Seychelles Archipelago Research Articles

Minor Architectures of the Plantationocene: A Colonial Family Romance

This article unfolds environmental stories of a plantation house and grounds on the Seychelles archipelago by reclaiming the importance of the minor architectures that support and resist its imperial hold. The Seychelles, first colonised by the French, then ceded to the British, claimed independence in 1976, before a coup d’état brought about a single party state that maintained power for fifteen years. Using feminist autotheory and field philosophy as its primary methodologies, the article draws on oral history interviews with Seychellois cultural workers, family archives, and spatial memories passed down through the generations of a former plantation owning family. Thinking with the scholarship of decolonial feminist scholar and activist Françoise Vérges, a colonial family romance is satirically told of the blind spots and lacunae articulating spatial memories of colonial architectures. How can alternative spatial and environmental narratives be foregrounded that seek emancipation and resist power when it becomes most oppressive?

Coral Larvae Journey Far and Wide in the Western Indian Ocean

Researchers mapped coral reef connectivity across the Seychelles archipelago to inform conservation efforts in the face of climate change.

First record of the Argentine ant, Linepithema humile (Mayr, 1868) (Hymenoptera: Formicidae), from the Malagasy region

Summary The Argentine ant, Linepithema humile (Mayr, 1868), is a highly invasive species with serious detrimental consequences to native fauna and flora in invaded territories. Native to South-Central South America, it was first reported from continental Africa in 1893 but, to date, had never been recorded from the Malagasy region (encompassing Madagascar, Comoros, Seychelles, and Mascarene archipelago). Here, we report the first record of this invasive species on the island of La Réunion, a French overseas territory part of the Mascarene archipelago. The species was identified using both morphological and molecular analysis. We discuss potential ecological consequences of the presence of this ant on the insular ecosystems of La Réunion.

Balclutha jafara (Hemiptera: Cicadellidae): integrative identification of a species introduced in the Western Hemisphere, and notes on other Balclutha.

Leafhopper specimens of the genus Balclutha Kirkaldy, found in southern Florida (Palm Beach and Collier Counties), United States, beginning in 2020, and in shipments of plant products originating from Colombia and entering the United States beginning in 2019, are identified as B. jafara Webb. This species was previously known only from the Seychelles and Aldabra Islands, which are parts of the Seychelles archipelago in the Indian Ocean east of mainland Africa. Identifications were made by comparison with type specimens, both morphologically and through molecular analysis. Specimens in Palm Beach Co. were swept from commercial rice (Oryza sativa L.) paddies. Mitochondrial cytochrome c oxidase I (COI) barcodes of specimens from Florida and Colombia were closely matched to each other and to partial barcodes obtained from paratype specimens of B. jafara. The COI barcodes also closely matched sequences from previously unidentified Balclutha specimens in the Barcode of Life Data Systems (BOLD) from Kenya and South Africa, several of which were confirmed later morphologically as B. jafara. Previously unidentified museum specimens from South Sudan, Zambia, and Zimbabwe were determined as B. jafara. Together, these specimens show that B. jafara has a more widespread African distribution than was known previously, and that it arrived in the Western Hemisphere by 2019. Balclutha jafara is redescribed and illustrated. Further studies on the Balclutha fauna of Florida were performed. COI barcode data were generated for Floridian specimens of B. caldwelli Blocker, B. curvata Caldwell, B. flavescens (Baker), B. frontalis (Ferrari), B. incisa (Matsumura), and B. lucida (Butler). A phylogenetic analysis of COI data was conducted using publicly available sequences and those generated here. A key to the Balclutha species known from Florida is provided. The names that have been applied and mis-applied to Western Hemisphere species are discussed. To clarify the identity of some species, illustrations are given for: the female holotype and a male paratype of Eugnathodus virescens Osborn (=B. flavescens); the holotype of Nesosteles robustus Caldwell (=B. robusta); and the holotype of Balclutha curvata Caldwell. Additional barcoded specimens of Balclutha from Kenya and Pakistan were provided for examination by the BOLD research group and determined as B. sujawalensis Ahmed, previously known only from India and Pakistan, and this species is also illustrated here.

