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International audience; Biophysical interactions are influential in determining the scale of key ecological processes within marine ecosystems. For oceanic predators, this means foraging behaviour is influenced by processes shaping the distribution of prey. However, oceanic prey is difficult to observe and its abundance and distribution is regionally generalised. We use a spatiotemporally resolved simulation model to describe mid‐trophic prey distribution within the Southern Ocean and demonstrate insights that this modelled prey field provides into the foraging behaviour of a widely distributed marine predator, the southern elephant seal.From a five‐year simulation of prey biomass, we computed climatologies of mean prey biomass (average prey conditions) and prey biomass variability (meso‐scale variability). We also compiled spatially gridded metrics of seal density and diving behaviour from 13 yr of tracking data. We statistically modelled these metrics as non‐linear functions of prey biomass (both mean and variability) and used these to predict seal distribution and behaviour. Our predictions were consistent with observations (R2adj = 0.23), indicating that seals aggregate in regions of high mesoscale activity where eddies concentrate prey. Here, seals dived deeper (R2marg = 0.12, R2cond = 0.51) and spent less time hunting (R2marg = 0.05, R2cond = 0.56), likely targeting deep but profitable prey patches. Seals generally avoided areas of low eddy activity where prey was likely dispersed. Most seals foraged south of the Subantarctic Front, despite north of the front exhibiting consistently high simulated prey biomasses. This likely reflects seal prey or habitat preferences, but also emphasises the importance of mesoscale prey biomass variability relative to regionally high mean biomass. This work demonstrates the value of coupling mechanistic representations of prey biomass with predator observations to provide insight into how biophysical processes combine to shape species distributions. This will be increasingly important for the robust prediction of species’ responses to rapid system change.

International audience; Background and aims - Despite the ongoing taxonomical revision of the entire (sub)-Antarctic diatom flora, our knowledge on the ecology and community associations of moss-inhabiting diatoms is still rather limited. In the present study, our research aim was to survey the diversity together with the environmental factors structuring the epiphytic moss diatom communities on Ile Amsterdam (TAAF), a small volcanic island in the southern Indian Ocean. Material and methods - A morphology-based dataset and (physico)chemical measurements were used for the ecological and biogeographical analysis of moss-inhabiting diatom flora from Ile Amsterdam. In total, 148 moss samples were examined using light microscopy. Key results - The analysis revealed the presence of 125 diatom taxa belonging to 38 genera. The uniqueness of the Ile Amsterdam diatom flora is mainly reflected by the species composition of the dominant genera Pinnularia, Nitzschia, Humidophila, and Luticola, with a large number of unknown and often new species. This highly specific diatom flora, together with differences in the habitats sampled and the isolated position of the island, resulted in very low similarity values between Ile Amsterdam and the other islands of the Southern Ocean. From a biogeographical point of view, 40% of the taxa have a typical cosmopolitan distribution, whereas 22% of all observed species can be considered endemic to Ile Amsterdam, with another 17% species showing a restricted sub-Antarctic distribution. The NMDS analysis, based on a cluster dendrogram, divides the samples into six main groups. For each group, indicator species were determined. Both environmental data and diatom distributions indicate that apart from elevation, specific conductance, pH, and moisture are the major factors determining the structure of moss-inhabiting diatom communities on Ile Amsterdam. Conclusion - The isolated geographic position and unique climatological and geological features of the island shaped the presence of a unique diatom flora, characterised by many endemic species. The results of the study are of prime importance for further (palaeo-)ecological and biogeographical research.

International audience; The southern Indian Ocean is believed to be a natural territory for blue and fin whales. However, decades after commercial and illegal whaling decimated these populations, little is known about their current status, seasonal habitat or movements. Recent passive acoustic studies have described the presence of 4 acoustic populations of blue whales (Antarctic and 3 ‘pygmy’ types), but are generally limited temporally and geographically. Here, we examine up to 7 yr of continuous acoustic recordings (2010-2016) from a hydrophone network of 6 widely spaced sites in the southern Indian Ocean, looking for the presence of Antarctic and pygmy blue and fin whales. Power spectral density analyses of characteristic and distinct frequency bands of these species show seasonal and geographic differences among the different populations, and the overall patterns for each display interannual consistencies in timing and occurrence. Antarctic blue and fin whales are recorded across the hydrophone network, mainly from austral autumn to spring, with peak intensity in winter. Pygmy blue whales show spatial variation: Madagascan pygmy blue whales are mainly present in the west of the network, while the Australian call type is heard at the eastern sites. Both populations share a common seasonality, with a presence from January to June. Finally, the Sri Lankan call type is recorded only on a single site in the northeast. These results confirm the importance of the southern Indian Ocean for several populations of endangered large whales and present the first long-term assessment of fin whales in the southern Indian Ocean.

The influence of northern high latitude climate variability on the South Asian Summer Monsoon has been extensively studied using both instrumental and proxy based climate data. In comparison, only a few studies have attempted to explore the southern high latitude association of the South Asian Summer Monsoon. Here we present a 145 kyr long new data (oxygen and carbon isotopic abundance of two depth-stratified species of foraminifera viz. Globigerinoides ruber and Globorotalia menardii) from a sediment core on sub-millennial to millennial scale resolution from the southwestern tropical Indian Ocean - a region swept by the southeasterly wind during boreal summer (referred to as ‘summer’ hereafter), which transforms to the southwest monsoon wind after crossing the equator. The available records of past summer monsoon variability are predominantly based on reconstruction of downstream hydrology, which is identifiable with the thermodynamics of the system. The present study is a reconstruction of the dynamics of the summer monsoon circulation from an upstream region which is ideally suited for exploring its link with the southern high-latitude climate. We identified several occurrences of interchanging intense and weak monsoon circulation events during the 145 kyr period. We further find that warm (cold) conditions in Antarctica show a near one-to-one coupling with weak (strong) monsoon phases, suggesting a strong mechanistic link between them during the period.

