Southwestern Indian Ocean Region Research Articles

Tropical cyclones position and intensity in the Southwest Indian Ocean as represented by CFS and ERA5 atmospheric reanalysis datasets

AbstractTropical cyclones are the most devastating meteorological systems that affect the Southwestern Indian Ocean (SWIO) bordering nations. The understanding of their track and intensity evolution is essential for the characterization of the systems. The National Centers for Environmental Prediction–Climate Forecast System (CFS) dataset and the ECWMF fifth‐generation reanalysis (ERA5) are evaluated against best‐track data from the International Best‐Track Archive for Climate Stewardship (IBTrACS) from 1980 to 2019 cyclone seasons. The cyclones were tracked within the reanalyses using a tracking algorithm based on relative vorticity and identified using a spatiotemporal matching method. Climatology from IBTrACS showed significant negative (positive) trend in the total number (number of intense) of systems; however, the evaluation of trends has to be cautious because it may be limited due to uncertainties in the first decades of data. Results for reanalyses showed that both performed similarly although some peculiarities were noted. CFS presented a slightly higher probability of detection, related to its special treatment of tropical cyclone‐like vortex, being able to reproduce all systems between 2000 and 2019. For positions, the majority of the systems have average errors around 50–60 km and the errors generally decrease with the intensity of the systems in both reanalyses, with ERA5 being slightly better during the early stages, while CFS outperforms ERA5 for intensity beyond the IBTrACS's moderate tropical storm category. Intensity follows a reverse pattern of position, with reanalyses largely degrading systems' intensity as they intensify. CFS (ERA5) appeared to be slightly better in terms of maximum wind (minimum sea‐level pressure), representing stronger systems although both datasets were unable to reproduce wind intensities beyond the tropical cyclone category. All evaluated parameters showed improvements when the most recent data period (2000–2019) is considered, especially in ERA5, tailored to an improved quality of the observations that are used to generate best‐track data and also to nudge the reanalyses through data assimilation. Based on the reanalyses characteristics revealed here, the choice of the most suitable dataset to address a specific study within the SWIO region may be dependent on the desired parameters and period.

Seasonal Prediction of Tropical Cyclones and Storms over the Southwestern Indian Ocean Region Using the Generalized Linear Models

Tropical cyclones (TCs) and storms (TSs) are among the devastating events in the world and southwestern Indian Ocean (SWIO) in particular. The seasonal forecasting TCs and TSs for December to March (DJFM) and November to May (NM) over SWIO were conducted. Dynamic parameters including vertical wind shear, mean zonal steering wind and vorticity at 850 mb were derived from NOAA (NCEP-NCAR) reanalysis 1 wind fields. Thermodynamic parameters including monthly and daily mean Sea Surface Temperature (SST), Outgoing Longwave Radiation (OLR) and equatorial Standard Oscillation Index (SOI) were used. Three types of Poison regression models (i.e. dynamic, thermodynamic and combined models) were developed and validated using the Leave One Out Cross Validation (LOOCV). Moreover, 2 × 2 square matrix contingency tables for model verification were used. The results revealed that, the observed and cross validated DJFM and NM TCs and TSs strongly correlated with each other (p ≤ 0.02) for all model types, with correlations (r) ranging from 0.62 - 0.86 for TCs and 0.52 - 0.87 for TSs, indicating great association between these variables. Assessment of the model skill for all model types of DJFM and NM TCs and TSs frequency revealed high skill scores ranging from 38% - 70% for TCs and 26% - 72% for TSs frequency, respectively. Moreover, results indicated that the dynamic and combined models had higher skill scores than the thermodynamic models. The DJFM and NM selected predictors explained the TCs and TSs variability by the range of 0.45 - 0.65 and 0.37 - 0.66, respectively. However, verification analysis revealed that all models were adequate for predicting the seasonal TCs and TSs, with high bias values ranging from 0.85 - 0.94. Conclusively, the study calls for more studies in TCs and TSs frequency and strengths for enhancing the performance of the March to May (MAM) and December to October (OND) seasonal rainfalls in the East African (EA) and Tanzania in particular.

