Southeastern Mediterranean Sea Research Articles

On the occurrence of three blennid species in the South-eastern Mediterranean coast of Turkey

In the present study, three blennid species of Aidablennius sphinx (Valenciennes, 1836) Parablennius tentacularis (Brünnich, 1768) and Scartella cristata (Linnaeus, 1758) were reported from the southeastern Mediterranean waters with visual records during an underwater survey conducted on October 19, 2015 in the Konacik and, on July 30, 2016 in the Çevlik coast at a depth ranges of 2-10 m. The present report is the occurrence and is the first confirmation of three blennid species from Iskenderun Bay, Turkey (South-eastern Mediterranean Sea). Besides, this study will be useful fisheries biology and ecology and also contribute to fisheries scientists.Keywords: Blenniidae, Combtooth blennies; Iskenderun Bay; Mediterranean Sea; observation

Exceptionally high levels of total mercury in deep-sea sharks of the Southeastern Mediterranean sea over the last ∼ 40 years

Deep-sea habitats are currently recognized as a hot spot for mercury (Hg) accumulation from anthropogenic sources, resulting in elevated concentrations of total mercury (THg) in deep-sea megafauna. Among them, deep-sea sharks (Class Chondrichthyes) are characterized by high trophic position and extended longevity and are, therefore, at high risk for mercury contamination. Despite this, sharks are overexploited by fishing activity in increasingly deeper water, worldwide, imposing health risks to human consumption. While it is imperative to better understand long-term mercury contamination in deep-sea megafauna, few historical data sets exist to capture this process. Here we explore four decades (1985–2022) of THg accumulation in five species of deep-sea sharks (G. melastomus, E. spinax, S. rostratus, C. granulosus, and D. licha) of the ultra-oligotrophic Southeastern Mediterranean Sea (SEMS) sampled during 19 research cruises. We exhibited exceptionally high THg levels (per length/weight), the highest as 16.6 μg g−1 (wet wt.), almost entirely (98.9 %; n = 298 specimens) exceeding the limit for safe consumption (0.3–0.5 μg THg g−1 wet wt.). The maximal THg levels of the long-lived species D. licha and C. granulosus in the SEMS were enriched by a factor of ∼ 7 and >10 compared to counterpart species from other oceanic areas, respectively. We attribute this to the ultra-oligotrophic conditions of the SEMS, which cause slower growth rates and dwarfism in deep-sea sharks, resulting in an extended exposure time to mercury contamination. In the long-lived species, C. granulosus and D. licha, a temporal increase of average THg levels of ∼ 80 % was recorded between 1987–1999 and 2021–2022. This likely reflects the long-term accumulation of historical anthropogenic Hg in deep-sea environments, which is further amplified in marginal seas such as the Mediterranean, impacted by global air pollution crossroads and surrounded by land-based pollution sources. Future consumption of products from deep-sea sharks is potentially high risk to human health.

Active microbial communities facilitate carbon turnover in brine pools found in the deep Southeastern Mediterranean Sea

Discharge of gas-rich brines fuels productive chemosynthetic ecosystems in the deep sea. In these salty, methanic and sulfidic brines, microbial communities adapt to specific niches along the physicochemical gradients. However, the molecular mechanisms that underpin these adaptations are not fully known. Using metagenomics, we investigated the dense (∼106 cell ml−1) microbial communities that occupy small deep-sea brine pools found in the Southeastern Mediterranean Sea (1150 m water depth, ∼22 °C, ∼60 PSU salinity, sulfide, methane, ammonia reaching millimolar levels, and oxygen usually depleted), reaching high productivity rates of 685 μg C L−1 d−1 ex-situ. We curated 266 metagenome-assembled genomes of bacteria and archaea from the several pools and adjacent sediment-water interface, highlighting the dominance of a single Sulfurimonas, which likely fuels its autotrophy using sulfide oxidation or inorganic sulfur disproportionation. This lineage may be dominant in its niche due to genome streamlining, limiting its metabolic repertoire, particularly by using a single variant of sulfide: quinone oxidoreductase. These primary producers co-exist with ANME-2c archaea that catalyze the anaerobic oxidation of methane. Other lineages can degrade the necromass aerobically (Halomonas and Alcanivorax), or anaerobically through fermentation of macromolecules (e.g., Caldatribacteriota, Bipolaricaulia, Chloroflexota, etc). These low-abundance organisms likely support the autotrophs, providing energy-rich H2, and vital organics such as vitamin B12.

