Grande Comore Research Articles

Gas Geochemistry at Grande Comore and Mayotte Volcanic Islands (Comoros Archipelago), Indian Ocean

AbstractThe Comoros archipelago is an active geodynamic region of intra‐plate volcanism within which the youngest and oldest islands (Grande Comore and Mayotte respectively) are characterized by recent volcanic activity. The frequent eruptions of the large shield volcano Karthala on Grande Comore (last eruption 2007), and the recent birth of a large submarine volcano since 2018 at the submarine base of Mayotte are associated with permanent fumarolic emissions, bubbling gas seeps, and soil gas emissions, which are studied in detail here for the first time. CO2 fluxes and chemical and isotopic gas compositions acquired during two surveys in 2017 and 2020 are integrated with older data sets collected between 2005 and 2016, permitting the identification of a possible influence of the recent volcanic and magmatic activity at Mayotte. At Karthala, high gas fluxes with high temperature, and a marked magmatic signature are concentrated close to the summit crater area, while only weaker emissions with a stronger biogenic signature are found on the volcano flanks. At Mayotte, lower temperature and higher CH4 content are recorded in two main seep areas of CO2‐rich fluid bubbling, while soil emissions on land record a higher proportion of magmatic fluids compared to Karthala. Our preliminary results reveal two quite separate gas emission patterns for each island that are distinct in composition and isotopic signatures, and well correlated with the present state of volcanic activity. This work may potentially provide support for local observation infrastructures and contribute to the improvement in volcanic and environmental monitoring.

New records of phytoseiid mites (Acari: Mesostigmata) of Grande Comore Island (Comoros Archipelago)

Grande Comore is the larger Island of the four main islands constituting Comoros Archipelago. It is the fourth Island starting from Madagascar after Mayotte, Anjouan and Mohéli and closer to the African coast (Mozambique and Tanzania). So far, only five species of the mite family Phytoseiidae had been reported from this island. We report in this paper the results of a survey conducted at the end of 2018 in Grande Comore Island, in which 29 species have been recorded.

Phytoseiid mites (Acari: Mesostigmata) of Mohéli Island (Comoros Archipelago)

Mohéli is one of the four main islands constituting Comoros Archipelago, with Mayotte, Anjouan and Grande Comore Islands. It is the third Island closer from Madagascar after Mayotte and Anjouan. So far, no species of the mite family Phytoseiidae had been reported from this island. We report in this paper the results of a survey conducted at the end of 2018 in Mohéli Island, in which 18 species have been recorded.

Phytoseiid mites (Acari: Mesostigmata) of Anjouan Island (Comoros Archipelago)

Anjouan is one of the four main islands constituting Comoros Archipelago, with Mayotte, Mohéli and Grande Comore Islands. It is the second Island closer from Madagascar after Mayotte. So far, no species of the mite family Phytoseiidae (Acari: Mesostigmata) had been reported from this island. In this paper, 18 species are recorded from a survey conducted at the end of 2018 in Anjouan Island.

Human population genetics of Comoros islanders: Alu polymorphisms and the peopling of the three major islands

BackgroundThe Comoros archipelago is located in the Indian Ocean between Madagascar and the East African coast. Their geographic localization yielded an admixed population of sub-Saharan African, Middle Eastern, and Austronesian influences. AimTo evaluate the genetic diversity whithin and between the three major islands (Grande Comore, Anjouan, and Moheli) using Alu polymorphisms, and to assess their genetic relationships with Africans, Middle Easterns and South Eastern Asians. - To investigate the peopling of these islands. Subjects & methods18 polymorphic Alu insertions have been typed in 295 unrelated individuals from Comoros archipelago: Grande Comore (122), Anjouan (95), and Moheli (78). The data were analyzed for intra and inter-population genetic variations. ResultsThe Comoros archipelago showed a high level of intra-population genetic diversity and a strong genetic homogeneity between the three islands (FST = 0.0037). The MDS analyses showed higher affinity between the Comorians and nerby sub-Saharans. Admixture estimates highlight a high sub-Saharan component in the genetic background of the current Comorians with some Middle Eastern and Southeast Asian contributions. ConclusionThe Alu polymorphisms used in the present study provided interesting results about the peopling of the Comoros. They showed a high level of genetic diversity probably shaped by successive migratory waves from the three historically related regions and underlined also a high genetic homogeneity among the three islands, probably originated by their common demographic history and/or the geographic proximity.

