NW Mediterranean Sea Research Articles

Dual quantitative PCR assay for identification and enumeration of Karlodinium veneficum and Karlodinium armiger combined with a simple and rapid DNA extraction method

Karlodinium is a dinoflagellate genus responsible for massive fish mortality events worldwide. It is commonly found in Alfacs Bay (NW Mediterranean Sea), where the presence of two Karlodinium species (K. veneficum and K. armiger) with different toxicities has been reported. Microscopy analysis is not able to differentiate between these two species. Therefore, new and rapid methods that accurately and specifically detect and differentiate these two species are crucial to facilitate routine monitoring, to provide early warnings and to study population dynamics. In this work, a quantitative real-time PCR (qPCR) method to detect and enumerate K. veneficum and K. armiger is presented. The ITS1 region of the ribosomal DNA was used to design species-specific primers. The specificity of the primers together with the melting curve profile provided a reliable qualitative identification and discrimination between the two Karlodinium species. Additionally, a simple and rapid DNA extraction method was used. Standard curves were constructed from 10-fold dilutions of cultured microalgae cells. Finally, the applicability of the assay was tested with field samples collected from Alfacs Bay. Results showed a significant correlation between qPCR determinations and light microscopy counts (y = 2.838 x + 564; R2 = 0.936). Overall, the qPCR method developed herein is specific, rapid, accurate, and promising for the detection of these two Karlodinium species in environmental samples.

Spatial distribution of marine litter along italian coastal areas in the Pelagos sanctuary (Ligurian Sea - NW Mediterranean Sea): A focus on natural and urban beaches

Our paper will show data on quantity, typology, distribution of beach litter (Anthropogenic Marine Debris - AMD) within a coastal macroarea surrounding the Pelagos Sanctuary, an International Protected Area in the NW Mediterranean Sea. AMD Monitoring and characterisation have been performed by using SEACleaner Protocol: an adapted version of UNEP/IOC, OSPAR and EU guidelines. 11 beaches located in 5 different areas, have been monitored with a total amount of thirty three surveys, from January 2014 to December 2015, during different seasons. Three kinds of beaches have been considered: Natural (belonging to MPAs), Urbanized and Urban. A total of 34,027 items on a total area of 32,154 m2 have been removed and classified. Spatial difference in abundance and composition of AMDs - as well as beach environmental quality - has been detected. Natural sites, and particularly protected areas close to river mouths show a major density compared to other areas.

Seasonal dynamics of transparent exopolymer particles (TEP) and their drivers in the coastal NW Mediterranean Sea

Transparent Exopolymer Particles (TEPs) are a subclass of organic particles with high impact in biogeochemical and ecological processes, such as the biological carbon pump, air-sea interactions, or the microbial loop. However, the complexity in production and consumption makes TEP dynamics hardly predictable, calling for the need of descriptive studies about the in situ dynamics of these particles. We followed monthly TEP dynamics and combined them with a dataset of environmental variables during three years in a coastal site of the oligotrophic North Western Mediterranean (Blanes Bay). TEP concentration, ranging from 11.3 to 289.1μgXGeqL−1 (average 81.7±11.7μgXGeqL−1), showed recurrent peaks in early summer (June–July). TEP were temporally disconnected from chlorophyll a maxima, that occurred in late winter and early spring (maxima 1.21μgL−1), but they were significantly related to the abundance of specific phytoplankton groups (diatoms and dinoflagellates) and also coincided with periods of low nutrient concentrations. The fraction of particulate organic carbon in the form of TEP (the TEP:POC and TEP:PM ratios) were also highest in early summer, indicating that TEP-enriched particles of low density accumulate in surface waters during stratified periods. We hypothesize that the accumulation of these particles affects the microbial food web by enhancing the activity of specific prokaryotic extracellular enzymes (esterase, β-glucosidase and alkaline phosphatase) and promoting the abundance of heterotrophic nanoflagellates.

