International audienceA combination of morphobathymetric studies, very high-resolution seismics, core sampling and radiocarbon age data is used to investigate the latest stage of the sedimentary infilling of incised valleys in southern Brittany, related to the Holocene transgression. Owing to the bedrock morphology of this highly irregular rocky coast, two main types of valleys are defined by topographic rocky highs parallel to the coastline: 1) wide and rather shallow incised valleys offshore from a topographic sill, 2) narrow and relatively deep valleys between the sill and the coast (ria-type valley). The sedimentary infilling in both types of valleys becomes highly differentiated as the transgression advances onto the coastal area. In the wide valley seaward of the topographic sill, the infilling consists mainly of offshore heterolithic facies while, in the ria-type valley, most of the infill is composed of brackish mudflat deposits and estuarine tidal muddy sands. As the transgression proceeds, the rocky highs are flooded and the whole area is finally covered by the offshore facies. Radiocarbon dating indicates that: 1) the marine ravinement surface is highly diachronous (a few thousand years cross-shore); 2) the top of the offshore facies, coarser and very shelly, represents an episode of condensed sedimentation from about 3000 to 4000 years ago, amalgamating the maximum flooding surface (MFS) and the highstand systems tract (HST). However, we observe a muddy drape, strongly bioturbated in places, in the most proximal areas, overlying the offshore facies. It is thought to represent the modern and most recent stage of sedimentary infilling. This mud cover is made of fine-grained sediments of fluvial and biological origin, and is interpreted as a prograding HST. It reflects an increased influx, partly due to human activities. Finally, the main features of incised valley sedimentary infilling in a rocky coast context with low sediment supply can be characterized by (i) the very strong control of bedrock morphology, (ii) the diachronous character of the transgression, (iii) the late position of the MFS, and (iv), the highly reduced volume of the HST

Flatfishes bury themselves for camouflage and protection. Whereas species-specific preferences for certain sediments were previously shown, the role of scales in interaction with sediment has not been investigated. Here, scale morphology and sediment friction were examined in four European pleuronectiforms: Limanda limanda, Platichthys flesus, Pleuronectes platessa, and Solea solea. All species had different scale types ranging from cycloid to ctenoid scales. On the blind side, the number of scales is higher and scales have less ctenial spines than on the eye side. The critical angle of sediment sliding (static friction) significantly depended on the grain size and was considerably higher on the eye side. The effect of mucus was excluded by repeated measurements on resin replicas of the skin. Our results demonstrate the impact of scale morphology on sediment interaction and give an insight about the ability of scales to keep sand. Exposed scales and a higher number of ctenial spines on the eye side lead to an increase of friction forces, especially for sediments with a smaller grain size. Our results suggest that the evolution of scales was at least partly driven by their interactions with sediment which confirms the relevance of sediment for the distribution and radiation of Pleuronectiformes.

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Estuaries are coastal areas controlled by hydrodynamic factors such as sea-level changes, waves and tidal currents, and river discharge. This study focuses on the Vilaine Estuary which M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT27/06/2015, page 2/38 is strongly impacted by human activity after construction of Arzal dam in 1970. The purpose of this research is to differentiate the role of natural from anthropogenic factors on sediment dynamics within the Vilaine Estuary. We are proposing a hypothetical model based on the hydrodynamic modification and morpho-sedimentary development by analyzing the natural estuarine evolution and the impact of human alteration to the natural system by utilizing datasets including river discharge, tidal currents, winds and wave activities to further combine with photographic, bathymetric, topographic and sedimentary surveys.Results show that waves carry sediment from the sea and rework local sediments. The river damming is reducing the tidal prims and leads to the fall of tidal currents. This new situation supports the sediment deposition and reduces at the same time the accommodation space which decrease tidal currents in feed-back. The Vilaine Estuary is therefore coming close to a bay-type functioning which leads to a channel narrowing, a drastic increase of the tidal flat zone, an acceleration of erosional processes affecting the main channel, salt marsh and all associated depositional systems. We propose a hypothetical model showing that this evolution took place in two steps and we show that the dam has an effect to accelerate a natural infilling of the estuary.