Manolis Mandalakis

• PhD
• Researcher at Hellenic Centre for Marine Research

Satellite-derived observations of ocean colour provide continuous data on chlorophyll-a concentration (Chl-a) at global scales but are limited to the ocean’s surface. So far, biogeochemical models have been the only means of generating continuous vertically resolved Chl-a profiles on a regular grid. MULTIOBS is a multi-observations oceanographic da...

As the global population continues to grow, so does the demand for longer, healthier lives and environmentally responsible choices. Consumers are increasingly drawn to naturally sourced products with proven health and wellbeing benefits. The marine environment presents a promising yet underexplored resource for the cosmetics industry, offering bioa...

The devil firefish Pterois miles (Bennett 1828) is recognized as one of the 100 worst invasive alien species (IAS) in the Mediterranean Sea with significant socioeconomic and ecological implications. A total of 363 individuals were collected between April 2021 and March 2022 from the Levantine Sea (the Eastern Mediterranean), aiming to assess the c...

Bioassays are the main tool to decipher bioactivities from natural resources thus their selection and quality are critical for optimal bioprospecting. They are used both in the early stages of compounds isolation/purification/identification, and in later stages to evaluate their safety and efficacy. In this review, we provide a comprehensive overvi...

Marine sponges are highly efficient in removing organic pollutants and their cultivation, adjacent to fish farms, is increasingly considered as a strategy for improving seawater quality. Moreover, these invertebrates produce a plethora of bioactive metabolites, which could translate into an extra profit for the aquaculture sector. Here, we investig...

Given the dramatic increase in the L. sceleratus population in the southeastern Aegean Sea, there is growing interest in assessing the toxicity of this pufferfish and the factors controlling its tetrodotoxin (TTX) content. In the present study, liver, gonads, muscle and skin of 37 L. sceleratus specimens collected during May and June 2021 from the...

Given the dramatic increase of L. sceleratus population in southeastern Aegean Sea, there is growing interest in assessing the toxicity of this pufferfish and the factors controlling its tetrodotoxin (TTX) content. In the present study, liver, gonads, muscle and skin of L. sceleratus specimens from Rhodes island, Greece were subjected to multi-anal...

Tetrodotoxin (TTX) is a potent marine neurotoxin involved in poisoning cases, especially through the consumption of puffer fish. Knowledge of the toxicity equivalency factors (TEFs) of TTX analogues is crucial in monitoring programs to estimate the toxicity of samples analyzed with instrumental analysis methods. In this work, TTX analogues were iso...

Besides the release of organic matter from uneaten feed and fish excreta, a considerable amount of deleterious chemicals may also end up into the marine environment from intensive aquaculture. A fraction of these pollutants remains freely dissolved and pose a threat to marine life due to increased bioavailability. Given the filter-feeding ability o...

Natural Products (NP) are essential for the discovery of novel drugs and products for numerous biotechnological applications. The NP discovery process is expensive and time-consuming, having as major hurdles dereplication (early identification of known compounds) and structure elucidation, particularly the determination of the absolute configuratio...

Chronic discharge of surplus organic matter is a typical side effect of fish aquaculture, occasionally leading to coastal eutrophication and excessive phytoplankton growth. Owing to their innate filter-feeding capacity, marine sponges could mitigate environmental impact under integrated multitrophic aquaculture (IMTA) scenarios. Herein, we investig...

Alterations in phytoplankton biomass, community structure and timing of their growth (phenology), are directly implicated in the carbon cycle and energy transfer to higher trophic levels of the marine food web. Due to the lack of long-term in situ datasets, there is very little information on phytoplankton seasonal succession in Cyprus (eastern Med...

The invasion of the tetrodotoxin (TTX)-bearing silver-cheeked toadfish and potential poisoning due to its consumption (tetrodotoxication) threatens public safety in the Mediterranean Sea. In this study, TTX and TTX analogues of Lagocephalus sceleratus (Gmelin, 1789) were measured using liquid chromatography tandem mass spectrometry (LC-MS/MS) in fi...

The histological process of gonadal differentiation, together with the endocrine changes of sex steroid hormones and some of their precursors, was studied in hatchery-produced greater amberjack Seriola dumerili from 101 until 408 days post-hatching (dph), with samplings conducted every 50 days. Histological processing showed that sex differentiatio...

The majority of studies focusing on microbial functioning in various environments are based on DNA or RNA sequencing techniques that have inherent limitations and usually provide a distorted picture about the functional status of the studied system. Untargeted proteomics is better suited for that purpose, but it suffers from low efficiency when app...

