Hellenic Centre for Marine Research
Recent publications
Epigenetic changes such as DNA methylation modifications at specific loci in the genome in response to environmental cues can appear long before the appearance of transcriptomic or other phenotypic changes with potential consequences for performance. Thus, epigenetic DNA methylation-based biomarkers hold great promise in aquaculture and conservation biology because they can have prognostic value. However, to the best of our knowledge, a clear demonstration of such biomarkers has not been provided yet. Temperature during early stages of development is the main abiotic factor determining larval quality, with effects potentially persisting until adulthood and influencing performance. The objective of this study was to test whether epigenetic biomarkers could be developed as reliable indicators of the quality of the thermal environment during European sea bass (Dicentrarchus labrax) early development and their relation to long-lasting phenotypic consequences. We exposed European sea bass embryos and newly hatched larvae to different temperature regimes and sampled fish thereafter at three time points: at larval, juvenile and adult stages. Here, we provide an analytical strategy combining Reduced Representation Bisulfite sequencing (RRBS) and RNA-sequencing (RNA-seq) to develop epigenetic and transcriptomic biomarkers with both prognostic and diagnostic value. Specifically, we report a series of DNA-methylation biomarkers linked to short-term, mid-term, long-term, and very-long term effects of temperature in both somatic and reproductive tissues. Among the different biomarkers identified, one promising example is the methylation status of keratin-associated protein 10–4 (krtap10–4), which fulfills the criteria of an epigenetic biomarker with both prognostic and diagnostic value. This study constitutes a first step toward providing the European sea bass farming sector with a set of epigenetic biomarkers that can be used to screen batches of larvae to determine the quality of their thermal environment and to anticipate their performance when juveniles and adults. Our study provides the way for similar developments for other species, farmed or not.
This chapter describes general concepts about temporal changes of water mass properties in the Mediterranean Sea, focusing in particular on the second half of 20th century and the beginning of the 21st century. The changes (both gradual and abrupt) that have been observed over the past decades in the Eastern and in the Western Mediterranean Sea are examined, putting them in relation to what is happening in the Atlantic Ocean. The description is done in the context of global changes occurring in the oceans.
Sustained observations and forecasting systems are fundamental to advance our knowledge and understanding of the functioning of the Mediterranean Sea and its ecosystems, and to efficiently respond to maritime emergencies, societal needs, and preservation threats. This chapter describes the present status of the Mediterranean observing and forecasting systems that were successfully developed over the recent decades, thanks to both national and regional investments and fruitful international collaborations. On the one hand, the complementarity between global observing systems and multiplatform regional observatories enables a systematic monitoring of the Mediterranean Sea from the basin to the coastal scales. On the other hand, operational high-resolution modeling combined with data assimilation procedures provide the base for integrated model-data forecasting systems generating timely predictions of the short-term evolution of marine conditions and realistic representations of past periods. Data assembly centers are essential backbone of these systems, allowing data standardization, quality control, distribution, and archiving.
This chapter aims at introducing the reader to general concepts about the main forcings of the Mediterranean Sea, in terms of exchanges through the Strait of Gibraltar, and air-sea exchanges of heat, freshwater, and momentum. These forcings are also responsible for the peculiar characteristics of Mediterranean water masses. Therefore, the chapter continues with giving a general explanation on water mass analysis, and then it describes the properties and vertical and horizontal distributions of the main Mediterranean water masses. To conclude, the reader is introduced to the use of other (biogeochemical, and chemical) tracers of water masses, with a focus on the Mediterranean Sea.
Despite being the busiest transient sea in the world due to the Suez Canal, radionuclide distribution studies in seawater and sediment of the Red Sea remain rare. A sampling expedition in the Red Sea was conducted from June 9 to July 6, 2021, visiting a transect of several deep sampling stations located along the central axis of the basin from the Gulf of Aqaba to the southern Red Sea (near Farasan Island, Saudi Arabia). The collected seawater profile samples were analyzed for tritium, radiocarbon and oxygen-18. The observed tritium levels in surface waters of the Red Sea peaked at 0.3–0.4 TU, similar to the values observed in the western Arabian Sea (decay corrected). The values observed at waters below 150 m were around 0.2 TU, however, at depths of 450 and 750 m, tritium minima (<0.2 TU) were observed, which could be associated with a partial return flow of bottom waters from the southern to the northern Red Sea. At two stations at the depth of about 550 m, deep Δ¹⁴C minima were observed as well (−4‰ and −10‰), documenting ongoing transport of carbon in the water column, important for sink of anthropogenic carbon.
