Bay Of Toulon Research Articles

Estimation of harbor and bay resonances by MMS-FEM model with application to the Bay of Toulon, France

Bay and harbor resonances are investigated in this work, taking into account the variable bathymetry of the semi-enclosed basin. The Modified Mild-Slope (MMS) equation is implemented for the description of combined refraction-diffraction effects, from which the eigenperiods and eigenmodes are calculated by means of a low-order Finite Element Method (FEM scheme). The model is first applied to a coastal-port region of Toulon, France, illustrating the versatility of the model to easily include coastal structures such as detached breakwater. Next, the present model is applied to the extended nearshore area of Toulon including the Gulf of Giens showing the applicability of the developed MMS-FEM model for the estimation of harbor and bay resonances, as well as more extended nearshore regions where variable bottom topography effects become important. The calculated resonant frequency depends on the domain characteristics and the size of the open sea boundary and accurately reproduces the measurements within Toulon Bay. On the other hand, for open bays such as the Gulf of Giens, a discrepancy is observed between calculated and measured eigenperiods which is due to a very wide opening of the sea boundary that cannot accurately describe the seiching. This underlines the difficulty of accurately calculating the resonance frequency for open bays, in contrast to the classic studies carried out for ports, which are considered virtually closed basins, and confirms the complementary nature of long-term water level measurements and numerical calculations, for better quantification of the risks associated with energetic meteorological and/or oceanographic events.

Ecological succession of pico- and nanophytoplankton in a coastal bay of NW Mediterranean sea

The long-term evolution of pico- and nanophytoplanktonic communities in two coastal contrasting sites from the bay of Toulon was studied using monthly flow cytometry analyses during a seven-year period. Results highlighted higher abundance of both pico- and nanophytoplanktonic communities in the more eutrophic site (i. e. the Little Bay). Moreover, even if both sites were widely dominated by Synechococcus spp. population, it represented more than 90% of the population during summer in the Large Bay. Using diversity indices and rank frequency diagrams to study ecological successions in both sites, communities from the Little Bay (the most polluted site) appeared, paradoxically, as more diversified and more mature than that from the Large Bay. Communities from the Large Bay appeared as less diversified and juvenile linked to the dominance of Synechococcus spp. The complementarity of diversity indices and rank frequency diagram was revealed in this present work.

Integration of spatio-temporal variations of surface metabolomes and epibacterial communities highlights the importance of copper stress as a major factor shaping host-microbiota interactions within a Mediterranean seaweed holobiont

BackgroundAlthough considered as holobionts, macroalgae and their surface microbiota share intimate interactions that are still poorly understood. Little is known on the effect of environmental parameters on the close relationships between the host and its surface-associated microbiota, and even more in a context of coastal pollutions. Therefore, the main objective of this study was to decipher the impact of local environmental parameters, especially trace metal concentrations, on an algal holobiont dynamics using the Phaeophyta Taonia atomaria as a model. Through a multidisciplinary multi-omics approach combining metabarcoding and untargeted LC-MS-based metabolomics, the epibacterial communities and the surface metabolome of T. atomaria were monitored along a spatio-temporal gradient in the bay of Toulon (Northwestern Mediterranean coast) and its surrounding. Indeed, this geographical area displays a well-described trace metal gradient particularly relevant to investigate the effect of such pollutants on marine organisms.ResultsEpibacterial communities of T. atomaria exhibited a high specificity whatever the five environmentally contrasted collecting sites investigated on the NW Mediterranean coast. By integrating metabarcoding and metabolomics analyses, the holobiont dynamics varied as a whole. During the occurrence period of T. atomaria, epibacterial densities and α-diversity increased while the relative proportion of core communities decreased. Pioneer bacterial colonizers constituted a large part of the specific and core taxa, and their decrease might be linked to biofilm maturation through time. Then, the temporal increase of the Roseobacter was proposed to result from the higher temperature conditions, but also the increased production of dimethylsulfoniopropionate (DMSP) at the algal surface which could constitute of the source of carbon and sulfur for the catabolism pathways of these taxa. Finally, as a major result of this study, copper concentration constituted a key factor shaping the holobiont system. Thus, the higher expression of carotenoids suggested an oxidative stress which might result from an adaptation of the algal surface metabolome to high copper levels. In turn, this change in the surface metabolome composition could result in the selection of particular epibacterial taxa.ConclusionWe showed that associated epibacterial communities were highly specific to the algal host and that the holobiont dynamics varied as a whole. While temperature increase was confirmed to be one of the main parameters associated to Taonia dynamics, the originality of this study was highlighting copper-stress as a major driver of seaweed-epibacterial interactions. In a context of global change, this study brought new insights on the dynamics of a Mediterranean algal holobiont submitted to heavy anthropic pressures.2JHQi1qXvSzhvtywNrdzBEVideo abstract