Passive larval transport explains recent gene flow in a Mediterranean gorgonian

Understanding the patterns of connectivity is required by the Strategic Plan for Biodiversity 2011–2020 and will be used to guide the extension of marine protection measures. Despite the increasing accuracy of ocean circulation modelling, the capacity to model the population connectivity of sessile benthic species with dispersal larval stages can be limited due to the potential effect of filters acting before or after dispersal, which modulates offspring release or settlement, respectively. We applied an interdisciplinary approach that combined demographic surveys, genetic methods (assignment tests and coalescent-based analyses) and larval transport simulations to test the relative importance of demographics and ocean currents in shaping the recent patterns of gene flow among populations of a Mediterranean gorgonian (Eunicella singularis) in a fragmented rocky habitat (Gulf of Lion, NW Mediterranean Sea). We show that larval transport is a dominant driver of recent gene flow among the populations, and significant correlations were found between recent gene flow and larval transport during an average single dispersal event when the pelagic larval durations (PLDs) ranged from 7 to 14 d. Our results suggest that PLDs that efficiently connect populations distributed over a fragmented habitat are filtered by the habitat layout within the species competency period. Moreover, a PLD ranging from 7 to 14 d is sufficient to connect the fragmented rocky substrate of the Gulf of Lion. The rocky areas located in the centre of the Gulf of Lion, which are currently not protected, were identified as essential hubs for the distribution of migrants in the region. We encourage the use of a range of PLDs instead of a single value when estimating larval transport with biophysical models to identify potential connectivity patterns among a network of Marine Protected Areas or even solely a seascape.

Suprabenthic crustacean assemblages subjected to high-energy hydrodynamic events in the Blanes Canyon and adjacent slope (NW Mediterranean Sea)

Submarine canyons and adjacent slopes from the NW Mediterranean Sea are subjected to high seasonal and inter-annual variability in hydrodynamic processes. Such an environmental setting has a profound influence in the spatial and temporal variability of deep-sea benthic assemblages. We analyzed the suprabenthic crustacean assemblages from the Blanes Canyon and the adjacent slope along a bathymetric gradient. Macer-Giroq sledge hauls were taken from 900 to 2250 m depth in the canyon axis and southwestern adjacent slope in the autumn of 2008, 2009 and 2012. From the twenty four hauls sampled, one hundred and seventy one species were identified. Major changes in densities, number of species and diversity were only found at particular depths or years. In general the samples yielded variable densities (from approx. 10 to 539 ind.100 m−2), mostly owing to temporal fluctuations in motile fauna such as amphipods and mysids, in relation to the occurrence of energy-driven events. The environmental conditions associated to these events coupled with particular topographic features at the shallowest sites (namely at 900 m depth) lead to contrasting biodiversity patterns in the canyon and adjacent slope: high dominance and subsequent depressed diversity in the canyon and the highest diversity on the slope at similar depths. At the deepest sites, suprabenthic diversity reached similar values in the canyon and adjacent slope, probably owing to the decreased influence of disturbance processes at greater depths. Trophic diversity decreased with depth only in the slope, while in the canyon it remained constant likely owing to the relatively enhanced trophic conditions found in the canyon at all depths. However, the community composition differed significantly between the canyon and adjacent slope and at contrasting depths (<1200 m vs. >1200 m). At shallowest depths, the canyon sites were characterized by a high contribution of motile omnivores while the slope sites were characterized by a high contribution of detritivores to the total abundance. Highly motile predators on zooplankton were dominant at deepest sites in both environments. Our results suggest that taxonomic and trophic diversity in the northwestern Mediterranean may be influenced by the abrupt topography and its interaction with hydrodynamic conditions (intensification of currents; variable intensity of disturbance/hydrodynamic events; food pulses linked to food availability). These are major drivers which influence the spatial and temporal availability of food sources to the various faunal compartments eventually propagating up the food web.