Sustained Decadal Warming Phase in the Southwestern Indian Ocean since the Mid-1990s

Regardless of the slowdown in global warming during the hiatus period, sea surface temperatures (SSTs) in the southwestern Indian Ocean (SWIO) have experienced sustained decadal warming for more than two decades since the mid-1990s. The SWIO SSTs warmed steadily during 1996–2016, causing a warming hot spot of 0.4 K decade−1 in a large region east of Madagascar. An upper-layer heat budget analysis indicated that heat advection by ocean currents was the greatest contributor to the warming of the SWIO SSTs. The existence of an anticyclonic geostrophic current along the western boundary of the SWIO tended to maintain such warming by transporting warmer water from the west into the SWIO region. In addition, net positive heat transport by ocean currents also occurred at the southern boundary of the SWIO as the climatological northward transport of cold water from the Southern Ocean weakened. This reduction in northward ocean currents at the surface was caused by local wind stress changes, leading to a southward Ekman current. Below the surface, an anticyclonic geostrophic current pattern existed around the warming center near the southeastern SWIO, which reduced the transport of cold waters from the Southern Ocean and warmed the SWIO. These processes near the two boundaries formed a self-sustaining positive feedback mechanism and favored the maintenance of sustained warming in the SWIO. More attention is needed to analyze the sustained long-lasting warming in the SWIO, as it is a unique phenomenon occurring under the background of the ongoing global warming.

Upeneus floros, a new goatfish from South Africa and Mozambique, with updated taxonomic accounts for U. guttatus and U. pori and a key to Western Indian Ocean Upeneus species (Mullidae).

The highly diverse goatfish genus Upeneus (Mullidae) requires enhanced attention regarding the possible occurrence of undescribed species in insufficiently explored regions. This study focuses on the South-Western Indian Ocean region (SWIO), and on the so-called japonicus-group, a taxonomic species group of Upeneus. Based on in-situ observations and collections in Sodwana Bay, KwaZulu-Natal, South Africa, the Floros goatfish, U. floros n. sp., is described. Detailed comparative studies of colour patterns and morphological characters of all other 13 japonicus-group species were undertaken as well as COI barcoding. The new species occurs in the coastal area between Angoche, N Mozambique and KwaZulu-Natal and partly overlaps in distribution with two similar species, U. guttatus, widely distributed in the Indo-W Pacific, and U. saiab, assumed to be endemic in a small area off Angoche. Two additional japonicus-group species occurring in the SWIO, U. seychellensis from the Seychelles Bank and U. pori from the Mediterranean Sea (as Lessepsian migrant), Northern Red Sea and Madagascar, were also compared. Because specimens as well as in-situ photographs of U. floros have been erroneously identified as either U. guttatus or U. pori during previous studies, updated taxonomic accounts and diagnoses are provided for these species taking size-related and population differences into account. For U. pori, of which a single preserved specimen from SW Madagascar was known so far, a new record from NE Madagascar is reported based on three specimens and a fresh-colour photo. Upeneus floros can be distinguished from U. guttatus and U. pori by a combination of three characters: head length, first dorsal-fin height and number of gill rakers. Upeneus guttatus can be distinguished from the other two species by disproportionally higher anterior dorsal-fin spines vs. a proportional decrease of dorsal-fin spines in height, barbels mostly yellow vs. white or creamy-white, and slightly fewer pectoral-fin rays. COI barcoding detected a clear distinction between U. guttatus and U. floros and U. pori, respectively, but no significant divergence between the two latter species. COI barcoding also failed to differentiate several other Upeneus species which are clearly distinguished morphologically. Possible interrelationships between species distribution patterns and physical oceanography are discussed. An identification key for the 22 WIO Upeneus species is provided.

