International audienceThis 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 infuencing 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 thesouthwestern 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, specially of volcanic origin, but the physical habitat selection (geomorphology, substrate rugosity, percentage of soft substrate) seems to have littleimportance, while at least on the trophic structure and the distribution of endemic species
Recent survey of the epilithic diatoms in the running waters of Réunion Island led to the discovery of a new species of Achnanthidium. Achnanthidium palmeti sp. nov. belongs to the group of Achnanthidium taxa with terminal raphe fissures curved to the same side of the valve. The new species differs from other taxa in this group by a higher stria density and the areolae morphology along the axial area; moreover, apart from Achnanthidium latecephalum H. Kobayasi, A. palmeti sp. nov. is the only species having raphe vestiges. The new species was found in oligotrophic waters with very low conductivity and circumneutral pH.
The genus Kobayasiella includes species difficult or even impossible to identify in LM. Only EM allows observation of the ultrastructural features helping in diagnostic species circumscription. Recent surveys of the epilithic diatoms in the running waters of Reunion Island led to the discovery of a new species, K. bebourensis. This species differs from all previously described ones by the uniseriate striae composed of areolae occluded by a cribrum. Besides, two other species, the so rarely recorded K. jaagii (F. Meister) Lange-Bert. and K. micropunctata (H. Germ.) Lange-Bert., were collected in two alpine lakes of the French Pyrenees. K. jaagii lacks an umbilicus in the raphe, which is considered one of the most important diagnostic criterions of the genus. However, this species shows a combination of characteristics including it within the genus Kobayasiella. K. micropunctata is a typical representative of the genus Kobayasiella matching all the ultrastructural features of the genus. K. bebourensis and K. micropunctata have a cingulum composed of at least three connecting bands.
Recent surveys of the epilithic diatoms of Réunion Island led to the discovery of three new species: Crucicostulifera bebourensis, Encyonopsis cilaosensis, Encyonopsis palmeti. Crucicostulifera bebourensis is the second species to be included in this recently described genus typified by Crucicostulifera areolata (Hustedt) Taylor & Lange-Bertalot. Both species share the main diagnostic features of the genus. However, Crucicostulifera bebourensis differs from Crucicostulifera areolata (Hustedt) Taylor & Lange-Bertalot in the cingulum composed of at least three open bands whereas the latter species has a single valvocopula on each valve. Encyonopsis cilaosensis and Encyonopsis palmeti can be differentiated from other Encyonopsis species by a combination of characters including valve outline, number of striae in l0 µm, maximum length/breadth ratio, areolae structure and presence or absence of intermissio. Both new species show a particular organization of the cingulum. Crucicostulifera bebourensis occurs in acidic waters with very low conductivity and nutrient concentration. Encyonopsis cilaosensis is found in alkaline waters with high conductivity whereas Encyonopsis palmeti is reported from slighty alkaline waters with low conductivity.
Diatoms (Bacillariophyta) are ubiquitous microalgae, which present a huge taxonomic diversity, changing in correlation with differing environmental conditions. This makes them excellent ecological indicators for various ecosystems and ecological problematics (ecotoxicology, biomonitoring, paleo-environmental reconstruction …). Current standardized methodologies for diatoms are based on microscopic determinations, which is time consuming and prone to identification uncertainties. DNA metabarcoding has been proposed as a way to avoid these flaws, enabling the sequencing of a large quantity of barcodes from natural samples. A taxonomic identity is given to these barcodes by comparing their sequences to a barcoding reference library. However, to identify environmental sequences correctly, the reference database should contain a representative number of reference sequences to ensure a good coverage of diatom diversity. Moreover, the reference database needs to be carefully taxonomically curated by experts, as its content has an obvious impact on species detection. Diat.barcode is an open-access library for diatoms linking diatom taxonomic identities to rbcL barcode sequences (a chloroplast marker suitable for species-level identification of diatoms), which has been maintained since 2012. Data are accumulated from three sources: (1) the NCBI nucleotide database, (2) unpublished sequencing data of culture collections and more recently (3) environmental sequences. Since 2017, an international network of experts in diatom taxonomy curate this library. The last version of the database (version 9.2), includes 8066 entries that correspond to more than 280 different genera and 1490 different species. In addition to the taxonomic information, morphological features (e.g. biovolumes, chloroplasts, etc.), life-forms (mobility, colony-type) and ecological features (taxa preferences to pollution) are given. The database can be downloaded from the website (www6.inrae.fr/carrtel-collection/Barcoding-database/) or directly through the R package diatbarcode. Ready-to-use files for commonly used metabarcoding pipelines (Mothur and DADA2) are also available.
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