Uranium isotope geochemistry in modern coastal sediments: Insights from Toulon Bay, France

Abstract By assessing U geochemistry in marine sediments of Toulon Bay (NW Mediterranean Sea), authigenic U accumulation was found to be tightly linked to that of Mo and V with slight differences in accumulation rate depending on sediment redox conditions. In sediments collected on a transect along a river plume, the authigenic accumulation of these redox-sensitive elements appears to be linked to sediment grain size which probably drives the redox status of the sediments. A typical U loss in re-oxidized sediments was observed in sediments that had been previously disturbed. However, the dissolved U profiles do not show a simple and typical depletion trend but rather a depletion in the top 10 cm followed by release in deeper pore waters that could be linked to a potential reoxidation/mobilization of authigenic U(IV). The released U could be further scavenged as a U-P precipitate. The U isotopic data (δ238U), which are the first reported for the coastal hypoxic sediments of Toulon Bay, average −0.12 ± 0.12‰ in surface sediments. However, sediments situated in front of river mouths show higher values of δ238U (up to +0.75‰); these high values are reported for the first time in sediments below an oxic water column.

Variability of ultraplankton composition and distribution in an oligotrophic coastal ecosystem of the NW Mediterranean Sea derived from a two-year survey at the single cell level.

Ultraplankton [heterotrophic prokaryotes and ultraphytoplankton (<10 μm)] were monitored weekly over two years (2009 & 2010) in a coastal area of the NW Mediterranean Sea. Six clusters were differentiated by flow cytometry on the basis of their optical properties, two heterotrophic prokaryote (HP) subgroups labelled LNA and HNA (low and high nucleic acid content respectively), Prochlorococcus, Synechococcus, autotrophic picoeukaryotes and nanoeukaryotes. HP represented an important component of the microbial assemblage over the survey with relatively small abundance variation through seasons. The carbon biomass ratio HP/ultraphytoplankton averaged 0.45, however this ratio exceeded 1 during spring. Ultraphytoplankton biomass made about 50% of the total autotrophic carbon estimates but this contribution increased up to 97% and 67% during the 2009 and 2010 spring periods respectively. Within ultraphytoplankton, nanoeukaryote represent the most important ultraphytoplankton group in terms of autotrophic carbon biomass (up to 70%). Picoeukaryote maximum abundance occurred in winter. Synechococcus was the most abundant population (maximum 1.2 x 10 5 cells cm-3) particularly in spring where it represented up to 54% of ultraphytoplankton carbon biomass. The warmer winter-spring temperatures and the lengthening of the stratification period created a favorable situation for the earlier appearance of Synechococcus and its persistence throughout summer, paralleling Prochlorococcus development. Prochlorococcus was dominant over summer and autumn with concentrations up to 1.0 × 10 5 cells cm-3. While the abundance of Synechococcus throughout survey was of the same order as that reported in western Mediterranean Sea, Prochlorococcus was more abundant and similar to the more typical oligotrophic and warm waters. The abundance variation of the ultraplankton components through the survey was relatable to variations in the hydrological and nutrient conditions.

Distribution of phthalates in Marseille Bay (NW Mediterranean Sea)

Phthalic Acid Esters (PAEs) are a group of emerging organic contaminants that have become a serious issue because of their ubiquitous presence and hazardous impact on the marine environment worldwide. Seawater samples were collected monthly from December 2013 to November 2014 in the northwestern Mediterranean Sea (Marseille Bay). The samples were analyzed for dissolved organic carbon (DOC) as well as the molecular distribution of dissolved PAEs by using solid phase extraction followed by gas chromatography and mass spectrometry (GC/MS) analyses. The results demonstrated the occurrence of six PAEs, including dimethyl phthalate (DMP), diethyl phthalate (DEP), di-isobutyl phthalate (DiBP), di-n-butyl phthalate (DnBP), benzylbutyl phthalate (BzBP) and diethylhexyl phthalate (DEHP), with total concentrations ranging from 130 to 1330ngL−1 (av. 522ngL−1). In Marseille Bay, the highest concentrations were detected in the bottom water from June to November 2014 and in the whole water column during the winter mixing period. This result suggests that resuspension of PAE-rich sediment, in relation to the accumulation of plastic debris above the seabed, or the higher degradation rate in the upper layer of the water column, plays a significant role in the PAE dynamics in coastal water. DEHP was the most abundant PAE in all of the surface samples and the summer bottom samples, followed by DiBP and DnBP, which also represent the largest fractions in the other bottom samples.

