Publications
Spatial organisation and functional composition of benthic reef assemblages across a depth gradient in western Aldabra Atoll
Aldabra Atoll's western seaward reefs exhibit a resilient, post-disturbance state dominated by stress-tolerant massive corals, with spatial organization shifting deterministically from shallow aggregated frameworks to deeper fragmented nucleated patches. This study, using 300 high-resolution video-still quadrats across two depth contours (8 m and 15 m), revealed that environmental filtering, rather than stochastic neutral drift, drives post-bleaching recovery. Multivariate dispersion analysis highlighted increased patchiness with depth, while statistical niche modeling confirmed substrate stability as a physical bottleneck, with Isopora spp. thriving on rock pavement and Goniopora spp. dominating mobile rubble. These findings underscore the role of niche-driven processes in shaping benthic community structure following climate-induced disturbances.
Assessing blue carbon in mangrove ecosystems of Seychelles
Seychelles' mangrove ecosystems store approximately 2.5 million tonnes of carbon dioxide equivalent (CO₂e), with Aldabra Atoll, a UNESCO World Heritage and Ramsar site, holding the highest carbon stocks at 67% of the country's total. This first blue carbon assessment for Seychelles reveals that soils account for 70% of these stocks, despite a shallow organic layer due to limestone dominance. The study highlights the critical role of mangroves in climate mitigation and adaptation, particularly for Small Island Developing States vulnerable to climate change impacts like sea level rise and cyclones. Field data underscores their potential to support Seychelles' Nationally Determined Contributions (NDCs) commitments, with 85% of its 2195 hectares of mangroves already protected.
Centipedes (Myriapoda, Chilopoda) of Aldabra Atoll (Seychelles)
Aldabra Atoll hosts a unique centipede fauna comprising 12 species, with affinities primarily traced to East Africa and the Western Indian Ocean. This is the first comprehensive checklist of Aldabran centipedes, including newly identified species such as Lamyctes tristani and Scolopendra morsitans, alongside revisions to taxonomic classifications. Notably, the study designates Hovanyx and Mixophilus as junior synonyms of Tuoba, while questioning the validity of Cryptops daszaki based on type material examination. The research leverages historical Royal Society survey data (1968–1975) to document morphological variation and infer biogeographical origins, contributing critical insights into the island's myriapod diversity.
Disentangling the gut microbiota of Aldabra giant tortoises of different ages and environments
The gut microbiota of Aldabra giant tortoises is primarily shaped by environment rather than age, with wild tortoises exhibiting greater microbial diversity due to varied diets. A study analyzing 52 fecal samples from Seychelles and Italy revealed that geolocation significantly influences microbiota composition, while age had a lesser impact. Certain bacterial families, such as Spirochaetota and Fibrobacterota, were more prevalent in environments with higher fiber intake, reflecting dietary differences. Additionally, some bacteria were specific to individuals on Curieuse Island but not elsewhere. Centenarian tortoises showed reduced microbial complexity compared to younger adults. These findings highlight the importance of environmental factors in gut microbiota diversity and can inform conservation strategies for this long-lived species.
Red-footed booby population thriving at globally significant Aldabra Atoll: insights from unmanned aerial vehicle surveys
Aldabra Atoll hosts the world's most significant red-footed booby colony, with populations surging to at least 45,817 breeding pairs by 2023—a dramatic increase from previous estimates. Traditional boat surveys revealed 36,720 pairs, but unmanned aerial vehicle (UAV) surveys uncovered an additional 5,574 inland breeding pairs, previously undocumented. This breakthrough highlights the atoll's global importance for seabird conservation and demonstrates UAVs as a powerful tool for monitoring low-lying mangrove colonies. The study suggests earlier population counts may have been underestimated, underscoring Aldabra’s critical role in sustaining this threatened species in the Indian Ocean.
Supporting resilience-based coral reef management using broadscale threshold approaches
Aldabra Atoll, a remote marine protected area (MPA) in the western Indian Ocean, demonstrates high coral reef resilience comparable to well-managed MPAs. A study assessing reef condition against broadscale ecological thresholds—including structural complexity, fish biomass, and juvenile coral density—found that seven of eight seaward reefs met or exceeded expected resilience levels even after the 2016 mass bleaching event, with minimal impact from nearby research activities. The findings support the use of broadscale thresholds for resilience-based management, particularly in data-limited regions, while also highlighting the need to expand threshold categories and incorporate site-specific factors for more nuanced assessments.
