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Coralligenous bioconstructions represent an outstanding example of calcareous build-ups of biogenic origin of the Mediterranean Sea. They provide sensitive and vulnerable habitats actually included in the list of endangered habitats by governmental organizations and conservation agencies (e.g. OSPAR; red list habitats). They are especially sensitive to the ongoing global change (i.e. ocean acidification) that can produces a negative impact on the calcification of the organisms’ skeleton of which they are formed (mainly calcareous algae and invertebrates). The extent to which the coralligenous bioconstructions can modify the submarine environment, affecting the evolution of submerged landforms is extremely variable. Within the framework of the BIOMaP Project (BIOcostruzioni Marine in Puglia, - P.O. FESR 2007/2013), promoted by Puglia region, Italy, new high resolution acoustic data were acquired in order to identify and locate Coralligenous Habitats along the Apulian continental shelf (South Adriatic Sea – Northern Ionian Sea), from 10 down to 100 meters of water depth, in 21 Site of Community Interest and 3 Marine Protected Areas. The dataset covered an area of 1000 km2 and was obtained through the use of MultiBeam Echosounder Systems and Side Scan Sonars. Ground-truthing were collected by 3 ROV dives (Prometeo ROV) and more than 30 underwater camera transects. The present study is based on a new experimental methodology designed to analyze multibeam data by means of geomorphometric analyisis in order to (1) figure out relationships between the observed morphologies and the associated distribution and (2) quantify the total volume of selected Coralligenous build-ups. Our work underlines the importance of combining acoustic survey techniques and geomorphometric analysis in order to offer quantitative information for a new understanding of the importance of Coralligenous Habitat as carbonate deposits of the Mediterranean shelf

Several geochemical and micropaleontological proxies were studied in a well developed sapropel S5 from a core collected south of Crete to investigate the causes and the mechanisms of its deposition, to reconstruct the paleoenvironmental and paleoceanographical conditions at time of its formation and to detect the roles played by productivity and anoxia. The geochemical proxies are also used to unravel the sediment provenance and therefore to help tracing water circulation patterns and freshwater sources. The multiproxy approach reveals that the sapropel layer has high internal variability and five different depositional phases can be identified, four within the visible sapropel layer. An increase in temperature and the development of a Deep Chlorophyll Maximum characterise the onset of the sapropel (phase 1), with enhanced productivity being favoured by local riverine input, not clearly ascribable to Nile river freshwater discharge, and by the shoaling of the pycnocline/nutricline. Surface water stratification and productivity develop, together with strong seafloor dysoxia/anoxia. Phase 2 is characterised by lower stratification, slightly lower temperature and/or higher seasonal contrast, and still high productivity. Phase 3 records high productivity, high temperature and high stratification, probably more sustained by the Nile input. A sudden partial re-oxygenation takes place at the end of this phase, changing the main features of the sapropel. In the fourth phase, productivity starts to decrease, water stratification seems to be partially broken down and sediment oxygenation increases. A transitional phase (phase 5) occurs between the end of the visible sapropel and the normal pelagic post-sapropel sedimentation, where productivity is still high and oxygenation improves compared to the visible sapropel layer. The massive occurrence of Polysphaeridium zoharyi, cyst of a red tide forming dinoflagellate, also characterises this phase. The geochemical proxies indicate that pre-sapropel and post-sapropel sediments are quite different from each other, and the provenance shifts from a more mixed to a more markedly southern origin of sediments.

Hyperspectral imagers enable the collection of high-resolution spectral images exploitable for the supervised classification of habitats and objects of interest (OOI). Although this is a well-established technology for the study of subaerial environments, Ecotone AS has developed an underwater hyperspectral imager (UHI) system to explore the properties of the seafloor. The aim of the project is to evaluate the potential of this instrument for mapping and monitoring benthic habitats in shallow and deep-water environments. For the first time, we tested this system at two sites in the Southern Adriatic Sea (Mediterranean Sea): the cold-water coral (CWC) habitat in the Bari Canyon and the Coralligenous habitat off Brindisi. We created a spectral library for each site, considering the different substrates and the main OOI reaching, where possible, the lower taxonomic rank. We applied the spectral angle mapper (SAM) supervised classification to map the areal extent of the Coralligenous and to recognize the major CWC habitat-formers. Despite some technical problems, the first results demonstrate the suitability of the UHI camera for habitat mapping and seabed monitoring, through the achievement of quantifiable and repeatable classifications.