Changing Patterns of Malaria in Grande Comore after a Drastic Decline: Importance of Fine-Scale Spatial Analysis to Inform Future Control Actions

Malaria has long been endemic in the Union of Comoros reaching an incidence of 15,045 cases for 100,000 inhabitants in 2010 (103,670 cases). Since then, strengthened control actions based on the distribution of Long-Lasting Insecticidal mosquito Nets and mass treatment have reduced malaria to a low level. However, it persists more specifically in Grande Comore, where 82% of cases were diagnosed between 2010 and 2016. This situation remains a challenge for health authorities seeking to eliminate malaria, by targeting transmission sites more precisely. In this context, this study aimed at mapping malaria at the finest scale, in order to describe its spatial distribution and identify possible environmental indicators. The National Malaria Control Program provided the 2016 data, the only year that could be mapped at the level of localities. This mapping revealed spatial autocorrelation between localities, especially in the east of the island with a major cluster around Itsinkoudi (using the Kulldorff’s spatial scan test). Secondary clusters showed that malaria remains present throughout the island in both rural and urban areas. We also analyzed satellite images (SPOT 5) with remote sensing techniques (Object-Based Image Analysis) to look for environmental indicators. Landscape analysis shows that malaria incidence is correlated across the island with low altitudes, and a larger proportion of grasslands or a fewer proportion of forested areas nearby (at less than 1km around villages). More locally in the east, malaria is linked to larger shrub areas. These relationships could be associated with the fact that lower altitude localities are more interconnected, such facilitating malaria transmission. In 2016, malaria persists in Grande Comore, showing new patterns with more cases in the eastern part of the island and the possibility of high incidences during the dry season. Precise mapping of epidemiological data and landscape analysis allow the identification of clusters and active transmission foci. They are important tools for health surveillance in order to optimize control actions on key transmission locations.

Phytoseiid mites of Mayotte Island (Acari: Mesostigmata)

Mayotte is one of the four main islands constituting Comoros Archipelago, with Anjouan, Mohéli and Grande Comore. Among them, it is the closest island to Madagascar. So far, only one species of the mite family Phytoseiidae (Acari: Mesostigmata) had been reported from this island in an early study. In addition, only five species were recently collected from Grande Comore. In this paper, we report the results of a survey conducted at the end of 2018 in Mayotte Island, in which 18 species are reported for the first time for the Mayotte Island.

Genetic diversity of Plasmodium falciparum in Grande Comore Island

BackgroundDespite several control interventions resulting in a considerable decrease in malaria prevalence in the Union of the Comoros, the disease remains a public health problem with high transmission in Grande Comore compared to neighbouring islands. In this country, only a few studies investigating the genetic diversity of Plasmodium falciparum have been performed so far. For this reason, this study aims to examine the genetic diversity of P. falciparum by studying samples collected in Grande Comore in 2012 and 2013, using merozoite surface protein 1 (msp1), merozoite surface protein 2 (msp2) and single nucleotide polymorphism (SNP) genetic markers.MethodsA total of 162 positive rapid diagnostic test (RDT) samples from Grande Comore were used to extract parasite DNA. Allelic families K1, Mad20 and RO33 of the msp1 gene as well as allelic families IC3D7 and FC37 of the msp2 gene were determined by using nested PCR. Additionally, 50 out of 151 samples were genotyped to study 24 SNPs by using high resolution melting (HRM).ResultsTwo allelic families were predominant, the K1 family of msp1 gene (55%) and the FC27 family of msp2 gene (47.4%). Among 50 samples genotyped for 24 SNPs, 42 (84%) yielded interpretable results. Out of these isolates, 36 (85%) were genetically unique and 6 (15%) grouped into two clusters. The genetic diversity of P. falciparum calculated from msp1 and msp2 genes and SNPs was 0.82 and 0.61, respectively.ConclusionIn summary, a large genetic diversity of P. falciparum was observed in Grande Comore. This may favour persistence of malaria and might be one of the reasons for the high malaria transmission compared to neighbouring islands. Further surveillance of P. falciparum isolates, mainly through environmental management and vector control, is warranted until complete elimination is attained.