A new endemic species of Sagina L., Sagina hookeri Timana, sp. nov. (Caryophyllaceae) is described for the flora of Ile Amsterdam, in the southern Indian Ocean (French Southern and Antarctic Lands). Differences between this taxon and S. diffusa (Hook.f.) Timana (endemic to the neighboring island of Saint-Paul) and S. procumbens L. (introduced in several circum-austral islands) are discussed, and an identification key to those three Sagina species occurring in Saint-Paul and Amsterdam islands is presented.

International audience; Diatom and water chemistry samples were collected during the austral summer of 2007 from lakes, streams and bogponds on Ile Amsterdam (TAAF), a small island located in the southern Indian Ocean. A diverse diatom flora of 104 taxa was found, dominated by several Pinnularia taxa, Frustulia lebouvieri, Kobayasiella subantarctica, Eunotia paludosa, E. muscicola and Planothidium subantarcticum. Biogeographically, the Ile Amsterdam freshwater diatom flora is composed of cosmopolitan, sub-Antarctic and endemic elements. The biogeographical analysis showed that almost 17% of all observed taxa can be considered endemic to Ile Amsterdam with an additional 14% showing an exclusive sub-Antarctic distribution. The flora can be considered as typical for oceanic islands based on its disharmonic composition with several genera lacking and other being overrepresented. Canonical Component Analysis was used to classify the samples based on their chemical characteristics, revealing that, specific conductance, sulphate and pH were the main factors dividing the samples into four different groups. The geological history of the island in combination with the climate and the specific environmental features of the main habitat in the Caldera most likely shaped the composition of the actual diatom communities.

International audience; Lichens collected in 2007 on Ile Amsterdam and Ile Saint Paul in the Indian Ocean are reported. The diversity is rather poor, with 77 and 40 species collected, respectively. Of those, the islands share 25 species. Caloplaca amsterdamensis Aptroot & Ertz is newly described. Two species, viz. Lecanora subsulphurata and Opegrapha consimillima are the only other endemic species known from these islands. The lichen flora is distinctly temperate to subtropical, with only a few subantarctic elements. Temperate oceanic islands in other oceans share significantly more species with Ile Saint Paul and/or Ile Amsterdam than the neighbouring subantarctic islands. All previously reports of lichens from these islands have been examined and cross-referenced, leading to the new synonymization of several species previously described from Ile Saint Paul, viz. Buellia sancti-pauli, Caloplaca fulgescens, Lecidea conioptoides, L. parasemopsis, L. sancti-pauli, and Verrucaria aethioboliza. It also transpired that the previous report of the genus Orceolina from Ile Saint Paul is incorrect, with the effect that the genus is still only known from Kerguelen. Nearly all species are new records for Ile Amsterdam and most are new for Ile Saint Paul. Some species, viz. Bacidia arnoldiana, B. egenula, B. fraxinea, C. limonia, C. oasis, C. ulcerosa, Fuscopannaria ignobilis, Pertusaria amarescens, Porina curnowii, Porpidia ochrolemma, Pyrenula laevigata, Scoliciosporum intrusum (with the new synonym S. camptosporum), and Verrucaria dolosa are reported for the first time from the Southern Hemisphere.

7 páginas, 2 figuras, 3 tablas, The coastal octopus at Saint Paul and Amsterdam Islands is Octopus vulgaris Cuvier 1797. Meristic and morphological characters, along with phylogenetic analysis of COI and COIII DNA sequences, were used to identify 11 animals collected in 2000 or 2001. The range of the species is therefore expanded to include the oceanic islands of the central southern Indian Ocean. The trees also depicted the genus Octopus as polyphyletic and O. vulgaris sense Cuvier or sensu stricto as monophyletic, The study was partially supported by a FCT grant (PTDC/BIA-BEC/098553/2008) to MP-L. ÁR was supported by a fellowship (Introduction to Research and JAE pre-doctoral) from the CSIC

Large particles (> 60 mu m) were collected using in situ pumps deployed at 30 and 200 m depth at 2 typical stations in the southern Indian Ocean (Polar Front Zone [PFZ] and Sub-Antarctic Area [SAr]). The samples were incubated in vitro with their own bacterial assemblages for 7 to 17 days in batches under oxic conditions in the dark. Particulate organic carbon (POC) and sugars were monitored over time. Particulate sugars (PCHO-C) accounted for 5 to 20% of POC in the SAr, while they represented 5 to 8% of POC in the PFZ station at the beginning of the experiments. Molecular level analysis indicated that at the time of collection, ribose was among the most abundant sugars (18 to 30 wt% of PCHO-C) at the PFZ station and was rapidly degraded (k = 0.051 to 0.058 d(-1)) over the course of the experiment, while this sugar was below detection limits in the SAr. Our results also showed an increase in the relative abundance of deoxysugars (fucose and rhamnose), suggesting that these sugars have the potential to be used as indicators of the bacterial activity and evaluate the degradation status of POM in both areas. The kinetic study indicated that pentoses were degraded faster than hexoses, while deoxysugars exhibited the lowest degradation rates. This study demonstrated that total sugar degradation rates do not reflect the rates of all individual components, but rather a disparate collection of rates among sugars classes and individual sugars, which very likely can vary significantly in relation to the origin of particles.