A new species of Synalpheus Spence Bate, 1888 (Caridea: Alpheidae) from Aldabra
A new species of the snapping shrimp genus Synalpheus, named S. calypso, has been discovered from Aldabra Atoll, a UNESCO World Heritage Site in the Seychelles. This discovery was made using specimens collected during Cousteau's 1954 expedition to Aldabra aboard the vessel Calypso. The new species is distinguished by unique morphological features such as densely arranged, distally-curved setae on its minor cheliped dactylus and specific characteristics of its basicerite, major cheliped merus, pleuron, and telson. These traits differentiate S. calypso from other Indo-West Pacific species, particularly S. spongicola, with which it shares similarities as a sponge-dweller. The study highlights the morphological diversity within this genus and contributes to our understanding of its evolutionary adaptations.
Blueprint for Blue Carbon: Lessons from Seychelles for Small Island States
Seychelles' blue carbon ecosystems, including mangroves and seagrasses, hold significant potential for climate change mitigation as small island developing states (SIDS) seek to leverage nature-based solutions. Dominated by mangroves (2195 ha, 80% in Aldabra Atoll) and extensive seagrass beds (142,065 ha), these ecosystems could contribute substantially to national climate commitments while providing multiple ecosystem services. However, threats such as rising sea levels, coastal squeeze, erosion, severe storms, and human activities pose risks to their stability. The study highlights the need for robust carbon inventories, continuous monitoring, and policy frameworks to ensure accurate accounting, sustainable financing, and long-term protection. Insights from Seychelles offer a blueprint for SIDS to integrate blue carbon into climate strategies while addressing challenges related to ownership rights, certification, and market dynamics post-COP27.
Evidence for seasonal shift in the reproduction of Aldabra giant tortoises (Aldabrachelys gigantea) in managed care in the Northern hemisphere compared to the natural habitat in the Southern hemisphere
Aldabra giant tortoises (Aldabrachelys gigantea) exhibit a seasonal shift in reproduction when moved from their natural habitat on Aldabra Atoll to managed care in the Northern Hemisphere, leading to suboptimal reproductive output. The study found that while mating behavior was not a limiting factor, lack of ovulation and subsequent follicular atresia were the primary reasons for reduced fecundity. This suggests that temperature conditions and the temporal alignment of external triggers like photoperiod are critical for successful reproduction in ex situ settings. Researchers analyzed hormone patterns, follicular development, and mating behavior in four sexually mature tortoises under controlled conditions, comparing them with wild individuals in their native habitat. The findings highlight the complex interplay between intrinsic and extrinsic factors in reptile reproduction and underscore the challenges of sustainable ex situ management for seasonally reproducing species.
Exploring Aeromonas dhakensis in Aldabra giant tortoises: a debut report and genetic characterization
Aeromonas dhakensis (A. dhakensis), an emerging pathogen with global significance, has been identified for the first time in Aldabra giant tortoises, expanding its known host spectrum. The study, led by Zhao et al., isolated a strain (HN-1) from a deceased tortoise and characterized it using clinical observation, MALDI-TOF/MS, and gene sequencing. The strain exhibited seven virulence genes and caused severe hemorrhage in mice, with an LD50 of 2.05 × 10^7 CFU/mL. It also showed resistance to multiple antibiotics, including amoxicillin and penicillin. These findings highlight the potential threat of A. dhakensis to both wildlife and human health, underscoring the need for One Health surveillance and further research to mitigate its spread across environments.
Fine-scale foraging ecology and habitat use of sympatric green and hawksbill turtles in the Western Indian ocean
Green and hawksbill turtles at Aldabra Atoll exhibit distinct foraging ecologies with minimal niche overlap, highlighting the ecological importance of seagrass and mangrove habitats. Stable isotope analysis revealed that green turtles primarily consume seagrass and brown algae, while hawksbills focus on mangroves and invertebrates. A dietary shift in green turtles was observed with size, suggesting age-related changes in foraging behavior. The study also found evidence of small-scale foraging site fidelity, indicating that turtle tissues reflect site-specific prey consumption. This research underscores the unique role of these species in controlling algal biomass at Aldabra, a relatively undisturbed atoll in the Seychelles, and provides the first detailed examination of their foraging ecology in the Western Indian Ocean.