Modeling Lahars on a Poorly Eroded Basaltic Shield: Karthala Volcano, Grande Comore Island

Lahars impose significant secondary hazards on highly populated volcanic islands by remobilising volcanic ash deposits. Karthala, on Grande Comore Island, is a basaltic shield volcano with sporadic occurrence of ash-forming phreatic eruptions. In 2005, two mildly explosive episodes emplaced tephra blankets on the summit area. Heavy precipitation subsequently triggered the repetitive occurrence of small-volume secondary lahars up to 2012. These lahars impacted the settlements at the foot of Karthala, damaging roads and hundreds of houses, affecting thousands of inhabitants. This study aims at gaining insights into the effectiveness of two simple tools to reproduce the lahars’ extent in this data-poor context. To understand the physical characteristics of the lahars, we first documented the extent and characteristics of the debris deposits at the foot of Karthala volcano and in the ravines that guided the flows. Our observations suggest that the debris was emplaced by small-scale (volumes ≤105 m³), rain-triggered and predominantly low sediment concentration lahars. The spatial extent of the deposits served to calibrate and compare numerical lahar simulations from the widely used volume-limited LaharZ model with results from Q-LavHA, a recent probabilistic flow model originally developed for lava flows. Our comparison demonstrates that LaharZ outperforms Q-LavHA for small-scale lahar simulations. While Q-LavHA has features that mitigate some limitations of LaharZ, such as its ability to simulate flow bifurcations and the transition from constrained to unconstrained flow, it typically underestimates the actual inundated area. Nevertheless, both models show rather poor performance, encountering difficulties in delineating lahar flow paths due to the smooth topography of the volcanic edifice. We therefore also evaluated the potential to increase simulation accuracy by updating a 10-meter resolution Digital Elevation Model (DEM) with channel topography measurements. While this approach led to improved simulation accuracies for both models compared to using un-adapted DEMs, it did not prevent simulations to miss the hazard-prone position of settlements actually affected by the hazard. This study helps inform numerical volcanic flow simulation strategies on young and poorly dissected volcanic edifices, such as basaltic shields, and forms a basis for further developing numerical simulation tools more adapted to these particular environmental settings.

First occurrence of the pest Drosophila suzukii (Diptera: Drosophilidae) in the Comoros Archipelago (Western Indian Ocean)

Drosophila suzukii (Matsumura, 1931) is an Asian pest of grapes and other soft fruits that has invaded North America and Europe during the last decade. Here we report its recent occurrence on two islands of the Comoros archipelago in the Mozambique Channel, namely Mayotte and Ngazidja (Grande Comore), in April 2017 and November 2018, respectively. We also document its absence from other African islands in the Mozambique Channel and the Western Indian Ocean including Mayotte until 2013. Drosophila ashburneriTsacas, 1984 is the only member of the suzukii species subgroup known from the Comoros, but it is morphologically distinct and likely distantly related to D. suzukii. Drosophila suzukii has likely been recently introduced to the Comoros archipelago, perhaps from La Reunion island where it first appeared in November 2013. On all of these tropical islands, D. suzukii was found in high-altitude habitats in agreement with its adaptation to cold environments. These results suggest the high susceptibility of highlands in eastern and southern Africa to be infested by this pest in the near future.

The baobabs of the Comoro Islands: some biogeographical factors towards the protection and conservation of a neglected asset

This study aims to provide some information about the area of presence and geographical breakdown of baobabs belonging to the Adansonia digitata species on the four Comoro Islands. Two of the eight known species of baobabs in the world are present in the Comoro Islands. Whilst they have asset value, a thorough study of their geographical distribution has yet to be produced and there is very little existing action to protect and conserve the asset. An inventory of the A. digitata populations on the islands (Grande Comore, Mohéli, Anjouan and Mayotte) and islets of the archipelago was carried out. From this, it was possible to map the geographical breakdown and analyse the spacial distribution of the baobabs. Their distribution seems to be strongly associated to their proximity to the coastline, suggesting the seeds are dispersed by marine hydrochory. The ecological status of this species based on IUCN status assessment, is known from the threats and pressures incurred and its distribution according to their ecological preferences. The species is categorized as Endangered (ER). The data from this study should contribute to improved management and conservation of the Adansonia species in the Comoros, a growing requirement in the light of concerns about anthropogenic pressure.