Natural capital and environmental flows assessment in marine protected areas: The case study of Liguria region (NW Mediterranean Sea)

A methodology based on emergy analysis for the calculation of the biophysical value of the stocked biomass (natural capital) was applied to the Marine Protected Areas (MPAs) of Portofino (PF) and Cinque Terre (CT). The resources exploited, on a yearly base, to maintain the natural capital itself alive (environmental flows) were accounted too. Emergy analysis is an accounting method useful to identify and convert in a single unit of measure all resources feeding a system. This allows the implementation of a system overall assessment and then the conversion of the obtained value in money terms. The studied MPAs are located in the northwestern part of Italy, are both tourism oriented and subdivided in zones with different protection degree. The habitats occupying both the MPAs bottoms have been identified together with the biomass stored on their surface, identifying units named FBHA (fishes and benthos habitat assemblage). The calculation of biomass stocked in the benthic organisms and in the fishes associated to each FBHA represents the basis for the assessment of MPA natural capital value and of environmental flows. From these values, the trophic network of each habitat was modeled allowing calculating the inputs to emergy analysis.The value of PF natural capital, expressed as resources employed through space and time to store the existing biomass, is equal to over 10 million Euros while the CT natural capital amounts to over 30 million.The high value habitats, where biomass is concentrated and stored, represent hot spots that are restricted in a limited surface and that can be maintained only if the resources they need are provided by adjacent lower value habitats. Through the applied methodology, a balance is performed to understand if an MPA is self-sufficient or dependent on external areas. Therefore, if an MPA is correctly planned, as CT is, the wider low value areas are able to provide resources to the deficit FBHAs and even to export resources to other systems. In this case, the MPA lies in a surplus condition. On the contrary, the MPA is not able to maintain itself and depends on external systems not subjected to protection and then potentially posed at risk.If information about natural capital, flows and balance is synthesized in a Geographical Information System, it represents an effective tool to MPAs managers to measure the efficacy of protection established.

Occurrence of microplastics in surface waters of the Gulf of Lion (NW Mediterranean Sea)

Between 2014 and 2016 a total of 43 microplastic samples were collected at six sampling stations in the eastern section of the Gulf of Lion (located in the northwestern Mediterranean Sea), as well as upstream of the Rhône River. Microplastics were found in every sample with highly variable concentrations and masses. Concentrations ranged from 6 · 103 items km−2 to 1 · 106 items km−2 (with an average of 112 · 103 items km−2), and mass ranged from 0.30 g km−2 to 1018 g km−2 DW (mean 61.92 ± 178.03 g km−2). The samples with the highest and lowest microplastic count originate both from the Bay of Marseille. For the Bay of Marseille, it is estimated that the total microplastic load consist of 519 · 103 –101 · 106 items weighing 0.07–118 kg. Estimations for daily microplastic transport by the Northern Current and the Rhône River, two important hydrologic features of the northwestern Mediterranean Sea, range from 0.18 to 86.46 t and from 0.20 to 21.32 kg, respectively. Particles < 1 mm2 clearly dominated sampling stations in the Northern Current, the Rhône River and its plume (52, 53 and 61%, respectively), suggesting a long exposure time in the environment. Items between 1 mm2 and 5 mm2 in size were the most abundant microplastics in Marseille Bay (55%), which suggests coastal pollution sources or the removal of smaller particles from surface waters e.g. by ballasting owing to the presence of epibionts.

