Mediterranean Sea In Relation Research Articles

Drawing the borders of the mesophotic zone of the Mediterranean Sea using satellite data

The 30–150 m bathymetric range is commonly adopted in the literature to constrain the mesophotic zone. However, such depth interval varies depending on sunlight penetration, which is primarily a function of solar radiation incidence and water clarity. This is especially obvious in the Mediterranean Sea with its peculiar biophysical properties. Integrating information on light regime in the estimation of the bathymetric range of the mesophotic zone would provide a more robust definition, orienting conservation actions targeting its ecosystems. We present a first assessment of the spatial and vertical extension of the mesophotic zone in the Mediterranean Sea based upon light penetration, comparing our prediction with literature data. Our study also represents a baseline to monitor future variations in the bathymetric interval associated with the mesophotic zone in the Mediterranean Sea in relation to global changes.

Environmental drivers influencing the abundance of round sardinella (Sardinella aurita) and European sprat (Sprattus sprattus) in different areas of the Mediterranean Sea

Data on Sardinella aurita (round sardinella) and Sprattus sprattus (European sprat) in the Mediterranean Sea are limited due to their scarce commercial interest, at least in European countries. Yet, these two small pelagic fish, sitting at opposite ends of the thermal range, could be interesting sentinel species to monitor the effects of climate change in the basin. Using the Mediterranean International Acoustic Surveys (MEDIAS) – the most extensive source of information on these species – we analyzed their biomass in several geographical subareas of the central and western Mediterranean Sea in relation to satellite-derived environmental parameters. Our findings highlight that the S. aurita biomass responded to temperature, salinity, chlorophyll concentration and sea level anomaly, depending on the GSA examined, whereas the S. sprattus biomass correlated significantly with salinity in GSA 6, with salinity and chlorophyll concentration in GSA 7, and with sea level anomaly in GSA 17. These data widen our knowledge of the factors that contribute to the ecology of these species. Further studies of their spatial distribution and of their interactions with other small pelagic species, predators and prey are needed to depict a more comprehensive scenario.

Phytoplankton size changes and diversity loss in the southwestern Mediterranean Sea in relation to long-term hydrographic variability

Structural changes in plankton primary producers have large implications for food web dynamics, energy fluxes and the vertical export of biogenic particulate carbon. Here we examine phytoplankton data spanning the period 1993–2008 from the Bay of Tunis, southwestern Mediterranean Sea, in relation to long term hydroclimate variability. We show a conspicuous shift in the structure of the phytoplankton community characterized by an increase of small-sized species and diversity loss, revealing a dominance of smaller blooming diatoms and cyanobacteria. Such changes were concurrent with marked modifications in hydroclimatic patterns experienced in the Bay of Tunis consisting of a shift towards enhanced winter precipitation together with rising temperatures. This novel study shows an overall rise in the proportion of small phytoplankton cells and a decreasing trend in phytoplankton diversity in the southern Mediterranean area. These findings warn of a potential decline of trophic efficiency and lesser food web stability resulting from mean size reduction and the diversity loss.

Exploitation of the Moroccan maritime potential in tidal energy

Morocco has two coasts, an Atlantic coast that stretches over 3000 km and a Mediterranean facade 500 km long which gives it a considerable maritime potential. It is committed to a policy of environmental preservation, the fight against global warming and the reduction of greenhouse gas emissions to promote all renewable energies [1]. The assessment of Morocco's maritime potential can be studied using marine information from sea currents, waves, wind, water temperature, water salinity and other types of parameters required for this diagnosis [2]. To do this, we used monthly data of sea currents, winds and surface temperature from the MARINE COPERNICUS site and processed by statistical methods using computer tools such as MATLAB software to highlight the main characteristics of our site facades: Atlantic and Mediterranean Sea in relation to the parameters studied to exploit them to study the possibilities of installation of marine renewable energies especially tidal energy.

