Seawater physics and chemistry along the Med-SHIP transects in the Mediterranean Sea in 2016.

The Mediterranean Sea has been sampled irregularly by research vessels in the past, mostly by national expeditions in regional waters. To monitor the hydrographic, biogeochemical and circulation changes in the Mediterranean Sea, a systematic repeat oceanographic survey programme called Med-SHIP was recommended by the Mediterranean Science Commission (CIESM) in 2011, as part of the Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP). Med-SHIP consists of zonal and meridional surveys with different frequencies, where comprehensive physical and biogeochemical properties are measured with the highest international standards. The first zonal survey was done in 2011 and repeated in 2018. In addition, a network of meridional (and other key) hydrographic sections were designed: the first cycle of these sections was completed in 2016, with three cruises funded by the EU project EUROFLEETS2. This paper presents the physical and chemical data of the meridional and key transects in the Western and Eastern Mediterranean Sea collected during those cruises.

Depth-driven patterns in lytic viral diversity, auxiliary metabolic gene content, and productivity in offshore oligotrophic waters.

Introduction: Marine viruses regulate microbial population dynamics and biogeochemical cycling in the oceans. The ability of viruses to manipulate hosts' metabolism through the expression of viral auxiliary metabolic genes (AMGs) was recently highlighted, having important implications in energy production and flow in various aquatic environments. Up to now, the presence and diversity of viral AMGs is studied using -omics data, and rarely using quantitative measures of viral activity alongside. Methods: In the present study, four depth layers (5, 50, 75, and 1,000 m) with discrete hydrographic features were sampled in the Eastern Mediterranean Sea; we studied lytic viral community composition and AMG content through metagenomics, and lytic production rates through the viral reduction approach in the ultra-oligotrophic Levantine basin where knowledge regarding viral actions is rather limited. Results and Discussion: Our results demonstrate depth-dependent patterns in viral diversity and AMG content, related to differences in temperature, nutrients availability, and host bacterial productivity and abundance. Although lytic viral production rates were similar along the water column, the virus-to-bacteria ratio was higher and the particular set of AMGs was more diverse in the bathypelagic (1,000 m) than the shallow epipelagic (5, 50, and 75 m) layers, revealing that the quantitative effect of viruses on their hosts may be the same along the water column through the intervention of different AMGs. In the resource- and energy-limited bathypelagic waters of the Eastern Mediterranean, the detected AMGs could divert hosts' metabolism toward energy production, through a boost in gluconeogenesis, fatty-acid and glycan biosynthesis and metabolism, and sulfur relay. Near the deep-chlorophyll maximum depth, an exceptionally high percentage of AMGs related to photosynthesis was noticed. Taken together our findings suggest that the roles of viruses in the deep sea might be even more important than previously thought as they seem to orchestrate energy acquisition and microbial community dynamics, and thus, biogeochemical turnover in the oceans.

Thirty years of a bottom oxygen depletion-renewal cycle in the coastal yet deep environment of the West Saronikos Gulf (Greece): Its drivers and the impact on the benthic communities.

In the period 1987-2017, a series of physical and chemical measurements related to oxygen variability at a trough area with a maximum depth of ~420 m in the West Saronikos Gulf, reveal the following: In the early 90s, deep winter mixing occurred resulting in an oxygenation down to ~420 m followed by an oxygen decline. This decline reached near-bottom hypoxic conditions (O2 < ~62 µM (µmol/L)) after 1998, while a denitrification phase occurred after 2000 and a complete bottom anoxia in 2005. In June 2012, an oxygenation down to ~350 m was detected that most likely occurred in winter 2012. The 2012 oxygenation raised the until-then anoxic bottom concentrations to hypoxic ones in the years towards 2017 via vertical diffusive oxygen transfer. Observations of the benthic communities during the hypoxia, severe hypoxia (O2 < ~15 µM) and oxygen recovery phases showed a peak of opportunists in the hypoxia and a long faunal depletion in the severe hypoxia phases. A reversal in the benthic community structure appeared after the oxygenation of 2012 with the (re)appearance of opportunists while, in 2017, the community showed signs of retreat to earlier stages. The main anthropogenic pressure that could tentatively affect the oxygen concentration in the study area is posed by the Athens treated-sewage outfall at ~40 km away from the trough, which inputs organic matter into the Saronikos Gulf through effluent water of reduced salinity that, in addition, may alter the stratification opposing the vertical mixing. We show that the treated sewage output had no influence on a) the stratification, b) the particulate and dissolved organic carbon and c) the sewage-derived organic matter. Instead, the long-term dissolved oxygen variability with the deep renewal events was mostly driven by the large-scale atmosphere-ocean conditions (heat exchange and evaporation-minus-precipitation budget) that determine the hydrographic characteristics and the winter mixing.

Exploring microplastic pollution in a Mediterranean river: The role of introduced species as bioindicators.

