,6 subsistence fishing has been restricted to specific zones around the atoll (SIF, 2016a). Subsistence fishing is strictly monitored by staff, including location, species, and size of each fish caught(State Party of Seychelles, 2021). Certain species are restricted and therefore returned if caught, and staff are trained in release techniques.
Subsistence fishing for Aldabra residents was previously unrestricted, but since 201,6 subsistence fishing has been restricted to specific zones around the atoll (SIF, 2016a). Subsistence fishing is strictly monitored by staff, including location, species, and size of each fish caught(State Party of Seychelles, 2021). Certain species are restricted and therefore returned if caught, and staff are trained in release techniques.
Changes in Physical & Chemical Regimes, Changes in Temperature Regimes, Changes in Precipitation & Hydrological Regime
(Temperature extremes)
Inside site
, Widespread(15-50%)
Outside site
Climate-driven changes are already impacting the coral reef (Koester, 2020) and may impact vegetation ecology, with impacts that then cascade through the ecosystem (e.g. plant-animal interactions, such as herbivory, pollination, seed dispersal). The impacts of such changes are as yet unquantified on the flora and fauna of the property but are also likely to affect the reproductive biology and demography (sex ratio) of sea turtles and giant tortoises for example. Potentially also impacting activity patters of giant tortoises, an important island ecosystem engineer species (Falcon et al., 2017). According to the CVI report for Aldabra Atoll, the OUV is extremely sensitive to extreme temperature events (Heron et al. 2021).
Changes in Precipitation & Hydrological Regime
(Increased frequency of droughts)
Inside site
, Widespread(15-50%)
Aldabra's terrestrial vegetation is being impacted by changes in rainfall patterns and increased drought frequency, which could also pose a threat to the giant tortoise population (Haverkamp et al., 2017). Analysis of the long-term monthly rainfall data between 1969 and 2013 revealed that rainfall has declined and the average number of drought months per annum has increased three-fold, from an average of two to six drought month per annum (State Party of Seychelles, 2021). Open mixed scrub and grasslands, the preferred habitats of tortoises, showed the greatest variation in response between drought and non-drought months. In the short term, tortoises could be impacted by a reduction in the quality and quantity of food and shade available, and in the long term by changing habitat composition on the atoll (Haverkamp et al., 2017). A reduction in rainfall and increased droughts could also impact other types of vegetation such as the mangrove communities and other terrestrial fauna. According to the CVI report for Aldabra Atoll, the OUV is extremely sensitive to drought. The sensitivity of OUV to extreme temperature events and drought were each determined as high, indicating potential for loss or alteration of
many key WH values (Heron et al. 2021).
many key WH values (Heron et al. 2021).
Changes in Temperature Regimes
(Coral bleaching)
Inside site
, Throughout(>50%)
Outside site
Aldabra was subject to coral bleaching during the first global mass coral bleaching event in 1997/1998 (Soutier et al., 2000; Stobart et al., 2005; Heron et al., 2017). The coral reefs within the property were also heavily impacted by the third global bleaching event from 2014 - 2017 (Cerutti et al., 2020). The marine monitoring programme on Aldabra detected changes in the status of the coral reef. The results of seawater temperature monitoring revealed that temperatures were higher than normal over the years leading up to 2016, during which there were excessively high temperatures that were sustained for several months. These conditions occurred during the third global mass coral bleaching event and resulted in bleaching and subsequent mortality around Aldabra. Seawater temperatures at 15m depth were above average for a long period of time, reaching a maximum of 36.2oC in April 2016, which is close to 5oC above the maximum temperatures recorded in other years. Between 69-99% of all coral colonies bleached in 2016 and coral cover declined by 50% between 2014 and 2016 (SIF Newsletter May, 2016; Cerutti et al., 2020). The highest overall coral cover remaining was ca. 23-28% at two sites within the lagoon. These sites also had the highest cover of coral recruits and the highest proportion of herbivores in relation to total fish abundance on shallow surveys across all survey sites. In 2020, mean hard coral cover across all sites and depths continues to increase following the 2016 bleaching event with overall cover reaching 16.5% (± 1.39% SE), up from 14.3% in the previous season (SIF Season 7 Marine Monitoring Report). Additional bleaching has occurred at Aldabra in 2024 and 2025, indicating the shrinking windows for recovery between coral mortality events.
Garbage & Solid Waste
(Marine litter)
Inside site
, Throughout(>50%)
Outside site
Aldabra is remote but the beaches are often inundated with marine litter, reflecting the increase in this problem within the region and at a global scale (State Party of Seychelles, 2021). Low lying parts of the coastline are affected by marine litter and other debris brought in by the tide (plastics, fishing nets, rope, buoys, glass bottles, flip flops, drinks cans etc.). The accumulation rate of litter arriving on different parts of the island varies depending on monsoon season. Regular clean-up activities are carried out on the sandy beaches around the atoll, particularly those visited as part of the regular turtle monitoring activities. Marine litter can however accumulate in other less frequently visited parts of the atoll, especially on Grande Terre, the south island. The trash poses a threat to wildlife that use the beaches (e.g. turtles, seabirds and waders), as they may consume or become entangled in the litter that washes up on the beaches. The litter can also spread inland and affect coastal grasslands, the favoured grazing areas for giant tortoises. Marine wildlife on the coral reef and in the pelagic zone are also at risk. Lost fishing gear, line and nets including the nets attached to drifting fish aggregating devices (FADS) for example, can become caught on the reef and cause breakages of the coral (pers. obs.). Fishes, turtles, and marine mammals may also be affected. There is also some potential for reduced coral health and increased disease through micro-plastics and leachate re-entering the marine system from coastal run-off and wave action. In 2019 SIF launched the Aldabra Clean-Up Project, combining an expedition to clean-up these remoter areas, coupled with research and raising awareness of the issue (State Party of Seychelles, 2021). The clean-up removed 25 tonnes of marine plastic litter and estimated there is ca. 500 tonnes of litter remaining on Aldabra, the highest accumulation reported for any one island worldwide (Burt et al., 2020). A subsequent clean-up in 2023 also removed around 20 tonnes of litter. Clearing the remaining accumulated litter would require substantial resources.