Composition and seasonal dynamics of the parasite communities of Scyliorhinus canicula (L., 1758) and Galeus melastomus Rafinesque, 1810 (Elasmobranchii) from the NW Mediterranean Sea in relation to host biology and ecological features

The parasite communities of Scyliorhinus canicula and Galeus melastomus are studied for the first time in the Mediterranean. Their seasonal and geographical variations, and their relationship with environmental and fish biological data were tested. The parasite communities of both sharks were characterized by low richness and diversity, and high dominance. Infracommunity structure and composition differed between both species probably due to the consumption of different prey associated with their different bathymetric distributions. For G. melastomus, parasite infracommunity structure and the abundance of some parasites differed across seasons and/or localities due to different dynamics of intermediate hosts populations, in turn linked to different environmental conditions. While Ditrachybothridium macrocephalum was more abundant in juvenile specimens of G. melastomus as a result of ontogenic diet shifts, Grillotia sp. accumulated in adult hosts. The abundance of Proleptus obtusus was significantly higher in S. canicula, likely due to its shallower distribution coupled with higher consumption of reptantian decapods with respect to G. melastomus. Monogenean parasites were associated to high turbidity and temperature levels, which are known to enhance monogenean infection and reproductive success. Cestodes of G. melastomus were linked to high turbidity and O2 levels, which increase zooplankton biomass, favouring the transmission of heteroxenous parasites.

Habitat use, vertical and horizontal behaviour of Atlantic bluefin tuna (Thunnus thynnus) in the Northwestern Mediterranean Sea in relation to oceanographic conditions

We investigated the habitat utilization, vertical and horizontal behaviour of Atlantic bluefin tuna Thunnus thynnus (ABFT) in relation to oceanographic conditions in the northwestern Mediterranean Sea, based on 36 pop-up archival tags and different environmental data sets. Tags were deployed on early mature ABFT (127–255cm) between July and November in 2007-2014, on the shelf area off Marseille, France. The data obtained from these tags provided 1643 daily summaries of ABFT vertical behaviour over 8years of tag deployment. Based on a hierarchical clustering of this data, we could identify four principle daily vertical behaviour types, representing surface (≦10m) and subsurface (10–100m) orientation, moderate (50–200m) and deep (≧200m) diving behaviour. These vertical behaviour types showed seasonal variations with partly opposing trends in their frequencies. Accordingly, ABFT were more surface orientated during summer, while moderate diving behaviour was more common during winter. Depth time series data further revealed inverted day-night patterns for both of these periods. Tagged ABFT frequented the surface waters more regularly during daytime and deeper waters during the night in summer, while the opposite pattern was found in winter. Seasonal changes in the vertical behaviour of ABFT were accompanied by simultaneous changes in environmental conditions (SST, chla, thermal stratification). Accordingly, surface orientation and moderate diving behaviour appeared to be triggered by the thermal stratification of the water column, though less pronounced than previously reported for ABFT in the North Atlantic, probably indicating adaptive vertical behaviour related to the availability of epipelagic food resources (anchovies and sardines). Deep diving behaviour was particularly frequent during months of high biological productivity (February-May), although one recovered tag showed periodic and unusual long spike dives during summer-autumn, in relation to thermal fronts. Regional effects on the vertical behaviour of ABFT were identified through GAMs, with surface orientation being particularly pronounced in the Gulf of Lions, highlighting its suitability for an ongoing annual aerial survey program to estimate ABFT abundance in this region. In addition, increased levels of mesoscale activity/productivity (e.g. related to oceanic fronts) were detected in an area regularly utilized by ABFT, south of the Gulf of Lions, underlining its attractiveness as foraging ground. Kernel densities of geolocation estimates showed a seasonal shift in the horizontal distribution of ABFT from this “high-use” area towards the Gulf of Lions during summer, probably linked to the enhanced availability of epipelagic food resources at this time.