Mapping the National Seagrass Extent in Seychelles Using PlanetScope NICFI Data

Seagrasses provide ecosystem services worth USD 2.28 trillion annually. However, their direct threats and our incomplete knowledge hamper our capabilities to protect and manage them. This study aims to evaluate if the NICFI Satellite Data Program basemaps could map Seychelles’ extensive seagrass meadows, directly supporting the country’s ambitions to protect this ecosystem. The Seychelles archipelago was divided into three geographical regions. Half-yearly basemaps from 2015 to 2020 were combined using an interval mean of the 10th percentile and median before land and deep water masking. Additional features were produced using the Depth Invariant Index, Normalised Differences, and segmentation. With 80% of the reference data, an initial Random Forest followed by a variable importance analysis was performed. Only the top ten contributing features were retained for a second classification, which was validated with the remaining 20%. The best overall accuracies across the three regions ranged between 69.7% and 75.7%. The biggest challenges for the NICFI basemaps are its four-band spectral resolution and uncertainties owing to sampling bias. As part of a nationwide seagrass extent and blue carbon mapping project, the estimates herein will be combined with ancillary satellite data and contribute to a full national estimate in a near-future report. However, the numbers reported showcase the broader potential for using NICFI basemaps for seagrass mapping at scale.

THE HERBARIUM OF MACROPHYTES OF THE A.O. KOVALEVSKY INSTITUTE OF BIOLOGY OF THE SOUTHERN SEAS OF RAS (SIBS), AND THE STAGES OF ITS FORMATION

The paper presents the results of a retrospective analysis of the history of the formation of the macrophyte herbarium of Kovalevsky Institute of Biology of the Southern Seas of RAS (IBSS, Sevastopol, until 1963 – Sevastopol Biological Station, SBS). For the analysis, the electronic database of the herbarium, sources and archival materials published over a period of more than a hundred years, memoirs of the oldest employees of the SBS were used. Three stages of the herbarium fund formation were distinguished, its beginning dating back to 1878. The first herbarium specimens were collected and designed by S.M. Pereyaslavtseva, the first Russian female zoologist and the first head of the SBS. According to archival data, by the beginning of the World War II, the herbarium contained about 3 000 herbarium sheets; like all museum collections of the SBS, it burned down in 1942. The beginning of its restoration dates back to 1945, today it contains 30914 sheets of 715 species and 198 genera from 734 localities, it is included in the international herbarium database Index Herbariorum (its acronym is SIBS). The paper summarizes the data on collection sites in the Atlantic, Arctic, Pacific, Indian and Southern Oceans. The historical collections of famous algologists N.V. Morozova-Vodyanitskaya (collection from 1920 to 1931) and A.A. Kalugina-Gutnik (from 1960 to 1991), and of a collector of the Karadag Biological Station G.M. Stanilovsky (from 1924 to 1946) are characterized; they account for 71% of the total volume of the fund. It is shown that the key macroalgae of the Black Sea are represented by collections for more than half a century from the same locality (Phyllophora crispa (Hudson) P.S. Dixon, Ericaria crinita (Duby) Molinari et Guiry, Gongolaria barbata (Stackhouse) Kuntze, Ulva rigida C. Agardh, etc.). There are unique macroalgae specimens from the underwater uplifts of the Mediterranean Sea, 14 islands and atolls of the Seychelles archipelago, the islands of Antarctica, of the seagrasses of the Indian Ocean, whose localities are not found in the herbaria of the world. To expand access to the herbarium fund, it is necessary to export data to the global bank and the global biodiversity information system (GBIF). On the basis of the studies performed, a rationale was prepared of naming the herbarium of macrophytes of world ocean IBSS after A.A. Kalugina-Gutnik (1929–1994), taking into account her significant contribution to the preservation of scientific heritage and traditions, and the creation of the collection fund.

