Pore-water nutrient concentrations variability under different oxygen regimes: A case study in Elefsis Bay, Greece.

Anthropogenic pressures considerably affect coastal areas, increasing nitrogen and phosphorous loads that lead to eutrophication. Eutrophication sometimes results in hypoxic and/or anoxic conditions near the bottom water. Dissolved oxygen (DO) concentrations influence redox-sensitive nutrients, which can alter the benthic flux of nutrients. We retrieved sediment cores from two sites in the eastern and western parts of Elefsis Bay, a semi-enclosed area of the Eastern Mediterranean, Greece, during winter and summer. In the western part, seasonally hypoxic or anoxic conditions occurred. We analysed pore-water samples under normoxic, hypoxic and anoxic bottom water conditions to study the pore-water nutrient concentrations variability under different oxygen regimes. Ex situ incubation experiments were conducted at the site experiencing oxygen deficiency by manipulating the DO concentrations. The pore-water nutrient concentrations showed higher variability at the site experiencing oxygen deficiency. Notably, elevated ammonium concentrations were observed in the pore water during anoxic conditions, in the 2-20-cm sediment layer. However, the benthic fluxes of ammonium and phosphate at the 0-2-cm sediment layer were comparable under hypoxic and anoxic conditions. The results of the incubation experiments demonstrate a direct decrease in nitrate concentrations as the DO concentrations diminished in the overlying water. The incubations after re-oxygenating the overlying water show that phosphate was more efficiently scavenged when anoxic conditions prevailed in the bottom water. The incubation experiments indicate the rapid response of the seafloor to oxygen availability, particularly concerning processes that influence nitrate and phosphate concentrations. These observations highlight the dynamic nature of nutrient cycling in shallow, seasonally anoxic environments, such as Elefsis Bay, and emphasise the sensitivity of the seafloor ecosystem to changes in bottom water oxygen availability.

Microplastic ingestion and its effects οn sea urchin Paracentrotus lividus: A field study in a coastal East Mediterranean environment.

Microplastics (MPs) are recognized as an increasing threat to the marine environment, but little is known about their effects on benthic organisms, including sea urchins, when ingested. For this purpose, wild sea urchins (P. lividus) and seafloor sediment samples were investigated across three coastal areas of Zakynthos Island (Ionian Sea), each exposed to different anthropogenic pressures, revealing a consistent pattern in MP abundance, shape, and color. Biomarkers related to oxidative stress, neurotoxicity, and genotoxicity showed no significant effects of MP ingestion in the sea urchins, except for a positive correlation between GST activity and ingested MPs, suggesting a possible activation of their detoxification system in response to MP ingestion. While MP concentrations in sea urchins and sediments were within the low range reported in the global literature, it remains crucial to conduct further investigations in areas with MP pollution approaching predicted levels to fully comprehend the potential effects of MP pollution on marine organisms.

Drivers of litter ingestion by sea turtles: Three decades of empirical data collected in Atlantic Europe and the Mediterranean.

Sea turtles are considered as bio-indicators for monitoring the efficiency of restoration measures to reduce marine litter impacts on health. However, the lack of extended and standardised empirical data has prevented the accurate analysis of the factors influencing litter ingestion and the relationships with individual health. Historic data collected from 1988 and standard data collected from 2016 were harmonised to enable such analyses on necropsied loggerhead turtles (Caretta caretta) in eight Mediterranean and North-East Atlantic countries. Litter was found in 69.24 % of the 1121 individuals, mostly single-use and fishing-related plastics. Spatial location, sex and life history stage explained a minor part of litter ingestion. While no relationships with health could be detected, indicating that all individuals can be integrated as bio-indicators, the mechanistic models published in literature suggest that the high proportion of plastics in the digestive contents (38.77 % per individual) could have long-term repercussions on population dynamics.

COVID-19-related litter pollution on Greek beaches and nearshore shallow water environments.

COVID-19 pandemic has led to an increase in certain types of litter, many of which are expected to end up in the marine environment. The present study aimed to monitor the pandemic-related litter pollution along the Greek coastal environment. Overall, 59 beach and 83 underwater clean-ups were conducted. Litter was categorized as: PPE (face masks and gloves), COVID-19-related, single-use plastic (SUP) and takeaway items. PPE, dominated by face masks (86.21 %), accounted for 0.29 % of all litter. The average PPE density was 3.1 × 10-3 items m-2 and 2.59 items/ 100 m. COVID-19-related items represented 1.04 % of the total. Wet wipes showed higher densities (0.67 % of all litter) than in the pre-COVID era, while no increase in SUP and takeaway items was observed. Benthic PPE, dominated by gloves (83.95 %), represented 0.26 % of the total. The mean PPE density was 2.5 × 10-3 items m-2.