The process of site selection and spatial planning has received scarce attention in the scientific literature dealing with marine restoration, suggesting the need to better address how spatial planning tools could guide restoration interventions. In this study, for the first time, the consequences of adopting different restoration targets and criteria on spatial restoration prioritization have been assessed at a regional scale, including the consideration of climate changes. We applied the decision-support tool Marxan, widely used in systematic conservation planning on Mediterranean macroalgal forests. The loss of this habitat has been largely documented, with limited evidences of natural recovery. Spatial priorities were identified under six planning scenarios, considering three main restoration targets to reflect the objectives of the EU Biodiversity Strategy for 2030. Results show that the number of suitable sites for restoration is very limited at basin scale, and targets are only achieved when the recovery of 10% of regressing and extinct macroalgal forests is planned. Increasing targets translates into including unsuitable areas for restoration in Marxan solutions, amplifying the risk of ineffective interventions. Our analysis supports macroalgal forests restoration and provides guiding principles and criteria to strengthen the effectiveness of restoration actions across habitats. The constraints in finding suitable areas for restoration are discussed, and recommendations to guide planning to support future restoration interventions are also included.
Full-fat and defatted superworm Zophobas morio larvae meals were used in a feeding trial of 540 gilthead seabream, Sparus aurata, juveniles (3.4 g initial weight) in order to assess their immunomodulatory effects. Six isonitrogenous (52 %) and isoenergetic (21 MJ/Kg) diets were formulated where the fishmeal of the control diet was replaced by full-fat Z. morio meal at 5 % and 10 % (FF5 and FF10) or defatted Z. morio meal at 10, 20 or 30 % (LF10, LF20 and LF30). Fish were kept in 18 glass tanks (125 L) within a closed recirculation seawater system and fed to satiation twice a day, 6 days per week for 100 days. LF20 significantly increased the percentage of neutrophils compared to a control fish-fed fishmeal (FM)-based diet. The dietary Z. morio meal immunomodulated the fish as expressed through an increased complement-associated bacterial killing (FF5 and FF10), nitric oxide production (LF30), and a tendency for an increased activity of lysozyme (FF5, LF20 and LF30) and of myeloperoxidase (FF5 and LF20), while trypsin inhibition was significantly suppressed by dietary FF5 and all 3 LF-containing diets compared to control FM-fed fish. These findings suggest that dietary Z. morio can immunomodulate gilthead seabream but further infectious challenge studies will have to be performed to determine if these effects are translated into an increased resistance to diseases.
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.
Assessing the status of marine pollution at regional and sub-regional scales requires the use of comparable and harmonized data provided by multiple institutions, located in several countries. Standardized data management and quality control are crucial for supporting a coherent evaluation of marine pollution. Taking the Eastern Mediterranean Sea as a case study, we propose an approach to improve the quality control procedures used for sediment pollution data, thus supporting a harmonized environmental assessment. The regional ranges of contaminant concentrations in sediments were identified based on an in-depth literature review, and the lowest measured concentrations were evaluated to determine the “background concentrations” of chemical substances not yet targeted in the Mediterranean Sea. In addition, to verify the suitability of the approach for validating large data collections provided by multiple sources, the determined ranges were used to validate a regional dataset available through EMODnet data infrastructure.
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.