Datasets of solid and liquid discharges of an urban Mediterranean river and its karst springs (Las River, SE France).

This data paper presents: (1) the liquid and solid discharge characteristics of the Las River, an urban Mediterranean stream flowing to the Bay of Toulon (south of France), and (2) the water height of the main karst springs supplying the Las River. We assessed the river's discharge with hydrological observations and we explored floods characteristics influencing its solid discharge [1]. The location of the monitoring station near the river's mouth was selected accordingly to accessibility and technical constraints, as far downstream as possible. The vast majority of tributaries (such as possible underground springs, stormwater outlets, urban runoff) were taken into account. A multi-parameter probe (temperature, pressure, turbidity and electric conductivity) and a sediment trap were deployed continuously for 17 months, from October 2012 to March 2014. At the river's sources, probes (temperature, water height) were deployed to characterized karst springs. Times series were averaged at a daily time step, and water height converted in discharge when the rating curve was available. Sediment samples were analyzed for grain-size distribution. Datasets may help to estimate karsts' contributions to the Mediterranean Sea and to assess their influence on rivers discharge and solid yield. Stakeholders may also use the maximum water height to evaluate the flooding risk. Our data also contribute to linking the catchment freshwater to the coastal sea, a connection yet to be fully explored.

On the use of long-term observation of water level and temperature along the shore for a better understanding of the dynamics: example of Toulon area, France

A dense network of instruments has been deployed within harbors along the Mediterranean coast, in the Toulon Metropole area, between the Hyeres islands and the Sanary Bay in the framework of the observation network HTM-NET. Each station is equipped with two piezometric sensors, the first immersed and the second emerged, which allows the calculation of the water level. Both piezometric sensors are also equipped with a temperature sensor. Water level and temperature data are analyzed and discussed, also considering meteorological data provided by Meteo-France stations. The tide gauges provide information about tide harmonic components, extreme water level, and seiching. Moreover, significant differences are observed between sheltered zones in enclosed bays and offshore zones, such as between the back of the Bay of Toulon and at the Port-Cros Island. Differences in water level up to 0.10 m are indeed observed under windy conditions, of the same order as the tidal range (order of 0.20 m) or the annual level variability due to the volumetric expansion (order of 0.10 m). Water level variations, up to about 1 m, are found to be mainly due to atmospheric effects, with a more or less isostatic behavior according to the weather events. In addition, seiching with an amplitude of few centimeters is observed within the Little Bay of Toulon, for east wind conditions. The near-surface water temperature is measured at the submerged piezometer location (depth of immersion range 0.10–1.80 m according to the station and to the water level). The analysis of the temperature associated with the weather conditions allows to detail a strong variability of the upwelling intensity under Mistral wind conditions in summer, leading to more or less pronounced temperature drops according to the shore configuration. The Bay of Toulon is more prone to the generation of upwellings than the neighboring bays. During winter, water exchanges between the Little Bay of Toulon and offshore are also clearly observed during windy conditions. The HTM-NET long-term observation network thus provides useful insights to increase our knowledge of the hydrodynamics and mass fluxes, and therefore enhances our modeling capacity and risk assessment at the scale of a bay.