High sensitivity of embryo-larval stage of the Mediterranean mussel, Mytilus galloprovincialis to metal pollution in combination with temperature increase

The present work aimed to assess the effects of two widespread metallic pollutants, copper and silver, along with environmentally-realistic temperature increases, on embryo-larval development of the Mediterranean mussel Mytilus galloprovincialis. First, mussel embryos upon fertilization were exposed for 48 h to increasing concentrations of Cu (0.5–500 μg/L) and Ag (0.1–100 μg/L) at different temperatures (18, 20, 22 or 24 °C) in order to characterize toxicity of each toxicant at the different tested temperatures. Increasing concentrations of a Cu-Ag mixture were then tested in order to assess the mixture effect at different temperatures (18, 20 or 22 °C). Embryotoxicity was measured after 48 h of exposure (D-larvae stage) considering both the percentage of abnormalities and developmental arrest in D-larvae. The results suggest that the optimum temperature for mussel larvae development is 18 °C (12.65± 1.6% malformations) and beyond 20 °C a steep increase of abnormal larvae was observed up to 100% at 24 °C. Ag was more toxic than Cu with a 50% effective concentration (EC50) at 18 °C of 6.58 μg/L and 17.6 μg/L, respectively. Temperature increased the toxicity of both metals as proved with the EC50 at 20 °C at 3.86 μg/L and 16.28 μg/L for Ag and Cu respectively. Toxic unit calculation suggests additive effects of Cu and Ag in mixture at 18 and 20 °C. These results highlight a possible impairment of M. galloprovincialis reproduction in the Mediterranean Sea in relation to increase of both pollutants and water temperature due to global warming.

Changes in the Floating Plastic Pollution of the Mediterranean Sea in Relation to the Distance to Land.

The composition, size distribution, and abundance of floating plastic debris in surface waters of the Mediterranean Sea were analyzed in relation to distance to land. We combined data from previously published reports with an intensive sampling in inshore waters of the Northwestern Mediterranean. The highest plastic concentrations were found in regions distant from from land as well as in the first kilometer adjacent to the coastline. In this nearshore water strip, plastic concentrations were significantly correlated with the nearness to a coastal human population, with local areas close to large human settlements showing hundreds of thousands of plastic pieces per km2. The ratio of plastic to plankton abundance reached particularly high values for the coastal surface waters. Polyethylene, polypropylene and polyamides were the predominant plastic polymers at all distances from coast (86 to 97% of total items), although the diversity of polymers was higher in the 1-km coastal water strip due to a higher frequency of polystyrene or polyacrylic fibers. The plastic size distributions showed a gradual increase in abundance toward small sizes indicating an efficient removal of small plastics from the surface. Nevertheless, the relative abundance of small fragments (< 2 mm) was higher within the 1-km coastal water strip, suggesting a rapid fragmentation down along the shoreline, likely related with the washing ashore on the beaches. This study constitutes a first attempt to determine the impact of plastic debris in areas closest to Mediterranean coast. The presence of a high concentration of plastic including tiny plastic items could have significant environmental, health and economic impacts.

Ostreopsis cf. ovata dynamics in the NW Mediterranean Sea in relation to biotic and abiotic factors

An expansion of the distribution of Ostreopsis cf. ovata, a dinoflagellate which produces palytoxin-like compounds, has been reported in recent years. Economical and social interests are affected by blooms, as they are responsible for respiratory and skin problems in humans and may cause damage to marine organisms. In order to identify the most influential environmental factors that trigger proliferations of O. cf. ovata in the area of the adjacent shallow rocky coast of the Ebro Delta (NW Mediterranean Sea) a three-year survey was performed on the metaphytic microalgae community growing on the macrophytes Jania rubens and Corallina elongata. Small-size diatoms were more abundant than dinoflagellates; O. cf. ovata was identified as the only species present from the genus. Seawater temperature was the primary driver defining the ecological niche of O. cf. ovata. Freshwater and groundwater fluxes were more pronounced in southern than in northern sites, which may have resulted in a distinct O. cf. ovata spatial distribution, with the highest records of abundance and more frequent blooms in the north. In consequence, negative correlations between the abundance of O. cf. ovata and nitrate concentrations and significant positive correlation with salinity were observed. The temporal pattern of O. cf. ovata dynamics from mid-July to early-November is probably due to the fact that this species is observed only above a certain threshold temperature of seawater. Metaphytic cells of O. cf. ovata were smaller in the northern site than in the south, possibly as a result of an increase in cell division, coinciding with higher abundance, and this could be an indicator of favorable conditions. Toxicity in planktonic cells was negatively correlated with cell abundance in the water column, achieving maximum concentrations of 25pg. PLTX eqcell−1.