The first comprehensive survey of habitat suitability and population size for the endangered Grande Comoro Scops Owl (Otus pauliani): implications for its conservation

The Grande Comoro Scops Owl (Otus pauliani) is an endangered, rare and elusive owl species restricted to the Karthala forest, Grande Comore. This scops owl species is listed among the most threatened animals of the Comoro archipelago. The species is subjected to strong anthropogenic pressures causing a high rate of habitat loss. Little is known about the species’ population size, habitat suitability and geographic distribution, making the establishment of relevant conservation strategies difficult. In this study we assessed the population density and abundance of the species using the distance sampling approach through (1) the conventional distance sampling method (CDS), and (2) density surface modeling (DSM). Based on DSM, we applied a species distribution modeling method to investigate habitat suitability and geographic distribution of the species to close this knowledge gap. Average population density was estimated to be ca. 27 individuals km−2. We estimated a global population size of 3452 individuals. Our DSM suggested that the Grande Comoro Scops Owl has a very limited distribution (133 km2), restricted to high elevations in Grande Comore’s remaining natural forests (between 800 and 2000 m altitude). However, the currently high level of habitat disturbance and conversion of natural forest into agricultural land could render the species vulnerable to extinction. To ensure the viability of the species and the biodiversity of the Karthala forest, we suggest (1) restoring forest and securing corridors in the Karthala remnant forest; (2) avoiding the conversion of secondary forest into agricultural land, and using existing agroforestry for plantation development; (3) involving a broad community of local individuals and entities in their conservation and management.

Alu elements within the human major histocompatibility class I region in the Comoros Islands: genetic variation and population relationships

Background: Alu elements are attractive markers for population genetics, disease, forensics and paternity analyses, due to their particular characteristics. Five polymorphic Alu insertions within the MHC class I region have been little examined in human populations.Aim: The analysis of the genetic diversity of autochthonous Comorians from the three major islands of the archipelago by these polymorphic MHC Alus and to assess their relationships together and with other populations.Subjects and methods: Two hundred and fifty-seven unrelated participants from the Comoros archipelago, Grande Comore (86), Anjouan (93) and Moheli (78), were examined for five MHC Alu insertions. The data were analysed for intra- and inter-population genetic variation.Results: All MHC Alu were polymorphic in the three samples and only one significant differentiation was observed between Anjouan and Moheli. According to the MDS and AMOVA results, the populations included in the inter-population analyses were grouped in three major clusters according to their genetic ancestry. The haplotype diversity showed by the Comorians is higher than in previously studied African populations and occupies an intermediate position between African and Asian clusters.Conclusion: MHC Alu insertions are useful markers to study micro-geographical genetic variations. Using these polymorphisms, new insights have been obtained about the biological history and evolution of the Comoros.

Assessing Nutritional Traits and Phytochemical Composition of Artisan Jams Produced in Comoros Islands: Using Indigenous Fruits with High Health-Impact as an Example of Biodiversity Integration and Food Security in Rural Development.

In the Comoros Islands, as in other developing countries, malnutrition and food insecurity affect a very large percentage of the population. Developing fruit-based products in order to make profit, reduce poverty and improve indigenous people diet could be very important for local population of countries as Comoros Islands. The aim of the present work was to study the chemical composition of jams and jellies produced from seven fruit species harvested in Grand Comore Island. The following parameters were studied sugars and organic acids, total phenolics, total anthocyanins and high-performance liquid chromatography (HPLC) fingerprint of the main phytochemicals. Antioxidant activity was also measured. A multivariate approach (Principal Component Analysis) was performed in order to better characterize the products and to set a potential analytical tool for jam characterisation. Results showed that the analysed products are a good source of polyphenolic constituents, as caffeic and gallic acids, catechin and quercetin and volatile compounds, as limonene and γ-terpinene: these molecules may be considered as suitable markers for these fruit-derived products as characterizing the chromatographic patterns. The characterisation of these products and their nutritional and nutraceutical traits is important as valorisation of local food production for poverty reduction and rural development. Further benefits of this approach include the maintenance of local agro-biodiversity as raw material for fruit-based products and the strengthening of food security practices.

