Marine invertebrates with limited dispersal often exhibit population structuring shaped by historical isolation, local adaptation and/or habitat fragmentation. In this study, we examined the population dynamics of the chiton Rhyssoplax olivacea across five coastal regions of the Hellenic Seas, spanning both the Aegean and Ionian basins. We combined mitochondrial cyctochrome c oxidase subunit I sequencing with geometrics of three shell valves to assess spatial structuring and genotype-phenotype congruence. Genetic analysis revealed 24 unique haplotypes among 52 individuals and identified three distinct clusters: Ionio, Pagasitikos and a mixed Aegean group (Chalkidiki, Chios and Limnos). A similar clustering pattern was observed for the shape of the tail valve, suggesting a strong association with genetic structure. In contrast, the head and intermediate valves showed partial discordance, with Limnos morphologically aligning with Ionio despite genetic similarity to the Aegean group. These findings highlight the influence of both genetic divergence and phenotypic plasticity on shell morphology. The association between tail-valve shape and genetic clusters underscores the value of tail-valve shape as a phylogeographic marker, while the weaker correlation with the other valves suggests a potential environmentally mediated morphological variation. This integrative approach sheds light on local adaptation and emphasizes the need to consider both molecular and morphological data in marine biogeographic studies.

European hake, common sole and European eel represent economically important species in the Mediterranean basin and are commonly sold all over Europe. Reviewing of literature revealed that these species are highly prone to substitution, such as Merluccius merluccius by other hake species, Solea solea by other low-cost flatfish, and Anguilla anguilla by other eel species from China. Here we present the development of three methods for the rapid and accurate detection of possible substitutes using COI and cytb mtDNA genes. Conventional PCR through agarose screening and real-time PCR protocols are deployed, showing that all methods are able to provide accurate results and differentiate the target species. However, the results are strongly associated with DNA quantity, with High-Resolution-Melting (HRM) analysis showing the higher efficiency compared to the low-melting curve real-time PCR and conventional PCR. In our dataset we detected mislabeling of frozen M. hubbsi filet by M. capensis. Moreover, S. aegyptiaca specimens were mislabeled as S. solea in fish markets. However, the latter may be due to the extremely difficult morphological identification of the two sole species. The findings demonstrate the necessity of regulating processed fish-containing seafood and the feasibility of the suggested technology for tracing them. The findings are discussed in terms of public health hazards and conservation consequences, in addition to the financial losses brought on by mislabeling and seafood species substitution.

Marine mammals are important ecological bio-indicators of marine ecosystems impacted by a plethora of anthropogenic and environmental threats. Genomics detects genetic variation, adaptation to environmental shifts, and susceptibility to diseases in marine mammal species. In this study, eDNA was utilized for the first time in the Pagasitikos Gulf over three consecutive years (2022–2024) in order to detect marine mammal species. Additionally, visual monitoring and eDNA results were compared to reveal the pros and cons of the two methodologies. The gulf was zoned into five different areas with respect to oceanographic features for sampling. DNA extraction was assessed by using a standard protocol of phenol–chloroform followed by PCR amplification using the 16S rRNA gene. A total of 5,209,613 highly filtered sequence reads were attributed to 108 species. Among these, Monachus monachus, Tursiops truncatus, and Ziphius cavirostris species were detected. This novel detection of Z. cavirostris in the relatively shallow waters of the Gulf of Pagasitikos raised the question of whether it was a random event or a new ecological trend. Z. cavirostris and M. monachus appeared to share the same marine areas within the gulf. In the era of the climate crisis, eDNA provides essential information on marine mammals’ ecological status, yields novel detections, and predicts behavioral changes essential to deep-diving species.

Understanding population connectivity and genetic structure is crucial for the effective management of exploited marine species. This study investigates the population genetics of the common European squid (Loligo vulgaris) across the Mediterranean Sea, focusing on samples from the Aegean Sea and comparative sequences from Western Mediterranean, Eastern Mediterranean, and Atlantic coasts. A total of 67 COI mitochondrial sequences were analyzed, identifying 12 haplotypes and 27 polymorphic sites. Population-level genetic diversity, pairwise FST values, and haplotype network analyses revealed pronounced genetic differentiation in the eastern Mediterranean contrasting with the genetic homogeneity observed among Western populations. The low haplotype diversity observed in the Greek populations of L. vulgaris may be influenced by a combination of ecological and historical factors, as the Aegean region is recognized as a hotspot of endemism and historical population fragmentation. The results indicate the existence of at least two genetically differentiated clusters within the Mediterranean basin. This study advances current knowledge of the genetic structure of Loligo vulgaris by providing novel genetic data on populations from the eastern Mediterranean, offering valuable insights for future conservation and management strategies for the species.