Despite progress achieved, there is limited available information about the antibacterial activity of constituents of essential oils (EOs) from different medicinal-aromatic plants (MAPs) against fish pathogens and the complex interactions of blended EOs thereof. The present study aimed to investigate possible synergistic antimicrobial effects of EO...

Submarine hydrothermal activity is responsible for heat and chemical exchanges through the seafloor. Shallow-water hydrothermal systems (SWHS), while identified around the globe, are often studied in a way that is less comprehensive than their deep-ocean counterparts (e.g., along ridges), where systematic optical and acoustic mapping is more preval...

The histological process of gonadal differentiation together with the endocrine changes of glucocorticoids and sex steroids was studied in hatchery produced greater amberjack ( Seriola dumerili ) from 101 until 408 days post-hatching. In the samplings, which were conducted every 50 days, no size dimorphism was observed between the sexes and sex rat...

Coastal countries have traditionally relied on the existing marine resources (e.g., fishing, food, transport, recreation, and tourism) as well as tried to support new economic endeavors (ocean energy, desalination for water supply, and seabed mining). Modern societies and lifestyle resulted in an increased demand for dietary diversity, better healt...

Coastal countries have traditionally relied on the existing marine resources (e.g., fishing, food, transport, recreation, and tourism) as well as tried to support new economic endeavors (ocean energy, desalination for water supply, and seabed mining). Modern societies and lifestyle resulted in an increased demand for dietary diversity, better healt...

Marine microbial communities are an untapped reservoir of genetic and metabolic diversity and a valuable source for the discovery of new natural products of biotechnological interest. The newly discovered hydrothermal vent field of Santorini volcanic complex located in the Aegean Sea is gaining increasing interest for potential biotechnological exp...

Although the rise of antibiotic and multidrug resistant bacteria is one of the biggest current threats to human health, our understanding of the mechanisms involved in antibiotic resistance selection remains scarce. We performed whole genome sequencing of 21 Pseudomonas strains, previously isolated from an active submarine volcano of Greece, the Ko...

The Aegean Sea, as part of the Mediterranean, is an ecologically and geologically diverse marine system, with a wide range of habitats including coastal and deep-sea oxic sediments, and submarine volcanoes with seafloor hydrothermal vents and CO2-venting active, and inactive, polymetallic (Au, Ag, Sb, Cu, Pb, Zn) hydrothermal chimneys. Generally, o...

Microorganisms are ubiquitous in the atmosphere with hundreds of taxa being identified in air samples collected around the world. Despite their importance on human and ecosystem health, the majority of air microbiological studies have been limited to cultivation-based methods that may not capture all of the microbial diversity in the air. The prese...

Marine organisms produce a vast diversity of metabolites with biological activities useful for humans, e.g., cytotoxic, antioxidant, anti-microbial, insecticidal, herbicidal, anticancer, pro-osteogenic and pro-regenerative, analgesic, anti-inflammatory, anti-coagulant, cholesterol-lowering, nutritional, photoprotective, horticultural or other benef...

The planktonic food web in the oligotrophic Mediterranean Sea is dominated by small-sized (<20 μm) microbes, with nanoflagellates being the major bacterial grazers and the main participants in nutrient cycling. Phosphate is a key nutrient in the P-limited Cretan Sea (NE Mediterranean) and P-availability can affect its trophic dynamics. Here, we exa...

Submarine hydrothermal activity is common at the flanks of volcanic islands, and in some cases, occurring at very shallow water (0-100 meter depth). These sites are a key target for systematic seafloor mapping to understand the location, geometry and nature of hydrothermal discharge. These data are also critical for monitoring the temporal variabil...

Whereas upper ocean pelagic sharks are negatively buoyant and must swim continuously to generate lift from their fins, deep-sea sharks float or swim slowly buoyed up by large volumes of low-density oils in their livers. Investigation of the Pressure, Volume, Temperature (PVT) relationships for liver oils of 10 species of deep-sea Chondrichthyes sho...

The administration of antibiotics in aquaculture has raised concern about the impact of their overuse in marine ecosystems, seafood safety and consumers' health. This "green consumerism" has forced researchers to find new alternatives against fish pathogens. The present study focused on 12 Mediterranean medicinal-aromatic plants as potential antimi...