Differential Acclimation of Juvenile Sea Urchins Transplanted Across a Metallic Trace Element Gradient within the Bay of Toulon (France)

Urbanized harbors and embayments scattered along marine shorelines act as important sources of a wide range of chemical contaminants, which include metallic trace elements (MTE). Within the semi-enclosed Mediterranean Sea, the high number of such areas might locally challenge the persistence of coastal marine species. In recent decades, biomonitoring studies, using sentinel species such as mussels, have increased knowledge of coastal contamination and provided a number of contentious potential environmental surveillance biomarkers, which contributed to a better comprehension toward the acclimation abilities of marine organisms, to actual anthropogenically derived environments. The aim of this study was to characterize the influence of the chemically, multi-contaminated, Bay of Toulon (France) on the young fauna, using juvenile sea urchins Paracentrotus lividus as a proxy. Hatchery-produced individuals were immersed, for 1 mo, within the bay, at four contrasted sites for MTE concentrations. At the end of the experiment, growth and transcript abundances of key genes, involved in the acclimation process, were assessed. Contrasted phenotypic and molecular responses were observed evidencing a significant environmental influence. Specifically, under the high metallic stress, a dwarfing response was observed, associated with a high level of metallothionein and a low level of hsp response. In addition, the level of DNA methyltransferase transcript abundance was inversely correlated with the level of MTE concentrations, highlighting that the chronic exposure to metallic contaminants would probably increase the risk of genetic mutations, such as those consecutive to transpositions. Overall, this study indicates that further in-depth research into the mechanisms driving plasticity and adaptive changes at the population level is required.

Impact of wind-driven circulation on contaminant dispersion in a semi-enclosed bay

Mediterranean semi-enclosed bays are often exposed to high levels of contaminants originating from anthropogenic activities in the bay. To assess their fate and impact on the environment, it is essential to investigate coastal circulation regimes which may play an important role in the dispersion of contaminants across the bay and beyond. In this study, a high resolution coupled hydrodynamic - passive tracer model was combined with ADCP observations, to identify major circulation patterns and associated dissolved contaminant dispersion pathways in the contaminated semi-enclosed bay of Toulon (South of France, NW Mediterranean Sea). Two dominant circulation patterns and two derived ones could be identified, driven by winds (Mistral and easterly winds) and offshore water intrusions. Medium to strong Mistral events (> 6 m s−1) with a WNW direction cause a bi-layer pattern with surface waters flowing out of the bay and marine waters entering at depth. Less frequently, west Mistral winds of medium to strong strength (> 6 m s−1) may generate an anticyclonic circulation. During easterly wind conditions (> 6 m s−1), an inward flow can be observed which is sometimes reinforced by offshore water intrusions, probably from the local boundary current, the Northern Current (NC). Furthermore, dissolved contaminant dispersion pathways were simulated under typical wind forcing conditions with three point sources of copper (Cu) that were identified based on surface Cu observations. While most of the WNW Mistral wind events transport dissolved copper plumes across and out of the bay, contaminant dispersion can remain confined to the bay under certain west mistral conditions. Conversely, during easterly wind events, contaminants are exiting the bay as a narrow vein along the Saint-Mandrier peninsula, before probably converging on the NC offshore. Accordingly, this study demonstrates the important impact of hydrodynamic-driven processes on the dispersion of contaminants within a semi-enclosed bay.

Spatial risk assessment in case of multiple nuclear release scenarios

This paper presents an approach aimed at assessing multiple criteria spatial risk, where several methods are used for decision aiding purposes, with an application on marine nuclear releases. The case study simulates a post-accident analysis evaluating the impact upon the bay of Toulon of an accidental nuclear release. The problem is characterized by the presence of spatial features, multiple criteria describing the involved assets and uncertainties represented through multiple release scenarios and their corresponding probabilities.