A near real-time automated oil spill detection and early warning system using Sentinel-1 SAR imagery for the Southeastern Mediterranean Sea

ABSTRACT The ecological and environmental impact of marine oil pollution underlines the importance and necessity of an oil spill surveillance system. This study proposes an operational automated oil spill detection and early warning system to help take quick action for oil combating operations. Oil slicks in the spaceborne Sentinel-1 synthetic aperture radar (SAR) data are detected by a trained deep learning-based oil object detector. These detected oil objects are segmented into binary masks based on the similarity and discontinuity of the backscattering coefficients, and their trajectory is simulated. The detection process was tested on one-year SAR acquisitions in 2019, covering the Southeastern Mediterranean Sea; the false discovery rate (FDR) and false negative rate (FNR) are 23.3% and 24.0%, respectively. The system takes around 1.5 h from downloading SAR images to providing slick trajectory simulation. This study highlights the capabilities of using deep learning-based techniques in an operational oil spill surveillance service.

The expansion of the Atlantic–Mediterranean ghost crab Ocypode cursor (Linnaeus, 1758): Distribution, environmental niches and future perspectives

AbstractThe tufted ghost crab Ocypode cursor (Linnaeus, 1758) found in the Mediterranean Sea and the Atlantic Ocean is currently a great example that elucidates concerns within scientific and conservation communities. This species, native to the subtropical Atlantic Ocean and the warmest southeastern Mediterranean Sea (Egypt), has been extending its distribution in both regions since the 1980s, likely due to the warming sea temperatures. These small nocturn crabs are typically found inhabiting sandy beaches and dune environments. This species is an opportunistic predator eating terrestrial and marine prey, especially on sea turtle eggs. Despite its status as a threatened species by two European conventions, there is a lack of knowledge of its ecology and biology. Sometimes considered as an indicator of good ecological status of beaches where it lives, this ghost crab could nevertheless benefit from climate change to extend its distribution range. This review aims to create a baseline on the current knowledge and gaps in the published scientific literature on the ghost crab. Additionally, through an analysis of the existing literature, we also offer insights into the potential risk of beach erosion associated with the expansion of this species.

Far-field effects of the Nile damming on the silica cycle in the Southeastern Mediterranean Sea

Silica plays a key role in the growth of silicifying primary producers (e.g., diatoms) and hence the ocean carbon pump. The Mediterranean Sea's eastern Levantine Basin (ELB) is a low silica (and low N and P) ultra-oligotrophic basin. Before 1965, Nile autumn floods were a major source of dissolved silica (DSi) and other nutrients to primary producers of the ELB continental shelf, also known as the Nilotic cell. The construction of the Aswan High Dam (AHD) in the mid-1960s, blocked these floods, drastically diminishing the autumn-diatom blooms offshore the Nile delta. However, the far-reaching and long-lasting effects of the Nile damming on the Si cycle in the ELB remain unclear. Here, we studied the changes in DSi in the surface water offshore Israel and the distribution of biogenic silica in deep-sea short sediment cores, collected hundreds of kilometers from the Nile outlet, at depths range of 1100–1900 m, offshore the ELB Israeli coast. We show post dam reduction and termination in flood related seasonality of DSi and a concurrent decrease (of up to 79 %) in biogenic silica (BSi) accumulation rates in surficial sediments relative to underlying sediments. These changes reflect the effects of Si (dissolved and particulate) retention by the AHD on diatoms production, export and burial in the ELB. This far-field effect was demonstrated in deep-sea areas subjected to intense lateral transport of resuspended sediments from the shelf via intermediate nepheloid layers and to coastal water intrusions, along the path of the pre-dam, flood plumes. Our core records show that the AHD worsened nutrient-diminished, exceptionally unfavorable conditions for diatoms that persisted in the deep ELB at least during the last four millennia.