Characterization of seasonal and inter-annual changes in the abundance of species of marine Cladocera on the Turkish coast of the northeastern Levantine Basin

The purpose of this study was to describe temporal variations in the abundance of cladocerans in the Mediterranean Sea in relation to environmental parameters. The study was conducted between 2008 and 2011 at five sampling stations located in the coastal waters of İskenderun Bay. Zooplankton samples were seasonally collected for four years using a 200-μm mesh WP-2 zooplankton net. The contribution of cladocerans to the total zooplankton community was 22.8% in 2008 and 9.3% in 2009. In 2010 (59.4%) and 2011 (63.4%), the annual mean abundance of cladocerans increased markedly from 473 ind. m−3to 3917 ind. m−3and accounted for more than half of the zooplankton population. A total of five species of Cladocera were found:Penilia avirostrisDana, 1849,Pseudevadne tergestina(Claus, 1877),Evadne spiniferaP. E. Müller, 1867,Pleopis polyphaemoides(Leuckart, 1859) andPodon intermediusLilljeborg, 1853.Penilia avirostriswas the most abundant species during all seasons, especially in April and July, for all four years of the study. The abundance of total cladocerans andP. avirostriswas negatively correlated with salinity () and picoplankton abundance ().P. avirostrisalso exhibited a positive correlation with phytoplankton abundance (), as well as withE. spinifera. In addition, the abundance ofE. spiniferaandP. tergestinawas positively correlated with temperature (), butP. tergestinacorrelated negatively with chlorophyll a. In conclusion, species composition and abundance of cladocerans seems to be greatly affected by the amount of available food and other environmental factors, such as temperature and salinity.

Marine Invasion in the Mediterranean Sea: The Role of Abiotic Factors When There Is No Biological Resistance

The tropical red alga Womersleyella setacea (Rhodomelaceae, Rhodophyta) is causing increasing concern in the Mediterranean Sea because of its invasive behavior. After its introduction it has colonized most Mediterranean areas, but the mechanism underlying its acclimatization and invasion process remains unknown. To understand this process, we decided i) to assess in situ the seasonal biomass and phenological patterns of populations inhabiting the Mediterranean Sea in relation to the main environmental factors, and ii) to experimentally determine if the tolerance of W. setacea to different light and temperature conditions can explain its colonization success, as well as its bathymetric distribution range. The bathymetric distribution, biomass, and phenology of W. setacea were studied at two localities, and related to irradiance and temperature values recorded in situ. Laboratory experiments were set up to study survival, growth and reproduction under contrasting light and temperature conditions in the short, mid, and long term.Results showed that, in the studied area, the bathymetric distribution of W. setacea is restricted to a depth belt between 25 and 40 m deep, reaching maximum biomass values (126 g dw m−2) at 30 m depth. In concordance, although in the short term W. setacea survived and grew in a large range of environmental conditions, its life requirements for the mid and long term were dim light levels and low temperatures. Biomass of Womersleyella setacea did not show any clear seasonal pattern, though minimum values were reported in spring. Reproductive structures were always absent. Bearing in mind that no herbivores feed on Womersleyella setacea and that its thermal preferences are more characteristic of temperate than of tropical seaweeds, low light (50 µmol photon m−2 s−1) and low temperature (12°C) levels are critical for W. setacea survival and growth, thus probably determining its spread and bathymetric distribution across the Mediterranean Sea.

Barnacles (Cirripedia, Thoracica) and associated epibionts from sea turtles in the central Mediterranean

The association patterns and ecology of sea turtle epibionts, and especially obligate epibionts, are still poorly known. Epibiont communities were investigated in the central Mediterranean Sea in relation to the host habitat and seven species of barnacles, three amphipods, one crab, and one tanaid were found on 117 loggerhead sea turtles, Caretta caretta. Particular attention was given to barnacles, some of them being obligate turtle epibionts, with a total of 3330 individuals examined, among which high intraspecific aggregation was observed. Results indicate that (i) the species composition of barnacles varies among turtles frequenting not only different geographic areas but also different habitats in the same area, (ii) different species have marked preferences for hosts frequenting pelagic vs. benthic habitats, and also (iii) for body parts of the host representing microhabitats with different features and trophic opportunities, (iv) settlement is favoured by the presence of conspecific individuals and possibly also (v) by individuals of related species, notably Chelonibia testudinaria that may act as a pioneer species, and finally (vi) barnacles show rapid turnover on turtles, with relatively short lives, rapid growth, and high juvenile mortality.