A one-dimensional ecosystem numerical model is used to simulate the ecosystem changes that could have occurred in the open ocean areas of the Eastern Mediterranean Sea during the Climatic Optimum interval (9500-6000 B.P., Mercone et al. [Mercone, D., Thomson, J., Croudace, I.W., Siani, G., Pateme, M., Troelstra, S., 2000. Duration of S1, the most recent sapropel in the eastern Mediterranean Sea, as indicated by accelerator mass spectrometry radiocarbon and geochemical evidence. Paleoceanography 15, 336-347]). In this period the S1 sapropel was deposited. S1 is the most recent sapropel in the succession of organic carbon-rich layers intercalated in normal Neogene sedimentary sequences. Different theories have been invoked in order to explain the deposition of this peculiar layer. Our simulations seem to indicate that the modified thermohaline circulation, supplying oxygen only in the first 500 m of the water column, is responsible for the sapropel deposition when higher productivity is allowed in the euphotic zone. The model shows the importance in this process of bacteria that consume oxygen by decomposing the Particulate Organic Matter (POM) produced in the upper water column. The sinking velocity of POM partially regulates the timescale of the occurrence of anoxia at the bottom and in the whole water column, allowing the relatively rapid onset of sapropel deposition. (c) 2005 Elsevier B.V. All rights reserved.

In the Mediterranean Sea, crustose coralline algae form endemic algal reefs known as Coralligenous (C) build-ups. The high degree of complexity that C can reach through time creates notable environmental heterogeneity making C a major hotspot of biodiversity for the Mediterranean basin. C build-up can variably modify the submarine environment by affecting the evolution of submerged landforms, although its role is still far from being systematically defined. Our work proposes a new, ad-hoc semi-automated, GIS-based methodology to map the distribution of C build-ups in shallow coastal waters using high-resolution bathymetric data, collected on a sector of the southern Apulian continental shelf (Southern Adriatic Sea, Italy). Our results quantitatively define the 3D distribution of C in terms of area and volume, estimating more than 103,000 build-ups, covering an area of roughly 305,200 m2, for a total volume of 315,700 m3. Our work firstly combines acoustic survey techniques and geomorphometric analysis to develop innovative approaches for eco-geomorphological studies. The obtained results can contribute to a better definition of the ocean carbon budget, and to the monitoring of local anthropogenic impacts (e.g., bottom trawling damage) and global changes, like ocean warming and acidification. These can affect the structural complexity and total volume of carbonate deposits characterizing the Mediterranean benthic environment.

1. Introduction Water is one of the most sensitive elements of the environment and a prerequisite for human well-being and the development of its activities as it provides several ecosystem services (Piroddi et al. 2016). However, there are several factors that can influence its ecological status. Human activities and climate change induced ecosystem vulnerability can provoke several coastal morphology changes that can also negatively influence on the land-ocean interface (Ochoa-Hueso et al. 2017), which is a particularly fragile, sensitive and complex environment. Thus, the effect induced by progressive anthropic changes on the hydrodynamic characteristics of the coastal and estuarine waters (Morrow et al. 2017), and as well on the ocean circulation (Grifoll et al. 2016), can lead to a high variability of marine biogeochemical processes, and cause negative impacts on the status and services of the near shore ecosystem, on which coastal societies depend. Moreover, these changes can drive to dramatic economic and human health impacts (Powley et al. 2014). In the near shore in general, and specifically, in the Mediterranean Sea, due to the existing strong demographic and economic pressures and to other environmental drivers (i.e. wind speed, acidification, eutrophic depth, thermohaline depth, evaporation-precipitation abundance) the boundary status and the water column stability across the longitudinal environmental gradient can result directly impacted (Reygondeau et al. 2017)

In this work, we present preliminary results of the first application in the Mediterranean Sea of a hyperspectral camera, a device commonly used for satellite or airborne remote sensing, adapted for the underwater environment. The spectral analysis was carried out on hyperspectral images acquired in two different environmental settings in the southern Adriatic Sea. This new technology shows high potentialities of application for benthic habitat mapping and monitoring.