Seagrass as major source of transparent exopolymer particles in the oligotrophic Mediterranean coast

Abstract. The role of seagrass, Posidonia oceanica, meadows as a source of transparent exopolymer particles (TEPs) to Mediterranean coastal waters was tested by comparing the TEP dynamics in two adjacent coastal waters in the oligotrophic NW Mediterranean Sea, one characterized by oligotrophic open-sea waters and the other accumulating seagrass leaf litter, together with an experimental examination of TEP release by seagrass litter. TEP concentrations ranged from 4.6 to 90.6 µg XG (xanthan gum) Eq L−1, with mean (±SE) values of 38.7 (± 2.02) µg XG Eq L−1 in the site devoid of seagrass litter, whereas the coastal beach site accumulating leaf litter had &gt; 10-fold mean TEP concentrations of 487.02 (± 72.8) µg XG Eq L−1. Experimental evaluation confirmed high rates of TEP production by P. oceanica litter, allowing calculations of the associated TEP yield. We demonstrated that P. oceanica is an important source of TEPs to the Mediterranean Sea, contributing an estimated 76 Gg C as TEPs annually. TEP release by P. oceanica seagrass explains the elevated TEP concentration relative to the low chlorophyll a concentration in the Mediterranean Sea.

Comparison of in situ microstructure measurements to different turbulence closure schemes in a 3-D numerical ocean circulation model

In situ measurements of kinetic energy dissipation rate ε and estimates of eddy viscosity KZ from the Gulf of Lion (NW Mediterranean Sea) are used to assess the ability of k−ɛ and k−ℓ closure schemes to predict microscale turbulence in a 3-D numerical ocean circulation model. Two different surface boundary conditions are considered in order to investigate their influence on each closure schemes’ performance. The effect of two types of stability functions and optical schemes on the k−ɛ scheme is also explored. Overall, the 3-D model predictions are much closer to the in situ data in the surface mixed layer as opposed to below it. Above the mixed layer depth, we identify one model’s configuration that outperforms all the other ones. Such a configuration employs a k−ɛ scheme with Canuto A stability functions, surface boundary conditions parameterizing wave breaking and an appropriate photosynthetically available radiation attenuation length. Below the mixed layer depth, reliability is limited by the model’s resolution and the specification of a hard threshold on the minimum turbulent kinetic energy.

Conditions for assessing zooplankton abundance with LOPC in coastal waters

Recent technical advances in laser-based systems to measure zooplankton distribution have opened new perspectives in ecological and behavioral studies by significantly improving the horizontal and vertical sampling resolution, providing information on zooplankton patchiness and on the influence of small scale physical processes. The application of laser-based systems also led to new challenges on the identification of organisms vs. particulate matter. In areas with high detritus abundances, zooplankton abundances might be overestimated by counting plankton and detritus together. We investigated the contribution of detritus in Laser Optical Plankton Counter (LOPC) data collected during two cruises on the continental shelf of the Gulf of Lion (NW Mediterranean Sea). The study area was characterized by several types of ecoregions owing to the influence of winds, freshwater runoff and intrusion of oligotrophic waters from offshore. We identified the main mechanisms leading to the formation of detritus as a function of environmental conditions and developed a method to assess the contribution of detritus in LOPC counts based on the proportion of large particles (multi-element plankton, MEPs). Highest percentages of detritus (up to 90% of the counts, mainly particulate organic matter from various sources) were found in stratified conditions associated with relatively high chlorophyll a concentration (chl-a; ca 2 mg m−3). Discontinuities in density profiles alone also resulted in peaks of particles concentrations. We suggested a threshold of 2% of MEPs in LOPC counts above which the LOPC is most likely counting more detritus than organisms. This easy check of the detritus contribution to total LOPC counts was applied to datasets from different marine ecological situations (glacial input, clear water, productive shelf) and gave successful results in different biogeographical regions (e.g. high latitude and tropical habitats).