Sex allocation theory predicts that species with reversed sexual size dimorphism frequently overproduce the cheapest sex at the brood level. A sex ratio deviation from parity is frequently documented among the offspring of raptors and is largely produced by sex-biased survival or parental adjustment as a response to environmental variability or demographic conditions. The Eleonora's falcon is a long-distance migrant wintering in Madagascar and southeast Africa and breeding colonially primarily in the Mediterranean Sea and the Canary Islands. It feeds on migratory passerines and thus depends greatly on the autumn migration flow and the prevailing winds. Being sexually size dimorphic (i.e. females are larger than males) and depending greatly on the migration, the species is a good case for investigating whether brood sex ratio variation is adaptive. In the present study, we examined the proportion of males and females reared during 2009–2020 in a falcon colony in southeast Crete (Greece) in relation to specific ecological and biological attributes. Female nestlings were shown to be costlier to produce as they are heavier than males. Overall, an unbiased sex ratio was observed across the years, although a consistent trend was recorded towards females early in the breeding season and first-hatched chicks and males late in the breeding season and third-hatched chicks. Our results provide strong evidence that parental condition, habitat quality and a brood reduction effect were the significant drivers for the observed sex ratio patterns. The overproduction of the costlier sex and a high survival of the cheaper one during food-rich years should be regarded as an adaptive evolutionary strategy of the species for maximizing its fitness returns per clutch and for maintaining a balanced offspring sex ratio in the population.
We developed a zooplankton-based water-quality evaluating method using indices of alpha diversity. Two key objectives were set: (i) the comparison of two—different quality—samples from different areas, and the verification of their differentiation, based on mesozooplankton biodiversity indices; and (ii) the development of a methodology, which was able to assess the quality of new marine water samples. Our analysis was based on a 24-year-long in situ dataset (1987–2010) of 139 samples in which 86 mesozooplankton taxa were identified. High-diversity and high evenness values were reported in the case of the “good” status sample, while low diversity, low evenness and high dominance values occurred at the lower quality one. A linear discriminant analysis (LDA) was conducted that discriminated the tested samples at 100%. This LDA was then used to evaluate samples of unknown quality. Finally, 90% of them were classified with a probability of correct classification (posterior probability) >95%. The present study proves that mesozooplankton diversity indices can discriminate different levels of anthropogenic impacts. In this sense, it can be used as a reliable indicator for environmental assessment in the pelagic habitats of the Mediterranean Sea.
Microbial mats are vertically stratified communities of microorganisms characterised by pronounced physiochemical gradients allowing for high species diversity and a wide range of metabolic capabilities. High Throughput Sequencing has the potential to reveal the biodiversity and function of such ecosystems in the cycling of elements. The present study combines 16S rRNA amplicon sequencing and shotgun metagenomics on a hypersaline marsh in Tristomo bay (Karpathos, Greece). Samples were collected in July 2018 and November 2019 from microbial mats, deeper sediment, aggregates observed in the water overlying the sediment, as well as sediment samples with no apparent layering. Metagenomic samples’ co-assembly and binning revealed 250 bacterial and 39 archaeal metagenome-assembled genomes, with completeness estimates higher than 70% and contamination less than 5%. All MAGs had KEGG Orthology terms related to osmoadaptation, with the ‘salt in’ strategy ones being prominent. Halobacteria and Bacteroidetes were the most abundant taxa in the mats. Photosynthesis was most likely performed by purple sulphur and non-sulphur bacteria. All samples had the capacity for sulphate reduction, dissimilatory arsenic reduction and conversion of pyruvate to oxaloacetate. Overall, both sequencing methodologies resulted in similar taxonomic compositions and revealed that the formation of the microbial mat in this marsh exhibits seasonal variation.
Fisheries have important impacts on marine biodiversity. In this work, combined information on the abundance, species richness, diversity indices, species composition, trophic level and vulnerability index were examined for the first-time to detect differences in five units related to trawl fishing: the fish assemblage entering the trawl codend, and the escaping, retained, discarded and landed fractions, derived by the gear and fisher selection practices. The work was based on a case study conducted in the Mediterranean Sea, using three different meshes in the trawl codend (40mm-40D and 50mm-50D diamond meshes, and 40 mm-40S square meshes) and a cover of the codends with small mesh size. In general, trawl fishing produces an escaping fraction that was always lower in abundance, richness, and vulnerability index, similar in diversity indices and trophic level, and different in species composition compared to the fish assemblage entering the codend. In almost all cases, fishers selected as landings a fraction that was the lowest in diversity indices, and the highest in trophic level. In contrast, fishers discarded a fraction that was the highest in diversity and vulnerability index, and the lowest in trophic level. Although the three codends did not differ significantly in the fraction of escapees in terms of diversity indices, trophic level, and vulnerability index, the 40S codend showed a significantly higher percentage in the escaping number of species and individuals, and less differences in the species composition; in addition, lower percentage in abundance of discards and higher of landings in the retained catch (0.6:1) than did the other two codends (0.9:1). It was suggested that an urgent modification of the trawl for the elimination of the discarded highly vulnerable species (e.g. Elasmobranchs) is needed, and that trawl species-selectivity should be improved by allowing escape or avoiding catch of the discarded fraction to minimize biodiversity losses.