Eudontomyzon lampreys were recently discovered in the Almopaios River’s main stem approximately 30 river kilometers downstream of Aridea river tributary, where specimens are known to have a stronghold in the past and have been collected recently as well. Molecular analyses assert that these lampreys belong to the taxon provisionally named Eudontomyzon sp. Almopaios, a brook lamprey; however, this species has not yet been formally described. Our genetic analysis provided a firm phylogenetic position for this population showing that their nearest relative is Eudontomyzon danfordi which has a center of distribution in the mid-Danube tributary basin, the River Tisza’s catchment area. With the discovery and molecular confirmation of new specimens, this taxon’s known distribution is presented for the first time; and particularly, the southernmost distribution area is located within a Natura 2000 protected area. However, this area is planned to be altered by a dam and river diversion. Conservation initiatives and steps towards further study are proposed.

Tenacibaculosis, caused by Tenacibaculum maritimum, poses a significant threat to Mediterranean aquaculture, notably impacting the gilthead seabream (Sparus aurata; Linnaeus, 1758). This study aimed to assess the efficacy of dietary supplementation with essential oils of Thymus vulgaris (0.25%, 0.5%) and Artemisia annua (0.25%, 0.5%) in mitigating the effects of experimental T. maritimum infection. Fish were fed supplemented diets for 15 days pre-infection and monitored for 20 days post-infection. Results showed T. vulgaris at 0.5% significantly reduced mortality to 2.2% compared to controls (18.9%), while A. annua at 0.5% yielded intermediate mortality (4.4%). Both oils reduced infection prevalence (T. vulgaris 0.5%: 2.2% vs. control: 16.7%), with T. vulgaris groups exhibiting milder histopathological lesions. Notably, A. annua at 0.5% induced focal renal hemorrhages, suggesting dose-dependent toxicity. Thyme essential oil demonstrates promise as a functional feed additive, whereas A. annua warrants further safety evaluation.

Many species of marine mammals are threatened and their populations decline worldwide due to the increase of anthropogenic activities such as fishing, shipping, pollution and climate change. Our understanding of marine mammal behavior/ecology remains poor and under-documented since studies of the kind are extremely challenging in practice and theory. Applied anthropology can help provide effective strategies based on cultural compatibility. Marine biology has already validated that biodiversity is beneficial to the ecosystem and so should anthropology promote the significance of mutualism in society.

This study reports on a new translocated population of the Western Greece Goby (Economidichthys pygmaeus Holly, 1929) within the Thrace freshwater ecoregion in Northeastern Greece, approximately 370 km east of the species' native range (Ionian freshwater ecoregion; Western Greece). Specimens were identified by morphological examination and molecular confirmation. Based on a literature review and anecdotal information the Western Greece Goby was possibly introduced within the last two to five years, perhaps associated with fish farm imports from Western Greece. Population characteristics of the species in the new locations indicate that the species is fully established within an important biodiversity hotspot, the Aggitis sub-basin of the Strymon River, a transboundary river shared with Greece, Bulgaria and North Macedonia. This record represents the easternmost range expansion of the Western Greece Goby. In addition, it confirms a noticeable trend of expansion of this species since it has been also documented in the Southeastern Adriatic (Albania, North Macedonia) and the Western Aegean (southern Greece) during the last decade. This introduction may trigger ecological consequences, including the homogenization of formerly isolated ichthyofaunas.

Holothuria poli is one of the most in-demand sea cucumber species and has attracted the interest of markets in Mediterranean regions. The present study is the first attempt to determine the reproductive cycle of H. poli in a coastal area of the Central Aegean Sea. Samples of H. poli as well as environmental and biometric data were collected monthly for 1 year. The sample population exhibited a female predominance, a size at first maturation of 156.3 mm and a distinctive reproductive pattern that reached its mature stage in the summer months. These findings contribute to the overall understanding of the reproductive physiology of the species and provide information for the sustainable management of sea cucumber stocks in the Hellenic Seas.