Rhodolith beds are priority marine benthic habitats for the European Community, because of their relevance as biodiversity hotspots and their role in the carbonate budget. The high-Mg calcite calcified thalli promote their preservation through time, resulting in their common occurrence in the fossil record, thus making rhodoliths a significant archive of past environmental and climate changes. The present temperate Mediterranean Sea is home to rhodolith-rich up to rhodolith-dominated habitats which have been targeted over the years for ecological research and management actions. Furthermore, the Mediterranean Basin hosts an important fossil legacy of rhodolith beds that formed under contrasting climatic scenarios since the Neogene. Most examples of Mediterranean rhodolith beds lay within the depth range (30-75 m), while far less is known about deeper occurrences. An outstanding rhodolith bed has been recently identified off the Egadi Archipelago (70-95 m, Central Mediterranean Sea) in the frame of the Italian Marine Strategy Framework Directive project. The rhodolith bed carpets an area >7 km2 between Marettimo and Favignana Islands (Egadi Archipelago), with a cover of live rhodoliths up to 95%. The dominant rhodolith morphotype is pralines, ellipsoidal to discoidal in shape (average size 11 mm, maximum size 31 mm) associated with biogenic gravelly-sand. They present both seafloor bedforms (megaripples and ripples) and frequent bioturbations by epifaunal and semi-infaunal sea urchins. Old algal nodules, biogenic sand/mud, or, less frequently, terrigenous particles serve as nucleus of individual rhodoliths. Living calcareous algae are Lithothamnion valens, L. cf. minervae, Phymatolithon lenormandii, and Lithothamnion spp. The latter characterize also the dead algal association close to the nucleus, with the subordinate presence of Lithophyllum sp. Benthic fauna corresponds to the circalittoral environment, with exclusive species of the Coastal Detritic biocoenosis or related to coarse sediments. Moreover, the general textural aspects and bedforms are in line with moderate water energy at the seafloor. Radiocarbon ages reveal that the cores of rhodoliths date back to 2334, 2159 and 1997 BP, which correspond to the Roman Warm Period. Calculated growth rate provides a very low figure (0.004 mm/yr). The inception of such rhodolith bed occurred under warmer climate conditions, but its development is continuing at present because of the persistence of adequate light conditions and bottom hydrological regime, with a very slow growth-rate. Therefore, the Egadi case history certifies a rare example of a deep-water resilient rhodolith bed, which should be taken into consideration for the potential recognition of fossil analogs in the Mediterranean Basin.

Sea floor mapping along the Apulia continental shelf (Italy) verified the abundance of autochthonous red algae build-ups, mapped as coralligenous habitats (CHs), in a water depth range of 5-100 m. In general, CHs were found to develop three dimensional structures, with a rigid framework and to represent an important geomorpho-logical and sedimentological element on the Mediterranean shelf. Here, we provide the first geomorphological description of CHs (thus poorly categorized) using acoustic data obtained from Side Scan Sonar (SSS) and MultiBeam (MB) echosounder surveys, ground-truthed using a ROV and underwater camera. In SSS mosaics, CHs generally yielded intermediate to high backscatter in response to a rigid cavernous framework. According to the various shapes and the lateral continuity that coralligenous build-ups displayed in explored locations, two distinct textures were determined to be present. Various geomorphological expressions of CHs were noted within our dataset and in images obtained from MB bathymetry. We determined that coralligenous build-ups are typically represented by positive-relief structures that vary from isolated blocks (randomly scattered on a generally flat mobile soft bottom) to a field of blocks (adjacent or even coalescent), and/to ridge with several metres of lateral continuity. In most cases, CHs occurred on flat mobile soft bottom, thus representing an example of coralligenous de plateau. Our results characterize for the first time the CHs through seafloor mapping techniques, which demonstrated to represent an instrumental tool for their geomorphological characterization.

Coralligenous has a relevant role in submarine landscape formation and demise through geological times, producing various morphotypes on the seafloor. Several terms are used to define coralligenous morphotypes, but their application through different geological and environmental settings still remains inconsistent. Through a systematic analysis of seafloor acoustic remote data (multibeam, side scan sonar and subbottom profiler) along Apulia continental shelf, ground-truthed by video observations and direct sampling, we detected a number of coralligenous morpho-acoustic facies as 0.2 up to 4 m topographic reliefs with steep flanks and a rigid inhomogeneous biogenic framework, characterized by medium to strong SSS backscatter and a variable plan-view geometry. The observed pattern led to the identification of coralligenous meso- and macrohabitat in which the biogenic frameworks (i.e. coralligenous) prevail as sole biocommunity on the seafloor or are associated with other type of habitats: (i) coralligenous sensu stricto, (ii) coralligenous and detritic bottom, (iii) coralligenous and muddy bottom, (iv) coralligenous and Posidonia meadow. Finally we improve the geomorphological definition of bank, proposing this new descriptive rigorous categorization for coralligenous morphotypes on sub-horizontal substrate: 1) tabular bank, 2) discrete relief, and 3) hybrid bank.