Trace element contamination status of surface marine sediments of Greece: an assessment based on two decades (2001-2021) of data.

This study is a first attempt to assess the trace element contamination status in the surface sediments of the Hellenic Seas since the first environmental studies in the country commenced in the mid-1970s. All available trace element data from the last 20 years have been collected and assessed using sediment quality guidelines and application of single- and multielement pollution indices. Although Hellenic marine sediments initially appear as anthropogenically enriched in Cr and As, this enrichment is attributed to the natural background. Central Greece appears more polluted, followed by Northern Greece and lastly Southern Greece. The element pollution indices featured the influence of industrial activities such as mining, steel industry and chemical factories, shipyards, and secondarily the influence of port activities.

Spatiotemporal assessment of the environmental quality of bottom waters through the study of benthic foraminifera in a semi-enclosed gulf.

The evolution of the bottom water in Amvrakikos Gulf in Ionian Sea at western Greece for a 50-year timespan was assessed by benthic foraminifera assemblages. The degradation of the bottom water of Amvrakikos has been a catalyst for the surface water degradation. The east basin has shown permanent low environmental quality in bottom waters since 1980, while the west basin has been under seasonal hypoxic regime since 2000. The most adverse environmental conditions occurred in 1990-2000 and 2005-2010 coinciding with the recorded fish mortality events. The major cause of the environmental quality improvement of the bottom water is the intrusion of seawater. In western areas of the gulf, where the influence of the seawater is high, the decreased temperature improves the environmental conditions, while in the areas influenced by river discharges (east and northern), the environmental conditions are depended on multiple causes like organic matter input and surface salinity.

Using Boops boops (osteichthyes) to assess microplastic ingestion in the Mediterranean Sea.

This study assesses microplastic ingestion in Boops boops at different geographical areas in the Mediterranean Sea. A total of 884 fish were caught at 20 coastal sites in Spain, France, Italy and Greece and analyzed using a common methodological protocol. Microplastics were found in 46.8% of the sampled fish, with an average number of items per individual of 1.17 ± 0.07. Filaments were the predominant shape type, while polyethylene and polypropylene were indicated by FTIR as the most common polymer types of ingested microplastics. The frequency of occurrence, as well as the abundance and proportion of types (size, shape, color and polymer) of ingested microplastics, varied among geographical areas. The spatial heterogeneity of the abundance of ingested microplastics was mainly related to the degree of coastal anthropogenic pressure at the sampling sites. Our findings further support the suitability of B. boops as bioindicator of microplastic pollution in the Mediterranean Sea.

Evidence of ingested plastics in stranded loggerhead sea turtles along the Greek coastline, East Mediterranean Sea.

Plastic debris has become a major threat to the marine environment and wildlife. Sea turtles are particularly vulnerable, and are known to ingest plastic debris globally; however, information from Greek waters is still absent. In this study, 36 stranded dead loggerhead turtles (Caretta caretta) were collected from the Greek coastline area, and their gastrointestinal content was analysed for ingested plastic debris. Twenty-six individuals (72%) were found to have ingested plastic, with an average of 7.94 ± 3.85 (SE) plastic items per turtle. In total, 286 plastic items were counted and categorised by size, shape, colour, and polymer type. Fourier Transform Infrared Spectrometry revealed that polypropylene and polyethylene were the dominant polymer plastic types found. Results indicated a variation in plastic ingestion amongst life stages of the loggerhead specimens. This study provides evidence of plastic ingestion by loggerhead turtles in Greek waters.

Dataset on the major and trace elements contents and contamination in the sediments of Saronikos Gulf and Elefsis Bay, Greece.