The risk of new and potentially invasive species being introduced to the atoll (e.g., crazy ants) is being addressed through the implementation of a biosecurity plan. However, the risk of arrival of such species has increased substantially with the development of a luxury resort on neighbouring Assumption Island. The devastating impacts of climate change, particularly the impact of increased sea temperatures on the intensity and frequency of coral bleaching, are a stark reminder of the potential damage that could be caused in the future. Warming sea water temperatures, sea level rise, ocean acidification and severe storms could all cause serious damage to Aldabra and to the values for which it was inscribed. Further assessment of the potential impact of climate change on Aldabra’s ecosystem and biodiversity, including modeling exercises to assess possible climate driven changes to habitats, as well as species focused predictions on the reproductive biology and demography (sex ratio) of sea turtles and giant tortoises for example, are needed as these may help anticipate additional management interventions to limit the impact of these changes.
Invasive Non-Native/ Alien Species
(Invasive bird species)
Inside site
, Extent of threat not known
Outside site
Aldabra has now reclaimed the title as the largest tropical island free from invasive birds (SIF Newsletter March, 2017; Bunbury et al., 2019). In 2012, two invasive alien bird species, the red-whiskered bulbul and Madagascar fody, were discovered on Takamaka, during the goat eradication campaign (Bunbury et al., 2013a; Bunbury et al., 2013b). These species posed a major threat to native bird populations through competition for food, disease transmission and hybridisation with endemic species (Roberts, 1988). Genetic research showed that the Madagascar fody (Foudia madagascariensis) had begun to hybridse with the Aldabra fody (Foudia eminentissima aldabrana). The eradication campaign took 3 years to complete, and was implemented at the same time as a campaign on the adjacent island of Assumption, which was suspected to be the original source of the invasive birds. As Assumption is situated only 27 km from Aldabra, it was considered critical that both species were eliminated simultaneously from both islands in order to lessen the likelihood that Aldabra would be invaded again. After several follow up missions, Assumption was declared free from both invasive bird species in January 2017 and Aldabra was declared free from both species in March 2017 (SIF Newsletter March, 2017; Bunbury et al., 2019). Both bird species are still present on other islands in the Seychelles so the risk of reintroduction remains, but it is now considered to be much lower than before.
Shipping Lanes
(Chemical and oil spills and collisions)
Outside site
The installation of solar panels in 2012, supporting 96% of power on Aldabra, allowed to reduce the amount of fuels to be transported onto the atoll for boats and the back-up diesel generator, thus the risk of oil spillage for local needs (State Party of Seychelles, 2021). Nonetheless, Aldabra Atoll is situated very close to the major shipping lane along the east African coast, and there is a potential risk of collisions and oil or chemical spills. While the risk is small, the potential for damage is great. There is a 30 NM oil tanker avoidance area around Aldabra. A new lighthouse was installed on the atoll in 2012 to help mitigate the risk of collisions and spills. The extension to the boundary of the MPA could also be designated as an International Maritime Organisation Particularly Sensitive Sea Area.
Invasive Non-Native/ Alien Species
(Introduction of non-native species)
Inside site
, Throughout(>50%)
The potential risk of marine or terrestrial invasive species being introduced to the atoll (e.g. crazy ants, African landsnail, myna) is being addressed through the implementation of a biosecurity plan that includes strict measures to prevent such introductions. Work is ongoing to fully implement the plan and adapt efforts to changing conditions and any new threats identified.
A proposal to develop the nearby island of Assumption with a resort and to increase the level of tourism on the island, including development of the airstrip, significantly increases the risk of invasive species reaching the Atoll and having a potential devastating impact on the values. This will require a significant increase in the biosecurity programme for the Atoll, although given its remote nature the risk of unnoticed introductions is significant.
A proposal to develop the nearby island of Assumption with a resort and to increase the level of tourism on the island, including development of the airstrip, significantly increases the risk of invasive species reaching the Atoll and having a potential devastating impact on the values. This will require a significant increase in the biosecurity programme for the Atoll, although given its remote nature the risk of unnoticed introductions is significant.
Changes in Precipitation & Hydrological Regime
(Cyclones and coastal flooding, increase in extreme weather events)
Inside site
, Widespread(15-50%)
Seychelles is situated outside the cyclone belt in the Indian Ocean. However, as the global climate continues to change, sea water temperatures continue to rise, weather patterns across the wider region are likely to become more unstable, and other climate hazards, such as cyclones, may also pose a threat (State Party of Seychelles, 2021; Heron et al., 2021). In April 2017, cyclone Fantala destroyed infrastructure and vegetation on the island of Farquhar. Fantala was the strongest cyclone on record in the south-west Indian Ocean, matched only by cyclone Agnielle in November 1995. The damage to Farquhar was a stark reminder of the vulnerability of Seychelles’ outer islands. In 2016, a cyclone shelter was constructed on Aldabra to provide refuge to staff located on the island.