Low average shoreline change rate in 51 years on the raised Aldabra Atoll
Aldabra Atoll, a raised atoll and UNESCO World Heritage Site in the Indian Ocean, has demonstrated remarkable resilience to sea level rise over 51 years. Despite regional sea level increases of 2–3 mm per year, 61% of its shoreline remained unchanged, while only 24% experienced low average change rates of 0.25 ± 0.36 meters per year—significantly lower than global atoll averages. Accretion and erosion were nearly balanced, affecting similar percentages (12%) of the shoreline, though localized changes included notable transformations like a sandy beach converting to mangrove habitat over 214 meters. Erosion impacted critical turtle nesting sites and the research station, while the lagoon shoreline showed more rapid changes than the ocean shoreline, particularly in areas exposed to wind and waves. The study, using aerial and satellite imagery analyzed via Digital Shoreline Analysis System, suggests that Aldabra’s adaptive capacity is comparable to other Indo-Pacific atolls, emphasizing the need for ongoing monitoring to inform conservation strategies and minimize local impacts on sediment dynamics.
Post-nesting migrations of green turtles from Aldabra Atoll, Seychelles: satellite tracking, flipper tag returns and marine protected areas
Post-nesting green turtles from Aldabra Atoll, a UNESCO World Heritage site and one of the largest nesting populations of Chelonia mydas in the Western Indian Ocean, migrate along distinct routes to widely dispersed foraging sites across Tanzania, Madagascar, Somalia, Kenya, Mozambique, and Seychelles. Satellite tracking of 21 turtles (2011-2014 and 2022) revealed that over 40% of their final locations were within or near marine protected areas (MPAs), while 57.9% passed through MPAs post-nesting. This highlights the critical role of existing MPAs in protecting migratory corridors but also underscores the need to expand these areas to enhance connectivity and conservation efforts. The study, combining satellite tracking with historical flipper tag data, expanded known foraging destinations, particularly in remote or less-reported regions like Somalia and northern Madagascar, emphasizing the importance of pooling multi-source data for targeted conservation strategies.
Regional foraging areas of green turtles (Chelonia mydas) nesting at Aldabra Atoll: insights from stable isotopes and satellite telemetry
Green turtles nesting at Aldabra Atoll primarily forage along the East African coast (Tanzania and Somalia) or northern Madagascar, according to stable isotope analysis and satellite telemetry. This study, combining isotopic data from 90 turtles with nine satellite tracks, identified these two key foraging areas, revealing complex migration patterns in the Western Indian Ocean. While latitudinal isotopic patterns were absent, longitudinal variations in δ13C and δ15N were observed, offering new insights into turtle foraging ecology. The research highlights both the potential and limitations of stable isotope analysis for characterizing coastal foraging habitats under human pressure.
Seabird nutrient subsidy alters size and resource use of functionally important mangrove macroinvertebrates
Seabird-derived nutrient enrichment significantly alters the size and resource use of mangrove macroinvertebrates at Aldabra Atoll, potentially enhancing mangrove ecosystem services. The study found that seabird guano increased nitrogen content in basal food sources and herbivorous littorinid gastropods and sesarmid crabs, leading to larger mean carapace widths (6–11% increase) in these species compared to non-seabird sites. Isotopic analysis revealed a shift in resource contributions, with seabird sites showing higher reliance on epiphytic macroalgae and guano (>50%) versus mangrove leaves and sediment organic matter at non-seabird sites. These findings suggest that seabird nutrient subsidies can modify trophic interactions, benefiting mangrove crab fisheries and ecosystem resilience.
Small-scale movements and site fidelity of two sympatric sea turtle species at a remote atoll
Aldabra Atoll serves as a critical study area for understanding the movement and site fidelity of immature green and hawksbill sea turtles. Analysis of long-term capture–mark–recapture (CMR) data from 1981 to 2021 reveals that green turtles exhibit lower site fidelity compared to hawksbill turtles, with some sites showing avoidance behavior. This behavior is not correlated with season or turtle size and varies between species, indicating distinct ecological roles. The study highlights the potential of CMR methods for detecting fine-scale movement patterns but underscores the need for further research into habitat characteristics to fully understand these behaviors.