A new fossil subspecies of booby (Aves, Sulidae: Papasula) from Mauritius and Rodrigues, Mascarene Islands, with notes on P. abbotti from Assumption Island.

A new subspecies of Papasula booby is described from fossil remains collected in the Mascarene Islands of Mauritius and Rodrigues, southwestern Indian Ocean. The Mascarene Booby Papasula abbotti nelsoni ssp. nov., larger than nominate Abbott's Booby P. a. abbotti from Christmas Island, northeast Indian Ocean, was approximately the same size as the extinct Hiva Oa Booby P. a. costelloi from the Marquesas in the Eastern Pacific. Mentioned in early accounts of Mauritius in 1668 and in 1725-26 and 1761 on Rodrigues, the Mascarene booby became extinct by the end of the 18th century. Members of another isolated but now extirpated population of Papasula abbotti from Assumption Island in the Seychelles Archipelago, the island from which the type specimen was collected, are identical to extant Christmas Island birds in size and colouration and discussed in detail herein.

Acoustic detections and sightings of blue whales Balaenoptera musculus in the Seychelles, western tropical Indian Ocean (2020-2022)

Historically, the Seychelles archipelago was an opportunistic whaling ground for fleets en route to and from the Antarctic. Soviet whalers illegally killed 500 blue whales near the Seychelles in the 1960s. Since then, no dedicated research has occurred to understand the ecological importance of this region for blue whales. Based on opportunistic sightings, we undertook 2 expeditions to assess the occurrence of blue whales. The overall goals were to determine blue whale distribution, obtain photo-identification data and collect the first acoustic data on this species in this region using a hydrophone deployed for a year. The expeditions consisted of vessel-based visual surveys that focused on the slope habitat (500-2000 m) off the northern portion of the Mahé Plateau. Over the 2 expeditions, a total of 5 sightings of up to 10 animals were seen. The results of our acoustic monitoring off Seychelles demonstrate that blue whales occur there regularly, primarily from December to April, and that the acoustic population identity matches that from near Sri Lanka. Published records and the results of our work suggest that blue whales from the northwestern Indian Ocean are seasonally present in the western equatorial Indian Ocean.

Evaluation of the limiting factors affecting the Seychelles Kestrel Falco araeus on Praslin Island (Seychelles) and considerations regarding a possible reintroduction of the species

Summary The Seychelles Kestrel Falco araeus is an endemic species confined to the larger granitic islands in the Seychelles archipelago. It is classified as “Vulnerable” and became extinct on Praslin and La Digue islands in the 1970s, leading to an attempt of reintroduction in 1977. This reintroduction was not a success, with the last census reporting only four breeding pairs on Praslin Island. Studies on the Seychelles Kestrel are very limited and dated, and a lack of data on the biology and ecology of the species has made it difficult to make a thorough assessment of the cause of the current decline of the Praslin population. In order to determine the limiting factors on Praslin we investigated the following ecological parameters: nest-site availability, trophic availability, predatory pressure, and interspecific competition. Data were collected on Mahé and Praslin islands in three habitats (i.e. urban, suburban, and forest areas) and compared to determine if limiting factors differed among islands, habitats, and islands*habitat. We only found a significant difference in nest-site availability, with Praslin showing a marked lack of nesting cavities. Breeding pairs on Praslin are probably forced to nest in suboptimal sites. Indeed, the breeding success rate on Praslin is very low, and most of the nests there fail. The Seychelles Kestrel population on Praslin is in decline and cannot be sustained without human intervention. Such an intervention must take into account the ecological parameters highlighted in the present study.

Ribosomal DNA Instability as a Potential Cause of Karyotype Evolution.