Changes in Physical & Chemical Regimes
(Sea level rise and ocean acidification)
Inside site
, Throughout(>50%)
Outside site
Sea level rise has the potential to directly impact the property and the values for which is was inscribed. A rise in the sea level could result in the loss of all low lying habitats around the atoll and this could result in a loss of critical habitats such as beaches, mudflats, mangroves, coastal grasslands, with implications for associated flora and fauna. While a recent study has indicated 61% of the shoreline of the atoll has remained unchanged over the past 51 years, localised changes to the shoreline were pronounced (Constance et al., 2024).
Marine organisms are highly susceptible to changes in ocean chemistry. The ocean currently absorbs approximately half of the CO2 produced by burning fossil fuel. When CO2 dissolves in seawater it forms carbonic acid, and as more CO2 is taken up by the ocean, the pH decreases becoming more acidic. Ocean pH has already decreased by about 30%; by 2100 it is predicted that ocean acidity will increase by about 150%. Such a monumental shift in basic ocean chemistry will have implications for ocean life, especially for those organisms that require calcium carbonate to build shells or skeletons. Ocean acidification thus poses a potentially high threat to many forms of marine life.
Marine organisms are highly susceptible to changes in ocean chemistry. The ocean currently absorbs approximately half of the CO2 produced by burning fossil fuel. When CO2 dissolves in seawater it forms carbonic acid, and as more CO2 is taken up by the ocean, the pH decreases becoming more acidic. Ocean pH has already decreased by about 30%; by 2100 it is predicted that ocean acidity will increase by about 150%. Such a monumental shift in basic ocean chemistry will have implications for ocean life, especially for those organisms that require calcium carbonate to build shells or skeletons. Ocean acidification thus poses a potentially high threat to many forms of marine life.
Recreational Activities
(Impact of tourism)
Inside site
, Localised(<5%)
Tourism interest in Aldabra has increased substantially since the cessation of pirate activity in the region. A number of cruise companies now visit Aldabra several times a year (State Party of Seychelles, 2021). Whilst this brings key finance to support the site, it also must be regulated to ensure minimal impact. In 2014-2017 new tourism regulations were implemented and monitored, these included reducing the areas accessible to tourists, especially the frigate bird colonies.
Involvement of stakeholders and rightsholders, including indigenous peoples and local communities, in decision-making processes
Seychelles Islands Foundation (SIF) runs various activities throughout the year to engage and inform Seychellois about Aldabra and the other World Heritage property managed by the organisation, the Vallee de Mai. SIF produces a monthly newsletter, runs a website, facebook, instagram, and twitter account. The outreach activities also include a school competition, the winners visiting Aldabra. SIF is once again planning to construct a building on Mahé, called Aldabra House. The building will serve as the SIF headquarters and as a visitor attraction featuring outdoor and indoor exhibits, displays and activities designed to recreate the magic of Aldabra (SIF, 2016a). In 2022/23 SIF ran a stakeholder engagement survey to gauge stakeholders opinions on various aspects of Aldabra management.
Legal framework
The Aldabra Atoll Special Reserve was declared under the National Parks and Nature Conservancy Act (1969). A review of the protected areas legislation resulted in the preparation of the Seychelles Protected Area Policy (2013), which stated that the current suite of legislation and regulations that directly or indirectly apply to protected area management are mostly out of date, incomplete and sometimes contradictory. This led to a process to update this legislation and resulted in the Nature Reserves and Conservancy Act, 2023 (Republic of Seychelles, 2025). In March 2020 the Seychelles Government announced an expansion of the marine protected area around Aldabra including a High Biodiversity Protection Area which has been gazetted under the original 1969 Act.
Governance arrangements
The property is managed by the Seychelles Island Foundation, which has a permanent office on Mahe. SIF is a non-profit charitable organisation that was established as a public trust by the government of Seychelles in 1979. SIF manages and protects Aldabra Atoll and the Vallée de Mai World Heritage site and has the President of Seychelles, Wavel Ramkalawan, as Patron. SIF is managed by a Board of Trustees of 15 members who are appointed by the President. This board represents individuals and organisations from both Seychelles and overseas who are concerned with the conservation of biodiversity and ecosystems, and bring relevant expertise and knowledge to the management of SIF. The manned research station on Aldabra ensures timely implementation of all monitoring and management decisions (SIF, 2016a). Management of the property is complicated given its isolation and the distance from the main Island of the Seychelles but the presence of permanent staff dedicated to management of the property helps address these challenges. The management framework for the property includes statutory considerations including the development of a management plan, protected area boundary, a suitable zoning scheme, appropriate regulations and policies, as well as human and financial resources (SIF, 2016a).
Integration into local, regional and national planning systems (including sea/landscape connectivity)
SIF, as the organisation responsible for the managerment of Aldabra, is an active partner in several national and regional planning programmes. SIF were active participants in the UNDP/GEF funded Protected Areas through NGO Modalities project. One component of that project explored the potential to expand the terrestrial and marine protected area boundaries to meet with CBD targets and the Seychelles government commitment to achieve 30% protection on land and in the sea. SIF was also actively participating in the follow on project, led by TNC to develop a Marine Spatial Plan for the Seychelles entire Exclusive Economic Zone (EEZ), which has been completed and included the expansion of the Aldabra MPA boundaries (Republic of the Seychelles, 2025). The implementation stage of the SMSP is now underway and Aldabra/SIF have been deeply involved in the development of a standardised management plan template.