Ancient DNA elucidates the lost world of western Indian Ocean giant tortoises and reveals a new extinct species from Madagascar
A new extinct species of giant tortoise from Madagascar, previously unknown to science, has been identified using ancient DNA analysis. This discovery sheds light on the lost biodiversity of the western Indian Ocean, revealing a complex history of colonization and extinction. Researchers combined ancient DNA, phylogenetic, ancestral range, and molecular clock analyses with radiocarbon and paleogeographic evidence to trace the evolutionary journey of these tortoises. Findings indicate that the ancestor of extinct Mascarene tortoises dispersed from Africa in the Eocene, colonizing now-sunken islands northeast of Madagascar before spreading to the Mascarenes. Another dispersal event in the latest Eocene/Oligocene led to the evolution of giant, large, and small tortoise species on Madagascar, with two giants and one large species disappearing around 1000 to 600 years ago. The study also traces the colonization of the Granitic Seychelles from Madagascar in the Early Pliocene and Aldabra from the Seychelles in the Late Pleistocene, highlighting the impact of human activity on these populations.
Differences in foraging range between white-tailed tropicbirds breeding on inner and outer Seychelles islands
A new study reveals significant differences in foraging behavior between white-tailed tropicbirds breeding on Aride Island (inner Seychelles) and Aldabra Atoll (outer Seychelles), with birds from Aride traveling twice as far (231 km vs. 105 km). The research, the first to track these seabirds' movements, found that both populations forage beyond protected zones and show variation between incubation, chick-rearing stages, and sexes. Habitat modeling suggests a preference for deep waters, possibly influenced by human activities. This groundbreaking insight into white-tailed tropicbird ecology in the Western Indian Ocean provides critical data for conservation efforts.
Growth rate and projected age at sexual maturity for immature hawksbill turtles and green turtles foraging in the remote marine protected area of Aldabra Atoll, Seychelles
A 40-year study at Aldabra Atoll reveals significant insights into the growth rates and projected ages at sexual maturity for immature green turtles (Chelonia mydas) and hawksbill turtles (Eretmochelys imbricata). Analyzing capture-mark-recapture data from 1981 to 2021, researchers found that green turtles exhibit a mean annual growth rate of 3.2 cm/year, with the highest growth in larger size classes (50–69.9 cm), while hawksbill turtles show a non-monotonic growth pattern, peaking in the same size class but declining in the largest (70–79.9 cm). The study suggests that both species may spend over 8 and 18 years, respectively, foraging at Aldabra. These findings underscore the importance of long-term monitoring for understanding population dynamics in remote marine protected areas.
Impacts of coral bleaching on reef fish abundance, biomass and assemblage structure at remote Aldabra Atoll, Seychelles: insights from two survey methods
Aldabra Atoll, a remote UNESCO World Heritage Site, experienced a 50% coral mortality due to the 2015/16 bleaching event. Research revealed contrasting impacts on reef fish communities depending on survey methods used. Indicator surveys showed no significant change in fish abundance or biomass post-bleaching, with increases mainly driven by herbivores and omnivores responding to elevated turf algae cover. However, extended surveys detected a 55–60% reduction in overall fish abundance and a 69% decrease in biomass on shallow reefs, highlighting the importance of comprehensive survey methods to capture ecological responses. Multivariate analysis confirmed immediate and lasting shifts in community composition, primarily affecting herbivorous, omnivorous, and piscivorous taxa. This study underscores the value of diverse survey techniques in understanding the delayed and nuanced impacts of coral bleaching on reef ecosystems.
Marked differences in foraging area use and susceptibility to predation between two closely-related tropical seabirds
Two closely-related tropical seabirds, the white-tailed and red-tailed tropicbirds, exhibit complete spatial segregation in their foraging areas despite similar behaviors at sea. This finding challenges ecological theories on niche partitioning among sympatric species, particularly in resource-poor tropical environments like Aldabra Atoll. Using GPS, immersion, depth, and accelerometry loggers, researchers tracked the birds' movements and revealed that red-tailed tropicbirds forage further and in different areas than white-tailed tropicbirds. Additionally, nest predation by both native avian predators and invasive rats drives population declines, with each species targeted differently. The study underscores the need for large-scale marine protection around tropical seabird colonies and highlights the importance of rat eradication and potential measures to protect nests from native predators.