Karyotype refers to the configuration of the genome into a set of chromosomes. The karyotype difference between species is expected to impede various biological processes, such as chromosome segregation and meiotic chromosome pairing, potentially contributing to incompatibility. Karyotypes can rapidly change between closely related species and even among populations of the same species. However, the forces driving karyotype evolution are poorly understood. Here we describe a unique karyotype of a Drosophila melanogaster strain isolated from the Seychelles archipelago. This strain has lost the ribosomal DNA (rDNA) locus on the X chromosome. Because the Y chromosome is the only other rDNA-bearing chromosome, all females carry at least one Y chromosome as the source of rDNA. Interestingly, we found that the strain also carries a truncated Y chromosome (YS) that is stably maintained in the population despite its inability to support male fertility. Our modeling and cytological analysis suggest that the Y chromosome has a larger negative impact on female fitness than the YS chromosome. Moreover, we generated an independent strain that lacks X rDNA and has a karyotype of XXY females and XY males. This strain quickly evolved multiple karyotypes: two new truncated Y chromosomes (similar to YS), as well as two independent X chromosome fusions that contain the Y-derived rDNA fragment, eliminating females' dependence on the Y chromosome. Considering that Robertsonian fusions frequently occur at rDNA loci in humans, we propose that rDNA loci instability may be one of driving forces of karyotype evolution.

Spatio-temporal variability in drifting Fish Aggregating Device (dFAD) beaching events in the Seychelles Archipelago

AbstractPurse-seine fisheries use drifting Fish Aggregating Devices (dFADs), human-made floating objects, to facilitate the capture of tropical tunas. Currently, the majority of dFADs are constructed primarily of highly durable non-biodegradable materials and there is no legal obligation to recover dFADs after deployment, leading to beaching events and potentially negative environmental impacts. We assessed beachings as a function of intra- and inter-annual trends, water depth, distance from land, seasonality, and benthic habitat within the local context of the Seychelles Archipelago using trajectories of dFADs deployed by French purse seiners over 2008–2020. Overall, 3842 beaching events associated with 2371 distinct dFAD tracking buoys were identified. Beachings occurred most frequently during the winter monsoon (December–March). Due to the shallow Mahé Plateau, beachings occurred in both nearshore (≤ 5 km from land) and offshore (> 5 km) regions, predominantly in estimated depths less than 60 m. Despite representing < 20% of overall mapped habitat, the benthic habitat “Coral/Algae” had the highest beaching rate (35.3% of beachings), and therefore, beachings pose a significant concern for conservation. Our results provide a detailed view of the spatio-temporal pattern of beachings in the Seychelles, supporting the development of mitigation and prevention methods to reduce marine debris and perturbations to the marine environment.

Are invasive hymenopteran species replacing native mud dauber wasp-associated taxa on the Seychelles Archipelago?

Nest aggregations of mud dauber wasps increase substrate heterogeneity and provide suitable sites for colonization by other invertebrate species. The mud dauber wasp Sceliphron fuscum Klug, 1801 (Hymenoptera: Sphecidae) abundantly occurs throughout the Seychelles Archipelago, Republic of Seychelles. Here, we estimated the taxonomic richness of the hymenopteran assemblage associated with S. fuscum’s nest aggregations, using material collected from the Inner Seychelles in 2016. Furthermore, we examine available historical survey data in order to assess possible changes in this association over decades. We discovered that from 1936 to 1938, seven hymenopteran species were associated with the nest aggregations of S. fuscum on Mahé and Praslin islands, representing six native taxa and one invasive species. From the material collected in 2016, we found one native and three invasive hymenopteran species associated to S. fuscum nests. Our findings could indicate a replacement of native species associated with the mud dauber wasps’ nest aggregations by recently introduced alien taxa on the Seychelles Archipelago.

Multilocus phylogeny, natural history traits and classification of natricine snakes (Serpentes: Natricinae)

Abstract Natricine snakes are geographically widespread, species rich (with ~250 extant species) and both morphologically and ecologically diverse. We present a multilocus DNA sequence phylogeny for 249 natricine specimens representing 189 named species, including 69 specimens and 21 species not previously sampled. Our inferred Bayesian and maximum likelihood trees form the basis for evaluations of genus-level classification, historical biogeography, lineage diversification, and dietary, habit and reproductive-mode diversity and evolution, although several, mostly deeper, relationships remain poorly resolved. The optimal trees support natricine origins in Asia, with dispersals to Australo-Melanesia, sub-Saharan Africa (including Seychelles Archipelago, excluding Aldabra), Europe and North Africa and into North and Central America. Viviparity appears to have evolved independently three times in Natricinae but was not significantly associated with an aquatic habit. We found limited associations between habit and diet categories. We propose generic reallocations for four natricine species and highlight other points of uncertainty in natricine classification.