Boundaries
The whole of Aldabra Atoll is included within the boundary of the site. An extension to the size of the protected area saw the marine protected area boundary extend to the approximate 3km depth contour line and increase the size of the protected area to 2,559.019 km². The proposed boundary extension for the MPA was approved by Cabinet and gazetted in December 2018 under the National Parks and Conservancy Act 1969.
Overlapping international designations
The boundary of Aldabra's RAMSAR designation includes the entire terrestrial area and lagoon as well as much of the fringing reef system. The focal point for the Convention on Wetlands of International Importance has been in occasional contact with the senior management of the Seychelles Islands Foundation (SIF), the organisation with the mandate to manage Aldabra Atoll, in order to be able to report on the implementation of the convention to its secretariat (State Party of Seychelles, 2021).
Implementation of World Heritage Committee decisions and recommendations
There is very little data to assess the implementation of committee decisions in regard to the property. A retrospective Statement of Outstanding Universal Value was agreed at the request of the committee and the only other decision relevant to the property was in reference to a boundary clarification. This request was responded to quickly and appropriately.
Climate action
The Climate Vulnerability Index (CVI) was assessed for Aldabra Atoll together with staff of the Seychelles Islands Foundation (Heron et al., 2021). The CVI process is a methodology to rapidly assess vulnerability through expert appraisal of the best-available climate science, applicable to all types of World Heritage properties (natural, cultural or mixed). Using the CVI Snapshot rapid assessment approach, the first phase of the CVI assessed the OUV Vulnerability. The analysis was conducted during three online sessions across several weeks in November and December 2021. Three key climate stressors were identified likely to impact the OUV of Aldabra Atoll as: Extreme temperature events; Drought (severity, duration, frequency); and Storm intensity and frequency.
Considering a high-emissions climate scenario (RCP8.5) and a timeframe for the analysis of ca. 2050, OUV Vulnerability was assessed as Moderate (on a three-point scale from Low to High), indicating that there is potential for some loss or alteration of some attributes that convey the OUV.
Given the majority of climate change impacts will originate from outside the site there is limited management actions that can be done within the site at this time, beyond establishing baselines and undertaking further monitoring for any impacts. The extensive monitoring system established for the values of the site will provide important indications of any changes, including those in response to climate impacts, and mitigation measures will allow to reduce the impact of climate change on the property. It is planned to develop a climate change adaption plan for the property (State Party of Seychelles, 2021).
Considering a high-emissions climate scenario (RCP8.5) and a timeframe for the analysis of ca. 2050, OUV Vulnerability was assessed as Moderate (on a three-point scale from Low to High), indicating that there is potential for some loss or alteration of some attributes that convey the OUV.
Given the majority of climate change impacts will originate from outside the site there is limited management actions that can be done within the site at this time, beyond establishing baselines and undertaking further monitoring for any impacts. The extensive monitoring system established for the values of the site will provide important indications of any changes, including those in response to climate impacts, and mitigation measures will allow to reduce the impact of climate change on the property. It is planned to develop a climate change adaption plan for the property (State Party of Seychelles, 2021).
Management plan and overall management system
The original management plan (Beaver and Gerlach, 1998) was replaced by an updated management plan in 2016 (SIF, 2016a). The 2016 plan covers 10 years, providing site managers with clear guidance on the key management strategies and identifies the priority actions needed to effectively manage and maintain values. As part of a national project in 2022 to develop a management plan template, SIF took the opportunity to conduct an in-depth management effectiveness assessment, gap-analysis and full review and revision of the Aldabra management plan. This was particularly important in light of the significant increase in the MPA size (Ernesta, 2018; TNC, 2020). The property has also taken part in Management Effectiveness projects and used MEE tools to develop and refine management processes (UNESCO, 2007).
Management of the property is complicated given its isolation and the distance from the main Island of the Seychelles but the presence of permanent staff dedicated to management of the property helps address these challenges. The property is managed by the Seychelles Islands Foundation, which has a permanent office on Mahe. The manned research station on Aldabra ensures timely implementation of all monitoring and management decisions (SIF, 2016a). The management framework for the property includes statutory considerations including the development of a management plan, protected area boundary, a suitable zoning scheme, appropriate regulations and policies, as well as human and financial resources (SIF, 2016a).
Management of the property is complicated given its isolation and the distance from the main Island of the Seychelles but the presence of permanent staff dedicated to management of the property helps address these challenges. The property is managed by the Seychelles Islands Foundation, which has a permanent office on Mahe. The manned research station on Aldabra ensures timely implementation of all monitoring and management decisions (SIF, 2016a). The management framework for the property includes statutory considerations including the development of a management plan, protected area boundary, a suitable zoning scheme, appropriate regulations and policies, as well as human and financial resources (SIF, 2016a).
Law enforcement
SIF have often partnered with the Seychelles Coast Guard, in particular to address the historic issues around piracy in the waters around Aldabra. This partnership has included periods with coast guard staff based on Aldabra on a full time basis as needed. In 2024 the partnership was formalized via an MoU and an additional staffing of coastguard on Aldabra, with review of Aldabra's new surveillance and enforcement plan by key coastguard staff. The ongoing challenge is resourcing surveillance and enforcement of the vast Aldabra MPA and the wider outer island protected area network.