Background: The European hake (Merluccius merluccius) is a commercially valuable demersal species widely distributed in the Mediterranean Sea. Assessing the condition of fish populations in their natural habitats is challenging due to the lack of reliable reference points. Objective: This study aimed to utilize hematological analysis as an economical method to evaluate the physiological and health status of European hake, addressing the gap in hematological data for this species. Methods: Blood samples were collected from the caudal vein of 40 adult European hakes caught from the Toroneos Gulf (northern Greece) using a commercial bottom otter trawl. An automated hematological analyzer was used to assess hematological parameters alongside biometric and biological indices. Results: Female hakes showed significantly higher white blood cell (WBC) counts, thrombocyte (TC) counts, and red cell distribution width (RDW) than their male counterparts. Strong correlations were observed among various hematological parameters, notably between WBC and red blood cells (RBCs), hematocrit (Ht), and hemoglobin (Hb); between RBC and both Ht and Hb; between TC and both mean platelet volume and platelet distribution width (PDW); and between mean corpuscular Hb concentration and RDW. Significant differences were noted in RBCs, Hb, and Ht compared to data from wild-caught European hake populations in Argentina and Denmark. Both trawling depth and duration were found to significantly affect RBC, WBC, Hb, and Ht values, while having no notable impact on TC. Fish captured at an average depth of 80 m and with a trawling duration of 30 min exhibited significantly elevated hematological indices. Conclusion: This study demonstrates that hematological analysis is a valuable, cost-effective tool for assessing the physiological and health status of European hake populations in the Mediterranean. Notable differences in hematological parameters based on sex, as well as significant correlations among key blood metrics, underscore the importance of understanding species-specific hematological profiles. The influence of trawling depth and duration on certain blood parameters highlights the need for standardized sampling protocols in population health assessments. These findings contribute essential baseline hematological data for European hake, facilitating more informed fisheries management and conservation strategies.

The European hake, Merluccius merluccius is a high-profile commercial species, inhabiting eastern Atlantic and Mediterranean Sea waters. Often, species at the edge of distribution are characterized by relatively low genetic diversity. This study aims to identify the genetic diversity of the M. merluccius in Greek waters and compare it with that of western Mediterranean and Atlantic Ocean populations. Six populations distributed all along the Greek waters, along with one in western Mediterranean and two in the Atlantic were analysed using the cytochrome oxidase subunit I (COI). Median-joining network analyses revealed two distinct haplotype clusters in the Greek waters, with the north-eastern Aegean favoring a unique region-specific haplotype. FST and Bayesian inference also support the genetic differentiation of the north-eastern Aegean population, which is also considered as the edge of dispersion of the species. The present study contributes to increase current knowledge of the genetic structure of M. merluccius providing new genetic information for the eastern Mediterranean stocks, and it should be useful for future species conservation and management plans.

The aim of the present work was to study the microbiota profile of gilthead seabream (Sparus aurata) fillets stored either aerobically or under Modified Atmosphere Packaging (MAP) conditions at 0, 4, 8 and 12 degrees C, via 16S rRNA metabarcoding sequencing. Throughout storage, sensory assessment was also applied to estimate fillets' end of shelf-life. Results indicated that storage conditions strongly influenced the shelf-life of the fillets, since the sensorial attributes of air-stored samples deteriorated earlier than that of MAP-stored fillets, while higher temperatures also contributed to a more rapid products' end of shelf-life. Metataxonomic analysis indicated that Pseudomonas was by far the dominant genus at the end of fillet's shelf-life, in the vast majority of treatments, even though a sporadic but noteworthy presence of other genera (e.g, Shewanella, Carnobacterium, Brochothrix etc.) at the middle stages of MAP-stored fillets is also worth mentioning. On the other hand, a completely different profile as well as a more abundant bacterial diversity was observed at the end of shelf-life of MAP-stored fillets at 12 degrees C, in which Serratia was the most dominant bacterium, followed by Kluyvera, Hafnia, Rahnella and Raoultella, while Pseudomonas was detected in traces. The findings of the present work are very important, providing useful information about the spoilage status of gilthead seabream fillets during several storage conditions, triggering in parallel the need for further studies to enrich the current knowledge and help stakeholders develop innovative strategies that delay the growth of key spoiler players and consequently, retard spoilage course.