The present study aimed to evaluate the impact of polycyclic aromatic hydrocarbons (PAHs) produced by multiple emission sources on prokaryotic communities in sediments chronically affected by anthropogenic pressures. In this context, surface sediments were investigated in three Mediterranean touristic ports over three sampling periods and in differ...

While aquaculture is outpacing food production from capture fisheries and expected to play a major role in future economies, it exerts pressure to adjacent marine habitats mainly via the release of organic load and other substances. Among bioremediation candidates to mitigate organic pollution, sponges appear prominent due to specific traits includ...

Studies of submarine hydrothermal systems in Mediterranean Sea are limited to the southern Italian volcanism, while are totally missing in the Aegean. Here, we report on the geochemistry of high-temperature fluids (up to 220°C) venting at 500 m b.s.l. from the floor of Kolumbo submarine volcano (Hellenic Volcanic Arc, Greece), which is located 7 km...

The abundance and grazing effect of small (< 5 μm) pigmented (PNF) and heterotrophic (HNF) nanoflagellates on prokaryotic picoplankton stock (i.e. heterotrophic bacteria (HB) and Synechococcus) were assessed during April 2016 at four stations along a longitudinal transect in the ultra-oligotrophic Eastern Mediterranean Sea and at two selected depth...

As ocean acidification intensifies, there is growing global concern about the impacts that future pH levels are likely to have on marine life and ecosystems. By analogy, a steep decrease of seawater pH with depth is encountered inside the Kolumbo submarine volcano (northeast Santorini) as a result of natural CO2 venting, making this system ideal fo...

In the original publication there is a mistake in the supplementary material. The correct supplementary material is provided in this correction article.

Soil proteomics, the large-scale characterization of the entire protein complement in soils, provides a promising approach for deciphering the role of microbial functioning in terrestrial ecosystems. However, the extraction of soil proteins in sufficient quantities and of adequate purity remains a challenging task mainly due to the co-extraction of...

Mediterranean marine caves remain largely unexplored, while particularly limited information is available about microbial life in these unique environments. This study is a preliminary assessment of the composition of the active anaerobic microbial community colonizing the walls of newly explored systems of underwater caves and small cavities in Za...

Vibrio alginolyticus is a common marine bacterium implicated in disease outbreaks in marine farmed fish and invertebrates. Due to the inappropriate use of antibiotics in aquaculture, alternative therapies have been proposed. One of the most promising options is the use of lytic bacteriophages to control pathogenic bacteria. This work describes the...

Over the last decades, there has been growing interest about the ecological role of hydrothermal sulfide chimneys, their microbial diversity and associated biotechnological potential. Here, we performed dual-index Illumina sequencing of bacterial and archaeal communities on active and inactive sulfide chimneys collected from the Kolumbo hydrotherma...

The Mediterranean Sea is one of the busiest areas worldwide in terms of maritime activity, facing considerable anthropogenic disturbance, such as pollution by hydrocarbons and heavy metals. The present study has evaluated the environmental and benthic biodiversity characteristics of three touristic ports, Cagliari (Sardinia, Italy), Heraklion (Cret...

Chlorophyll a (Chl a) is the predominant pigment in every single photosynthesizing organism including phytoplankton and one of the most commonly measured water quality parameters. Various methods are available for Chl a analysis, but the majority of them are of limited throughput and require considerable effort and time from the operator. The prese...

The response of phytoplankton populations from surface ultra-oligotrophic waters of the Eastern Mediterranean Sea to Saharan dust additions was studied during a 10-day mesocosm experiment in May 2014. A set of triplicate mesocosms entitled “Single Addition” treatment (SA) was amended with Saharan dust once, while another triplicate set entitled “Re...

Organotin compounds are toxic substances released into the marine environment from antifouling paints. Sixty-two years following their first application and 9years after the complete ban on their use as biocides in 2003 (EC No. 782/2003), their negative impact on mollusks was still evident, as illustrated by imposex (i.e. the masculinization of fem...

The structure of phytoplankton community in the salinity-stratified Northeastern Aegean frontal area adjacent to the Dardanelles Straits was investigated on a seasonal basis (autumn, spring and summer) and in relation to circulating water masses: the modified Black Sea Water (BSW) and the Levantine Water (LW). By employing High Performance Liquid C...

Submarine volcanism represents ~80% of the volcanic activity on Earth and is an important source of mantle-derived gases. These gases are of basic importance for the comprehension of mantle characteristics in areas where subaerial volcanism is missing or strongly modified by the presence of crustal/atmospheric components. Though, the study of subma...

