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The PAH contamination level and biochemical composition of sinking particles and surficial sediments (0–0.5 cm layer) were assessed at a rural coastal site in the northwestern Mediterranean Sea. Surficial sediment contamination (≈20 ng g−1) was considerably lower than at other Mediterranean sites, yet particles collected in sediment traps had 6–8 times more PAH. Contaminated particles were mostly marine in origin. Temporal variation of contamination levels correlated with organic content of the particles, but some of the observed variability could be attributed to seasonal changes in pyrolytic PAH production. Sinking organic particles were potentially as readily digestible as surficial sediments for prospective consumers however, transfer of PAHs along the benthic food chain is probably enhanced because of the particles'' higher nutritional value. [Copyright &y& Elsevier]

A cost-effective technology has emerged which combines multispectral sensors mounted on Unmanned Aerial Vehicles (UAVs). This technology has a promising potential for monitoring water quality in coastal environments. Our study aimed at evaluating this technology to infer the spatial distribution of chlorophyll a concentration [Chl-a] (in µg·L−1) and turbidity (FNU) in surface waters. The multispectral sensor measured reflectance at 4 distinct wavelength bands centered on 448 nm, 494 nm, 550 nm and 675 nm, hence providing 4 datasets {R(448), R(494), R(550), R(675)}. We investigated the potential of estimating [Chl-a] and turbidity based on reflectance ratios and indexes calculated from two different wavelength bands. The calibration functions were formulated based on the property that any of the reflectance measurements was linearly correlated to any other one. The calibration was performed from 35 measurements of reflectance, [Chl-a] and turbidity collected in seven sites in the U.K. between May and August 2017. Two calibration functions derived from the index δ=(R(550) − R(448))/(R(550) + R(448)) presented the best fit and explained 78% of the total variance for [Chl-a] and 74% for turbidity measurements, respectively. Calibration functions were then inversed to estimate [Chl-a] and turbidity from reflectance measurements. Finally, we performed a validation test using independent measurements from three sites in France, in July 2017. The resulting maps show a pattern with higher [Chl-a] in lower turbidity areas. However, discrepancies between the observed and re-calculated values and difficulties in validating low turbidity values suggest that site-specific calibrations should be performed at each investigated location. [ABSTRACT FROM AUTHOR]

An integrated analysis of the pelagic ecosystems of the Ligurian Sea is performed combining time series (1995-2005) of several zooplankton groups (one group for copepods smaller than 0.724mm³ and nine groups for individuals larger than 0.724 mm³, i.e. large copepods, decapod larvæ, other crustaceans, chaetognaths, appendicularians, pteropods, thaliaceans, gelatinous predators and other zooplankton), chlorophyll-α, nutrients, salinity, temperature, density, and local weather at Point B coastal station (Northern Ligurian Sea). From 1995 to 2000 winters were wet and mild resulting in lower winter sea surface density. These years showed lower than average nutrients and zooplankton concentrations while chlorophyll-α biomass was high. After 2000, winters were colder and dryer resulting in higher sea surface density. Nutrients and zooplankton showed higher concentrations while chlorophyll-α was lower than average. The ca. 2000 change was observed for most zooplankton groups with a one-year delay for some groups. Inter-annual variability within each period was also observed. The observed patterns suggest that the pelagic ecosystem trophic state at the studied point is mostly set by the winter forcing on the vertical mixing that upwells nutrients to the surface sustaining primary production. Surprisingly, low chlorophyll-α biomass in high nitrate and zooplankton conditions during the well mixed years suggest that phytoplankton biomass is controlled by grazers. The proposed mechanisms of stronger winter vertical mixing hold for most of the time series, but specific years with contradicting patterns suggest also the possible influence of the summer climate. A review of recent literature suggests that changes in the pelagic ecosystem are not limited to the studied site but concern also the central Ligurian Sea. [ABSTRACT FROM AUTHOR]