Decadal scale variability of sea surface temperature in the Mediterranean Sea in relation to atmospheric variability

Twenty-four years of AVHRR-derived sea surface temperature (SST) data (1985–2008) and 35 years of NOCS (V.2) in situ-based SST data (1973–2008) were used to investigate the decadal scale variability of this parameter in the Mediterranean Sea in relation to local air–sea interaction and large-scale atmospheric variability. Satellite and in situ-derived data indicate a strong eastward increasing sea surface warming trend from the early 1990s onwards. The satellite-derived mean annual warming rate is about 0.037°C year–1 for the whole basin, about 0.026°C year–1 for the western sub-basin and about 0.042°C year–1 for the eastern sub-basin over 1985–2008. NOCS-derived data indicate similar variability but with lower warming trends for both sub-basins over the same period. The long-term Mediterranean SST spatiotemporal variability is mainly associated with horizontal heat advection variations and an increasing warming of the Atlantic inflow. Analysis of SST and net heat flux inter-annual variations indicates a negative correlation, with the long-term SST increase, driving a net air–sea heat flux decrease in the Mediterranean Sea through a large increase in the latent heat loss. Empirical orthogonal function (EOF) analysis of the monthly average anomaly satellite-derived time series showed that the first EOF mode is associated with a long-term warming trend throughout the whole Mediterranean surface and it is highly correlated with both the Eastern Atlantic (EA) pattern and the Atlantic Multidecadal Oscillation (AMO) index. On the other hand, SST basin-average yearly anomaly and NAO variations show low and not statistically significant correlations of opposite sign for the eastern (negative correlation) and western (positive correlation) sub-basins. However, there seems to be a link between NAO and SST decadal-scale variations that is particularly evidenced in the second EOF mode of SST anomalies. NOCS SST time series show a significant SST rise in the western basin from 1973 to the late 1980s following a large warming of the inflowing surface Atlantic waters and a long-term increase of the NAO index, whereas SST slowly increased in the eastern basin. In the early 1990s, there is an abrupt change from a very high positive to a low NAO phase which coincides with a large change in the SST spatiotemporal variability pattern. This pronounced variability shift is followed by an acceleration of the warming rate in the Mediterranean Sea and a change in the direction (from westward to eastward) of its spatial increasing tendency.

Summer distribution and diversity of aerobic anoxygenic phototrophic bacteria in the Mediterranean Sea in relation to environmental variables

Aerobic anoxygenic phototrophic bacteria (AAP) represent an important fraction of bacterioplankton assemblages in various oceanic regimes. Although their abundance and distribution have been explored recently in diverse oceanic regions, the environmental factors controlling the population structure and diversity of these photoheterotrophic bacteria remain poorly understood. Here, we investigate the horizontal and vertical distributions and the genetic diversity of AAP populations collected in late summer throughout the Mediterranean Sea using pufM-temporal temperature gel gradient electrophoresis (TTGE) and clone library analyses. The TTGE profiles and clone libraries analyzed using multivariate statistical methods demonstrated a horizontal and vertical zonation of AAP assemblages. Physicochemical parameters such as pH, inorganic nitrogen compounds, photosynthetically active radiation, total organic carbon and to a lesser extent particulate organic nitrogen and phosphorus, and biogenic activities (e.g. bacterial production, cell densities), acted in synergy to explain the population changes with depth. About half of the pufM sequences were <94% identical to known sequences. The AAP populations were predominantly (~80%) composed of Gammaproteobacteria, unlike most previously explored marine systems. Our results suggest that genetically distinct ecotypes inhabiting different niches may exist in natural AAP populations of the Mediterranean Sea whose genetic diversity is typical of oligotrophic environments.