Reconstruction of plant\u2013pollinator networks from observational data

Empirical measurements of ecological networks such as food webs and mutualistic networks are often rich in structure but also noisy and error-prone, particularly for rare species for which observations are sparse. Focusing on the case of plant–pollinator networks, we here describe a Bayesian statistical technique that allows us to make accurate estimates of network structure and ecological metrics from such noisy observational data. Our method yields not only estimates of these quantities, but also estimates of their statistical errors, paving the way for principled statistical analyses of ecological variables and outcomes. We demonstrate the use of the method with an application to previously published data on plant–pollinator networks in the Seychelles archipelago and Kosciusko National Park, calculating estimates of network structure, network nestedness, and other characteristics.

Ancestral transoceanic colonization and recent population reduction in a nonannual killifish from the Seychelles archipelago.

Whether freshwater fish colonize remote islands following tectonic or transoceanic dispersal remains an evolutionary puzzle. Integrating dating of known tectonic events with phylogenomics and current species distribution, we find that killifish species distribution is not explained by species dispersal by tectonic drift only. Investigating the colonization of a nonannual killifish (golden panchax, Pachypanchax playfairii) on the Seychelle islands, we found genetic support for transoceanic dispersal and experimentally discovered an adaptation to complete tolerance to seawater. At the macroevolutionary scale, despite their long-lasting isolation, nonannual golden panchax show stronger genome-wide purifying selection than annual killifishes from continental Africa. However, progressive decline in effective population size over a more recent timescale has probably led to the segregation of slightly deleterious mutations across golden panchax populations, which represents a potential threat for species preservation in the long term.

Phylogeny and taxonomic revision of the genus Craterispermum (Rubiaceae) in the Seychelles Archipelago

The genus Craterispermum (Craterispermeae, Rubiaceae) is distributed in the tropical rain forests of Africa and Madagascar, with one morphologically variable species (Craterispermum microdon) hitherto recognized in the Seychelles Archipelago. We conducted a Bayesian analysis of the combined ETS and ITS sequence data to: 1) test the monophyly of the Seychellois species of Craterispermum; and 2) assess the phylogenetic relationships between the island populations. Our analyses supported the monophyly and, therefore, the single Malagasy origin of the Seychellois Craterispermum. The phylogenetic relationships between the three island populations were unresolved, since the Seychellois plants display a very low level of molecular variation. However, both herbarium and field studies revealed that the Craterispermum taxa occurring on the islands of Mahe, Praslin, and Silhouette, are morphologically distinct and geographically separated. As a result of these studies, two new species, Craterispermum praslinense and C. silhouettense, are described, to accommodate the Praslin and Silhouette populations, respectively, and C. microdon is restricted to the population on Mahe Island. A new taxonomic account for the Seychellois Craterispermum, and an identification key to the three species present in the archipelago, are provided. A provisional conservation status of each species, according to the IUCN Categories and Criteria, is presented.

Understanding Seasonal Displacements of Antanartia borbonica (Oberthür, 1880), a Necessity for Its Conservation (Lepideroptera: Nymphalidae)

In the face of butterfly species extinction on Seychelles and Mascarene archipelagos, there is an urgent need of increasing our knowledge about species, especially those which have been extinct from one island. Here, we focus on Antanartia borbonica (Oberthur, 1880), a threatened Mascarene butterfly, extinct from Mauritius and considered locally endangered (EN) on Reunion by the French IUCN committee. On Reunion, we investigated the way A. borbonica distribution changes throughout the year depending on elevation and temperature. We confirm previous observations suggesting a seasonal displacement along the elevational gradient: A. borbonica spends the winter in low-elevation areas and moves to higher ones during summer. This biological trait implies conservation actions considering the restoration of suitable habitats for this species along the elevational gradient. The priority, to ensure the long-term conservation of this species, is to create refuges especially in urban and secondary habitats located in lowland areas where relatively preserved ecosystems no longer exist.

