Source-resolved PAHs links with microbial diversity and community structure in a multi-stressed coastal system, Saronikos Gulf, Greece (Eastern Mediterranean Sea) Ester Skylaki, Alexandra Zachariadou, Savvas Genitsaris, Constantine Parinos, Konstantinos Proios, Ioannis Hatzianestis, Dimitris Velaoras, Aikaterina Rektsini, Maria Moustaka-Gouni, Alexandra Gogou Marine Pollution Bulletin, 2026 Polycyclic aromatic hydrocarbons (PAHs) are organic pollutants widely abundant in multi-stressed coastal environments worldwide. Herein, seawater (dissolved phase/suspended particles) and sediment samples were collected during a survey on June 2024 across five stations, reflecting multiple anthropogenic stressors, at the heavily impacted Saronikos Gulf, Greece. In the collected samples, 47 PAH homologues were monitored by gas chromatography - mass spectrometry, resolved into source-related profiles by employing the EPA's Positive Matrix Factorization model and examined in relation to bacterial community composition inferred from eDNA metabarcoding sequencing. Our aim was to assess the potential links of PAH sources to microbial diversity and community structure, providing a targeted tool to support coastal monitoring of complex PAHs mixtures in multi-stressed environments. Total PAHs (TPAH₄₇) concentrations ranged between 127 and 462 ng L −1 in the dissolved phase with alkylated 2- and 3-ring compounds dominating, 5.78–10.4 ng L −1 in suspended particles and 860–5450 ng g −1 in sediments, dominated by high-MW 4- to 7-ring compounds. Bacterial community composition based on 16S rRNA gene metabarcoding differed between seawater and sediments. In seawater, community co-varied with physicochemical gradients (temperature, salinity, dissolved oxygen, chlorophyll-a), while PAH source profiles showed weaker associations. In sediments, bacterial assemblages exhibited a stronger statistical association with source-resolved PAH profiles based on the constrained ordination framework. In the dissolved phase the taxa Flavobacterium , Sulfitobacter , and Labedella gwakjiensis , in the suspended particles the genus Algiphilus , and in sediments the species Parahaliea maris were identified as source-associated candidate indicator taxa, highlighting compartment-specific potential bioindicators that require functional validation with -omics tools. • A source-resolved assessment of PAH-microbial linkages in a stressed coastal system • PAH sources/phase associations shape microbial responses more than concentrations. • Sediments show the strongest PAH source-microbial associations. • Phase-specific bacterial taxa identified as PAH source bioindicator candidates • Parahaliea maris identified as a potential PAH bioindicator in sediments
Bridging marine microbiota ecology and IMO policy: rethinking open-loop scrubber environmental impacts Savvas Genitsaris, Natassa Stefanidou, Evangelia Michaloudi, Leonidas Ntziachristos, Maria Moustaka-Gouni Sustainable Microbiology, 2026 Laboratory single-species ecotoxicity tests provide early-warning indicators of hazards from shipping open-loop scrubber effluent. However, such tests, conducted under highly controlled, microbiota-free conditions, neglect contaminant interactions with diverse microbial communities (billions of cells L⁻¹) prior to encountering larger marine organisms. Extrapolating results of single-species experiments and their modeling outcomes to marine ecosystems can overestimate ecological risk and can result in policies such as banning open-loop scrubbers. In fact, scrubbers may not only result in reduced SOx emissions but may also lower atmospheric Polycyclic Aromatic Hydrocarbons (PAHs) emissions, especially in port areas, thus contributing to improved air quality. Obviously, such trade-offs between cleaner air and cleaner seas present challenges to policymakers. Mesocosm ecotoxicity experiments show bacterioplankton, phytoplankton, and metazoan plankton communities’ resilience to diluted effluent in seawater and the increase of bacterial xenobiotic biodegradation gene machinery. These experiments indicate a fast bacterial biodegradation of abundant PAHs affecting the exposure levels to the rest of marine organisms. Another key factor mitigating PAH impacts in mesocosms is diatom-dominated phytoplankton as their enlarged phycosphere is a microhabitat for PAH-degrading bacteria. Marine microbes can quickly break down pollutants and sustainable environmental risk assessment policies must weigh this natural resilience alongside the air-quality gains from scrubbers.