Otolith fingerprints as natural tags to identify juvenile fish life in ports

The construction of ports has caused substantial habitat destruction in coastal areas previously used as nursery grounds by many fish species, with consequences to fish stocks. These artificial coastal areas might provide alternative nursery habitats for several species for juvenile fish abundances and growth in ports, although their contribution to adult stocks had never been estimated. The variability of otolith composition in the juveniles of two Diplodus species was investigated in three contrasting port areas and two adjacent coastal juvenile habitats of the Bay of Toulon (northwestern Mediterranean) in order to determine the possible use of otolith fingerprints as natural tags for the identification of juvenile fishes in ports. The global accuracy of discrimination between ports and coastal areas was very high (94%) irrespective of species, suggesting that otolith fingerprints can be used with confidence to retrospectively identify past residency in the ports of this bay. However, Ba was systematically the most discriminating element, since its concentrations in otoliths were generally higher outside ports than in inside them, probably due to river runoff. Moreover, otolith signatures varied greatly by species and between sampling sites. Furthermore, although Cu and Pb concentrations in water were at least 2.3–34-fold higher inside ports than outside, this was not consistently reflected in fish otoliths, confirming that spatial differences in otolith concentrations depend on the species and do not directly reflect differences in environmental contamination levels. Therefore, it seems unlikely that otolith microchemistry could provide a universal fingerprint capable of discriminating ports from other coastal areas. Nevertheless, the contribution of ports to adult fish populations can be determined well by establishing a library of otolith fingerprints for all juvenile habitats.

Hydro-sedimentary model as a post-accidental management tool: Application to radionuclide marine dispersion in the Bay of Toulon (France)

The coastal city of Toulon, located in southern France, is the homeport of the French navy's nuclear-powered vessels, and is the largest nuclearized harbour in Europe. Therefore, an accidental release of radioactive material would have major consequences for the marine ecosystem and the economy of the region. A hydro-sedimentary model is presented to better understand the dispersion of a hypothetical release of radionuclides and to gain insights into the potential effects on the surrounding ecosystem, especially on sea sediments. The aim of the model is to provide the foundation of a management tool for experts and stakeholders in decision making in case of an accidental release. We simulate a numerical radionuclide discharge in the military harbour under several climatic conditions and we compute 137Cs, which might have substantial impacts on the marine ecosystem, and 239Pu for its high affinity for solid phase. Results show that wind conditions and solid discharges from the Las River are the primary influences on sediment-bed contamination, and the hydro-sedimentary dynamics following the first days of release have an important influence on the distribution of radionuclides.

Growth, condition and metal concentration in juveniles of two Diplodus species in ports

High abundances of juvenile fish in certain ports suggest they might provide alternative nursery habitats for several species. To further investigate this possibility, post-settlement growth, metal uptake and body condition were estimated in 127 juveniles of two seabream species, collected in 2014–15, inside and outside the highly polluted ports of the Bay of Toulon. This showed that differences in local pollution levels (here in Hg, Cu, Pb and Zn) are not consistently mirrored within fish flesh. Muscle metal concentrations, below sanitary thresholds for both species, were higher in ports for Cu, Pb and V only. Otherwise, fish muscle composition principally differed by species or by year. Juvenile growth and condition were equivalent at all sites. Higher prey abundance in certain ports might therefore compensate the deleterious effects of pollution, resulting in similar sizes and body conditions for departing juvenile fish than in nearby natural habitats.

A chronicle of the changes undergone by a maritime territory, the Bay of Toulon (Var Coast, France), and their consequences on PCB contamination.

This study evaluated the distribution of polychlorinated biphenyls (PCBs) in 39 surface sediment samples and four cores collected in Toulon Bay, a semiclosed area submitted to various anthropogenic inputs. The concentration of PCBs in the superficial sediment samples ranged from 1.7 to 2530 ng g−1 dry weight. The spatial distribution of these compounds suggested that the high concentrations of these contaminants are located in the small bay and are related to human activities. In the larger bay, the concentrations were in the same order of magnitude than those reported in others locations around the world. Comparison of the levels with target values from the French legislation shows that, except for four polluted sites with critical values (N2: values ≥1 mg kg−1 dry weight) in the smaller bay, PCBs levels throughout the larger and the smaller bay are lower than the accepted values (N1: values <0.5 mg kg−1 dry weight). The PCBs in the sediment cores ranged from 0.8 to 739 ng g−1 dry weight dependent core. Vertical profiles indicated earlier usage of PCBs which coincided with the history of the Toulon Bay. In this study, using alkane, we could follow the PCBs pollution history over about 80 years and estimate a sedimentation rate of about 0.32 cm year in the small Bay of Toulon.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-016-2715-2) contains supplementary material, which is available to authorized users.