Ecohydraulic models have commonly used the flow velocity, water depth, and substrate type (i3 models) as the three fundamental determinants of the distribution of freshwater biota, but a fourth determinant has largely been neglected: stream vegetation. In this study, we provide the hydraulic and habitat information required to develop vegetation-adapted ecohydraulic models (i4 models) in streams. We calculated drag forces and Manning’s roughness coefficients (nV) for nine types of submerged, emergent, and overhanging stream vegetation. In addition, we developed habitat suitability curves (HSCs) for benthic macroinvertebrates for these stream vegetation types. Hydraulic modules can now be upgraded to simulate stream vegetation by including the vegetation-adapted nV values within an additive approach in which nV is added to the n value of the inorganic substrate to which the vegetation is rooted. Habitat modules can also be upgraded to include macroinvertebrate HSCs for stream vegetation, again by adding the vegetation-adapted habitat suitability to that of the inorganic substrate to which the vegetation is rooted. In combination, i4 ecohydraulic models (including vegetation) can now be designed and applied, and we suggest that ecohydraulic research should further focus on including a fifth variable (water temperature) to ultimately advance to i5 ecohydraulic models that will optimally simulate the hydroecological reality.
This study is the first attempt to understand the coccolith flux and its seasonal variability at the deepest part of the Mediterranean Sea. Samples were obtained from the deepest Mediterranean time-series sediment trap (4300 m) moored in the SE Ionian Sea (Nestor site) from January 2015 to November 2017. Throughout the study period, the coccolith fluxes displayed a seasonality signal with high values during the late winter-early spring convective mixing period (February to April) and low flux values during summer except for some solitary peaks in June. The maximum coccolith flux was observed in March 2015 while the minimum value was recorded in November 2017. Among the nineteen identified species of heterococcoliths, the dominant species in all the samples was Emiliania huxleyi reaching up to 79%, followed by Florisphaera profunda that comprised up to 33% of the total coccolith count. For the annual cycle of 2015, the average coccolith flux for the Nestor Site at a relatively shallower depth (2000 m) was comparable and for some time intervals was lower than the coccolith flux recorded in the present study at 4300 m, while coccolith flux peaks appeared simultaneously in both traps indicating a fast sinking rate. The higher E. huxleyi, F. profunda, Gladiolithus flabellatus, and Calciosolenia brasiliensis coccolith flux at 4300 m compared with their corresponding fluxes at 2000 m can be attributed to lateral advection, resuspension, and/or the influence of Eastern Mediterranean Deep Waters (EMDWs).
There is a growing recognition that an advanced understanding of the trophic characteristics of an invasive consumer can provide important information on its ecological impact. In recent years, the blue swimming crab Portunus segnis, one of the earliest Lessepsian invaders, has considerably expanded its distribution range in the Mediterranean Sea, yet, its trophic habits in invaded areas remain scarcely investigated. In this study, we used carbon and nitrogen stable isotopes analysis (SIA) to determine the trophic position and isotopic niche of the crab compared with other representatives of the flora and fauna occurring in Elounda Bay (Crete). P. segnis showed a trophic position of 3.9, higher than the values determined by SIA or conventional gut content analysis in other areas of the Mediterranean Sea or in the native range. Crab specimens showed a high inter-individual variability in both δ13C and δ15N values; further analysis indicated negligible differences in the isotopic niche of adult males and females. Conversely, δ15N values were significantly related to the size of the specimens, ultimately suggesting an ontogenetic dietary shift. This study represents the first attempt to characterize the trophic habits of the blue swimming crab in the context of an invaded food web and may contribute to the implementation of long-term management strategies of control and mitigation of its ecological impact.