Studies of plastic contamination in freshwater ecosystems and their biota remain scarce, despite the fact that the vast majority of plastic waste initially passes through lotic ecosystems. Biomonitoring provides valuable information regarding plastic pollution and microplastic threats to biota and human health. The aim of this study was to explore the potential use of a non-indigenous fish species as a bioindicator of microplastic pollution in an Eastern Mediterranean River. Our study area is located in a heavily modified and vastly impacted urban river which flows through the largest part of the Metropolitan area of Athens, Greece. We used an introduced chub species (Squalius vardarensis) to assess microplastic ingestion in the river. The results indicated moderate occurrence and abundance of microplastics in the fish gastrointestinal tracts; one-third of specimens (35%) contained microplastics, although the average number of microplastics per specimen was relatively low (1.7 ± 0.2). Overall, the abundance of microplastics in the water confirmed the moderate level of microplastics contamination in our study area. The major polymer types of microplastics identified by FT-IR analysis were: polyethylene (PE), polyvinyl alcohol (PVA) and polypropylene (PP); reflecting the fragmentation of larger litter from industrial packaging and/or household goods. Surface runoff of the urban environment, via motorways and major road networks, could be the contributing factor to the reported microplastics. Our results suggest that generalist's non-indigenous species such as chubs could be used as bioindicators of microplastics in inland waters. Introduced fishes can be a feasible, nondestructive, and cost-effective option for the assessment of microplastics in freshwater ecosystems, while freshwater chubs' high abundance and omnipresence in European rivers further serve this scope. However, it is worth noting that the suitability of any particular species as a bioindicator of microplastics may depend on a variety of factors, including their feeding behavior, habitat, and exposure to microplastics in their environment.

The impact of combining data sets of fluorescence excitation - emission matrices of dissolved organic matter from various aquatic sources on the information retrieved by PARAFAC modeling.

Despite that fluorescence spectroscopy coupled with Parallel Factor Analysis (PARAFAC) has been widely used in the investigation of Fluorescent Dissolved Organic Matter (FDOM) in aquatic systems, the proper performance of PARAFAC analysis on datasets originating from various sources is not to be taken for granted. In this study, we examine the impact of the co-analysis of datasets from various natural water systems located in the same geographical region in the Eastern Mediterranean Sea. For this purpose three datasets were formed representative of open sea waters (SW), rivers and streams (RV) and lagoons (LG). The Excitation Emission Matrices (EEMs) derived from fluorescence analysis were subjected to individual PARAFAC analysis per dataset as well as combined analyses i.e.: SWRV, SWLG, RVLG, ALL (SW-RV-LG). We evaluated the reliability of the components that were validated in the combined models through the investigation of model's residuals and components correlation. We also assessed the similarity of the common identified components among models in regards of: (a) spectral position, by calculating the Tucker congruence coefficient (TCC) of the excitation and emission loadings of the PARAFAC components, and (b) fluorescence intensity, through regression analysis of Fmax, among models. Our analysis showed that for natural waters of various sources within the same geographical region, combined PARAFAC modeling can have both negative as well as positive impact. In the case of the combined SWLG and RVLG models, the PARAFAC analysis was able to resolve the fulvic component that was initially observed only in the LG dataset and thus a new component for SW and RV datasets was resolved. The fulvic-like component was actually identified for the first time in the open sea using the combined datasets. Moreover in the combined SWRV analysis tyrosine-like component was resolved which was found initially only in the RV dataset. Contrary, tyrosine-like component was lost in the combined RVLG dataset. We also show that the resolution of extra components in a combined analysis is not always a good fit for the dataset and the model should be assessed in terms of residuals prior acceptance. Finally, our study proposes that the similarity of the common components between combined and individual models is largely dependent on the similarity between the components of the individual models and that the estimation of the Fmax of a component is probably less affected by data diversity compared to the estimation of its spectral position.

A harmonized and coordinated assessment of the abundance and composition of seafloor litter in the Adriatic-Ionian macroregion (Mediterranean Sea).

Marine litter is a threat to marine life and an economic burden for coastal communities, but efforts to address the issue are hampered by the lack of data for many countries. We performed the first harmonized assessment of seafloor litter (trawl and visual surveys) in six countries of the Adriatic-Ionian macroregion. Seafloor litter showed an uneven distribution throughout the area, with large differences in litter densities and composition among countries and locations. An emerging problem in the area resulted in short-term & single-use objects that represented the largest fraction of litter. Packaging was the economic sector contributing most to seafloor litter on the continental shelf and upper slope, while in some areas aquaculture (mussel farming) represented a key activity producing marine litter. In coastal areas and bays (e.g. Boka Kotorska bay, Montenegro), seafloor litter was mainly related to construction activities and electronic goods, which are a consequence of fly-tipping/illegal dumping.

Microplastics in mussels and fish from the Northern Ionian Sea.