Sustainable finance
Aldabra is situated 1000km from the inner islands of the Seychelles and basic operational costs (e.g. transferring staff, equipment and supplies) are therefore very high. Aldabra is part-financed by entrance fees for the SIF-managed UNESCO World Heritage site Vallée de Mai on Praslin and by external project funding. While the Vallée de Mai generates a substantial and fairly consistent income stream, project funding is much less predictable. The current funding situation for Aldabra remains adequate, but vulnerable (State Party of Seychelles, 2021). Funding is at least in part dependent on the number of international tourists visiting the Seychelles and the Vallée de Mai. An economic recession or adverse events that affect the Vallée de Mai (e.g. a fire or the COVID-19 outbreak) could jeopardize this source of income. The installation of a decentralized photo-voltaic system in 2012, in combination with a switch to energy-efficient appliances and a revised environmental management protocol, substantially reduced operational costs as the permanent research station is now 97% self-sufficient in its energy requirements (Quartz et al., 2013; SIF, 2019a). SIF has also prepared a sustainable financing plan as part of the management planning process (SIF, 2016a). One of the potential funding sources identified was Aldabra House, the visitor centre that SIF had planned to construct on Mahé. This project was cancelled initially due to impacts from high density development around the land earmarked for the centre but has now been resurrected. Another possible source of funding is landing fees for tourists to the atoll. The increase in tourism predicted due to the nearby development of Assomption Island may increase revenue, however, any increase in tourism comes with other impacts on the property.
Staff capacity, training and development
Human resources only partly meet the property’s management needs. Despite that no site based capacity building programme is in place, efforts are made to identify capacity building opportunities and staff are encouraged on a personal basis to further their education and engage in deepening their skills (State Party of Seychelles, 2021). For example, staff have been encouraged to participate in Massive Online Open Courses (MOOC's) including a course on biodiversity and climate change from the University of Zurich, providing university level information and mentorship by top level scientists. Staff members are encouraged to make presentations to other staff on topics of their choice, building their confidence in public speaking and expanding everyone's knowledge on the selected topics. One of the main problems that SIF encounters is that given the remote location of the atoll it can sometimes be difficult to retain staff. Although not ideal, establishing a rolling system of staff training is one way to address this issue and providing access to training courses when staff are back on Mahe would also assist. SIF have developed extensive and detailed protocols, along with training videos to ensure high quality and consistency in all aspects of the science programme. Recent database development, maintenance and data analysis frameworks has led to increased real-time data analysis on site. Multiple SIF staff have successfully pursued postgraduate degrees in ecology focusing on Aldabra as a direct result of SIF management support and mentorship.
Education and interpretation programmes
SIF has dedicated outreach staff that ensure a high visibility of Aldabra in the Seychelles’ society and beyond. The Visitor’s Centre at Vallée de Mai has improved people’s knowledge of the management link mentioned above. Since 2012, SIF has launched a monthly e-newsletter, a popular Facebook profile and a Twitter page, in addition to regular newspaper and magazine articles. All of these forums have helped to increase the visibility of Aldabra. In addition to this SIF runs a regular schools competition the winner of which gets to visit Aldabra (State Party of Seychelles, 2021). SIF had also developed plans for a large visitor centre on Mahe - Aldabra House. These plans were cancelled in 2019 due to infrastructure pressures on the land earmarked for the centre.
Tourism and visitation management
Aldabra Atoll has significant potential as an ecotourism destination. The designation of the Atoll as a World Heritage site has further enhanced the protected area’s marketability. Tourism on Aldabra is restricted to day-time visitors from boats mooring outside the reef of the research station and there are strict visitor protocols. When visiting the protected area, tourists can participate in wildlife viewing, snorkelling and SCUBA diving but must be accompanied and supervised by a staff member (State Party of Seychelles, 2021). The remoteness of the Atoll and the cost to get there have been the main factors limiting tourism development, as well as the threat of piracy between 2009 and 2013. Tourism has increased steadily since then, except the 2020/2021 lull due to Covid. With this increase in visitation and numbers comes increased potential for introducing other threats, such as increased damage to the coral reefs through indiscriminate anchoring, disturbance of the terrestrial flora and fauna, fishing, and the introduction of non-native species. The management plan provides guidance for site managers on how to mitigate these issues and ensure that site values are maintained (e.g. protocols for marine ecotourism). The Aldabra zoning plan restricts tourism activities to a very small area of the atoll, there is one anchoring location over sand, so no damage to coral reefs should take place. Sensitive frigatebird colonies are now fully-protected and there are strict rules for zodiacs inside the lagoon. The new biosecurity measures now implemented for all tourist vessels are stringent, with a biosecurity briefing to all passengers provided by SIF staff, plus a biosecurity video, followed by cleaning of shoes, bags and clothes and checks to all personnel and items going ashore.
Sustainable use
Subsistence fishing for Aldabra residents could easily cause localised depletion of targeted fish even though the numbers of staff based on the island is low (SIF, 2016a). Fishing activities have now been restricted to specific zones around the atoll (SIF, 2016a). The fishing activities are monitored by staff to help ensure that localised depletion does not occur. Collection and entry of subsistence fishery data has also recently been streamlined to enable site managers to respond more quickly to any concerns.