Seasonal abundance of non-commercial demersal fish in the eastern Mediterranean Sea in relation to hydrographic and sediment characteristics

Fish-habitat associations were investigated for twenty-five non-commercial demersal species in the Aegean Sea (eastern Mediterranean) using Generalized Additive Modeling techniques. Fishery related abundance indices, derived from experimental bottom trawl surveys, were linked to various habitat variables: substrate characteristics, area, season, depth, temperature and salinity. Depth was the most important factor for all species. Eleven species showed decreasing abundance with depth, while the remaining species were more abundant in specific depth zones either on the continental shelf or in the upper continental slope. Most species were associated with specific substratum characteristics such as the dry weight percentage of sand-gravel and the carbonate content. The dry weight percentage of sand-gravel in the sediments was selected as a predictor of the relative abundance of most (twenty three) species. Seasonal patterns in the relative abundance of species were observed, related in most cases to the seasonal differentiation of temperature. The effect of temperature was more pronounced in summer and autumn, when a marked thermocline is observed, while it was much less intense in winter. For most of the species, the preferable habitat was identified, that contributes valuable information for the successful implementation of an ecosystem approach to fisheries management.

Bottom up effects on bacterioplankton growth and composition during summer-autumn transition in the open NW Mediterranean Sea

Abstract. We examined the vertical and temporal dynamics of nutrients, ectoenzymatic activities under late summer-fall transition period (September–October 2004) in NW Mediterranean Sea in relation to temporal change in factors limiting bacterial production. The depth of the mixed layer (12.8±5.3 m) was extremely stable until the onset of the destratification period after 11 October, creating a zone where diffusion of nutrient from the much deeper phosphacline (69±12 m) and nitracline (50±8 m) was probably strongly limited. However after 1st October, a shallowing of nutriclines occured, particularly marked for nitracline. Hence, the nitrate to phosphate ratio within the mixed layer, although submitted to a high short term variability, shifted the last week of the cruise from 1.1±1.2 to 4.6±3.8, and nitrate increased by a factor 2 (0.092±0.049 μM). A corresponding switch from more than one limitation (PN) to P-only limitation of bacterial production was observed during the month as detected by enrichment bioassays. Differences in the identity of the limiting nutrient in surface (5 m: N and P at the beginning, strictly P at the end of the study) versus 80 m (labile carbon) influence greatly bacterial community structure shift between these two layers. The two communities (5 and 80 m) reacted rapidly (24 h) to changes in nutrient concentrations by drastic modification of total and active population assemblages resulting in changes in activity. For bacterial production values less than 10 ng C l−1 h−1 (associated to deeper layers), aminopeptidase and lipase exhibited higher activity relative to production whereas phosphatase varied in the same proportions than BP on the range of activities tested. Our results illustrate the effect of bottom-up control on bacterial community structure and activities in the epipelagic NW Mediterranean Sea.

Poly-aromatic hydrocarbon (PAH) inputs from the Rhône River to the Mediterranean Sea in relation with the hydrological cycle: Impact of floods

The concentrations of dissolved and particulate polycyclic aromatic hydrocarbons (PAHs) were monitored in waters of the Rhône River (France) every fortnight for a full calendar year, from June 1994 to May 1995. All flood events occurring over the course of the experiment were sampled at higher frequency to better quantify the impact of these extreme hydrological episodes on the annual export of PAHs to the Mediterranean Sea. This time-series indicates that more than 90% of the annual load of particulate PAHs is transported during flood episodes, with 77% discharged during the course of only one extreme flood event occurring in November 1994. During these intense events, riverine particles are depleted in PAHs while at low river discharge particles are PAH-enriched. Dissolved PAHs were less variable and less abundant than adsorbed PAHs, consistently with the low solubility of these compounds.