Chromosome-level genome assembly for the Aldabra giant tortoise enables insights into the genetic health of a threatened population
Researchers have generated the first chromosome-level genome assembly for the Aldabra giant tortoise (Aldabrachelys gigantea), providing critical insights into the genetic health of a vulnerable species. This high-quality assembly, spanning 2.37 billion base pairs and resolving into 26 chromosomes, enables comprehensive genomic studies. By analyzing low-coverage whole-genome resequencing data from 30 wild individuals and two zoo-housed tortoises, the study revealed genetic population structure in the wild and traced the geographic origins of ex situ individuals. The findings highlight the utility of advanced genomic tools for conservation efforts, including genetic diversity management and rewilding initiatives. Additionally, the assembly identifies putatively deleterious mutations that warrant monitoring to ensure the long-term survival of this endangered species.
DNA- and RNA-based bacterial communities and geochemical zonation under changing sediment porewater dynamics on the Aldabra Atoll
Aldabra Atoll's pristine carbonate sediments reveal distinct bacterial community shifts driven by geochemical zonation, contradicting initial expectations. Research found that while diversity decreases with depth, the lagoon's bacterial composition transitions from Pseudomonas-dominated sand to a complex mix of sulfate reducers (e.g., Desulfovibrio), sulfur oxidizers (Arcobacteraceae), and photo(hetero)trophs (Cyanobacteria) in anaerobic mud. Unexpectedly, deeper sediments showed high abundances of Halomonas or Alphaproteobacteria, linked to increased salinity and organic matter complexity. The study used 16S rRNA gene and transcript analysis to differentiate between live and dead bacterial populations, providing insights into sediment porewater dynamics under changing conditions.
Long-term changes in adult size of green turtles at Aldabra Atoll and implications for clutch size, sexual dimorphism and growth rates
Green turtle populations worldwide have faced declines in mean nesting size, raising concerns about reduced reproductive output. However, a 21-year study at Aldabra Atoll reveals that despite a slight decline in the curved carapace length of nesting females—from 111.43 cm to 110.08 cm over two decades—the total number of eggs produced annually increased from 1.3 million to 2.0 million, offsetting potential impacts on clutch size. The study analyzed over 4,500 individual measurements and found a mean growth rate of 0.14 cm per year for 391 recaptured turtles. Sexual dimorphism was also documented, with females consistently larger than males in carapace length (ratio: 1.09), width (1.10), and weight (1.25). These findings suggest that while adult size may decrease over time, compensatory increases in nesting numbers can sustain reproductive output.
Low‐coverage reduced representation sequencing reveals subtle within‐island genetic structure in Aldabra giant tortoises
Aldabra giant tortoises, one of the world's last two surviving giant tortoise species, exhibit subtle within-island genetic structure despite their large population size and apparent panmixia. Using low-coverage double-digest restriction-associated DNA (ddRAD) sequencing, researchers analyzed 33 tortoises from Aldabra Atoll's main islands, identifying 5426 variant sites that revealed no inter-island differentiation but subtle within-island structure. This unexpected finding underscores the importance of high-resolution genetic markers in conservation efforts, even for seemingly homogeneous populations. The study also demonstrates that low-coverage ddRAD sequencing offers a cost-effective alternative for conservation genomic projects involving non-model species with large genomes.
Soil nutrient content and water level variation drive mangrove forest aboveground biomass in the lagoonal ecosystem of Aldabra Atoll
Aldabra Atoll's lagoonal mangrove ecosystem stores approximately 66,100 Mg of carbon in standing biomass, with soil nutrient content and water level variation being key drivers of mangrove aboveground biomass (AGB). The study estimated a mean AGB of 82 ± 13 Mg ha−1 across 54 plots, totaling nearly 140,600 Mg for the mangrove area. Using a structural equation model, researchers found that soil nutrient content had the greatest influence on AGB variation, while high water level variation indirectly increased AGB by enhancing nutrient availability. These findings underscore the importance of nutrient cycling and hydrological processes in lagoonal mangrove conservation, offering insights for global mangrove protection strategies.