Accumulation of total mercury in deep-sea sediments and biota across a bathymetric gradient in the Southeastern Mediterranean Sea

This study explores the accumulation of total mercury (THg) in deep-sea sediments and demersal megafauna of the ultra-oligotrophic Southeastern Mediterranean Sea (SEMS) across bathymetric gradients in the range 35–1900 m, sampled in seven cruises during 2013, 2017–2021, and 2023. Measurements of THg were conducted in surficial (0.0–0.5 cm) and subsurface (9.0–10 cm) sediments, demersal sharks, demersal teleost fish, and benthic crustaceans. Sedimentary organic carbon and biota δ13C and δ15N values were determined to explore possible foraging habitats and dietary sources of THg. The results exhibit an increasing trend of THg in surficial sediments with increasing bottom depth, while in the subsurface, pre-industrial sediments, THg remains lower, slightly increasing with depth. Having no major terrestrial point sources in this area, this increasing trend of THg in surficial sediments across bathymetric gradients is controlled by atmospheric mercury deposition, scavenged by the biological pump, and by lateral transport of particulate Hg in winnowed fine particles from the shelf. Similarly, the THg in benthic crustaceans and demersal fish ranged between 0.02 and 2.71 μg g−1 wet weight (0.06 and 10.8 μg g−1 dry weight) and increased with muscle δ13C as a function of distance offshore, while presenting a low THg-δ15N bio-magnification power. Our results suggest that foraging habitats, longevity, and species-specific depth distribution control their muscle THg bioaccumulation. Despite this complexity, the pooling of THg in megafauna into specific deep zones reflected the trend of increasing anthropogenic THg across bathymetric gradients. Furthermore, many of the biota measurements exceeded safe consumption thresholds for Hg and therefore, should be considered carefully in the development and regulation of deep-sea trawling in this region.

First record of the phyllosoma larva of the pygmy locust lobster Scyllarus pygmaeus (Crustacea, Decapoda) in the eastern Mediterranean sea

Abstract Taxonomic intricacies and high interspecific similarity have hampered the identification of scyllarid phyllosoma larvae to the species level. The pygmy locust lobster, Scyllarus pygmaeus, is distributed across the Mediterranean Sea and in the eastern Atlantic; however, its phyllosoma larvae were previously recorded only from the western Mediterranean. We employed DNA barcoding using the mitochondrial COI gene to identify S. pygmaeus phyllosoma collected from the offshore waters of the southeastern Mediterranean Sea and described its morphology. We further discuss the lack of genetic structure in S. pygmaeus with potential implications for species connectivity and conservation.

Tar pollution event (2021) at the Southeastern Levantine oligotrophic basin, short-term impacts and operational oceanography perspectives

The Levantine basin (LB) in the Southeastern Mediterranean Sea is a high-risk oil pollution hot spot owing to its dense maritime traffic and intense oil and gas exploration and exploitation activities. In February 2021 the Israeli LB shorelines were impacted by an exceptional tar pollution event (~550 tons; average distribution: ~3 kg tar m−1 front beach) of an unknown oil spill source. Here we report on the immediate numerical modelling assessment of the oil spill propagation and tar distribution; operational use of underwater gliders for tracking water column anomalies of dissolved polycyclic aromatic hydrocarbons (PAHs) and turbidity signals; the beached tar composition and amounts and the short-term response of the microbial population along the ~180 km shoreline. This pollution event emphasizes the need for improving the early warning systems for oil spills and implementing continuous operational monitoring at high-risk, ecologically sensitive and valuable resource areas like the Israeli LB waters.