Shallow sediment lithology and stratigraphy were investigated at selected areas off Santa Maria di Leuca (SML) on the Apulian margin between 350 and 1200 m water depth, in order to define the sea-bottom character on which coral mounds have developed. According to existing geophysical data and in-situ observations, deep coral growth in the SML area creates patches of colonies typically settled on hard substrates on the upper flanks and/or near the top of mound-like structures and elongated ridges. The sedimentary stratigraphy is strongly influenced by the local topography, which is modeled by tectonic and geomorphological forcing: large-scale erosional features, slope failure and sediment mass accumulation are evident from seismic investigations. Additionally, sites of preferential sediment accumulation due to the action of bottom currents are identified. As a result, a complex sedimentary pattern characterizes this part of the Apulian margin, with strong lateral variability in sediment type and age. Although hemipelagic silty clay constitutes the main lithology, there are sites characterized by periodic accumulation of silt and fine sand and local re-deposition of coarse biogenic sand from the surrounding areas and from shallower depths. Excluding one site, where mid-Pleistocene sediments are brought very close to the bottom-surface due to wide-scale erosion, all collected sediments are late Pleistocene to Holocene in age and fall biostratigraphically within the Emiliania huxleyi acme nannofossil zone. Reworking, detected through nannofossil analysis, is common in most cores, excluding the ones taken from topographic highs, and is variable in extent from site to site and within the sediment column; it includes Cretaceous to Early Pleistocene species, suggesting provenance from extended successions or various stratigraphic levels, outcropping on the submerged Apulian margin or in adjacent land sections. Reworking is often associated with a high content of lithogenic particles and an increase in the coarser (silt) fraction. Coral debris was collected at many stations, both at the sediment surface and within the stratigraphic sequence, with varying abundance in relation to proximity to the coral colonies. Radiometric dating and micropaleontological analyses at some sites allow us to propose a sequence of coral colonization phases.

Living deep-water coral assemblages were discovered recently inhabiting the Mediterranean Sea between the depths of 300 and 1000 m off the Cape of Santa Maria di Leuca (Apulian platform, Ionian Sea). This living assemblage was dominated by two colonial scleractinian corals, Lophelia pertusa and Madrepora oculata. Two other corals, Desmophyllum crystagalli and Stenocyathus vermiformis were also recovered from this site, but were much less common. The composition of the metabolically active fraction of the microbial community associated with living specimens of L. pertusa was determined. Dead corals, proximal sediments and overlying seawater were also sampled and analyzed. Complementary 16S ribosomal DNA (crDNA) was obtained from total RNA extracted from all samples that had been subjected to reverse transcription-PCR amplification. Domain-specific 16S PCR primers were used to construct four different 16S crDNA libraries containing 45 Archaea and 201 Bacteria clones. Using Archaea-specific primers, no amplification products were obtained from any coral samples (live and dead). Living specimens of L. pertusa seem to possess a specific microbial community different from that of dead coral and sediment samples. The majority of all coral-associated riboclones was related to the Holophaga-Acidobacterium and Nitrospira divisions (80%). Moreover, more than 12% of all coral-associated riboclones formed a separate deep-branching cluster within the α- Proteobacteria with no known close relatives. The metabolically active fraction of the bacterial community colonizing the dead corals was dominated by Proteobacteria related to the gamma and epsilon subdivisions (74% and 26% of all clones, respectively). Phylogenetic analysis of the Archaea clone library retrieved from proximal sediments indicated an exclusive dominance by the members of Crenarchaea Marine Group I (MGI), a lineage of unculturable microorganisms, widely distributed in marine habitats. In contrast, bacterial diversity was considerably higher in this sample than archaeal diversity, with four abundant eubacterial phylotypes: Proteobacteria , Verrucomicrobia , Actinobacteria and Planctomycetes (95% of all clones analyzed). This is one of the first phylogenetic evaluation of the presumed metabolically active microbial community structure associated with the deep-sea scleratinian coral L. pertusa .