Submarine volcanism represents ∼80% of the volcanic activity on Earth and is an important ource of mantle-derived gases. These gases are fundamental for the comprehension of mantle characteristics in key sectors where subaerial volcanism is missing or strongly modified by mixing with crustal and atmospheric components. Though, the study of submarin...

Hydrothermal vents represent a deep, hot, aphotic biosphere where chemosynthetic primary producers, fueled by chemicals from Earth's subsurface, form the basis of life. In this study, we examined microbial mats from two distinct volcanic sites within the Hellenic Volcanic Arc (HVA). The HVA is geologically and ecologically unique, with reported emi...

The Kolumbo submarine volcano, located 7 km northeast of the island of Santorini, is part of Santorini’s volcanic complex in the south Aegean Sea, Greece. Kolumbo’s last eruption was in 1650 AD. However, a unique and active hydrothermal vent field has been revealed in the northern part of its crater floor during an oceanographic survey by remotely...

Organotins are toxic substances released into the marine environment from antifouling paints. Sixty two years following their first application and six years after their complete ban in EU ports, their negative impact on molluscs is still evident, as indicated by imposex (i.e. masculinization of female prosobranchs). Imposex is widely used as a TBT...

The deep eastern basin of the Mediterranean Sea is considered to be one of the world's most oligotrophic areas in the world. Here we performed pyrosequenicng analysis of bacterial and archaeal communities in oxic nutrient-poor sediments collected from the eastern Mediterranean at 1,025-4,393 m depth. Microbial communities were surveyed by targeting...

Hydrothermal fields are habitats with worldwide distribution in the seafloor where chemosynthetic primary producers form the basis of life. In this study, we examined microbial mat communities from volcanic sites within the Hellenic Volcanic Arc (HVA) located in the Aegean Sea. The HVA is a unique site geologically due to the occurrence of volcan...

Intensive microbial growth typically observed in laboratory rarely occurs in nature. Because of severe nutrient deficiency, natural populations exhibit near-zero growth (NZG). There is a long-standing controversy about sustained NZG; specifically, whether there is a minimum growth rate below which cells die or whether cells enter a non-growing main...

Three strictly anaerobic Gram-positive non-spore-forming rod-shaped motile bacteria designated as Oribacterium sp. ACB1T, ACB7T and ACB8 were isolated from the human subgingival dental plaque. All strains required yeast extract for growth. Strains ACB1T and ACB8 were able to grow on glucose, lactose, maltose, maltodextrin, and raffinose; strain ACB...

Deep sediments from the southern Cretan margin were analyzed to establish baseline levels for various types of organic pollutants before the anticipated intensification of anthropogenic activities. The total concentration of aliphatic hydrocarbons (ΣAH:326–3758 ng g−1, dry weight) was similar to those reported for deep sediments of the western Medi...

Deep sediments from the southern Cretan margin were analyzed to establish baseline levels for various types of organic pollutants before the anticipated intensification of anthropogenic activities. The total concentration of aliphatic hydrocarbons (ΣAH:326-3758ngg(-1), dry weight) was similar to those reported for deep sediments of the western Medi...

Pseudomonas species are capable to proliferate under diverse environmental conditions and thus have a significant bioremediation potential. To enhance our understanding of their metabolic versatility, this study explores the changes in the proteome and physiology of Pseudomonas putida F1 resulting from its growth on benzoate, a moderate toxic compo...

This study used a PCR-based molecular identification technique to examine bacterial assemblage composition in background aerosols of the eastern Mediterranean Sea during a rapid change of meteorological conditions. 16S rDNA fragments of 166 clones were identified and were affiliated with six bacterial phyla (Firmicutes, Actinobacteria, Proteobacter...

Two-dimensional Compound Specific Isotope Analysis (2D-CSIA), combining stable carbon and chlorine isotopes, holds potential for monitoring of natural attenuation of chlorinated ethenes (CEs) in contaminated soil and groundwater. However, interpretation of 2D-CSIA data sets is challenged by a shortage of experimental Cl isotope enrichment factors....

A strictly anaerobic Gram-positive non-spore-forming bacterium designated as Lachnospiraceae bacterium ACC2 strain DSM 24645T was isolated from the human subgingival dental plaque. Bacterial cells were 4-40 µm long non-motile rods often swollen and forming curved filaments up to 200 µm. Cells contained intracellular, poorly crystalline, nanometer-s...