Atmospheric nutrients in seawater under current and high pCO2 conditions after Saharan dust deposition: Results from three minicosm experiments

The Mediterranean basin receives among the highest dust fluxes in the world ocean, and also appears to be one of the regions the most strongly impacted by ocean acidification. The aim of this study was to assess, on a short time scale (one-week), the effect of ocean acidification on the dissolution of nutrients (inorganic nitrogen, phosphate and iron) from Saharan dust. Three experiments were performed in three distinct seasons: in May, after the spring bloom with low autotrophic biomass, in September, at the end of the oligotrophic period, and in January, during the winter bloom. On each occasion, a dust flux of 10 g m−2 was simulated at the surface of two minicosms (tanks of ∼0.3 m3) filled with filtered (<0.2 µm) seawater collected in the Bay of Villefranche (NW Mediterranean Sea). One minicosm served as a control and the other was acidified to reach a partial pressure of CO2 (pCO2) close to that projected for the end of this century (∼1250 μatm). Following a high-resolution sampling protocol, results showed that whatever the season and in situ biogeochemical conditions (1) all nitrogen from dust was soluble in seawater, allowing a large and stable increase in the stock of NOx (nitrate + nitrite) under the two pCO2 conditions (ambient and future), (2) transient increases in dissolved iron and phosphate concentrations were driven by scavenging processes, with a low dissolution percentage averaging 0.14 ± 0.08 and 4.7 ± 1.2%, respectively. While the absence of pCO2 effects on the release of atmospheric nitrogen was confirmed in the present study, no clear conclusion could be drawn for phosphate and dissolved iron as a consequence of very low concentrations and rapid (within less than 1 h) dissolved-particulate exchanges. Nevertheless, as the lifetime of these elements in solution is limited to a few hours, whatever the pH conditions, our results suggest that ocean acidification would have only a minor impact on their bioavailability for surface phytoplankton communities in such Low Nutrient Low Chlorophyll areas.

Major fertilization sources and mechanisms for Mediterranean Sea coastal ecosystems

AbstractThe Mediterranean Sea is considered an oligotrophic basin with a few biological production hotspots. Some of these productive regions are under the influence of large rivers’ discharges and have been described to suffer from eutrophication indications. In order to quantify the impact of the river‐borne inorganic nutrients on the pelagic production levels and bottom oxygen conditions in the northern coast of the Mediterranean Sea, two hindcast simulations using a coupled hydrodynamic‐biogeochemical model are compared. Both simulations cover a 60 yr period and are identical except for the rivers’ conditions, one is performed considering realistic inorganic nutrient levels in the rivers’ waters while the second has no inorganic nutrients coming from the freshwater discharges. Comparing these two simulations we found that inorganic nutrients in the rivers are responsible for a large fraction of the pelagic primary production and for the totality of bottom hypoxic zones in both the Adriatic and Aegean basin. On the contrary, river fertilization is of marginal importance for the coastal ecosystem of the NW Mediterranean Sea, where mesoscale processes and associated vertical transport of nutrients are the main processes responsible for the majority of the production. We, finally, discuss the consequences of these fundamental differences in fertilization for freshwater management and ecosystems status evaluation in the light of different policy options and within the context of future climate change.

In situ Occurrence, Prevalence and Dynamics of Parvilucifera Parasitoids during Recurrent Blooms of the Toxic Dinoflagellate Alexandrium minutum.