The "Santa Maria di Leuca" Cold-Water Coral (CWC) province (northern Ionian Sea) was investigated for the first time to detect eventual occurrence of methane anomalies as a possible indication of hydrocarbon seepage stimulating the coral growth. Most coral mounds have developed in correspondence with tectonic scarps and faults, orthogonal to the southern margin and trending NWSE, which could be potential sites of gas escape. A visual and instrumental inspection was performed by using a new deep-sea probe equipped with video-cameras, sonar. CTD, methane sensors, and a water sampler. Eight areas were explored by 10 surveys, depths ranging from 380 to 1100 m, for a total of more than 26 h of continuous video and instrumental recording. Sediments were also sampled by gravity corers and analysed in laboratory.The images allowed to assess distribution, abundance and geometry of the colonies, most of which are developed on morphological highs often characterised by tectonic scarps. All data indicate however the lack of a significant occurrence of methane, both in seawater and sediments. No direct or indirect expressions of gas seepage were recognised on the seabed. Weak methane anomalies were detected only in seawater at the base of some fault-linked scarps, where more reducing conditions and bacterial methanogenesis are possibly enhanced by less water circulation. The faults are not fluid-bearing as previously suggested by high-resolution geophysical signatures. The development of the coral colonies thus cannot be attributed to seeping fluids, but to a favourable physiographic position with exposure to nutrient-rich currents. (C) 2009 Elsevier Ltd. All rights reserved.

Urania basin in the deep Mediterranean Sea houses a lake that is >100 m deep, devoid of oxygen, 6 times more saline than seawater, and has very high levels of methane and particularly sulfide (up to 16 mM), making it among the most sulfidic water bodies on Earth. Along the depth profile there are 2 chemoclines, a steep one with the overlying oxic seawater, and another between anoxic brines of different density, where gradients of salinity, electron donors and acceptors occur. To identify and differentiate the microbes and processes contributing to the turnover of organic matter and sulfide along the water column, these chemoclines were sampled at a high resolution. Bacterial cell numbers increased up to a hundredfold in the chemoclines as a consequence of elevated nutrient availability, with higher numbers in the upper interface where redox gradient was steeper. Bacterial and archaeal communities, analyzed by DNA fingerprinting, 16S rRNA gene libraries, activity measurements, and cultivation, were highly stratified and metabolically more active along the chemoclines compared with seawater or the uniformly hypersaline brines. Detailed analysis of 16S rRNA gene sequences revealed that in both chemoclines δ- and ε-Proteobacteria, predominantly sulfate reducers and sulfur oxidizers, respectively, were the dominant bacteria. In the deepest layers of the basin MSBL1, putatively responsible for methanogenesis, dominated among archaea. The data suggest that the complex microbial community is adapted to the basin's extreme chemistry, and the elevated biomass is driven largely by sulfur cycling and methanogenesis.

Between 140 and 170 m water depth, more than 100 small-scale domes and peculiar ridges were mapped a few miles offshore of south-eastern Sicily along the Malta plateau (eastern Mediterranean Sea), Swath bathymetric data along with a dense grid of side scan sonar and seismic profiles were acquired in an area extending over 100 km 2 . Gravity cores, water samples and video observations were also collected at selected sites. Mapped domes were found from 50 to 200 m wide and no more than 5 m high occurring on the seafloor, isolated or arranged in clusters. Ridges consisted of large tabular sub-elongated structures, elevated from 5 to 10 m from the surrounding seafloor, and had flat tops on which numerous close-set, small cones occurred, appearing in video observation as carbonate buildings strongly colonized by gorgonians. Characteristic acoustic signatures (i.e. blank areas and/or turbidity zones and enhanced reflections in seismic records), measured gas anomalies in seawater samples and detected plumes on echosounder profiles suggest that both the domes and ridges are influenced by active seeps. In addition, their spatial distribution reflected patterns of tectonic lineaments produced by the late Miocene to present-day geo-dynamic evolution of the Malta plateau, which is also an important hydrocarbon province. Results from gravity cores suggest that mud extrusion seems to be the main process responsible for the origin of the domes, which are formed by gray mud with only a few centimeters of biogenic sand at the top, indicating that recent bioclastic material is not a major contributor to mound building. However, at present, active degassing appears to be the main process that controls the morphological and sedimentological expression of both the domes and ridges. Therefore, a quiescent or intermittent active stage for mud extrusion is considered.