Speleothems found in caves worldwide are considered the natural libraries of paleontology. Bacteria found in these ecosystems are generally limited to Proteobacteria and Actinomycetota, but rare microbiome and "Dark Matter" is generally under-investigated and often neglected. This research article discusses, for the first time to our knowledge, the diachronic diversity of Actinomycetota entrapped inside a cave stalactite. The planet's environmental microbial community profile of different eras can be stored in these refugia (speleothems). These speleothems could be an environmental "Microbial Ark" storing rare microbiome and "Dark Matter" bacterial communities evermore.

It is widely accepted that oxidative stress (OS) coming from a wide variety of causes has detrimental effects on male fertility. Antioxidants could have a significant role in the treatment of male infertility, and the current systematic review on the role of melatonin to ameliorate OS clearly shows that improvement of semen parameters follows melatonin supplementation. Although melatonin has considerable promise, further studies are needed to clarify its ability to preserve or restore semen quality under stress conditions in varied species. The present review examines the actions of melatonin via receptor subtypes and its function in the context of OS across male vertebrates.

Family Palaemonidae Rafinesque, 1815 is very diverse, with more than 1400 known shrimp species occurring globally. Brachycarpus biunguiculatus (Lucas, 1846), though that it has a cosmopolitan distribution, is the only species of the genus that inhabits Mediterranean Sea. In Hellenic waters, the species is known only known from the south Aegean Sea. The present study reports the second occurrence of the rare B. biunguiculatus from the region of Cyclades, from Sifnos Island. Also, it aims to discuss the status of the species based on the recent findings provided within.

In this review we propose the use of telomeric length (TL) as an authenticity marker that could provide an alternative method for differentiating fish and seafood samples or detecting fraud. Considering the ever-growing number of incidents of economically motivated fish and seafood adulteration using even more sophisticated methods to overcome current authenticity markers, the need to identify novel authenticity markers becomes essential. The TL of fish and seafood depends on individual characteristics (e.g., sex, age) and the environmental stimuli (e.g., temperature, water quality) to which these are exposed. Hence, both wild marine and freshwater populations occupying different geographical origin habitats might differ substantially because of the environmental cues affecting them. Moreover, the implementation of various rearing practices in aquaculture, such as different levels of fish and seafood density and increased ambient noise combined with site-specific environmental cues could affect TL, providing regulatory authorities with valuable information by distinguishing wild from reared populations and organic from conventional ones. In the present review the effects of both the environmental conditions and individual characteristics on the telomeric stability of fish and seafood telomeres are discussed, suggesting TL as a potential prospect authenticity marker that could be used to prevent fish and seafood adulteration.

The red porgy (Pagrus pagrus) and the common dentex (Dentex dentex) are Sparidae species of high commercial value, traded in the Greek market. In some cases, fish species identification from Greek fisheries is difficult for the consumer due to the strong morphological similarities with their imported counterparts or closely related species such as Pagrus major, Pagrus caeroleustictus, Dentex gibbosus and Pagellus erythrinus, especially when specimens are frozen, filleted or cooked. Techniques based on DNA sequencing, such as COI barcoding, accurately identify species substitution incidents; however, they are time consuming and expensive. In this study, regions of mtDNA were analyzed with RFLPs, multiplex PCR and HRM in order to develop a rapid method for species identification within the Sparidae family. HRM analysis of a 113 bp region of cytb and/or a 156 bp region of 16s could discriminate raw or cooked samples of P. pagrus and D. dentex from the aforementioned closely related species and P. pagrus specimens sampled in the Mediterranean Sea when compared to those fished in the eastern Atlantic. HRM analysis exhibited high accuracy and repeatability, revealing incidents of mislabeling. Multiple samples can be analyzed within three hours, rendering this method a useful tool in fish fraud monitoring.