Tar patties are hotspots of hydrocarbon turnover and nitrogen fixation during a nearshore pollution event in the oligotrophic southeastern Mediterranean Sea

Weathered oil, that is, tar, forms hotspots of hydrocarbon degradation by complex biota in marine environment. Here, we used marker gene sequencing and metagenomics to characterize the communities of bacteria, archaea and eukaryotes that colonized tar patties and control samples (wood, plastic), collected in the littoral following an offshore spill in the warm, oligotrophic southeastern Mediterranean Sea (SEMS). We show potential aerobic and anaerobic hydrocarbon catabolism niches on tar interior and exterior, linking carbon, sulfur and nitrogen cycles. Alongside aromatics and larger alkanes, short-chain alkanes appear to fuel dominant populations, both the aerobic clade UBA5335 (Macondimonas), anaerobic Syntropharchaeales, and facultative Mycobacteriales. Most key organisms, including the hydrocarbon degraders and cyanobacteria, have the potential to fix dinitrogen, potentially alleviating the nitrogen limitation of hydrocarbon degradation in the SEMS. We highlight the complexity of these tar-associated communities, where bacteria, archaea and eukaryotes co-exist, likely exchanging metabolites and competing for resources and space.

Origins of the Tsunami Following the 2023 Turkey–Syria Earthquake

AbstractOn 6 February 2023, a local tsunami was recorded in the southeastern Mediterranean Sea following the Mw 7.7 Turkey–Syria inland strike‐slip earthquake. Due to the lack of underwater observation, the tsunami generation mechanism remains mysterious. To understand the source mechanisms, we analyzed the tsunami waveforms of four nearby tide gauges and located possible sources using a backward tsunami ray tracing approach. We then conducted forward numerical modelings for a range of possible source parameters. We show that there were probably two tsunami sources, inside and outside Iskenderun Bay, which may be related to thick coastal sediments. A source inside the Bay with a characteristic length of 7 km produced dominant periods of 10–30 min with negative initial motion, possibly generated by a landslide. Another source of 6 km length outside the Bay produced dominant periods of 2–10 min with positive initial motions, possibly related with liquefaction.

Modified Water Quality Index and Multivariate Analysis for Water Quality Assessment in El-Mex Bay, Alexandria, Egypt: A Study of the Largest Drain in the Southeastern Mediterranean Sea

Modified Water Quality Index and Multivariate Analysis for Water Quality Assessment in El-Mex Bay, Alexandria, Egypt: A Study of the Largest Drain in the Southeastern Mediterranean Sea

Risk assessment of Golani’s round herring (Etrumeus golanii) in the Greek seas (northeastern Mediterranean Sea)

Greek waters are the recipient of several alien species, mainly through natural dispersal following invasion and establishment of non-indigenous species (NIS) in neighboring areas, making their monitoring and mitigating their effects of paramount importance. The European Union legislation framework toward alien species invasions considers risk assessments as the top of the spear for a first assessment of NIS and their potential to become invasive or not. The Union List has already included top priority species, with very few marine species. Golani’s round herring (Etrumeus golanii) is a species of round herrings in the family Dussumieriidae, a Lessepsian migrant and belonging to a group of NIS in the Mediterranean basin that are less studied. Its distribution range is mainly limited in the southeastern Mediterranean Sea, while in the Greek seas, it has not yet been observed in the north Aegean and Ionian seas, probably due to temperature and oceanographical reasons. Its presence in the basin is recorded by commercial fisheries landings in several countries (especially purse-seiners), indicating a potentially positive effect on commercial fisheries. A risk assessment of E. golanii in Greek waters was carried out in this work, based on the Risk Assessment Scheme developed by the GB Non-Native Species Secretariat (GB Non-Native Risk Assessment—GBNNRA). An overall semi-quantitative summary of risk, in terms of likelihood of events and magnitude of impacts, was facilitated for several attributors, including confidence levels for each one. The assessment highlighted a very likely possibility of introduction in the Greek seas from neighboring countries, as well as successful establishments of populations with high confidence levels. A moderate magnitude of impact regarding its further spread was deemed, while a minor one was indicated in terms of native species pressure and a minimal one in terms of economic costs and public health. Overall, E. golanii was not characterized as an invasive alien species (IAS) and local communities could benefit from its presence (commercial fisheries); however, further studies focusing on its reproduction and spawning grounds should be implemented.