Hydrological changes in the Mediterranean Sea in relation to changes in the freshwater budget: A numerical modelling study

The response of the Mediterranean Sea and the various sub-basins to changes in the freshwater budget are investigated in a process-oriented study, using the POM model. The model is first integrated using values of the Nile and Ebro rivers runoff, as well as of the Dardanelles freshwater input, typical of the fifties. The model reaches a steady state representative of that existing in the Mediterranean prior to the major damming period after 90 years of integration. Then the model is integrated using the reduced river runoff values typical of the after-damming period. The additional impact of decadal scale trends in the precipitation rate as well as of intense surface cooling periods/events on the thermohaline circulation during the last 40 years were also examined. The model results show that the dramatic reduction of the Nile freshwater input and to a lesser extent the reduction of the freshwater input from the Dardanelles Straits induced a large increase in the sea surface salinity in the Aegean and Levantine basins in the late sixties/early seventies, in agreement with observations. Furthermore, the Ebro runoff reduction during the same period further enhanced the salinity increase in the Levantine basin as higher salinity surface waters of the western basin reached the eastern basin via the Atlantic Water circulation. This saltier surface layer in the vicinity of the Rhodes Gyre favoured the preconditioning for the formation of the Levantine Intermediate Water, resulting in about 40% increase of its formation rate. This in turn resulted in the production of saltier and larger amounts of deep waters in the various deep-water formation sites. According to the model, the river damming and decreased precipitation since the eighties explain about 95% of the observed salinity increase in the Western Mediterranean Deep Water over the last 40 years. The major contributor to this increase was proved to be the Nile damming. The salt increase in the surface layer is proved to be insufficient to produce alone the two climatic transient events in the deep waters of the Eastern Mediterranean in the late sixties and early nineties, respectively. Surface cooling was found to be important, resulting in large deep water formation and thus allowing the propagation of the increased surface salinity signal to the deep layers. However, model results demonstrate that the river damming played an important role in the long-term salt preconditioning of the surface/intermediate layers, thus contributing in triggering the two events.

Vertical distribution of dissolved organic carbon (DOC) in the Western Mediterranean Sea in relation to the hydrological characteristics

Vertical profiles of dissolved organic carbon (DOC) from eight hydrological stations in the Tyrrhenian Sea, Sardinia Channel and Algerian Sea, are reported. DOC exhibits concentrations ranging from 58 to 88 μM in surface water, 43– 57 μM in the intermediate layer and 49– 63 μM in deep waters. The assessment of the hydrological characteristics allows different water masses in the study area to be identified; moreover, different hydrological processes are observed in the Tyrrhenian and Algerian basins. DOC exhibits different values in the different water masses. The lowest DOC concentrations (43– 46 μM ) were found in the Tyrrhenian Levantine Intermediate Water (LIW). Correlations between DOC and apparent oxygen utilization (AOU), investigated within each water mass, exhibit different behaviors in the intermediate and deep waters, suggesting the occurrence of different processes of oxygen consumption in the different water masses.

Distribution and Dominance of Two Introduced Turf-forming Macroalgae on the Coast of Tuscany, Italy, Northwestern Mediterranean Sea in Relation to Different Habitats and Sedimentation

The occurrence of filamentous turf-forming macroalgae assemblages has been widely reported in tropical and temperate oceans. In the Mediterranean Sea the development of dense and persistent turfs has recently started and has been linked to the spread of the two introduced filamentous Rhodophyta Acrothamnion preissii and Womersleyella setacea. In this work algal assemblages on rocky bottoms and rhizomes of Posidonia oceanica were studied during one year in three localities of the northwestern Mediterranean Sea (Leghorn, Vada Shoals and Gorgona Island) characterised by different sedimentation rate and composition of particulate matter. Dead matte of P. oceanica was also studied on Vada Shoals. Results showed that turfs are able to develop on all habitats investigated, but different patterns are found. Turfs were abundant on rhizomes of P. oceanica in all localities studied while on rocks they reached high cover at Leghorn and Vada but not on Gorgona Island. The dead matte of P. oceanica showed patterns similar to those found on rocky bottoms. Turfs seem positively influenced by sedimentation while neither the nature of particulate matter nor other polluting substances had any important result on their spread. The development of turfs negatively affects species number and diversity of invaded communities, while cover did not show significant variations. Womersleyella setacea replaced Acrothamnion preissii on rocky bottoms and on dead matte, but not on Posidonia oceanica rhizomes where Acrothamnion preissii was dominant everywhere. In spite of the occurrence of competition between the two algae, it did not seem to limit the development of turfs as they reached similar cover values independently of the dominant species.