Co-circulation and characterization of novel African arboviruses (genus Ephemerovirus) in cattle, Mayotte island, Indian Ocean, 2017.

SummaryMayotte is an island located in the Mozambique Channel, between Mozambique and Madagascar, in the South Western Indian Ocean region. A severe syndrome of unknown aetiology has been observed seasonally since 2009 in cattle (locally named “cattle flu”), associated with anorexia, nasal discharge, hyperthermia and lameness. We sampled blood from a panel of those severely affected animals at the onset of disease signs and analysed these samples by next‐generation sequencing. We first identified the presence of ephemeral bovine fever viruses (BEFV), an arbovirus belonging to the genus Ephemerovirus within the family Rhabdoviridae, thus representing the first published sequences of BEFV viruses of African origin. In addition, we also discovered and genetically characterized a potential new species within the genus Ephemerovirus, called Mavingoni virus (MVGV) from one diseased animal. Finally, both MVGV and BEFV have been identified in cattle from the same herd, evidencing a co‐circulation of different ephemeroviruses on the island. The clinical, epidemiological and virological information strongly suggests that these viruses represent the etiological agents of the observed “cattle flu” within this region. This study highlights the importance of the strengthening and harmonizing arboviral surveillance in Mayotte and its neighbouring areas, including Africa mainland, given the importance of the diffusion of infectious diseases (such as BEFV) mediated by animal and human movements in the South Western Indian Ocean area.

Genetic diversity and spatial population structure of a deepwater snapper, Pristipomoides filamentosus in the south-west Indian Ocean.

The crimson jobfish, Pristipomoides filamentosus Valenciennes, 1830 is an economically important demersal species largely distributed in the Indo-Pacific region. Pristipomoides filamentosus constitutes a significant portion of catch landed in demersal fisheries throughout the species' distribution range. Despite the species' economic importance, there is insufficient data to guide the species' conservation management, especially within the south-western (SW) Indian Ocean region. The aims of the present study were to conduct a population genetic analysis to determine the spatial genetic structure of the species and, whether different management units could be established in the region, using an analysis of both mitochondrial DNA fragment (mtDNA), and nuclear microsatellite loci. A total of 193 fin clips were collected from Seychelles, Kenya, Tanzania, Comoros, Madagascar, Mauritius and South Africa, with each having an established fishery of the species. Both haplotype diversity (h) and expected heterozygosity (HE) for mtDNA and microsatellite loci respectively were generally high for all localities, except for Seychelles where both diversity indices were at the lowest (i.e. h = 0.429 ± 0.134; HE = 0.647 ± 0.059). Even though mtDNA failed to detect population differentiation, the hypervariable microsatellite loci consistently indicated presence of four genetic clusters irrespective of the clustering approach applied. Based on present results, we propose recognising the four clusters as distinct fisheries management units of the species in the SW Indian Ocean region.

Chikungunya: Its History in Africa and Asia and Its Spread to New Regions in 2013-2014.

Chikungunya virus (CHIKV) is transmitted by Aedes aegypti and Aedes albopictus mosquitoes and causes febrile illness with severe arthralgia in humans. There are 3 circulating CHIKV genotypes, Asia, East/Central/South Africa, and West Africa. CHIKV was first reported in 1953 in Tanzania, and up until the early 2000s, a few outbreaks and sporadic cases of CHIKV were mainly reported in Africa and Asia. However, from 2004 to 2005, a large epidemic spanned from Kenya over to the southwestern Indian Ocean region, India, and Southeast Asia. Identified in 2005, the E1 glycoprotein A226V mutation of the East/Central/South Africa genotype conferred enhanced transmission by the A. albopictus mosquito and has been implicated in CHIKV's further spread in the last decade. In 2013, the Asian CHIKV genotype emerged in the Caribbean and quickly took the Americas by storm. This review will discuss the history of CHIKV as well as its expanding geographic distribution.