Microplastic ingestion by marine organisms presents an emerging threat to marine ecosystems; microplastics in different marine species are currently reported worldwide. This study aims to assess microplastic ingestion in four, highly commercial, marine species from Greek waters in the Northern Ionian Sea (Mediterranean Sea). Microplastics were found in mussels (Mytilus galloprovincialis) and all three fish species (Sardina pilchardus, Pagellus erythrinus, Mullus barbatus) examined. The frequency of occurrence of ingested microplastics was 46.25% in mussels, while among fish species, S. pilchardus showed the highest frequency of microplastic ingestion (47.2%). Microplastic abundance ranged from 1.7-2 items/individual in mussels and from 1.5-1.9 items/individual in fish. The majority of ingested microplastics were fragments, while their color and size varied. Fourier Transform Infrared Spectroscopy (FT-IR) indicated polyethylene as the most common polymer type in mussels and fish. Results can be used to set baseline levels for the assessment of microplastic pollution in the Ionian Sea.

Marine litter on the beaches of the Adriatic and Ionian Seas: An assessment of their abundance, composition and sources.

The abundance, composition and sources of marine litter were determined on beaches located in the seven countries of the Adriatic-Ionian macroregion, namely Albania, Bosnia and Herzegovina, Croatia, Greece, Italy, Montenegro and Slovenia. A total of 70,581 marine litter items were classified and recorded through one-year long surveys carried out in 31 sites. The average litter density of 0.67 items/m2 found within this study is considered to be relatively high. The beaches investigated differed in terms of human-induced pressures; their majority is classified either as semi-urban or semi-rural, while very few beaches could be characterized as urban or remote/natural. The majority of litter items were made of artificial/anthropogenic polymer materials accounting for 91.1% of all litter. Litter from shoreline sources accounted for 33.4% of all litter collected. The amount of litter from sea-based sources ranged in the different countries from 1.54% to 14.84%, with an average of 6.30% at regional level.

Beach litter dynamics on Mediterranean coasts: Distinguishing sources and pathways.

We assessed amounts, composition and net accumulation rates every ~15days of beach macro litter (≥2.5cm) on 4 Mediterranean beaches, on Corfu island, N. Ionian Sea, taking into account natural and anthropogenic drivers. Average net accumulation rate on all beaches was found 142±115N/100m/15d. By applying a Generalized Linear Model (GzLM) it was shown that sea transport is the dominant pathway affecting the amount and variability in beach litter loadings. Principal Component Analysis (PCA) on compositional data and indicator items discerned two more pathways of beach litter, i.e. in situ litter from beach goers and wind and/or runoff transport of litter from land. By comparing the PCA results to those from a simple item to source attribution, it is shown that regardless their source litter items arrive at beaches from various pathways. Our data provide baseline knowledge for designing monitoring strategies and for setting management targets.

Colored dissolved organic matter dynamics and anthropogenic influences in a major transboundary river and its coastal wetland.

Most transboundary rivers and their wetlands are subject to considerable anthropogenic pressures associated with multiple and often conflicting uses. In the Eastern Mediterranean such systems are also particularly vulnerable to climate change, posing additional challenges for integrated water resources management. Comprehensive measurements of the optical signature of colored dissolved organic matter (CDOM) were combined with measurements of river discharges and water physicochemical and biogeochemical properties, to assess carbon dynamics, water quality, and anthropogenic influences in a major transboundary system of the Eastern Mediterranean, the Evros (or, Марица or, Meriç) river and its Ramsar protected coastal wetland. Measurements were performed over three years, in seasons characterized by different hydrologic conditions and along transects extending more than 70 km from the freshwater end-member to two kilometers offshore in the Aegean Sea. Changes in precipitation, anthropogenic dissolved organic matter (DOM) inputs from the polluted Ergene tributary, and the irregular operation of a dam were key factors driving water quality, salinity regimes, and biogeochemical properties in the Evros delta and coastal waters. Marsh outwelling affected coastal carbon quality, but the influence of wetlands was often masked by anthropogenic DOM contributions. A distinctive five-peak CDOM fluorescence signature was characteristic of upstream anthropogenic inputs and clearly tracked the influence of freshwater discharges on water quality. Monitoring of this CDOM fluorescence footprint could have direct applications to programs focusing on water quality and environmental assessment in this and other transboundary rivers where management of water resources remains largely ineffective.

Short-term exposure of the European sea bass Dicentrarchus labrax to copper-based antifouling treated nets: copper bioavailability and biomarkers responses.

We studied if the levels of copper released from antifouling treated nets used in finfish mariculture could affect the immune defense mechanism and/or induce oxidative stress in Dicentrarchus labrax, after short term exposure in laboratory experiments. Dissolved copper concentration released from the treated nets, copper bioavailability and a set of biomarkers responses were measured. Biomarkers included hemoglobin concentration, activities of lysozyme, total complement, respiratory burst, glutathione S-transferase and acetycholinesterase and concentration of thiobarbituric acid reactive substances. Results indicated elevated copper concentration in seawater (184 µg L(-1)) but low concentration in muscle (1.5 µg g(-1)) and liver (117 µg g(-1)). Copper bioavailability was independent of copper complexes with dissolved organic carbon. However, formation of copper complexes with other matrices could neither be excluded nor justified. The released copper from the treated nets did not induce oxidative stress but affected the immediate immune defense mechanism of the exposed fish making them more easily vulnerable to diseases. Consequently, copper-based antifouling treated nets could be a risk factor for D. labrax health.