Monitoring
Terrestrial and marine monitoring programmes are carried out according to annual workplans and undertaken by staff based at the research station. Monitoring programmes cover key species, habitats and ecological processes on the land (e.g. flowering plant phenology, landbird and seabird nesting success) and in the sea (e.g. water quality, coral reef and associated fish species), as well as management-specific monitoring (e.g. invasive species). The long-term species monitoring programmes have been revised to ensure that they can accurately detect changes to the values of the site and address key management focused questions. The aim of the revision was to shift monitoring towards a more adaptive and responsive approach. This transition has been achieved through using new technologies, including the use of hand-held smart GPS devices with customized software (e.g. cybertracker) and applications for data visualization. These technologies are improving the ease of data management, as they streamline data collection and entry. A monitoring gap analysis was conducted in 2023, with new monitoring programmes in-development to fill these gaps for key ecological components and functions.
Research
SIF have long-term established collaborations with world-class research institutions on several aspects of the property and its values. These collaborations have been extremely productive both in terms of informing management but also peer reviewed articles. Recent publications include work on blue carbon (Wartman et al., 2025), seabirds (Appo et al., 2024a, 2024b, 2024c), impacts of climate change on the Aldabra shoreline (Constance et al., 2024), sea turtles (Mortimer et al., 2022, Pritchard et al., 2021, Richards et al., 2024, Sanchez et al., 2023, Sanchez et al., 2024a, 2024b), coral reefs (Burt et al., 2024), reef fishes (Koester et al., 2023), coconut crabs (Appo et al., 2021) and the Aldabra Giant Tortoise (Cilinger et al., 2022a, 2022b).
Effectiveness of management system and governance in addressing threats outside the site
The majority of threats to the property from outside the site are beyond the control of management of the site e.g. climate change and ocean pollution. As such there is little information available on the effectiveness of attempts to address these threats. Management of the property has undergone effectiveness assessments and the efforts to eradicate invasive bird species from the nearest neighbouring island of Assumption in order to prevent re-invasion of Aldabra are examples of the effective protection and management of threats outside the property. In 2019 SIF launched the Aldabra Clean-Up Project to shine a light on the issue of marine plastic pollution to the atoll, this project led to international news coverage (Sky News, 2019; State Party of Seychelles, 2021) and prompted increased attention of the issues from government, who then acceded to Annex 5 of the MARPOL Convention (Seychelles News Agency, 2019). Climate change poses a significant threat to the atoll and the renewed threat of invasive species linked to the approval of significant development on neighbouring Assumption Island will likely mean an increased investment in biosecurity. SIF are now planning for the eradication of rats and cats, which, if successful will have a number of positive cascading impacts outside of the site.
Effectiveness of management system and governance in addressing threats inside the site
The management system and governance arrangements for the site have been highly effective at addressing threats inside the site. Key threats including invasive species have been and continue to be addressed through admirable efforts and investment. The significant future threat posed by climate change means efforts to address threats inside the site are even more important, but threats from inside the site are relatively few given the isolation of the site and the low levels of human habitation. Significant efforts have been made to reduce the impacts of humans on the atoll with the transition to renewable energy systems and the removal of waste from the atoll. These efforts have helped to ensure minimal impacts from the residents whose presence is required for the effective management of the site.
SIF's management of Aldabra is extremely professional. Despite the atoll's remote location the site is well protected, legally and in practice. Protection of the marine areas around the atoll has improved in recent years including efforts to expand the marine protected area and partnerships with the Seychelles Coast Guard to address illegal activities within the waters of the property. In addition, monitoring programmes have been revised and new technologies introduced to allow site managers to track progress and respond more quickly to any new concerns as they emerge. A biosecurity plan and an up to date management plan, which includes a sustainable financing plan is in place. These documents provide the updated guidance needed to help SIF prioritize their activities to manage site values and ensure their conservation. The successful management of the property was acknowledged in 2019 when Aldabra was recognised as an outstanding marine protected area with a Blue Park designation by the Marine Conservation Institute. Nevertheless, while the Vallée de Mai generates a substantial and fairly consistent income stream, project funding is much less predictable. The current funding situation for Aldabra remains adequate, but vulnerable.
Good practice examples
The effective eradication of invasive alien species from Aldabra and the nearest neighbouring island of Assumption is an example of best practice. The efforts put into habitat mapping and the upgrading of the monitoring programmes, particularly the use of new technologies to streamline data management process are another example of best practice along side overall management of a property that is isolated and as a result presents complicated logistical and financial challenges.
Geomorphology
Good
Trend
Stable
Terrestrial (including categories for limestone areas, beaches, and freshwater pools), lagoon and forereef habitats (Hamylton et. al., 2018a; 2018b) have been mapped. These maps can be used to assess, e.g. seabed disturbance, land degradation, coastal erosion. A recent study has shown that over the past 51 years, on average Aldabra's shoreline has remained unchanged when compared to global atoll rates of change (Constance et al. 2024).
Terrestrial vegetation
Low Concern
Trend
Stable
Vegetation mapping has indicated no significant change in the area of Aldabra’s terrestrial vegetation (Walton, 2015). There are still some invasive species present although intensive efforts have seen the previously most predominant invasive species, sisal, eradicated from the atoll (Bunbury & van Dither, 2019). The eradication of goats in 2012 will likely have improved grazing conditions for giant tortoises.
Freshwater and brackish pools
Low Concern
Trend
Data Deficient
No trend data available but habitat maps which include freshwater pools as a category, can be used for future comparisons. Changes in rainfall and periods of drought may impact on these pools in the future. New satellite imagery is being commissioned in 2025 to map pool dynamics across seasons. Endemic red shrimps, especially on Picard Island, are found in some of the pools.