Do coastal bacterioplankton communities hold the molecular key to the rapid biodegradation of Polycyclic Aromatic Hydrocarbons (PAHs) from shipping scrubber effluent? Savvas Genitsaris, Natassa Stefanidou, Polyxeni Kourkoutmani, Evangelia Michaloudi, Meritxell Gros, Elisa García-Gómez, Mira Petrović, Leonidas Ntziachristos, Maria Moustaka-Gouni Environmental Research, 2025 ) coastal site. High-throughput 16S rRNA metabarcoding revealed differential responses of the bacterioplankton linked to their initial community structure and population abundances. Taxa known for their PAHs-degrading capacity were retrieved, including the genera Roseobacter, Porticoccus, Marinomonas, Arcobacter, Lentibacter, Lacinutrix, Pseudospirillum, Glaciecola, Vibrio, Marivita, and Mycobacterium, and were found to have increased roles in shifted communities by increasing their relative abundances at least 5-fold in treatments with high scrubber effluent additions. Additionally, metagenomic analysis of shotgun sequencing, indicated an increase on the number of Clusters of Orthologous Genes (COGs) associated with pathways involved in PAHs degradation. Up to 198 more COGs involved in signal transduction were retrieved in scrubber effluent enriched mesocosms compared to controls, while 15, 86, and 136 more COGs associated with naphthalene, aromatic compound, and benzoate degradation, respectively, were detected in the pristine mesocosms after effluent additions. In both experiments, bacterioplankton responses towards xenobiotic degradation under increased PAHs and alkyl-PAHs were coupled with a drop in their concentrations, below the limit of detection by Day 3 of the experiment in the eutrophic community, and by half in Day 6 in the pristine environment's community. Our findings indicate that PAHs and alkyl-PAHs impacts can be rapidly reduced in natural systems of high bacterial activity.
Effects of Land Use and Water Level Fluctuations on Phytoplankton in Mediterranean Reservoirs in Cyprus Polina Polykarpou, Natassa Stefanidou, Matina Katsiapi, Maria Moustaka-Gouni, Savvas Genitsaris, Gerald Dörflinger, Athena Economou-Amilli, Dionysios E. Raitsos Diversity, 2025 Land use composition, water level fluctuations (WLFs), and biogeographical factors are recognized as key drivers of phytoplankton dynamics in reservoir ecosystems. This two-year study presents the first assessment of the combined effects of catchment land use, WLFs, and geographical distance on phytoplankton biomass and community composition across twelve Mediterranean reservoirs in Cyprus, which serve primarily for drinking water supply and irrigation. The results show that higher phytoplankton biomass was recorded in reservoirs whose catchments had >30% coverage by developed land (urban and agricultural), suggesting that increased anthropogenic pressures may lead to nutrient enrichment and elevated productivity. However, despite elevated biomass, no consistent spatial patterns were observed in phytoplankton community composition. The geographical distance between reservoirs had only a minor effect on species distribution, implying that other factors—such as water residence time or hydrological variability—play a more prominent role in shaping community structure. Phytoplankton biomass maxima were most often recorded during periods of elevated water levels and were typically dominated by Chlorophyta, Dinoflagellata, Bacillariophyta, and Charophyta. The pronounced temporal variability in species composition across all reservoirs points to a highly dynamic system, where environmental fluctuations strongly influence community assembly. This study provides the first comprehensive data on phytoplankton in Cyprus reservoirs, highlighting the importance of land use and hydrological regulation for water quality management in similar settings. Importantly, this baseline dataset can support the implementation of the Water Framework Directive (WFD) by contributing to the definition of ecological status classes, establishing reference conditions, and guiding future monitoring and assessment efforts. Expanding such datasets through coordinated, basin-wide monitoring initiatives is essential to improve our understanding of phytoplankton dynamics and their role in ecosystem functioning under the pressures of climate change and intensified land use in this Mediterranean “hot spot”.
The invasion in the Greek islands continues: first record of the pond slider, Trachemys scripta scripta (Thunberg in Schoepff, 1792), from Andros Island, Cyclades, Aegean Sea Herpetology Notes, 2025
Phytoplankton Diversity and Blooms in Ephemeral Saline Lakes of Cyprus Polina Polykarpou, Matina Katsiapi, Savvas Genitsaris, Natassa Stefanidou, Gerald Dörflinger, Maria Moustaka-Gouni, Athena Economou-Amilli, Dionysios E. Raitsos Diversity, 2023 The ephemeral saline lakes of Cyprus in the Mediterranean, situated in close proximity to each other, demonstrate pronounced seasonal and interannual fluctuations in their environmental conditions. Despite their extreme saline conditions, these lakes support phytoplankton diversity and bloom-forming species. Anthropogenic activities, particularly urban and artificial land uses within their catchments, contribute to eutrophication, warranting conservation attention within the context of European legislation. Over two years (2018–2019), we examined phytoplankton abundance and diversity alongside salinity in six lakes, with samples collected every three weeks. Chlorophytes were the dominant and most diverse group, followed by cyanobacteria and diatoms. Increasing salinity correlated with reduced compositional diversity and species richness. The proximity of lakes to each other suggested airborne microbe colonization from one lake to another as a significant factor in shaping these communities, while similar land use within each lake’s catchment impacted bloom formation. The highly halotolerant chlorophyte Dunaliella frequently dominated phytoplankton blooms, occasionally coexisting with other taxa in less saline lakes. Our findings provide insight into the phytoplankton community dynamics in temporal saline lakes, essential for developing effective conservation strategies and sustainable management practices.