Proposition of indicators of anthropogenic pressure in the Bay of Toulon (Mediterranean Sea) based on zooplankton time-series

Zooplankton present characteristics of high interest in the frame of investigation for organisms sensitive to environmental changes and/or anthropogenic pressures. Such indicators are particularly needed in the present context of European legislation (Marine Strategy Framework Directive). However, zooplankton have not been given the interest they should have in regards to these issues. The aim of the present study is to provide an attempt of proposition of indicators of good environmental status and associated thresholds based on zooplankton data. Zooplankton time-series (2002–2013) from the Toulon Bay in the Mediterranean was used. This time-series presents the great characteristics that the sampling has be done jointly in two areas of the Bay of Toulon known to differ in term of anthropogenic pressures. The study focus on the copepod assemblage and different potential indicators are tested: ratio of copepod families on total copepod and diversity index (Piélou's evenness). The indicators relevance was evaluated per season by looking at the importance of the overlapping region between density's distributions for each indicator in both bays. This methodology well-recognized is commonly used, particularly in the medical sector, for a long time. The results show that the Oithonidae relative abundance and the Piélou's evenness index are the best indicators of anthropogenic pollution for this case study. Thresholds related to the selected indicators are also proposed in order to characterize the degree of anthropogenic pressure for the Toulon Bay and to provide a first evaluation for potential environmental management. Applicability of the selected indicators and future development needed are also discussed. This study is a first step in the investigation for operational zooplankton indicators and should open the way for additional studies in coastal anthropized area such as the Mediterranean coast where it is more urgently needed.

Wind-forced circulation model and water exchanges through the channel in the Bay of Toulon

A hydrodynamic model of the Bay of Toulon has been developed for use as a post-accident radionuclide dispersion simulation tool. Located in a Mediterranean urban area, the Bay of Toulon is separated into two basins by a 1.4-km long seawall. The Little Bay is semi-enclosed and connected to the Large Bay by a fairway channel. This channel is the site of significant water mass exchange as a result of both wind-driven currents and bathymetry. It is therefore a focal point for marine contamination. As part of the model calibration and validation process, the first step consisted of studying the water mass exchange between the two basins. An Acoustic Doppler Current Profiler was moored in the channel for 1 year. The present study analyses in situ data to determine the current intensity and direction, and also to better understand the vertical current profile, which is highly correlated with meteorological forcing. Comparisons of model-generated and measured data are presented, and various atmospheric forcing datasets are used to enhance computed results. It appears that accurate meteorological forcing data is needed to enhance the accuracy of the hydrodynamic model. This channel is an important location for water mass renewal in the Bay of Toulon, and model results are used to quantify these exchanges. The mean calculated annual water exchange time is approximately 3.4 days. However, this duration is strongly wind dependent and shortens during windy winter months. It ranges from 1.5 days during strong wind periods to 7.5 days during calm weather. Residence time values calculated through tracer dispersion modelling after release at the back of the Little Bay are found to be comparable to the mean exchange time values, especially for windy conditions.

Identification of Bacterial Strains Isolated from the Mediterranean Sea Exhibiting Different Abilities of Biofilm Formation

The Mediterranean Sea has rarely been investigated for the characterization of marine bacteria as compared to other marine environments such as the Atlantic or Pacific Ocean. Bacteria recovered from inert surfaces are poorly studied in these environments, when it has been shown that the community structure of attached bacteria can be dissimilar from that of planktonic bacteria present in the water column. The objectives of this study were to identify and characterize marine bacteria isolated from biofilms developed on inert surfaces immersed in the Mediterranean Sea and to evaluate their capacity to form a biofilm in vitro. Here, 13 marine bacterial strains have been isolated from different supports immersed in seawater in the Bay of Toulon (France). Phylogenetic analysis and different biological and physico-chemical properties have been investigated. Among the 13 strains recovered, 8 different genera and 12 different species were identified including 2 isolates of a novel bacterial species that we named Persicivirga mediterranea and whose genus had never been isolated from the Mediterranean Sea. Shewanella sp. and Pseudoalteromonas sp. were the most preponderant genera recovered in our conditions. The phenotypical characterization revealed that one isolate belonging to the Polaribacter genus differed from all the other ones by its hydrophobic properties and poor ability to form biofilms in vitro. Identifying and characterizing species isolated from seawater including from Mediterranean ecosystems could be helpful for example, to understand some aspects of bacterial biodiversity and to further study the mechanisms of biofilm (and biofouling) development in conditions approaching those of the marine environment.