The contrasting genetic patterns of two sympatric flying fox species from the Comoros and the implications for conservation

Pteropus livingstonii and Pteropus seychellensis comorensis are endemic fruit bat species that are among the most threatened animals in the Comoros archipelago. Both species are pollinators and seed dispersers of native and cultivated plants and are thus of crucial importance for the regeneration of natural forests as well as for cultivated plantations. However, these species are subject to strong anthropogenic pressures and face one of the highest rates of natural habitat loss reported worldwide. Yet little is known about the population genetic structure of these two species, making it difficult to define relevant conservation strategies. In this study, we investigated for the two flying fox species (1) the level of genetic diversity within islands, as well as across the archipelago and (2) the genetic structure between the two islands (Anjouan and Moheli) for P. livingstonii and between the four islands of the archipelago (Anjouan, Moheli, Grande Comore and Mayotte) for P. s. comorensis using mitochondrial and microsatellite markers. The results revealed contrasting patterns of genetic structure, with P. s. comorensis showing low genetic structure between islands, whereas P. livingstonii exhibited high levels of inter-island genetic differentiation. Overall, the genetic analyses showed low genetic diversity for both species. These contrasting genetic patterns may be the result of different dispersal patterns and the populations’ evolutionary histories. Our findings lead us to suggest that in terms of conservation strategy, the two populations of P. livingstonii (on Anjouan and Moheli islands) should be considered as two separate management units. We recommend focusing conservation efforts on the Anjouan population, which is the largest, exhibits the highest genetic diversity, and suffers the greatest anthropogenic pressure. As for P. s. comorensis, its four populations could be considered as a single unit for conservation management purposes. For this species, we recommend protecting roosting trees to reduce population disturbance.

Impact of East Coast fever on Grande Comore: assessment taking a participatory epidemiology approach.

East Coast fever (ECF), one of the most serious tick-borne diseases in sub-Saharan and eastern Africa, was introduced to the island of Grande Comore in 2002 through zebu import from Tanzania, resulting in at least a 10% loss of livestock. A participatory epidemiology initiative was launched in 2015 to gain a better understanding of ECF epidemiology. Thirty-six villages were investigated involving 36 focus group sessions and 120 individual questionnaires. Farmers' knowledge of ECF and of priority diseases affecting the country was assessed, and the impacts of ECF and other major diseases were compared by a scoring method. The results showed that 69.4% (95% CI [51.3, 87.5%]) of the farmers had good to very good knowledge of ECF. The most important cattle diseases on Grande Comore were considered to be East Coast fever, heartwater, babesiosis, and cutaneous diseases. About 58% of the farmers (95% CI [49.2, 66.8%]) use curative treatments when cattle were sick. Between January and September 2015, the ECF incidence was estimated at 18.5% (95% CI [15.5, 21.4%]), and 87.5% (95% CI [72.7, 100%]) of the cattle infected by ECF died. The ECF incidence estimated in our study was found to be less when compared to that observed in Tanzania even though the climatic conditions in the Union of the Comoros are suitable for the biological vector of ECF, the tick species Rhipicephalus appendiculatus. Access to chemical treatment and its effectiveness against ECF, as well as controlling borders and organizing quarantine, are discussed.

First records of Phytoseiidae (Acari: Mesostigmata) from one island of the Comoros archipelago

The Comoros Archipelago is constituted of four islands. These islands are located in the North Mozambique Channel in the Indian Ocean, one of the world’s hotspots of biodiversity. Despite this status of hotspot, only one species of Phytoseiidae was known from this Archipelago, from Mayotte: Phytoseius mayottae. No species were recorded from the three other islands. We report in this paper the results of a preliminary survey in Great Comoro or “Grande Comore” Island also called Ngazidja in the Comorian language (= Shikomori) with five species recorded.