Admixture and hybridization may play a key role in population dynamics and speciation with respect to habitat, demographic history, and adaptive selection. The present study examines the genetic diversity of two congeneric—but in different subgenera—holothurians that live in sympatry in mixed populations. Strong evidence of admixture was provided by analyzing RAD sequencing data from 90 and 67 individuals of Holothuria (Holothuria) tubulosa and Holothuria (Roweothuria) poli, respectively, from various areas of the Hellenic Seas (eastern Mediterranean). Coalescent demographic analysis revealed a recent directional gene flow from H. poli to H. tubulosa. The two species populations diverged around 13.5 thousand years ago, just after the Last Glacial Maximum. According to the pairwise sequential Markovian coalescent approach, the historical population effective sizes for both species declined during the last Pleistocene glaciations, probably due to population decline, followed by a relative rapid recovery as it is calculated using LD methods. The presented results imply a role for admixture upon secondary contact and are consistent with the recent suggestion that the genomic underpinning of ecological speciation often has an older, allopatric origin.

A fishery-independent survey with a commercial bottom otter trawl was conducted in the Pagasitikos Gulf, a semi-enclosed, trawl-restricted gulf in Greece. The study aimed to ecologically assess the fishery communities that are experiencing a decline in fishery landings. Twelve hauls of 30 min duration each were conducted in the eastern, western, and central parts of the gulf at depths between 62 and 97 m. In total, 57 species were captured, with the highest species number recorded in the west (35 species), followed by the center (32 species) and east (29 species). The highest numerical abundance was recorded at the center, followed by the east and west, with an opposing trend exhibited for biomass; however, GLM detected no significant spatial differences (in area or depth) or interaction. Ecological indices exhibited significantly lower values in the west–east area comparison. Linear Discriminant Analysis, mMDS, and hierarchical clustering indicated the presence of two main groups (east and west), with PERMANOVA showing a significant difference in the demersal communities among the identified groups. The results indicated moderately disturbed demersal communities and an increasing level of disturbance from east to west. Considering the economic value of Pagasitikos to the local fishing community, additional fishery management measures are deemed necessary to protect the fishery resources and mitigate the potential risks of overexploitation.

The authentication of food products and the verification of their identity are of major importance for consumers. Food fraud through mislabeling is an illegal practice consisting of the substitution of an expensive food product by a relatively cheaper one, misleading false labelling of their origin and adulteration in processed or frozen products. This issue is particularly of high importance concerning fish and seafood, which are easily adulterated primarily due to difficult morphological identification. Fish species of the Mullidae family are considered among the most high-valued seafood products traded in Greece and Eastern Mediterranean in general, in terms of the price and demand. Specifically, the red mullet (Mullus barbatus) and the striped red mullet (Mullus surmuletus) are both indigenous in the Aegean (FAO Division 37.3.1) and the Ionian (FAO Division 37.2.2) Seas, with high levels of consumers' preferences. However, they could be easily adulterated or misidentified by the invasive Aegean Sea Lessepsian migrator goldband goatfish (Upeneus moluccensis) as well as by the imported West African goatfish (Pseudupeneus prayensis). Keeping this in mind, we designed two novel, time-saving and easy-to-apply multiplex PCR assays and one multiple Melt-Curve analysis real-time PCR for the identification of these four species. These methodologies are based on species-specific primers targeting single nucleotide polymorphisms (SNPs) detected via sequencing analysis of the mitochondrial cytochrome C oxidase subunit I (CO1) and of the cytochrome b (CYTB) genes in newly collected individuals, with additional comparison with congeneric and conspecific haplotypes obtained from the GenBank database. Both methodologies, targeting CO1 or CYTB, utilize one common and four diagnostic primers, producing amplicons of different length that are easily and reliably separated on agarose gel electrophoresis, yielding a single clear band of diagnostic size for each species or a certain Melt-Curve profile. The applicability of this cost-effective and fast methodology was tested in 328 collected specimens, including 10 cooked samples obtained from restaurants. In the vast majority (327 out of the 328) of the specimens tested, one single band was produced, in agreement with the expected products with a single exception a M. barbatus sample that was identified as M. surmuletus, the identity of which was confirmed using sequencing, indicating erroneous morphological identification. The developed methodologies are expected to contribute to the detection of commercial fraud in fish authentication.