An operational model to simulate post-accidental radionuclide transfers in Toulon marine area: preliminary development

As part of its development of post-accident management tools, the French Institute for Radiological Protection and Nuclear Safety is setting up a model to simulate radionuclide dispersion in the Toulon marine area (one of France’s main military ports). The model is based on the MARS 3D code developed by IFREMER. It reproduces hydro-sedimentation phenomena in the Bay of Toulon with a horizontal spatial resolution of 100 m and 30 vertical sigma levels and also factors in radioactive decay and dissolved/particulate distribution of the radionuclides studied. With no tide, the major currents in this area are generated by the wind. The model effectively reproduces the resulting hydrodynamic phenomena, which were measured throughout the summer of 2009 in the channel that links the Little Bay to the Large Bay of Toulon. When the Mistral (wind from the West/Northwest) blows, a surface current quickly appears, which pushes water southwards from the Little Bay, and which is offset by a bottom current (upwellings). When the wind blows from the East, the currents move in the opposite direction, and southeasterly waves, dependent on wind strength and fetch, occur in the Large Bay. Here, we give an example of the simulated dispersion of radionuclides released directly into the surface waters near the Arsenal, demonstrating the constraint relative to dispersion generated by the half-closed configuration of the Little Bay. Sediment in the Little Bay also forms an area where the most highly reactive radionuclides would accumulate, and where the lack of waves has the effect of considerably limiting the phenomena of resuspension.

A new species of Cymbasoma (Copepoda: Monstrilloida) from the Mediterranean Sea with remarks on the female of C. tumorifrons (Isaac)

Monstrilloid copepods were collected during zooplankton surveys carried out off the coasts of the bay of Toulon, France, in the Western Mediterranean Sea. Among these specimens, females of two species of Cymbasoma Thompson, 1888 were found. One of them was determined to be a new species, C. nicolettae n. sp., which can be distinguished by its body proportions, its relatively long antennule, and by the structure of its fifth legs with a mammiliform inner lobe. This species is described following current upgraded standards. The other one is C. tumorifrons (Isaac), a very widely distributed species which can be distinguished mainly by details of the ornamentation of the head, and by the structure of the fifth leg. The species is re-described based on the Toulon specimen and on the type material. New characters, such as the complete armature of the antennules and of the swimming legs, and the cuticular ornamentation are added to the original description of this species and its known geographical range is extended. Both species are compared with morphologically similar forms of Cymbasoma.

Comparison of β-dimethylsulfoniopropionate (DMSP) levels in two mediterranean ecosystems with different trophic levels

