Cartography of Free-Living Amoebae in Soil in Guadeloupe (French West Indies) Using DNA Metabarcoding

Free-living amoebae (FLA) are ubiquitous protists. Pathogenic FLA such as N. fowleri can be found in hot springs in Guadeloupe, soil being the origin of this contamination. Herein, we analyzed the diversity and distribution of FLA in soil using a targeted metataxonomic analysis. Soil samples (n = 107) were collected from 40 sites. DNA was extracted directly from soil samples or from FLA cultivated at different temperatures (30, 37 and 44 °C). Metabarcoding studies were then conducted through FLA 18SrDNA amplicons sequencing; amplicon sequence variants (ASV) were extracted from each sample and taxonomy assigned against SILVA database using QIIME2 and SHAMAN pipelines. Vermamoeba were detected in DNA extracted directly from the soil, but to detect other FLA an amoebal enrichment step was necessary. V. vermiformis was by far the most represented species of FLA, being detected throughout the islands. Although Naegleria were mainly found in Basse-Terre region, N. fowleri was also detected in Grand Terre and Les Saintes Islands. Acanthamoeba were mainly found in areas where temperature is approx. 30 °C. Vannella and Vahlkampfia were randomly found in Guadeloupe islands. FLA detected in Guadeloupe include both pathogenic genera and genera that can putatively harbor microbial pathogens, therefore posing a potential threat to human health.

Connecting seismicity, gravity-driven erosion and deposition at submarine normal faults: Insights from mapping of the 2004 Mw 6.3 Les Saintes earthquake rupture (French Antilles)

<p>During the ODEMAR 2013 and SUBSAINTES 2017 cruises we mapped the full extent of the seafloor rupture associated with the 2004 Mw 6.3 Les Saintes extensional earthquake. Near-bottom bathymetry acquired both with ROVs and AUVs along the Roseau Fault reveal a normal fault scarp developing in an extensional graben within the Caribbean volcanic arc, between the islands of Guadeloupe and Dominica. Optical inspection during ROV dives along the scarp’s base, where fault mirrors are well-preserved, allowed us to identify and characterize the coseismic fault rupture, and measure the coseismic displacements using both laser calipers and measurements performed on video-derived, textured 3D models, with accuracies better than 1 cm.</p><p> </p><p>The 2004 rupture extends ~20 km along the Roseau Fault, with a vertical displacement exceeding 2.5 m at its center, and tapering towards its ends. Local variations in apparent fault slip within a single 3D model (fault lengths of ~10 to 300 m) document local deposition of gravity debris cones at the base of the scarp, extending laterally between a few to tens of m, and covering the coseismic markers. Gullies eroding the footwall and depositing debris cones on the hanging wall do not show any significant displacement. Fault scarps on either side of the gully mouth instead record significant displacements, suggesting that either erosion or deposition along the gully bottom efficiently obliterated markers of coseismic deformation.</p><p> </p><p>We inspected all overlapping seafloor imagery acquired in December 2013 and April 2017, >10 years after the 2004 Les Saintes earthquake, extending laterally over >3 km of the Roseau Fault rupture.  Neither the bed of gullies crossing the rupture, nor the debris and rubble at the base of the fault scarp show any noticeable seafloor change indicating mass wasting and transport, and only changes in mobile sediment (e.g., ripples) can be detected between both image sets.  We identified a single area, ~2m wide, with apparent deposition of pebbles during these 3.25 years period, and associated with a local mass-wasting event.</p><p> </p><p>These observations point towards a systematic triggering of mass-wasting during seismic events, with deposition of rubble and rocks both at dejection cones at the mouth of gullies, or at the base of fault scarp sections displaying fault mirrors, covering or obliterating the coseismic markers. Therefore, long-term erosion and deposition processes here are gravity-driven and triggered by the history and magnitude of seismic events. Similar seismic controls may enable denudation of exposed oceanic lithosphere at fault scarps developing along and flanking mid-ocean ridges.</p>

Quaternary coral reef complexes as powerful markers of long-term subsidence related to deep processes at subduction zones: Insights from Les Saintes (Guadeloupe, French West Indies)

Geodetic measurements reveal modern rates of tectonic deformation along subduction zones, but the kinematics of long-term deformation are typically poorly constrained. We explore the use of submarine coral reefs as a record of long-term coastal vertical motion in order to determine deformation rate and discuss its origins. The Lesser Antilles arc results from the subduction of the American plates beneath the Caribbean plate and undergoes regional vertical deformation. Uplifted reefs along forearc islands are markers of the interplay between tectonics and sea-level variations since the late Pleistocene. We compared results from a numerical model of reef-island profile development to high-resolution marine geophysical measurements of Les Saintes reef plateau (Guadeloupe, French West Indies), a ∼20-km-wide, 250-m-thick submerged platform that lies at 45 m below sea level along the volcanic arc, to constrain its vertical deformation history. Models explore different scenarios over wide parameter domains including start time, basement morphology, sea level variations, reef growth rate, subaerial erosion rate, and vertical motion history. The major features of the plateau (its depth, internal structure, unusual double-barrier) is only reproduced in a context of subsidence, with a constant rate of −0.3 to −0.45 mm/yr since the late Pleistocene, or in a context of increasing subsidence, presently of ∼–0.2 mm/yr. Discussed in the framework of the forearc vertical deformation history, this result indicates subsidence is promoted by local faulting, volcanic, and deep subduction processes. Coseismic deformation accumulation could be a mechanism by which deformation builds up in the long-term. We show that subduction can drive long-term subsidence of a volcanic arc, and demonstrate that submarine reefs are powerful markers of long-term vertical motion.