The use of cephalopod beaks in ecological and population dynamics studies has allowed major advances of our knowledge on the role of cephalopods in marine ecosystems in the last 60 years. Since the 1960’s, with the pioneering research by Malcolm Clarke and colleagues, cephalopod beaks (also named jaws or mandibles) have been described to species level and their measurements have been shown to be related to cephalopod body size and mass, which permitted important information to be obtained on numerous biological and ecological aspects of cephalopods in marine ecosystems. In the last decade, a range of new techniques has been applied to cephalopod beaks, permitting new kinds of insight into cephalopod biology and ecology. The workshop on cephalopod beaks of the Cephalopod International Advisory Council Conference (Sesimbra, Portugal) in 2022 aimed to review the most recent scientific developments in this field and to identify future challenges, particularly in relation to taxonomy, age, growth, chemical composition (i.e., DNA, proteomics, stable isotopes, trace elements) and physical (i.e., structural) analyses. In terms of taxonomy, new techniques (e.g., 3D geometric morphometrics) for identifying cephalopods from their beaks are being developed with promising results, although the need for experts and reference collections of cephalopod beaks will continue. The use of beak microstructure for age and growth studies has been validated. Stable isotope analyses on beaks have proven to be an excellent technique to get valuable information on the ecology of cephalopods (namely habitat and trophic position). Trace element analyses is also possible using beaks, where concentrations are significantly lower than in other tissues (e.g., muscle, digestive gland, gills). Extracting DNA from beaks was only possible in one study so far. Protein analyses can also be made using cephalopod beaks. Future challenges in research using cephalopod beaks are also discussed.
Recent spatial and vertical distributions of 137Cs activity concentration in the Aegean Sea are presented almost 30 years after the Chernobyl accident. The study aims to provide the current radioactivity levels of 137Cs in the Aegean Sea and to combine the 137Cs activity concentration with typical oceanographic parameters (T, S) in order to utilize them as tracers to identify/validate the different water masses that are present in the Aegean Sea. This work was performed in the frame of the “KRIPIS” project in 2017 for continuous investigations of the deep basins from all over the Aegean Sea and includes samplings from the water column layers of seven stations. The 137Cs activity concentrations were determined via lab-based gamma ray spectroscopy after appropriate chemical pre-concentration of 137Cs, while the salinity and temperature of the water column were obtained by in-situ measurements. The activity concentration values of 137Cs varied from 1.6 to 5.5 Bq m−3. Clear distinction of the Black Sea and Levantine Waters was obtained based on the combination of temperature and salinity values with 137Cs activity concentration. Furthermore, including 137Cs as a supplementary tracer, the Transitional Subsurface Aegean Waters were identified at the Myrtoan and Antikythera Straits, combining the salinity, temperature and 137Cs activity concentration.
The Mediterranean Sea (MED) is prone to species’ introductions, induced by human activities and/or climate change. Recent studies focus on the biological traits that result in such introductions, yet on a single-area-type approach. Here, we used, analyzed, and compared biological traits derived from FishBase for MED, non-indigenous (NIS) and neonative (NEO) in the Mediterranean, and adjacent Atlantic (ATL) and Red Sea (RS) species. A quantitative trait-based analysis was performed using random forest to determine the importance of traits in the successful establishment in the Mediterranean. MED fishes were mainly demersal, slow growing and small-medium sized, preferring intermediate temperatures. Conversely, ATL were mainly deep-dwelling species, preferring low temperatures. RS and NIS were predominantly reef-associated, thermophilus, and stenothermic. NEO species were stenothermic with preference to intermediate-high temperatures. Omnivores with preference to animals was the most common trophic group among regions. MED species exhibited higher phylogenetic uniqueness (PD50) compared to RS and NIS, indicating that they have long ancestral branches and few descendants. Preferred temperature, habitat type preference and maximum reported length (Lmax) and infinite length (Linf) were the most important predictors in the establishment process. Overall, the results presented here could serve as a baseline for future research, especially by using more refined and/or additional biological trail estimates.
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372 members
Argyro Zenetos
  • Institute of Marine Biological Resources and Inland Waters
Pantelis Katharios
  • Institute of Marine Biology, Biotechnology and Aquaculture
Ekaterini Souvermezoglou
  • Institute of Oceanography
Catherine Tsangaris
  • Institute of Oceanography
Anastasios Papadopoulos
  • Institute of Marine Biological Resources and Inland Waters
Anávyssos, Greece
Head of institution
Prof. Dr.-Ing. Sp. A. Mavrakos