Complete Chloroplast Genome Variants Reveal Discrete Long-Distance Dispersal Routes of Rhizophora in the Western Indian Ocean
Research on Rhizophora mangroves in the Western Indian Ocean (WIO) reveals distinct long-distance dispersal routes shaped by ocean currents and historical migration events. Using chloroplast genome analysis, scientists identified three major haplogroups of Rhizophora mucronata, with haplogroup A showing ancient origins in the Seychelles and eastern Madagascar, while haplogroup B indicates a recent expansion from northern Madagascar toward the African mainland. Haplogroup C, found south of Delagoa Bight, suggests a unique bottleneck dispersal event. The study also highlights spatial haplotype diversity at Aldabra Atoll, with nuclear ribosomal RNA variants confirming admixtures in the Seychelles and Aldabra. These findings provide critical insights into the origins and connectivity patterns of R. mucronata, offering valuable information for marine conservation efforts across the WIO.
Design of SNP markers for Aldabra giant tortoises using low coverage ddRAD-seq
Researchers have developed a set of 1674 single nucleotide polymorphism (SNP) markers for the Aldabra giant tortoise (Aldabrachelys gigantea), a critically important species for conservation and rewilding efforts in the Western Indian Ocean. These markers, identified using low-coverage double-digest restriction-associated DNA sequencing (ddRAD-seq), provide valuable genetic insights with high expected heterozygosity (0.33–0.5) and minor allele frequency (0.20–0.5). The study analyzed wild populations on Aldabra Atoll alongside captive-bred individuals, offering tools to inform conservation strategies, including large-scale translocations needed due to rising sea levels threatening the species' survival. This work bridges genetic research with practical conservation applications, aiding efforts to restore degraded ecosystems by functionally replacing extinct endemic tortoises.
Extent change of protected mangrove forest and its relation to wave power exposure on Aldabra Atoll
A 21-year study of mangrove forests on Aldabra Atoll, Seychelles—a UNESCO World Heritage Site with no direct human pressures—revealed a net increase of 60 hectares (0.23% annually) in mangrove extent despite global declines. Researchers found that stable mangrove areas experienced significantly lower wave power exposure compared to regions where mangroves gained or lost coverage, identifying critical thresholds: 2.3 W/m for stability and 7.1 W/m for survival. Using Landsat imagery and fetch/wind data, the study highlights the vulnerability of coastal ecosystems to climate change pressures like sea level rise and storm surges, offering insights for global mangrove conservation and restoration planning.
First insights into coral recruit and juvenile abundances at remote Aldabra Atoll, Seychelles
Aldabra Atoll, a remote UNESCO World Heritage Site, shows rapid coral recovery post-bleaching. Research reveals a 2-3 year increase in juvenile coral abundance from 7.4 ± 0.5 to 22.4 ± 1.2 colonies per m² between 2015 and 2019, with significant regional variations. Coral recruits, dominated by Pocilloporidae (64-92%), were 7-47 times more abundant inside the lagoon than outside, peaking at 2164 ± 453 recruits per m² in October-December 2018. This aligns with broadcast spawning during warmer water temperatures (26-29°C), suggesting a link between temperature and coral reproduction. The study provides critical baseline data for understanding reef resilience and connectivity in the Seychelles Outer Islands.
Green turtle population recovery at Aldabra Atoll continues after 50 yr of protection
Aldabra Atoll has demonstrated significant recovery in its green turtle population after 50 years of continuous protection. Research indicates a 173% increase in annual clutch production from 2014 to 2019 compared to the early 1980s, and a potential 410-665% increase since protection began in 1968. The study, which monitored 12 months of nesting seasons over five decades, found that clutch numbers have risen across most beach groups on the atoll, with notable recovery at Settlement Beach, historically the site of intense exploitation. Additionally, the data suggests a shift in nesting seasonality, with year-round activity peaking around May and potentially extending later into the year. This research underscores the importance of long-term protection for endangered species and highlights Aldabra Atoll's role as a global reference site for green turtle conservation.