Coastal marine sediments receive intensive stress from urbanization and industrialization, which is manifested by increased contents of heavy metals and organic pollutants. Saronikos Gulf and the small embayment of Elefsis, stretch along the coast of the greater Athens and Pireaus port, the most urbanized and industrialized areas in Greece. Here we present the data of a 20-year geochemical record on grain-size, organic carbon, and major and trace elements contents of the Saronikos Gulf sediments. A total of 216 sediment samples were collected within the period of 1999-2018 from the four sub-sectors of the gulf, namely, the Elefsis Bay, the Inner, Outer, and Western (Megara and Epidavros basin) Saronikos Gulf. Additionally, at least one core was obtained from each sub-sector. Sediments deposited at pre-industrial periods were recognized by 14C and 210Pb dating, and served for establishing regionalized background levels of metals. Factor analysis was conducted to reveal the inter-parametric relationships, thus their common sources, as well as transport and deposition pathways. Then, Enrichment Factors and the multi-elemental Modified Pollution Index (MPI) were calculated to assess the current environmental status of the sediments. Data of sampling sites with at least a five-year record, were assessed for temporal trends, to explore whether sustained, increasing or decreasing trends of the MPI are observed. The dataset and analyses presented here support the research article entitled Geochemistry of major and trace elements in surface sediments of the Saronikos Gulf (Greece): assessment of contamination between 1999 and 2018 [1].

Assessment of organophosphate flame retardants in Mediterranean Boops boops and their relationship to anthropization levels and microplastic ingestion.

Plastic litter pollution is increasing in the seas and oceans worldwide, raising concern on the potential effects of plasticizer additives on marine fauna. In this study, muscle samples of 30 bogues (Boops boops; Linneaus, 1758) from the North Western Mediterranean Sea were analysed to assess the concentrations of 19 organophosphate flame retardant (OPFR) compounds and to inspect any relationship with microplastic ingestion and relative levels of anthropization. Out of the 19 OPFRs analysed, 6 compounds were detected, being tri-n-butyl phosphate (TNBP), 2-ethylhexyldiphenyl phosphate (EHDPP) and triphenylphosphine oxide (TPPO) the most abundant. As expected, OPFR concentrations were higher in samples collected off the most anthropized area of the city of Barcelona than in those from the Cap de Creus Marine Protected Area, while no significant correlation was detected between OPFR concentrations and microplastic ingestion. The results of this manuscript provide a first evidence of OPFR presence in the muscle of the bogue and identify the coastal area off Barcelona as a possible concentration area for contaminants, further supporting the use of the bogue as an indicator species of plastic pollution in the Mediterranean Sea.

Exotic Halophila stipulacea is an introduced carbon sink for the Eastern Mediterranean Sea.

Carbon and nitrogen storage in exotic Halophila stipulacea were compared to that in native Posidonia oceanica and Cymodocea nodosa meadows and adjacent unvegetated sediments of the Eastern Mediterranean Sea and to that in native H. stipulacea of the Red Sea at sites with different biogeochemical conditions and level of human pressure. Exotic H. stipulacea possessed considerable storing capacity, with 2-fold higher Corg stock (0.71 ± 0.05 kg m-2 in the top 20 cm of sediment) and burial (14.78 gCorg m-2 y-1) than unvegetated areas and C. nodosa meadows and, surprisingly, comparable to P. oceanica. N (0.07 ± 0.01 kg m-2) and Cinorg (14.06 ± 8.02 kg m-2) stocks were similar between H. stipulacea and C. nodosa or unvegetated sediments, but different to P. oceanica. Corg and N stocks were higher in exotic than native H. stipulacea populations. Based on isotopic mixing model, organic material trapped in H. stipulacea sediments was mostly allochthonous (seagrass detritus 17% vs seston 67%). Corg stock was similar between monospecific and invaded C. nodosa meadows by H. stipulacea. Higher stocks were measured in the higher human pressure site. H. stipulacea introduction may contribute in the increase of carbon sequestration in the Eastern Mediterranean.

Data Collection on Marine Litter Ingestion in Sea Turtles and Thresholds for Good Environmental Status.

The following protocol is intended to respond to the requirements set by the European Union's Marine Strategy Framework Directives (MSFD) for the D10C3 Criteria reported in the Commission Decision (EU), related to the amount of litter ingested by marine animals. Standardized methodologies for extracting litter items ingested from dead sea turtles along with guidelines on data analysis are provided. The protocol starts with the collection of dead sea turtles and classification of samples according to the decomposition status. Turtle necropsy must be performed in authorized centers and the protocol described here explains the best procedure for gastrointestinal (GI) tract isolation. The three parts of the GI (esophagus, stomach, intestine) should be separated, opened lengthways and contents filtered using a 1 mm mesh sieve. The article describes the classification and quantification of ingested litter, classifying GI contents into seven different categories of marine litter and two categories of natural remains. The quantity of ingested litter should be reported as total dry mass (weight in grams, with two decimal places) and abundance (number of items). The protocol proposes two possible scenarios to achieve the Good Environmental Status (GES). First: "There should be less than X% of sea turtles having Y g or more plastic in the GI in samples of 50-100 dead turtles from each sub-region", where Y is the average weight of plastic ingested and X% is the percentage of sea turtles with more weight (in grams) of plastic than Y. The second one, which considers the food remain versus plastic as a proxy of individual health, is: "There should be less than X% of sea turtles having more weight of plastic (in grams) than food remains in the GI in samples of 50-100 dead turtles from each sub-region".