An integrated analysis of the pelagic ecosystems of the Ligurian Sea is performed combining time series of different zooplankton groups (small and large copepods, chaetognaths, appendicularians, pteropods, thaliaceans, decapods larvae, other crustaceans, other gelatinous and other zooplankton), chlorophyll-a and nutrients, seawater salinity, temperature and density and local weather at the Point B coastal station (Northern Ligurian Sea). From January 1995 to December 2005, a shift in most variables occurred ca. 2000. From 1995 to 2000 winters were wet and mild resulting in lower winter sea surface density. These years showed lower than average nutrients and zooplankton concentrations while phytoplankton biomass was higher. After 2000, winters were colder and dryer resulting in higher sea surface density. Nutrients and zooplankton showed higher concentrations while phytoplankton was lower than average. The ca. 2000 shift was observed for most zooplankton groups with a one year delay for certain groups. The observed patterns suggest that the pelagic ecosystem trophic state is mostly set by the winter forcing on the convection that upwells nutrients to the surface sustaining the spring bloom. However, low phytoplankton concentrations in higher nitrate and zooplankton conditions during the well mixed years suggest that phytoplankton is controlled by grazers. The proposed mechanisms of convection regimes hold for most of the time series, but specific years with contradicting patterns needed 20 to be explained by other factors. The limitation of phytoplankton growth by the light availability in spring/summer was then proposed as a secondary driving force that can moderate or even reverse the winter forcing. Finally, the eleven years of observation did not reveal a clear link with the North Atlantic Oscillation, suggesting a more complex dynamics linking large scale climate to Ligurian Sea ecosystems or that the length 25 of the plankton monitoring is not yet sufficient to detect those links. [ABSTRACT FROM AUTHOR]

The main objective was to formulate a deterministic model, which simulates the dynamics of the microalgal biomass in semi-enclosed littoral ecosystems, in order to test the hypothesis that resuspension of the microphytobenthos can occur without any concomitant sediment erosion. Benthic diatoms form a dense biofilm at the mud surface during daytime emersion periods. Cells in the first centimetre of the mud migrate to the surface to get a sufficient amount of light energy for photosynthesis and production. Cell renewal in the biofilm was taken into account, with an average residence time equal to 1h. When the “migration period” (i.e. the total amount of time spent by microalgae at the surface of the mud) exceeds the duration of the emersion period, the biofilm is resuspended at the beginning of the flooding tide. A critical biomass above which the biofilm is resuspended was calculated. The dynamics can reach equilibrium in the vicinity of this critical threshold, as long as the balance between production and losses is in favour of production. Even with a low initial biomass, below the maximum concentration in the biofilm, the convergence to equilibrium remained possible. Despite of the deterministic nature of the model, steady-state solutions are sensitive to initial conditions and occurrence of resuspension can only be predicted in terms of probability. This biofilm resuspension without any concomitant sediment erosion was observed in the Marennes-Oléron Bay (French Atlantic Coast), in conditions defined by the model. A good agreement between simulations and observations is a first significant step in the quantification of the overall microalgal productivity and in the estimate of the export of the biomass from the littoral zone. This study will permit to precise the role of the microphytobenthos in the global carbon cycle in semi-enclosed littoral ecosystems. [Copyright &y& Elsevier]

Abstract: Spatio-temporal changes in taxonomic composition and structure of an epipelic diatom assemblage from an intertidal mudflat on the French Atlantic coast was studied over an annual cycle along a cross-shore transect. The assemblage structure was described by estimating both relative abundance and contribution to biovolume of each species. Results showed that the assemblage was numerically dominated by small-sized species (mean relative abundance of 91%). Large species, however, significantly contributed to the total biovolume (mean contribution to biovolume of 49%). A factorial correspondence analysis indicated that the epipelic assemblage was relatively homogeneous along the cross-shore transect but emphasized the seasonal succession of diatom species. In relative abundance, the assemblage structure was characterized by the dominance of the small species Navicula phyllepta throughout the year with a seasonal succession of secondary species, including only one large diatom (Gyrosigma peisonis). In biovolume, small (N. phyllepta and Navicula gregaria) and large species (Pleurosigma angulatum and G. peisonis) alternatively dominated the assemblage. Describing the epipelic assemblage using cell volume emphasized the contribution of large species and revealed that the assemblage contained two diatom fractions, characterized by different biological and physiological behaviours, which may alternatively represent a large proportion of the biomass. [Copyright &y& Elsevier]