Larger Doesn't Mean Longer: Neither Body Size Nor Seed Size Affect the Gut Retention Times of Aldabra Giant Tortoises
Neither the body size of Aldabra giant tortoises nor the size of ingested seeds influences their gut retention times, challenging assumptions about seed dispersal dynamics. Researchers fed tortoises of varying sizes (ranging from 0.6 to 104 kg) with artificial seeds of different diameters (2, 4.5, and 10 mm). Despite expectations that larger dispersers or seeds would result in longer retention times, all beads were defecated within a consistent timeframe, averaging 14.6 ± 3.7 days post-ingestion. This finding has significant implications for understanding seed dispersal effectiveness and for rewilding projects involving Aldabra giant tortoises as proxies for extinct megafauna on other oceanic islands.
Pontibacillus sp. ALD_SL1 and Psychroflexus sp. ALD_RP9, two novel moderately halophilic bacteria isolated from sediment and water from the Aldabra Atoll, Seychelles
Researchers have identified two novel, moderately halophilic bacterial species—Pontibacillus sp. ALD_SL1 and Psychroflexus sp. ALD_RP9—from the unique saline environments of Aldabra Atoll in the Seychelles. Pontibacillus sp. ALD_SL1 stands out as the third facultatively anaerobic member of its genus, capable of fermenting pyruvate under low-oxygen conditions, while its genome uniquely harbors a megaplasmid. Psychroflexus sp. ALD_RP9 demonstrates exceptional pH tolerance, surviving up to pH 10.5—the highest recorded for its genus—and employs bacteriorhodopsins for energy production. Both species exhibit remarkable adaptations to high-salinity conditions, yet employ distinct survival strategies, highlighting the biodiversity and ecological resilience of Aldabra Atoll's extreme environments.
Population dynamics of the coconut crab Birgus latro on Aldabra Atoll, Seychelles
Aldabra Atoll, Seychelles, hosts one of the largest and most stable populations of the coconut crab Birgus latro, the world's largest terrestrial arthropod. A decade-long study (2007–2016) revealed an average density of 23.7 ± 1.1 individuals per hectare in Picard Island’s coastal area, suggesting a population of around 5,000 crabs—likely an underestimate due to the species' cryptic behavior. The population exhibited high spatial and temporal variability, with a male-biased sex ratio (3:1) and sexual dimorphism, where males were significantly larger than females. Breeding synchronized with the lunar cycle and overlapped with the wet season (December–March). Color polymorphism was observed in a 4:1:1 ratio of orange, blue, and intermediate forms. These findings underscore Aldabra’s role as a critical refuge for B. latro, potentially serving as a natural source population for regional conservation efforts.
Sedation and Anesthesia of Galapagos (Chelonoidis nigra), Aldabra (Aldabrachelys gigantea), and African Spurred Tortoises (Centrochelys sulcata): A Retrospective Review (2009–2019)
A retrospective review of anesthetic records from 2009 to 2019 reveals that sedation and general anesthesia can be successfully performed on Galapagos (Chelonoidis nigra), Aldabra (Aldabrachelys gigantea), and African spurred tortoises (Centrochelys sulcata) using a combination of an α2-adrenergic agonist, ketamine, and either midazolam or a μ-opioid receptor agonist. The study analyzed 64 anesthetic events across 34 tortoises, demonstrating minimal adverse effects and no mortality during the peri-anesthetic period. This finding provides critical insights into safe and effective anesthetic protocols for these imperiled species, which are often challenging to manage due to their size and unique physiological traits.
The “right” side of sleeping: laterality in resting behaviour of Aldabra giant tortoises (Aldabrachelys gigantea)
Aldabra giant tortoises exhibit a strong preference for resting with their heads positioned on the right side during sleep-like behavior, suggesting group-level lateralization. This study, involving 67 adult tortoises (both wild and under human care), found that 42% of individuals rested with their heads to the right compared to only 21% on the left. Additionally, asymmetrical positioning of forelimbs (88%) and hindlimbs (70%) was more common than symmetrical positions. The research also revealed a relationship between the position of forelimbs and hindlimbs during rest, with no significant differences observed between wild tortoises from Curieuse Island and those in human care at Mahè Botanical Garden. These findings contribute to the understanding of brain lateralization in reptiles, particularly chelonians, and hint at possible left-eye/right-hemisphere involvement in anti-predatory responses.