Dinoflagellate blooms are natural phenomena that often occur in coastal areas, which in addition to their large number of nutrient-rich sites are characterized by highly restricted hydrodynamics within bays, marinas, enclosed beaches, and harbors. In these areas, massive proliferations of dinoflagellates have harmful effects on humans and the ecosystem. However, the high cell density reached during blooms make them vulnerable to parasitic infections. Under laboratory conditions parasitoids are able to exterminate an entire host population. In nature, Parvilucifera parasitoids infect the toxic dinoflagellate Alexandrium minutum during bloom conditions but their prevalence and impact remain unexplored. In this study, we evaluated the in situ occurrence, prevalence, and dynamics of Parvilucifera parasitoids during recurrent blooms of A. minutum in a confined site in the NW Mediterranean Sea as well as the contribution of parasitism to bloom termination. Parvilucifera parasitoids were recurrently detected from 2009 to 2013, during seasonal outbreaks of A. minutum. Parasitic infections in surface waters occurred after the abundance of A. minutum reached 104–105 cells L−1, suggesting a density threshold beyond which Parvilucifera transmission is enhanced and the number of infected cells increases. Moreover, host and parasitoid abundances were not in phase. Instead, there was a lag between maximum A. minutum and Parvilucifera densities, indicative of a delayed density-dependent response of the parasitoid to host abundances, similar to the temporal dynamics of predator-prey interactions. The highest parasitoid prevalence was reached after a peak in host abundance and coincided with the decay phase of the bloom, when a maximum of 38% of the A. minutum population was infected. According to our estimates, Parvilucifera infections accounted for 5–18% of the total observed A. minutum mortality, which suggested that the contribution of parasitism to bloom termination is similar to that of other biological factors, such as encystment and grazing.

Long-term (1998 vs. 2010) large-scale comparison of soft-bottom benthic macrofauna composition in the Gulf of Lions, NW Mediterranean Sea

We achieved a long term (i.e., 1998 vs. 2010) large scale (i.e., whole Gulf of Lions) study of benthic macrofauna composition in the Gulf of Lions based on the resampling of 91 stations located along 21 inshore-offshore transects. Results show that the 3 main benthic communities identified in 1998 were still present in 2010 although their composition changed. Using only year and station of sampling we found a significant space-time interaction explaining changes in macrofaunal community composition, and, in this study, stations differ primarily in terms of depth and distance to the Rhône river mouth. Temporal changes in benthic macrofauna composition were clearly most important at shallow stations (i.e., in the Littoral Fine Sand community) than at deep ones (i.e., Terrigenous Coastal Mud community). These results are in good agreement with the current paradigm according to which climatic oscillations such as NAO (North Atlantic Oscillation) and WeMO (Western Mediterranean Oscillation) are indirectly (i.e., through changes in the frequency of occurrence and the intensity of storms) controlling benthic macrofauna composition in the Gulf of Lions. This hypothesis is further supported by a meta-analysis of changes in the average and maximal yearly abundances of the polychaete Ditrupa arietina. At last, the spatial modelling of 1998 and 2010 benthic macrofauna compositions both suggested a significant effect of Rhône River inputs on the spatial distribution of benthic macrofauna in the Gulf of Lions.

Environmental drivers of sardine (Sardina pilchardus) in the Catalan Sea (NW Mediterranean Sea)

ABSTRACTIn the area surrounding the Ebro Delta, similar to the rest of the north-western Mediterranean Sea, the sardine (Sardina pilchardus), one of the most exploited small pelagic fishes, has suffered a decreasing trend in abundance and biomass in the last decade, with low values in evidence since 2007. The dependence of this species on environmental factors makes it vulnerable to environmental changes; consequently, the abundance of the species is highly variable. Using segmented regression, we evaluated the presence of discontinuities in the temporal pattern of the seasonally adjusted landings per unit effort (LPUE), which was used as a proxy for abundance, between 2000 and 2013. The results suggested a sudden increase in mid-2005, followed by a sharp decrease starting in 2006. A generalized additive mixed model (GAMM), incorporating the linear correlation structure, was used to identify relationships between the seasonally adjusted LPUE and trends of the Western Mediterranean Oscillation index (WeMOI), sea surface temperature (SST), salinity (SAL) and the Zonal and Meridional Currents (ZC and MC, respectively). The variance inflation factors (VIFs) were calculated between all environmental variables to avoid high-dimensional collinearities. The final GAMM, selected using the Akaike information criterion, indicated that positive WeMOI values, which favour the productivity of the area, along with SAL (at ca. 38) and a northward-flowing MC, favoured LPUE. Our results, obtained by applying a method in which variation due to season, non-linearity, autocorrelation and collinearity of the covariates was taken into account, provided further evidence of the dependence of the sardine population upon specific hydrographic variables.