Marine flora of the Iles Eparses (Scattered Islands): A longitudinal transect through the Mozambique Channel

The diversity of marine macrophytes of small islands in the South Western Indian Ocean region has been poorly documented and little or no information is available for the Iles Eparses (or Scattered Islands) in the Mozambique Channel. We present the first species checklist for the three largest islands of the Iles Eparses: Europa, Juan de Nova and Glorioso. Overall, with a total of 321 marine macrophyte species recorded (incl. 56% Rhodophyta, 27% Chlorophyta, 15% Phaeophyceae and 2% Magnoliophyta; Europa: 134 spp., Juan de Nova: 157 spp. and Glorioso: 170 spp.) these islands harbour 23.5% of the total species recorded for the Mozambique Channel region. We report 36 new records for the Mozambique Channel including 29 undescribed new and cryptic species. Our results highlight a decrease in species richness southward in the Channel. Because of their longitudinal arrangement between the northern and the southern ends of the Channel and their central position, Europa, Juan de Nova and Glorioso Islands represent data points of particular biogeographical interest and could be critical ‘stepping stones’ for connectivity in the highly dynamic Mozambique Channel region.

First overview of the Culicoides Latreille (Diptera: Ceratopogonidae) livestock associated species of Reunion Island, Indian Ocean

This study establishes the first faunistic inventory of livestock associated Culicoides (Diptera: Ceratopogonidae) species of Reunion Island (Indian Ocean), where bluetongue and epizootic hemorrhagic disease are regularly recorded. Single night-catches were performed at 41 sites using light suction traps at altitudes ranging from 0 to 1525m, from March to April 2005. Five species were recorded: Culicoides imicola, Culicoides bolitinos, Culicoides enderleini, Culicoides grahamii, and Culicoides kibatiensis, among which at least the first three species are known to be involved in virus transmission to ruminants and equids. This is the first record of C. bolitinos, C. kibatiensis, and C. enderleini on the island. C. imicola was the most abundant species along the sea coast. C. bolitinos was more abundant inland and on two sites on the east coast. C. kibatiensis and C. grahamii were less abundant than the other three species and limited to two foci.Spatial distribution analysis of the different species showed that C. bolitinos, C. enderleini and C. imicola were collected at low altitudes, while the other two species were found at higher altitude. A morphological identification key for adult females and males is given, as well as cytochrome oxydase subunit I sequences. Phylogenetic reconstructions showed a clear divergence between C. bolitinos from Reunion Island and mainland Africa. This monograph will help to identify the Culicoides species in the poorly known entomological fauna of the south-western Indian Ocean region.

Fish community structure in relation to environmental variation in coastal volcanic habitats

This study constitutes one of the few works conducted on the colonization of recent lava flows by fish communities in coral reef environment. It attempted to describe the mechanisms of colonization and environmental variables influencing the structure of communities on the lava flows of the Piton de la Fournaise volcano at Reunion Island. It also proposed some hypotheses on the mechanisms of selection and speciation of endemic species of the southwestern Indian Ocean region, particularly diversified on the most recent lava flows of the Piton de la Fournaise, and provided a model of distribution of environmental and fish assemblage variables in four homogeneous patterns of colonization (landscapes) retained within the study area. The results showed fish community structure strongly related to measured environmental variables, of which depth, width of the island shelf, age of the lava flow and distance to the most recent lava flow were the most influential. It also appeared that the maximum endemic species richness was measured on the shallower stations, with narrow insular shelf, located on recent lava flows, near the lava flow from the eruption of 2007 (latest volcanic event). These characteristics define a harsh environment, to which endemic species seem well-adapted due in particular to their strong demographic and dietary flexibility. Finally, the patterns of colonization were characterized by significantly different environmental variables. The four homogeneous areas, defined by two geomorphological features, basalt blocks and drop-offs, nested within two locations, inside and outside the volcanic enclosure (current caldera), hosted fish communities whose dominant diets mainly depend on the nature, the abundance and the accessibility of available food resources. Overall, the study highlights that during early stages of ecological succession, site selection by fish communities is highly dependent on environmental constraints, especially of volcanic origin, but the physical habitat selection (geomorphology, substrate rugosity, percentage of soft substrate) seems to have little importance, while at least on the trophic structure and the distribution of endemic species.