Ecological risk assessment of selected contaminants in seawater, sediment and some fish species from Alexandria beaches, South-Eastern Mediterranean Sea, Egypt

The present study aims to investigate the hydrographical characteristics, nutrient salts, and heavy metals (HM) to estimate the contamination status of selected coastal beaches along the Alexandria coastal area in the southeast Mediterranean Sea. Water and sediment samples were collected from 8 beaches along the cost of Alexandria, while 122 fish samples representing 10 species were collected from 2 beaches representing two ports at Alexandria city. All samples were subjected to specific analyses to assessment of ecological risks at study area. The study indicated that the seawater quality of the investigated beaches varied between medium to good based on the Water Quality Index (WQI = 0.233–0.713). Moreover, the highest average concentration in water was observed for Fe (33.624 μgl−1) and the lowest was detected for Cd (0.050 μgl−1). HM in sediment have the same trend of these HM in water. The most of beaches’ sediments were classified as non-contaminated (PI < 1) with all examined HM. Hazard Quotient and Hazard Index (HQ &HI < 1) this indicated that the lack of non-carcinogenic impacts for children and adults due to dermal contact with sediments of all beaches. The most abundance HM in fish were Fe and Zn. Bioaccumulation factors (BAF) in fish muscles was evaluated. MPI (Metal Pollution Index) of HM in the investigated species ranged from (0.381–2.216) in Pomatomus saltatrix and Scomberomorus commerson species respectively. HQ, HI, EDI (Estimated Daily Intake), and TR (Target Risk) values showed that the examined species are still safe for human consumption.

Ecological impacts of invasive ecosystem engineers: A global perspective across terrestrial and aquatic systems

Abstract In both terrestrial and aquatic ecosystems, invasive species are a major driver of global change that is increasing in scope and impact due to the increase in global trade, habitat modification and climate change. Among invasive species, those that are known as ‘ecosystem engineers’ are considered a specific, highly influential, type of invaders, where an invader significantly alters the new environment, either physically or chemically. In this context, this perspective review discusses the different types of possible impacts of invasive ecosystems engineers (IEE) in terrestrial, freshwater, and marine ecosystems. Scanning the relevant literature on the topic, we find a 12‐year lag in the use of terms relevant to the concept of ecosystem engineers in invasion‐related publications since the first publication of the concept in 1994, with a steep increase in use between 2006 and 2014. A bibliometric mapping showed a high level of connectedness between related terms and clusters, suggesting an ample flow of concepts, ideas and knowledge between realms, ecosystems and regions, and researchers that study them. Throughout this essay, we illustrate with recent examples the context‐dependency of their (positive and negative) impacts in the three realms. We review the distinction between autogenic (altering the environment for other species with their body) and allogenic (altering the environment for other species with their actions) ecosystem engineering in the context of alien species. We also put a spotlight on the well‐studied engineering effects of IEE plants and macroalgae, terrestrial and aquatic bioturbators and burrowers as well as highly effective consumers. We finalize with discussing how IEE can strongly affect ecosystem services for human wellbeing and explore the possible contribution of IEE in restoring functions and services in the face of climate change in highly invaded and fast‐warming systems like the southeastern Mediterranean Sea or areas that face frequent fires for example. We claim that the last topic has received little attention from the scientific community and should be given priority in future studies. Read the free Plain Language Summary for this article on the Journal blog.

