Small giant clam, Tridacna maxima, widely distributed from French Polynesia to East Africa, has faced population declines due to over-exploitation. Comoros islands are an important biogeographic region due to potential richness of marine species, but no relevant information is available. In order to facilitate devising effective conservation management plan for T. maxima, nine microsatellite markers were used to survey genetic diversity and population differentiation of 72 specimens collected from three Comoros islands, Grande Comore, Moheli and Anjouan. A total of 51 alleles were detected ranged from 2 to 8 per locus. Observed and expected heterozygosity varied from 0.260 to 0.790 and from 0.542 to 0.830, respectively. All populations have high genetic diversity, especially the population in Moheli, a protected area, has higher genetic diversity than the others. Significant heterozygote deficiencies were recorded, and null alleles were probably the main factor leading to these deficits. F ST value indicated medium genetic differentiation among the populations. Although significant, AMOVA revealed 48.9 % of genetic variation within individuals and only a small variation of 8.9 % was found between populations. Gene flow was high (Nm = 12.40) between Grande Comore and Moheli, while lower (Nm = 1.80) between Grande Comore and Anjouan, explaining geographic barriers to genetic exchanges might exist in these two islands. Global gene flow analysis (Nm = 5.50) showed that larval dispersal is enough to move between the islands. The high genetic diversity and medium population differentiation revealed in the present study offer useful information on genetic conservation of small giant clams.

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In previous studies, an emphasis on the particular vulnerability of small island states to future sea-level rise and the intensity of increasing storm surges has been discussed. This preliminary assessment develops a Coastal Vulnerability Index (CVI) along the 202 km long coastline of Ngazidja Island (formerly Grande Comore, Comoros Archipelago), using eldwork, remote sensing, and geographic information system tools (GIS). The CVI considers ve structural variables: (a) geology, (b) geomorphology, (c) topography, (d) shoreline change, and (e) shoreline exposure). It also considers three physical process variables: (f) relative sea-level rise, (g) signi cant wave height, and (h) mean tide range). The land-use variable was added in this analysis to highlight the human asset exposure in the surrounding areas. Each variable was ranked based on local physical and hydrodynamic conditions and their vulnerability contribution to sea-level rise. The CVI was computed in 270 sections. According to the vulnerability index, approximately 57.5% of the coastline is under low and moderate vulnerability. High and very-high vulnerabilities refer speci cally to beaches and shores with old volcanic lava ows located mainly in the northern, northeastern, and southeastern parts of the island, approximately 42.5% of the coastline. The lowest value of CVI is 9.2 on high, rocky cliffs and the highest value is 160 on beaches. This vulnerability partition along the coastline is consistent with in situ indicators of coastal erosion and ooding. In a sealevel rise context, it is of prime importance to integrate coastal vulnerability maps with planning and sustainable management of the coastal zone.

The plant-microorganism interaction is a well-studied topic in the world of science due to the sustainable management of the ecosystems. The phyllosphere remains the habitat of some microorganisms where several interactions take place. In order to assess whether the mangrove leaves can harbor a bacterial population and analyze the abundance in these leaves microbiotas, leaf samples of mangroves species (Rhizophora mucronata) were collected in the mangroves of Ouroveni in East-Mbandjini, Grande-Comoros. Through the 16S rRNA genes sequencing, the results showed that in the different experimental group, 105303, 110873, 124703, 146954 and 112225 OTUs were identified respectively, where the canopy was open (C1), semi-open (C2), completely closed (C3), and where the plants are submerged (S) and non-submerged (NS) in seawater. The identified OTUs was positively correlated with leaves-wax (p < 0.05, r2 = 0.91), nitrogen (r2 = 0.72), phosphorus content (r2 = 0.62) and the factor “seawater” (r2 = 0.93). It was however highly and negatively correlated with the canopy cover (r2 = 0.93). Considering the factor "seawater", the relative abundance of bacteria in the submerged leaves was significantly higher compared to that from the non-submerged plants. By taking into account the factor “canopy cover”, it was revealed that more the canopy cover was open, the less was the relative abundance of bacteria. Thus, the finding of this present study affirm that the leaves of mangroves can be a major habitat to host a large population of bacteria that can be influenced by local abiotic factor.

Plants and microorganisms can coexist in such a way that each of these two heterospecific organisms benefit from this association. In the environment of plants there are several habitats of bacteria among them the phyllosphere which is the aerial part of the plant. The phyllosphere can be influenced by several factors including hydrocarbons. Thus, polycyclic aromatic hydrocarbons (PAHs) have been used to assess their influence on the phyllosphere microorganisms of the leaves of Gliricidia sepium. The results showed that the atmospheric concentrations of PAHs are rather high in rural areas. The spatial patterns of atmospheric concentrations of PAHs showed higher concentrations of naphthalene in the two experimental group due to the high road traffic. In the different experimental groups, 93626 and 96954 OTUs were identified in the leaves collected on the road (SR) and out of the road (SH), respectively. In this present study, the leaves harvested on the road which are more exposed to PAHs present a strongly elevated relative abundance of Actinobacteria and Bacilli. It can therefore easily deduce that these bacteria could have developed a kind of resistance to these road PAHs. On the other hand, bacteria belonging to the Alphaproteobacteria class are significantly less represented in this rural area.