Summary Viral and prokaryote abundance were investigated in a deep-hypersaline anoxic basin of the Eastern Mediterranean Sea (DHAB Atalante basin at c. 3000 m depth). This system was compared with two nearby deep-sea sites characterized by oxic conditions. Viral abundance and virus to prokaryote abundance ratio in hypersaline anoxic sediments displayed values close to those reported in oxic sites. The analysis of vertical profiles of viral abundance in the Atalante basin revealed the lack of significant changes with depth in the sediment, suggesting that benthic viruses in these anoxic and hypersaline conditions are preserved or resistant to decay. The anoxic basin displayed also very high concentrations of labile organic components (proteins and lipids) and extracellular DNA. These findings suggest that the DHAB sediments represent a reservoir for long-term preservation of benthic viruses and nucleic acids.

Deep hypersaline anoxic basins in the Mediterranean Sea are a legacy of dissolution of ancient subterranean salt deposits from the Miocene period. Our study revealed that these hypersaline basins are not biogeochemical dead ends, but support in situ sulfate reduction, methanogenesis, and heterotrophic activity. A wide diversity of prokaryotes was observed, including a new, abundant, deeply branching order within the Euryarchaeota . Furthermore, we demonstrated the presence of a unique, metabolically active microbial community in the Discovery basin, which is one of the most extreme terrestrial saline environments known, as it is almost saturated with MgCl 2 (5 M).

Several geochemical and micropaleontological proxies were studied in a well developed sapropel S5 from a core collected south of Crete to investigate the causes and the mechanisms of its deposition, to reconstruct the paleoenvironmental and paleoceanographical conditions at time of its formation and to detect the roles played by productivity and anoxia. The geochemical proxies are also used to unravel the sediment provenance and therefore to help tracing water circulation patterns and freshwater sources. The multiproxy approach reveals that the sapropel layer has high internal variability and five different depositional phases can be identified, four within the visible sapropel layer. An increase in temperature and the development of a Deep Chlorophyll Maximum characterise the onset of the sapropel (phase 1), with enhanced productivity being favoured by local riverine input, not clearly ascribable to Nile river freshwater discharge, and by the shoaling of the pycnocline/nutricline. Surface water stratification and productivity develop, together with strong seafloor dysoxia/anoxia. Phase 2 is characterised by lower stratification, slightly lower temperature and/or higher seasonal contrast, and still high productivity. Phase 3 records high productivity, high temperature and high stratification, probably more sustained by the Nile input. A sudden partial re-oxygenation takes place at the end of this phase, changing the main features of the sapropel. In the fourth phase, productivity starts to decrease, water stratification seems to be partially broken down and sediment oxygenation increases. A transitional phase (phase 5) occurs between the end of the visible sapropel and the normal pelagic post-sapropel sedimentation, where productivity is still high and oxygenation improves compared to the visible sapropel layer. The massive occurrence of Polysphaeridium zoharyi, cyst of a red tide forming dinoflagellate, also characterises this phase. The geochemical proxies indicate that pre-sapropel and post-sapropel sediments are quite different from each other, and the provenance shifts from a more mixed to a more markedly southern origin of sediments.

Background: Extracellular dissolved DNA has been demonstrated to be present in many terrestrial and aquatic environments, actively secreted, or released by decaying cells. Free DNA has the genetic potential to be acquired by living competent cells by horizontal gene transfer mediated by natural transformation. The aim of this work is to study the persistence of extracellular DNA and its biological transforming activity in extreme environments like the deep hypersaline anoxic lakes of the Mediterranean Sea. The brine lakes are separated from the upper seawater by a steep chemocline inhabited by stratified prokaryotic networks, where cells sinking through the depth profile encounter increasing salinity values and osmotic stress. Results: Seven strains belonging to different taxonomic groups isolated from the seawater-brine interface of four hypersaline lakes were grown at medium salinity and then incubated in the brines. The osmotic stress induced the death of all the inoculated cells in variable time periods, between 2 hours and 144 days, depending on the type of brine rather than the taxonomic group of the strains, i.e. Bacillaceae or gamma-proteobacteria. The Discovery lake confirmed to be the most aggressive environment toward living cells. In all the brines and in deep seawater dissolved plasmid DNA was substantially preserved for a period of 32 days in axenic conditions. L'Atalante and Bannock brines induced a decrease of the supercoiled form up to 70 and 40% respectively; in the other brines only minor changes in plasmid conformation were observed. Plasmid DNA after incubation in the brines maintained the capacity to transform naturally competent cells of Acinetobacter baylii strain BD413. Conclusion: Free dissolved DNA is likely to be released by the lysis of cells induced by osmotic stress in the deep hypersaline anoxic lakes. Naked DNA was demonstrated to be preserved and biologically active in these extreme environments, and hence could constitute a genetic reservoir of traits acquirable by horizontal gene transfer.