Highly Diverse Morbillivirus-Related Paramyxoviruses in Wild Fauna of the Southwestern Indian Ocean Islands: Evidence of Exchange between Introduced and Endemic Small Mammals

The Paramyxoviridae form an increasingly diverse viral family, infecting a wide variety of different hosts. In recent years, they have been linked to disease emergence in many different animal populations and in humans. Bats and rodents have been identified as major animal populations capable of harboring paramyxoviruses, and host shifting between these animals is likely to be an important driving factor in the underlying evolutionary processes that eventually lead to disease emergence. Here, we have studied paramyxovirus circulation within populations of endemic and introduced wild small mammals of the southwestern Indian Ocean region and belonging to four taxonomic orders: Rodentia, Afrosoricida, Soricomorpha, and Chiroptera. We report elevated infection levels as well as widespread paramyxovirus dispersal and frequent host exchange of a newly emerging genus of the Paramyxoviridae, currently referred to as the unclassified morbillivirus-related viruses (UMRVs). In contrast to other genera of the Paramyxoviridae, where bats have been shown to be a key host species, we show that rodents (and, in particular, Rattus rattus) are significant spreaders of UMRVs. We predict that the ecological particularities of the southwestern Indian Ocean, where small mammal species often live in densely packed, multispecies communities, in combination with the increasing invasion of R. rattus and perturbations of endemic animal communities by active anthropological development, will have a major influence on the dynamics of UMRV infection. Identification of the infectious agents that circulate within wild animal reservoirs is essential for several reasons: (i) infectious disease outbreaks often originate from wild fauna; (ii) anthropological expansion increases the risk of contact between human and animal populations and, as a result, the risk of disease emergence; (iii) evaluation of pathogen reservoirs helps in elaborating preventive measures to limit the risk of disease emergence. Many paramyxoviruses for which bats and rodents serve as major reservoirs have demonstrated their potential to cause disease in humans and animals. In the context of the biodiversity hot spot of southwestern Indian Ocean islands and their rich endemic fauna, we show that highly diverse UMRVs exchange between various endemic animal species, and their dissemination likely is facilitated by the introduced Rattus rattus. Hence, many members of the Paramyxoviridae appear well adapted for the study of the viral phylodynamics that may be associated with disease emergence.

The Indian Ocean in Transatlantic Slavery

Despite the considerable distance and danger in transporting slaves from the southwestern Indian Ocean region to the Americas, ships carried nearly 550,000 slaves to the Americas between 1624 and 1860. Prior attempts to understand the place of the Indian Ocean in the transatlantic slave trade have been limited in scope, but the transatlantic slave trade database provides us with access to unprecedented statistics and estimates that shed new light on this forced migration. The study of this slave trade also offers insights into the much larger movement of slaves across the Indian Ocean as a whole.

On the distribution of calcium, magnesium, sulphate and boron in the southwestern Indian Ocean region of the Southern Ocean : Naik, Sugandhini, R.J. Noronha, P.V. Shirodkar and R. Sen Gupta, 1983. In: Scientific Report of First Indian Expedition to Antarctica. Technical Publication No. 1; Department of Ocean Development, New Delhi, India; pp. 87–94

On the distribution of calcium, magnesium, sulphate and boron in the southwestern Indian Ocean region of the Southern Ocean : Naik, Sugandhini, R.J. Noronha, P.V. Shirodkar and R. Sen Gupta, 1983. In: Scientific Report of First Indian Expedition to Antarctica. Technical Publication No. 1; Department of Ocean Development, New Delhi, India; pp. 87–94