The current status of coral reefs and their vulnerability to climate change and multiple human stresses in the Comoros Archipelago, Western Indian Ocean

Coral bleaching and various human stressors have degraded the coral reefs of the Comoros Archipelago in the past 40 years and rising atmospheric CO2 levels are predicted to further impact marine habitats. The condition of reefs in the Comoros is poorly known; using SCUBA based methods we surveyed reef condition and resilience to bleaching at sites in Grande Comore and Mohéli in 2010 and 2016. The condition of reefs was highly variable, with a range in live coral cover between 6% and 60% and target fishery species biomass between 20 and 500 kg per ha. The vulnerability assessment of reefs to future coral bleaching and their exposure to fishing, soil erosion and river pollution in Mohéli Marine Park found that offshore sites around the islets south of the island were least likely to be impacted by these negative pressures. The high variability in both reef condition and vulnerability across reefs in the Park lends itself to spatially explicit conservation actions. However, it is noteworthy that climate impacts to date appear moderate and that local human pressures are not having a major impact on components of reef health and recovery, suggesting these reefs are relatively resilient to the current anthropogenic stresses that they are experiencing.

Temporal changes in genetic diversity of msp-1, msp-2, and msp-3 in Plasmodium falciparum isolates from Grande Comore Island after introduction of ACT.

BackgroundMalaria is still one of the serious public health problems in Grande Comore Island, although the number of annual cases has been greatly reduced in recent years. A better understanding of malaria parasite population diversity and transmission dynamics is critical for assessing the effectiveness of malaria control measures. The objective of this study is to investigate temporal changes in genetic diversity of Plasmodium falciparum populations and multiplicity of infection (MOI) in Grande Comore 10 years after introduction of ACT.MethodsA total of 232 P. falciparum clinical isolates were collected from the Grande Comore Island during two sampling periods (118 for 2006‒2007 group, and 114 for 2013‒2016 group). Parasite isolates were characterized for genetic diversity and complexity of infection by genotyping polymorphic regions in merozoite surface protein gene 1 (msp-1), msp-2, and msp-3 using nested PCR and DNA sequencing.ResultsThree msp-1 alleles (K1, MAD20, and RO33), two msp-2 alleles (FC27 and 3D7), and two msp-3 alleles (K1 and 3D7) were detected in parasites of both sampling periods. The RO33 allele of msp-1 (84.8%), 3D7 allele of msp-2 (90.8%), and K1 allele of msp-3 (66.7%) were the predominant allelic types in isolates from 2006–2007 group. In contrast, the RO33 allele of msp-1 (63.4%), FC27 allele of msp-2 (91.1%), and 3D7 allele of msp-3 (53.5%) were the most prevalent among isolates from the 2013–2016 group. Compared with the 2006‒2007 group, polyclonal infection rates of msp-1 (from 76.7 to 29.1%, P < 0.01) and msp-2 (from 62.4 to 28.3%, P < 0.01) allelic types were significantly decreased in those from 2013‒2016 group. Similarly, the MOIs for both msp-1 and msp-2 were higher in P. falciparum isolates in the 2006–2007 group than those in 2013–2016 group (MOI = 3.11 vs 1.63 for msp-1; MOI = 2.75 vs 1.35 for msp-2). DNA sequencing analyses also revealed reduced numbers of distinct sequence variants in the three genes from 2006‒2007 to 2013‒2016: msp-1, from 32 to 23 (about 28% decline); msp-2 from 29 to 21 (about 28% decline), and msp-3 from 11 to 3 (about 72% decline).ConclusionsThe present data showed dramatic reduction in genetic diversity and MOI among Grande Comore P. falciparum populations over the course of the study, suggesting a trend of decreasing malaria transmission intensity and genetic diversity in Grande Comore Island. These data provide valuable information for surveillance of P. falciparum infection and for assessing the appropriateness of the current malarial control strategies in the endemic area.

Larvivorous fish for preventing malaria transmission.

Larvivorous fish for preventing malaria transmission.