Sand beaches
Low Concern
Trend
Deteriorating
Sand beaches are impacted by marine litter and there is some evidence of erosion. Although erosion and accretion is part of a natural process, this may increase with climate change and changes in weather patterns. Coral mortality following bleaching events may contribute to beach erosion and beaches are also susceptible to changing sea levels. Habitat mapping will help to assess and quantify long-term trends.
Intertidal mudflats
Good
Trend
Stable
In good condition and apparently stable: habitat maps can be used for future comparisons; populations of wading birds that use this habitat are stable (SIF, unpublished data, 2016).
Mangrove communities
Good
Trend
Stable
A 2016 study showed that Aldabra’s mangrove communities have been stable and even increased slightly in the last 15 years (Constance, 2016).
Seagrass and macroalgal communities
Good
Trend
Stable
Seagrass beds and macroalgal communities appear to be stable (SIF marine monitoring programme, unpublished data, 2016). A recent national seagrass mapping exercise estimates Aldabra to have 3,495 ha of seagrass (Rowlands et al. 2024). There is seasonal variability which may need to be accounted for in the future.
Coral communities
High Concern
Trend
Improving
The 2016 bleaching event caused a substantial and widespread decline in hard and soft coral cover and is now being monitored for recovery (SIF marine monitoring programme, unpublished data, 2017; Cerutti et al, 2020). Mean hard coral cover across all sites and depths continues to increase following the 2016 bleaching event (SIF, Unpublished data, 2020). The bleaching caused an overall reduction in relative hard coral cover of 54% with substantial variation across sites (14–73% reduction). By early 2022, six years post-bleaching, hard coral cover at these sites reached 43–107% of the pre-bleaching cover. This highlights that live coral recovery (one component of ecosystem resilience) varied across sites. Findings showed that seven of the eight assessed seaward reefs at Aldabra displayed the resilience expected of a remote, well-managed marine reserve between 2016-2022 (Burt et al. 2025). However, additional bleaching has occurred at Aldabra in 2024 and 2025, indicating the shrinking windows for recovery between coral mortality events.
Marine water quality
Low Concern
Trend
Stable
Marine monitoring programme indicates conditions are stable (SIF marine monitoring programme, unpublished data, 2016).
Aldabra giant tortoises
Good
Trend
Stable
Aldabra hosts the largest extant population of giant tortoises worldwide (~150,000 animals, with recent research suggesting that the population is higher than all former estimates; in prep). Long-term monitoring data published in 2015 show that Aldabra giant tortoise populations in the last 15 years are highly stable (Turnbull et al., 2015).
Landbirds
Good
Trend
Improving
A paper published in 2015 by SIF staff showed that most endemic/native landbird species and sub-species are increasing in abundance, with one species (the Aldabra drongo) showing a stable trend (van de Crommenacker et al., 2015a). The Aldabra rail has expanded its re-introduced population size on Picard island to greater than the predicted carrying capacity on the island (Sur et al, 2013b). Genetic research has confirmed the Aldabra fody as a distinct species (van de Crommenacker et al., 2015b). A planned eradication of rats and cats on the islands would significantly increase populations for many bird species on Aldabra.
Other terrestrial fauna
Data Deficient
Trend
Data Deficient
Aldabra’s coconut crab Birgus latro population is stable but no trend data is available for other terrestrial invertebrate species including insects, molluscs, and crustaceans (SIF, unpublished data, 2016). New monitoring programmes are being implemented now to cover these fauna groups.
Sea and shorebirds
Good
Trend
Stable
Annual frigatebird census indicates stable or increasing numbers of both species (with substantial year-to year fluctuation); Tropicbird nest monitoring shows no decline in numbers of nest activity between 2009–2016, although nesting success is among the lowest recorded for the species (Burt et al. 2021). A red-footed boobie census in 2022/23 indicates a population of 22,628 breeding pairs (SIF, internal report). Wading bird populations are seasonal but stable (SIF, unpublished data, 2016).
Marine turtles
Good
Trend
Improving
Published data to 2008 showed a 500-800% increase in nesting green turtles over a 40-year period (Mortimer et al., 2011). Numbers of these turtles have continued to increase at the same rate since then (Pritchard, 2022).
Marine mammals
Low Concern
Trend
Improving
Aldabra’s dugong population appears to be larger than initially thought, with at least 23 individual animals counted in a 2022/23 survey of the lagoon (SIF, unpublished data, 2024). Several observations of female dugongs with juveniles in Aldabra’s lagoon suggest that the site plays an important regional role as a dugong breeding/nursery area (SIF Newsletter August 2016). The importance of the area for marine mammals was recognised with Aldabra being listed as an Important Marine Mammal Area (IMMA) in December 2019 (SIF, 2020).
Fishes
Good
Trend
Improving
Results of the marine monitoring programme indicate that fish abundances are increasing (SIF marine monitoring programme, unpublished data). Despite the current resilience of Aldabra’s fish communities, future health is threatened by climate change impacts on fish biomass and community structure as well as increasing poaching activity (Burt et al. 2025).
Marine invertebrates (other)
Data Deficient
Trend
Data Deficient
Marine monitoring programmes and biodiversity survey needed to increase knowledge of other marine invertebrates.