New records of rarely reported species in the Mediterranean Sea (July 2023)

This Collective Article presents new information about the occurrence of 23 marine taxa that belong to five Phyla: two Chlorophyta, one Annelida, six Mollusca, three Arthropoda, eleven Chordata (one Ascidiacea, one Elasmobranchii and nine Teleostei) and extending from the Western Mediterranean to the Levantine Sea. All these records were reported from nine countries from the western to the eastern Mediterranean Sea, with a broad biogeographical coverage as follows: Spain: first records of the sacoglossans Cyerce graeca and Placida tardyi for the Alboran Sea and first records of the nudibranch Marionia gemmii for the Mediterranean waters of Spain; first records of nudibranch Algarvia alba in the Mediterranean Sea. Italy: First report of the long-legged crab Paragalene longicrura, a further new Mediterranean record of the rare offshore rockfish Pontinus kuhlii, first documented record of the spiny butterfly ray Gymnura altavela in Sardinia (Tyrrhenian Sea), new record of the red‐spotted wrasse Lappanella fasciata from the Messina Strait, first documented record of the rarely observed brown moray Gymnothorax unicolor in the Ionian coast, first record of the colonial ascidian Botrylloides israeliensis, first record of the Morocco dentex Dentex maroccanus, first record of mottled shore crab Pachygrapsus maurus and of an adult specimen of barracudina Lestidiops sphyrenoides in the Adriatic Sea, and further new Mediterranean records of Ross worm Sabellaria spinulosa along the same coast. Tunisia: second record of smalleye squaretail Tetragonurus cuvieri from the African Mediterranean coast. Slovenia: first records of the sea slug Trapania graeffei and Melanochlamys wildpretii, with the last one also representing the northernmost finding of this species. Croatia: northernmost record of the endangered twaite shad Alosa fallax in the Adriatic coast. Albania: first records of the Mediterranean spearfish Tetrapturus belone. Türkiye: first record from the Aegean coasts for Türkiye of the green macroalgae Cladophora battersii and Valonia aegagropila. Israel: first record of the skeleton shrimp Caprella acanthifera in the Southeastern Mediterranean Sea. Syria: first record of the Smooth grenadier Nezumia aequalis from Syrian marine waters.

Tracing the introduction of Dictyota acutiloba (Dictyotales, Phaeophyceae) in the Mediterranean Sea, with a reassessment of its geographic distribution

ABSTRACT In this study we explore the introduction of the brown alga Dictyota acutiloba in the Mediterranean Sea and provide a substantive update on the geographic distribution of this species, which was long thought to be confined to the Pacific Ocean. A critical assessment of published distribution records and additional identifications based on cox1, psbA and rbcL genetic markers confirm the presence of D. acutiloba at a number of locations in the Indo-Pacific as well as three locations along the Israeli coastline in the south-eastern Mediterranean Sea. The close genetic affinity between introduced specimens and those from a population in Hurghada (Red Sea) strongly suggests an introduction via the Suez Canal. The occurrence of D. acutiloba in these regions is further supported by predictions made by correlative ecological niche models (ENMs), which show high suitability values in the northern Red Sea and the Levantine Basin. In contrast, environmental conditions in the western Mediterranean and parts of the north-eastern Mediterranean are currently less favourable, as evidenced by the lower predicted probability of occurrence. Under future scenarios, the suitability of these regions increases. The further spread of D. acutiloba in the eastern Mediterranean seems imminent, and the species may even extend its range to the western Mediterranean Sea, depending on the climate change scenario considered. While D. acutiloba can be relatively easily distinguished from the majority of Mediterranean Dictyota species, it remains difficult to differentiate this species from narrow growth forms of D. dichotoma. Therefore, we recommend the use of molecular markers such as cox1, psbA and rbcL, to unequivocally identify this species and monitor its further spread.