A few hours in the Seychelles with Alex du Toit in 1938

Alexander Logie du Toit (1878–1948) was South Africa’s most famous geologist during his lifetime, having authored five books which brought him world renown. In December 1937 to January 1938, accompanied by his wife Evelyn, he visited India in order to attend the Jubilee Indian Science Congress in Calcutta and to do field work in coal and diamond mines. On the return journey to Africa by ship, they stopped for a few hours in Port Victoria on Mahé Island in the Seychelles archipelago. They also passed by Silhouette Island. Du Toit recorded his activities in a diary, and his geological observations in a notebook, where he also drew a sketch of Mahé, and recorded steep structures on the east coast of Silhouette. Although he had not visited the Seychelles before, his deep understanding of the problems of Seychelles geology resulted from his comprehensive research on Indian Ocean geology for his 1937 book Our Wandering Continents. He made remarkably accurate observations on the geomorphology and structure, some of which were only confirmed decades later when the Seychelles were mapped in the 1960s to 1990s. His bold and prescient ideas on the breakup of the Gondwana continent, and on the formation of the Indian Ocean, have been amply confirmed by modern studies, especially by those of Lewis D. Ashwal and his collaborators.
 Significance:
 
 South African geologist Alexander Logie du Toit’s impressions of the Seychelles in 1938 are recorded for the first time, based on entries in his diaries. His observations of structures on Mahé and Silhouette Islands were prescient. His deep understanding of Seychelles geology was the result of his research for his 1937 book Our Wandering Continents. His bold conjecture that the Mascerene Ridge, made of continental crust, was the nucleus of Mauritius, was finally proved in 2017.

How to organise limited space: Micro-regionalisation of La Digue island (Seychelles)

Abstract Islands, especially small ones, are commonly studied as microcosms of natural and social processes. In this article, La Digue island (10 km2) in the Seychelles archipelago was treated as such. An attempt was made to analyse the significance of the natural environment for the features of spatial development under conditions of intense globalisation. For this purpose, functional micro-regions were determined, along with their genesis and evolution. Spatial dynamics and individual features of space are presented as chorème (Brunet 1986). The analysis was based on data from a library query and field observation and field studies in July 2018. Twelve functional regions were determined. Analysis of the distribution and evolution of their functions reveals a high dependence on natural environmental features, especially topography, and thus confirms (at the scale in question) a geographical determinism.

In the land of giants: habitat use and selection of the Aldabra giant tortoise on Aldabra Atoll

With habitat loss and fragmentation among the greatest threats to biodiversity, a better understanding of the habitat use of keystone species is critical in any conservation management strategy. Aldabra Atoll, in the Seychelles archipelago, has the largest population worldwide of giant tortoises. This endemic species (Aldabrachelys gigantea) could be vulnerable to habitat fragmentation and loss induced by climate change related reduction in rainfall. Here, we assess habitat use and selection by A. gigantea in its natural environment on Aldabra. We quantified the habitat areas of A. gigantea based on the first high-resolution terrestrial habitat map of Aldabra, produced for this purpose using satellite imagery. The resulting map was combined with 4 years of movement data to assess A. gigantea habitat use and selection at landscape and home range scales. Grassland or ‘tortoise turf’ habitat was most preferred by A. gigantea on Aldabra, at the landscape scale across seasons, followed by open mixed scrub. These two habitats cover only 30 km2 (19.2%) of the surface of the atoll (total area: 155.5 km2). At the home range scale, there was no significant preference shown and habitat was used randomly. Our results suggest that Aldabra’s grassland habitat, despite its small area, is of great importance to A. gigantea. Conservation management actions for A. gigantea on Aldabra and elsewhere should therefore focus on the protection and maintenance of this habitat.