Assessment of the current state and trend of World Heritage values
Stable
The terrestrial and marine monitoring programmes are showing that most habitats and species are generally in a good condition, and that populations of endemic or threatened species are either stable or improving. While the ecological integrity of the whole site is good and appears to be stable, there are differences in current state and trend of marine and terrestrial components of the site. Invasive mammals continue to pose the greatest threat to the status of terrestrial fauna. The high sea water temperatures and coral bleaching and mortality that happened in the past few years, have degraded the condition of the coral reef. Aldabra's coral reef is however recovering from past events quicker than in other areas that are subject to other pressures (e.g. overfishing and pollution). Climate variability and change currently pose the greatest threat to marine ecosystems and the frequency of similar coral bleaching events is likely to increase in future years.
Additional information
Importance for research
Aldabra provides a near-natural coral atoll laboratory, where terrestrial and marine components of atoll ecosystems and associated biodiversity can be studied in the absence of many of the factors that can so often otherwise obscure long term ecological trends (e.g. coastal development and other human uses, as well as pollution, etc). The protection of Aldabra has already provided significant benefits in terms of furthering knowledge related to the management of endemic species and research into the methods to control invasive species. Knowledge gained from existing programmes and the lessons learnt can be used to inform conservation, rehabilitation and restoration efforts on other islands and atolls around the world. The turtle monitoring programme, along with monitoring of other marine species, is contributing to regional knowledge of species movements and conservation (Sanchez et al., 2020). Aldabra could further expand this globally important role by developing programmes to detect changes in the marine and terrestrial island ecosystems that may already be happening in relation to climate change, and to track the substantial impacts of the eventual eradication of rats and cats.
Aldabra is a near-natural atoll laboratory, where research into and monitoring of the terrestrial and marine components can be conducted in the absence of many of the common pressures found elsewhere that can otherwise obscure long term ecological trends. The management of Aldabra provides an excellent case study in itself, particular the monitoring programmes, which are designed to provided managers with the information needed to allow them to respond should circumstances change while also supporting scientific research. These programmes enable adaptive and responsive management, which is particularly critical in a remote location like Aldabra, but are also directly relevant for other protected areas globally.
| № | Organization | Brief description of Active Projects | Website |
|---|---|---|---|
| 1 | Seychelles Islands Foundation | Indian Ocean Commission and European Union funded project to improve biosecurity measures for Aldabra, entitled, ‘Institutionalisation and implementation of biosecurity measures to ensure sustainable conservation management of biodiversity on Aldabra Atoll’. |
https://sif.sc/major-projects
|
| 2 | Oxford University and SIF - Aldabra Clean-up Project | Aldabra clean-up project, launched in 2018 and concluded in 2019. Results from the project will be included in a PhD thesis at Oxford by April Burt. Partners hope this project will lead to an even bigger clean up initiative. The focus of the project was to remove marine litter from remote locations on the Atoll. Funding sources were diverse, including crowd-funding, SIF support and private sources. |
https://aldabracleanupproject.wordpress.com/
https://www.queens.ox.ac.uk/news/aldabra-clean-project-gets-underway
|
| 3 | Seychelles Islands Foundation (SIF) | Aldabra House is an SIF project to establish a visitor and education centre on Mahe to enable more people to experience and learn about Aldabra. The project was cancelled in 2019 but resurrected in 2022. |
http://www.seychellesnewsagency.com/articles/20570/Seychelles+to+have+new+research+station+on+Aldabra+Atoll+and+%22AldabraHouse%22+on+Mahe
|
| 4 | SeyCCAT - Seychelles Conservation and Climate Adaptation Trust, SIF | The primary objective of this project is to safeguard the continuation of the Aldabra Reef Monitoring Programme for the next decade. This involves in-depth surveys of coral reef benthic and fish communities both in the outer reefs and lagoon sites of Aldabra. By ensuring that there is no data loss due to equipment failure, the project seeks to maintain the integrity and effectiveness of monitoring efforts, enabling the team to track the health and dynamics of Aldabra's coral communities accurately, particularly following the fourth global coral bleaching event. | |
| 5 | CEPF - Critical Ecosystems Partnership Fund, SIF | Invasive alien species, such as rats and cats, have significant negative impacts on island ecosystems. The severe degradation of ecosystems by invasive mammals reduces the ability of these ecosystems to adapt to and recover from the impacts of climate change. Eradication of invasive mammals from islands is therefore a crucial nature-based solution to boost ecosystem-based adaptation to the impacts of climate change. The success of mammal eradication efforts depends on extensive site-specific monitoring to inform the eradication strategy and methods. Under this project SIF will conduct an extensive three-year feasibility study to prepare for rat and cat eradication on Aldabra Atoll. |
https://www.sif.sc/major-projects
|
| 6 | SeyCCAT’s Blue Grant Fund #5; SIF | Dugongs (Dugon dugon) are marine mammals and are listed as Vulnerable to extinction on the IUCN Red List due to direct and indirect human influences on them (habitat loss, entanglement in fishing gear, illegal hunting, etc). Historically in Seychelles, dugongs occurred in large numbers, commonly sighted at Ile aux Vaches (now referred to as Bird Island). However, their numbers and occurrences diminished due to the population’s heavy exploitation for meat and oil. In 2001, they made a comeback and were spotted around Aldabra, and ever since, the Aldabra team have had several sightings of these special animals. Currently, Aldabra is the only known location in Seychelles that has had several sightings of dugongs over the years. The project aims to create a solid knowledge base of Seychelles’ last known dugong population through the first comprehensive aerial survey using unmanned aerial vehicles (UAV). |
https://www.sif.sc/major-projects
|
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