Determining suitable fish to monitor plastic ingestion trends in the Mediterranean Sea.

The presence of marine litter is a complex, yet persistent, threat to the health and biodiversity of the marine environment, and plastic is the most abundant, and ubiquitous type of marine litter. To monitor the level of plastic waste in an area, and the prospect of it entering the food chain, bioindicator species are used extensively throughout Northern European Seas, however due to their distribution ranges many are not applicable to the Mediterranean Sea. Guidance published for the Marine Strategy Framework Directive suggests that the contents of fish stomachs may be analyzed to determine trends of marine plastic ingestion. In order to equate transnational trends in marine plastic ingestion, the use of standardized fish species that widely occur throughout the basin is favoured, however for the Mediterranean Sea, specific species are not listed. Here we propose a methodology to assess how effective Mediterranean fish species, that are known to have ingested marine plastic, are as bioindicators. A new Bioindicator Index (BI) was established by incorporating several parameters considered important for bioindicators. These parameters included species distribution throughout the Mediterranean basin, several life history traits, the commercial value of each species, and the occurrence of marine litter in their gut contents. By collecting existing data for Mediterranean fish, ranked scores were assigned to each trait and an average value (BI value) was calculated for each species. Based on their habitat preferences, Engraulis encrasicolus (pelagic), Boops boops (benthopelagic), three species of Myctophidae (Hygophum benoiti, Myctophum punctatum and Electrona risso) (mesopelagic), Mullus barbatus barbartus (demersal) and Chelidonichthys lucerna (benthic), were identified as currently, the most suitable fish for monitoring the ingestion of marine plastics throughout the Mediterranean basin. The use of standardized indicator species will ensure coherence in the reporting of marine litter ingestion trends throughout the Mediterranean 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.

Cumulative impacts from multiple human activities on seagrass meadows in eastern Mediterranean waters: the case of Saronikos Gulf (Aegean Sea, Greece).

Ecosystem-based management (EBM) addresses the fundamental need to account for cumulative impacts of human activities with the aim of sustainably delivering ecosystem services. The Saronikos Gulf, a large embayment of the Aegean Sea, provides a wide range of ecosystem services that are impacted by multiple human activities, deriving from the metropolitan area of Athens (situated at the northeast part of the Gulf). The anthropogenic impacts affect the status of several marine ecosystem components, e.g., seagrass meadows. Cymodocea nodosa meadows are only present at the most confined western part of the Gulf, whereas Posidonia oceanica meadows are mainly distributed in the inner and outer part of the Gulf. The aim of this study is to assess the cumulative impacts from multiple human activities on the seagrass meadows in the Gulf. The main results indicated that most impacted meadows are P. oceanica in the inner part of the Gulf, adjacent to the most urbanized coastal areas, and near port infrastructures. Land-based pollution, as well as physical damage and loss seem to be the main pressures exerted on the meadows. Understanding cumulative impacts is crucial for informing policy decisions under an EBM approach.

Metal levels in sediments and transplanted mussels in Pagassitikos Gulf (Aegean Sea, Eastern Mediterranean).

Metal concentrations were determined in surface sediments and transplanted mussels in a shallow semi-enclosed bay, Pagassitikos Gulf, Aegean Sea. Cu, Zn, Pb, Hg, and As levels in sediments were enriched close to point sources of pollution, i.e., Volos Port and cement plant. Fe, Mn, Cr, and Ni spatial distributions in sediments were rather uniform with increasing concentrations towards deeper sites, suggesting natural enrichment, whereas levels found in the port, although elevated, were not the highest in the study area. Spatial variations in concentrations of most metals in mussels transplanted nearshore were generally in accordance to those in sediments, with the highest Fe, Mn, Cr, Ni, and Cu levels in the port and the highest Hg levels close to the cement plant. Concentrations of metals in sediments and transplanted mussels were comparable to those reported in Mediterranean areas. Results indicate that pollution point sources contribute to anthropogenic metal enrichment in the study area.