A new species of Neocirolana Hale, 1925 (Crustacea: Isopoda: Cirolanidae) collected during the Royal Society Expedition to Aldabra 1967–69, western Indian Ocean
A new species of isopod, Neocirolana taylori, has been discovered at Aldabra Atoll, a UNESCO World Heritage Site in the Seychelles. This marks the first record of its genus in the tropical Western Indian Ocean and elevates the known diversity of the genus to eleven species. The species is distinguished by its ovate body shape with a strongly vaulted dorsum, absence of dorsal nodules and pleotelson carinae, prominent coxae on pereonites 5 to 7, and robust pereopods. Collected from intertidal and shallow subtidal reef crest habitats during the Royal Society Expedition (1967–69), this discovery contributes to our understanding of biodiversity in this unique marine ecosystem.
An annotated checklist of myxomycetes from the Seychelles Islands, Indian Ocean
Isolated tropical islands, such as those in the Seychelles, can support a diverse assemblage of myxomycetes, despite their limited land area. This study, conducted across six granitic islands and including data from Aldabra Atoll, documents 143 species and infra-specific taxa, with Physarales being the most predominant order (74 taxa). The research involved extensive field collections using the moist chamber technique and literature reviews, revealing that only a single myxomycete species was shared among all six islands. Abundance varied significantly, with some species like Arcyria cinerea and Physarum compressum being particularly common. The study also highlighted the association of these organisms with different vegetation types, such as coastal and lowland areas, underscoring their ecological adaptability.
Changes in plasma oestradiol, testosterone an progesterone concentrations during an annual reproductive cycle in wild Aldabra giant tortoises (Aldabrachelys gigantea)
Aldabra giant tortoises (Aldabrachelys gigantea), currently listed as Vulnerable, face significant population threats from climate change. A study on Aldabra Atoll revealed distinct seasonal patterns in plasma hormone levels—testosterone in males and oestradiol in females—that align with known reproductive cycles. These findings provide critical insights for monitoring and managing captive breeding programs, both ex-situ and in-situ, to support conservation efforts and establish resilient populations. The research, conducted over a year on wild tortoises, analyzed monthly hormone concentrations alongside meteorological data, offering a foundation for endocrinological strategies in species preservation.
Early trajectories of benthic coral reef communities following the 2015/16 coral bleaching event at remote Aldabra Atoll, Seychelles
Coral reefs at remote Aldabra Atoll, Seychelles, show varying resilience to the 2015/16 bleaching event. While deep seaward reefs remained stable but dominated by turf algae and Halimeda, shallow reefs exhibited significant recovery, with hard coral cover increasing annually by 1.3% to 3.0%, reaching up to 93% of pre-bleaching levels in 2019. Shallow lagoonal reefs displayed lower initial coral loss (-34%) due to higher daily water temperature variability. However, full recovery at shallow seaward locations may still take five more years or longer, and deeper reefs face uncertain prospects. The study highlights that even rapid recovery may be insufficient to counteract long-term degradation from increasing bleaching events, even in minimally impacted remote sites.
Last Interglacial changes in sea level on Aldabra, western Indian Ocean
Aldabra Atoll's Pleistocene limestones reveal more complex sea-level dynamics during the Last Interglacial period than previously understood. Contrary to earlier models, sedimentological analysis shows significant variation, including reversals in sea-level trends that caused both depositional pauses and erosion during rises, as well as stillstands and erosion during falls. These findings challenge the traditional view of a rapid rise followed by gradual fall towards the Last Glacial Maximum's low sea levels. The study identifies key indicators such as coral morphology changes, discontinuities within depositional sequences, and biofacies shifts to explain radiometric age inconsistencies, while questioning the broader implications for interglacial cycles and their mechanisms.
The costs of removing the unsanctioned import of marine plastic litter to small island states
Aldabra Atoll, a remote UNESCO World Heritage Site, harbors the largest reported accumulation of marine plastic litter on a single island, with 513 tonnes estimated to remain after a 2019 clean-up effort. Researchers removed 25 tonnes of debris at a cost of $224,537, equivalent to approximately $8,900 per tonne or $10,000 per day of operations. The remaining litter, predominantly from the regional fishing industry (83%) and flip-flops (7%), poses significant threats to marine ecosystems. The study underscores the urgent need for clean-up efforts, despite high financial costs, while advocating for international funding to address this transboundary issue. Clean-up actions should complement broader policies aimed at reducing plastic waste inputs.
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