Temporal and vertical dynamics of diatoms and dinoflagellates in the southeastern Mediterranean Sea

AbstractThe temporal distributions of microphytoplankton were studied monthly over 2 years in the shelf and the offshore waters of the “low nutrients low chlorophyll” (LNLC) southeastern (SE) Mediterranean Sea. The microphytoplankton were comprised mostly of diatoms (0–542 cells L−1, ~4 × 106–44 × 106 cells m−2) of the genera Rhizosolenia, Thalassionema, Chaetoceros, Leptocylindrus and Pseudo-nitzschia, and dinoflagellates (1–89 cells L−1, ~1 × 106–10 × 106 cells m−2) of the genera Tripos (formally known as Ceratium), Ornithocercus, Protoperidinium, Ceratocorys and Dinophysis. During the winter mixing, microphytoplankton abundance was ~2-fold higher than during the stratified summer months, in accordance with the higher inorganic nutrient levels. Diatoms were mostly found in the upper illuminated layers (0–100 m), while dinoflagellate distribution was patchy and spread from surface down to 200 m. We also calculated that diatoms and dinoflagellates contribute negligibly (~4%) to the total vertical carbon flux in the offshore water, suggesting fast recycling of organic matter at the photic layer. Our results provide a baseline to better understand carbon and biogenic silica fluxes at the LNLC SE Mediterranean Sea.

Bioaccumulation and biomagnifications of toxic metals in tissues of loggerhead turtles (Caretta caretta) from the Mediterranean Sea coast, Egypt

Heavy metal concentrations in the different tissues of marine turtles are presented; the most frequently monitored elements are mercury, cadmium, and lead. Concentrations of Hg, Cd, Pb, and As in different organs and tissues (liver, kidney, muscle tissue, fat tissue, and blood) of loggerhead turtle Caretta caretta from the southeastern Mediterranean Sea were determined using Atomic Absorption Spectrophotometer, Shimadzu and mercury vapor unite (MVu 1A) for Hg measurements. The highest levels of cadmium and arsenic were found in the kidney (Cd: 61.17 µg g−1; As: 0.051 µg g−1 dry weight). For lead, the highest level was found in muscle tissue (35.80 µg g−1). Mercury tended to be higher in the liver than in other tissues and organs (0.253 µg g−1 dry weight) which showed a higher accumulation of this element. Fat tissue generally displays the lowest trace element burdens. The concentrations of As remained low in all the considered tissues, possibly the result of low trophic levels in sea turtles. In contrast, the diet of loggerhead turtles would result in significant exposure to Pb. This is the first study into metal accumulation in the tissues of a loggerhead turtle from the Egyptian Mediterranean coastline.

Modelling the barotropic sea level in the Mediterranean Sea using data assimilation

Abstract. This paper analyses the variability of the sea level barotropic components in the Mediterranean Sea and their reproduction using a hydrodynamic model with and without data assimilation. The impact of data assimilation is considered both in reanalysis and short-forecast simulations. We used a two-dimensional finite element model paired with an ensemble Kalman filter, which assimilated hourly sea level data from 50 stations in the Mediterranean basin. The results brought about a significant improvement given by data assimilation in the reanalysis of the astronomical tide, the surge, and the barotropic total sea level, even in coastal areas and far from the assimilated stations (e.g. the southeastern Mediterranean Sea). As with the reanalysis simulations, the forecast simulations, which start from analysis states, improve, especially on the first day (37 % average error reduction) and when seiche oscillations are triggered. Since seiches are free barotropic oscillations that depend only on the initial state, their reproduction improves very effectively with data assimilation. Finally, we estimate the periods and the energy of these oscillations by means of spectral analysis, both in the Adriatic Sea, where they have been extensively studied, and in the Mediterranean Sea, where the present documentation is scarce. While the periods are well reproduced by the model even without data assimilation, their energy shows a good improvement when using it.