Reproduction of Spatio-Temporal Patterns of Major Mediterranean Phytoplankton Groups from Remote Sensing OC-CCI Data

During the last two decades, several satellite algorithms have been proposed to retrieve information about phytoplankton groups using ocean colour data. One of these algorithms, the so-called PHYSAT-Med, was developed specifically for the Mediterranean Sea due to the optical peculiarities of this basin. The method allows the detection from ocean colour images of the dominant Mediterranean phytoplankton groups, namely nanoeukaryotes, Prochlorococcus, Synechococcus, diatoms, coccolithophorids and Phaeocystis-like phytoplankton. Here, we present a new version of PHYSAT-Med applied to the Ocean Colour – Climate Change Initiative (OC-CCI) database. The OC-CCI database consists of a multi-sensor, global ocean-colour product that merges observations from four different sensors. This retuned version presents improvements with respect to the previous version, as it increases the temporal range (since 1998), decreases the cloud cover, improves the bias correction and a validation exercise was performed in the NW Mediterranean Sea. In particular, the PHYSAT-Med version has been used here to analyse the annual cycles of the major phytoplankton groups in the Mediterranean Sea. Wavelet analyses were used to explore the spatial variability in dominance both in the time and frequency domains in several Mediterranean sub-regions, such as the Alboran Sea, Ligurian Sea, Northern Adriatic Sea and Levantine basin. Results extended the interpretation of previously detected patterns, indicating the dominance of Synechococcus-like versus prochlorophytes throughout the year at the basin level, and the predominance of nanoeukaryotes during the winter months. The method successfully reproduced the diatom blooms normally detected in the basin during the spring season (March to April), especially in the Adriatic Sea. According to our results, the PHYSAT-Med OC-CCI algorithm represents a useful tool for the spatio-temporal monitoring of dominant phytoplankton groups in Mediterranean surface waters. The successful applications of other regional ocean colour algorithms to the OC-CCI database will give rise to extended time series of phytoplankton functional types, with promising applications to the study of long-term oceanographic trends in a global change context.

A submesoscale coherent vortex in the Ligurian Sea: From dynamical barriers to biological implications

AbstractIn June 2013, a glider equipped with oxygen and fluorescence sensors has been used to extensively sample an anticyclonic Submesoscale Coherent Vortex (SCV) in the Ligurian Sea (NW Mediterranean Sea). Those measurements are complemented by full‐depth CTD casts (T, S, and oxygen) and water samples documenting nutrients and phytoplankton pigments within the SCV and outside. The SCV has a very homogeneous core of oxygenated waters between 300 and 1200 m formed 4.5 months earlier during the winter deep convection event. It has a strong dynamical signature with peak velocities at 700 m depth of 13.9 cm s−1 in cyclogeostrophic balance. The eddy has a small radius of 6.2 km corresponding to high Rossby number of −0.45. The vorticity at the eddy center reaches . Cross‐stream isopycnic diffusion of tracers between the eddy core and the surroundings is found to be very limited due to dynamical barriers set by the SCV associated with a diffusivity coefficient of about 0.2 m2 s−1. The deep core is nutrients‐depleted with concentrations of nitrate, phosphate, and silicate, 13–18% lower than the rich surrounding waters. However, the nutriclines are shifted of about 20–50 m toward the surface thus increasing the nutrients availability for phytoplankton. Chlorophyll‐a concentrations at the deep chlorophyll maximum are subsequently about twice bigger as compared to outside. Pigments further reveal the predominance of nanophytoplankton inside the eddy and an enhancement of the primary productivity. This study demonstrates the important impact of postconvective SCVs on nutrients distribution and phytoplankton community, as well as on the subsequent primary production and carbon sequestration.