β-dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) concentrations were recorded from September 1999 to September 2000 in two geographically close ecosystems, differently affected by eutrophication: the Little Bay of Toulon and the Niel Bay (N.W. Mediterranean Sea, France). Little Bay had higher nutrient levels ([NO 3 −] max. = 30.3 μM; [PO 4 3−] max. = 0.46 μM) and higher chlorophyll a concentrations ([chl a] mean = 2.4 μg/L) compared to Niel Bay ([NO 3 −] max. = 19.7 μM; [PO 4 3−] max. = 0.17 μM; [chl a] mean = 0.4 μg/L). In the two sites, we measured dissolved (DMSP d < 0.2 μm) and particulate DMSP (DMSP p > 0.2 μm) concentrations. The DMSP p was particularly analysed in the 0.2–5, 5–90 and > 90 μm fractions. In the eutrophicated Little Bay, DMSP d concentrations showed a clear seasonality with high values from January to March (124–148 nM). The temporal profile of the DMSP p concentrations was similar, peaking in February–March (38–59 nM). In the less eutrophic Niel Bay, DMSP p concentrations were much lower (6–9 nM in March–April), whereas DMSP d concentrations were relatively high (110–92 nM in February–March). DMS concentrations were elevated from the end of the winter to the spring in Little Bay, ranging from 3 nM in October to 134 nM in March. In the less eutrophic Niel Bay, lower DMS levels were observed, generally not exceeding 20 nM. Each particulate fraction (0.2–5; 5–90; > 90 μm) contained less DMSP in Niel Bay than in Little Bay. At both sites, the 5–90 μm fraction made up most of the DMSP p. This 5–90 μm fraction consisted of microphytoplankton, principally Dinophyceae and Bacillariophyceae. The 5–90 μm biomass calculated from cell biovolumes, was more abundant in Little Bay where the bloom at the end of the winter (165 μg/L in March) occurred at the same time as the DMSP peaks. The estimated DMSP p to biomass ratio for the 5–90 μm fraction was always higher in Little Bay than in Niel Bay. This suggests that the high DMSP levels recorded in Little Bay were not only due to a large Dinophyceae presence in this ecosystem. Indeed, the peak of DMSP p to biomass ratio obtained from cell biovolumes (0.23 nmol/μg in March) was consistent with the proliferation of Alexandrium minutum. This Dinophyceae species may account for between 50% (2894 cells/L) and 63% (4914 cells/L) of the total phytoplankton abundance in the Little Bay of Toulon.

Annual contribution of different plankton size classes to particulate dimethylsulfoniopropionate in a marine perturbed ecosystem

Dimethylsulfoniopropionate (DMSP) concentrations were observed from October 1999 to September 2000 in a Mediterranean ecosystem (Little Bay of Toulon) submitted to eutrophication. DMSP was measured in the particulate material (DMSP p), and more specifically in the >90, 5–90 and 0.2–5 μm fractions. DMSP was first converted into dimethylsulfide (DMS) by a cold alkali treatment. DMS was then analysed by gas chromatography equipped with a flame photometric detector (FPD). DMSP p concentrations were relatively high, showing a strong temporal variability with maxima in February–March (58.8 nM). The most elevated values were recorded in the 5–90 μm size class, and represented between 60% and 100% of the total DMSP p. This fraction was mostly composed of Dinoflagellates whose biomass was significantly correlated with DMSP p concentrations. These concentrations showed better correlations with Ceratium furca, Dinophysis acuminata, Prorocentrum arcuatum and also Alexandrium minutum. The intracellular contents of DMSP were much higher in Dinoflagellates (124.9±5.7 mM) than in Diatoms (25.1±1.1 mM). A. minutum produced the strongest intracellular concentrations (3387.6±121.9 mM). High DMSP contents were also found in D. acuminata (477.4±64.3 mM) and P. arcuatum (442.2±22.9 mM). The >90 μm size class had a minor importance in DMSP production, generally below 20% of the total DMSP p. However, DMSP in the >90 μm fraction was well correlated with cladoceran abundance. Plankton cells between 0.2 and 5 μm contained a low part of the DMSP p pool, lower than 20%. Besides, no correlation was found between their algal abundances and DMSP in the 0.2–5 μm size class. Temperature and photoperiod could have influenced the Dinoflagellate development, and consequently, the DMSP p concentrations. The strong autumnal rains affected the composition of the phytoplankton community and the production of sulfur compounds. These particular climatic conditions have induced an increase in nutrient concentrations and a drop in salinity, which may explain the low autumnal DMSP p concentrations.

Development of the Mediterranean extinction code (MEDEX)

The performance of electro-optical systems can be substantially affected by aerosol particles that scatter and absorb electromagnetic radiation. The model that is most frequently used for the prediction of aerosols and their effect on extinction in the marine atmosphere is the US Navy Aerosol Model (NAM). However, NAM can be significantly less reliable in coastal areas than on the open ocean. Based on an extensive series of measurements conducted on the island of Inisheer (Irish West Coast), an empirical aerosol model for the coastal zone formulated as an extension of NAM, in which coastal effects are modeled as a function of fetch, has been developed. This work is extended to the Mediterranean using an aerosol dataset recorded on the island of Porquerolles in the Bay of Toulon (France) and has been coupled with the Mie theory to give a code for the extinction, the code MEDiterranean EXtinction (MEDEX).