Novel Aspect A new statistical framework based on the experimental design and ROC analysis for the performance evaluation of quantitative proteomics. Introduction Many strategies including chemical labeling (e.g., iTRAQ, TMT) or new instrumentation and software have been developed to improve protein identification and quantitation in large-scale pr...

During a six-week intensive field campaign at a background marine site of the Eastern Mediterranean, consecutive 24-h air samples were collected and analyzed for combined (CAA) and free amino acids (FAA), as well as for key chemical characteristics of aerosols. The total concentration of CAA (719 ± 326 pmol m−3) was on average four times higher tha...

Compound-specific Cl-isotope analysis was performed on the persistent and bioaccumulating compound tris-(4-chlorophenyl)methane (4,4′,4″-TCPMe, referred to as TCPMe in this study) to elucidate whether its main source is natural or anthropogenic. Blubber from the Baltic grey seal (Halichoerus grypus) was extracted by continuous acetonitrile partitio...

The variability of bacterial community composition and diversity was studied by comparative analysis of five 16S rRNA gene clone libraries from deep-sea sediments (water column depth: 4000 m) of the Northeastern Pacific Ocean and Eastern Mediterranean Sea. This is the first comparison of the bacterial communities living in these deep-sea ecosystems...

Fine marine aerosols influence the climate system by acting as cloud condensation nuclei (CCN) in the atmosphere. The organic chemical composition and origin of the marine fine particulate matter are still largely unknown, because of the insufficient reports on in situ studies, the large variability in the emission from the sea, from the complex tr...

This review underlines the importance of indoor contamination as a pathway of human exposure to hexabromocyclododecanes (HBCDs), polybrominated diphenyl ethers (PBDEs), and perfluoroalkyl compounds (PFCs). There is ample evidence of substantial contamination of indoor dust with these chemicals and that their concentrations in indoor air exceed subs...

During a two-week intensive field campaign conducted at a background location of the Eastern Mediterranean, consecutive 10-h air samples were collected under intense photochemical conditions and analyzed for polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs). The average gas-phase concentration of total PCBs and PBDEs was 7...

The analysis of amino acids by gas chromatography mass spectrometry (GC-MS) after their derivatization with N-(t-butyldimethylsilyl)-N-methyltrifluoroacetamide was investigated as an alternative approach for the determination of free (FAA) and combined amino acids (CAA) in aerosols. This technique showed excellent linearity with r(2) values ranging...

Ambient concentrations, gas/particle partitioning and particle-size distribution of polybrominated diphenyl ethers (PBDEs) were investigated in two urban areas (Athens and Heraklion) of Greece. Atmospheric (gas+particle) concentrations of summation operatorPBDE varied from 21 to 30 pg m(-3) in the center of Athens and from 4 to 44 pg m(-3) in the s...

Recent development in compound-specific radiocarbon analysis (CSRA) now allows application of this analytical dimension toward source apportionment of natural and anthropogenic compounds in the atmosphere. CSRA studies of semi-volatile n-alkanes and polycyclic aromatic hydrocarbons (PAHs) in air collected at various locations throughout Europe comb...

This study is the first culture-independent report on the regional variability of bacterial diversity in oxic sediments from the unexplored southern Cretan margin (SCM). Three main deep basins (water column depths: 2670–3603 m), located at the mouth of two submarine canyons (Samaria Gorge and Paximades Channel) and an adjacent slope system, as well...

Air samples from automobile cabins were collected and analyzed for polybrominated diphenyl ethers (PBDEs), polybrominated dibenzofurans (PBDFs), and polybrominated dibenzo-p-dioxins (PBDDs). The concentration of total PBDEs (sigmaPBDE; sum of 19 congeners) varied from 0.4 to 2644 pg m(-3), with a median of 201 pg m(-3), while BDE 47, 99, and 209 co...

Airborne polybrominated diphenyl ethers (PBDEs) were measured in workplaces, homes and urban outdoor air in Greece. The geometric mean concentrations of total PBDEs (sum of 19 congeners) in offices (205 pg m(-3)), internet cafes/computer rooms (127 pg m(-3)) and computers/electronics shops (85 pg m(-3)) were significantly higher than those in furni...

Compound-specific chlorine isotope analysis (CSIA-Cl) is promising as a novel and powerful method for monitoring in situ degradation of organochlorines in the environment and for source fingerprinting purposes. In order to apply CSIA-Cl in field studies of polychlorinated biphenyls (PCBs), the chlorine isotopic composition (delta(37)Cl) of individu...