Microalgae is a promising raw material for several commercial applications however, the increased production costs remain the main challenge of algal cultivation today. To address this and to further enhance the financial and environmental sustainability of aquaculture, we developed a low-cost floating bioreactor for the cultivation of phytoplankton in-situ utilizing the excessive nutrients that are released by marine aquaculture. The bioreactors were deployed next to fish cages at two fish farms located in areas with different trophic status and the natural plankton community was used as inoculum. Our scope was to examine the growth potential of natural phytoplankton communities and to identify the most capable planktonic groups for cultivation in-situ. Our findings indicated that most groups of the natural phytoplankton community had increased positive growth rates inside the bioreactors, especially the diatom and OraNano (presumably cryptophytes) populations. OraNano cells increased in size, particularly at the oligotrophic site, increasing further the productivity of this group. Chaetoceros sp. was the dominant diatom species in the oligotrophic area while Pseudonitzschia sp., Leptocylindrus sp. and Nitzschia sp. were the most common species at the mesotrophic site. The cultivation of microalgae in the field can offer several significant advantages, while further optimization of the bioreactors’ design and the use of specific microbial consortia as inoculums could further increase the biomass productivity and bioremediation potential of this approach.

Many polycyclic aromatic hydrocarbons (PAHs), along with their nitrated and oxygenated derivatives (NPAHs and OPAHs), are known for their toxicity and ecotoxicity (Bandowe et al., 2014; Rengajaran et al., 2015; IARC, 2019; Nováková et al., 2020). These compounds are co-emitted with PAHs during fossil fuel and biomass combustion, or they form through photochemical and microbiological reactions involving PAHs in the atmosphere and soil (Tsapakis and Stephanou, 2007; Keyte et al., 2013; Bandowe et al., 2017; Wilcke et al., 2021).While laboratory and field studies have explored the sources, photochemistry, and atmospheric occurrence of these pollutants, their large-scale atmospheric lifetimes and environmental fate remain poorly understood. As semivolatile compounds resistant to biodegradation in soils and surface waters, their potential for long-range transport is further amplified by the "grasshopper effect" (Keyte et al., 2013; Mulder et al., 2014).We determined the concentration of 25 parent PAHs, 10 OPAHs and 17 NPAHs during summer in air and soils at a rural and near-coastal north European site (Birkenes, southern Norway), a north European forest site (Hyytiälä, southern Finland), a central European rural background site (Košetice, Czech Republic), and in air and surface seawater at two off-shore sites in the Aegean Sea and along transects across the Mediterranean Sea. Directions of diffusive air-soil and air-sea exchanges were derived from the fugacities.In the source area (central Europe), the diffusive vertical fluxes of most 2-4 ring PAHs, 2-nitronaphthalene and a number of 3-4 ring OPAHs were upward and the carcinogen 1-nitropyrene was found close to phase equilibrium. In the receptor area (northern Europe), acenaphthylene, acenaphthene, benzo(a)anthracene, two 3-4 ring OPAHs, dibenzofuran and 6H-benzo(c)chromen-6-one, were found to volatilise, and 2-nitrofluoranthene close to phase equilibrium (Mwangi et al., 2024). In the Mediterranean Sea, phenanthrene, fluoranthene, pyrene, 2-nitronaphthalene and few 3-4 ring OPAHs were found to volatilise from the sea surface or being close to equilibrium. These findings suggest that land and sea areas even far from the primary sources may indeed act as secondary sources for PAHs, NPAHs and OPAHs in the atmosphere and enable global transport by multihopping.Secondary emissions may include toxic species, such as e.g., the carcinogenic 1-nitropyrene. Because of neglected re-emissions (secondary sources), PAH emission inventories may be underestimated, in particular in receptor areas. Acknowledgements: Czech Science Foundation (GAČR, grants 07117S, 17534S), the Max Planck Society, the European Commission – H2020, JERICO-S3 (871153), ACTRIS-CZ (LM2023030), RECETOX (LM2023069) financed by the Czech Ministry of Education, Youth and Sports (MŠMT). References:Bandowe, B.A.M. et al. (2017) Sci. Total Environ. 581-582, 237-257.IARC (2019) IARC Monographs Eval. Carcinogenic Risks to Humans 92, 1–852Keyte, I.J. et al., Chem. Soc. Rev. 42 (2013) 9333-9391.Lammel, G. et al. (2025) Atmos. Poll. Res. 16, 102460.Mulder, M.D. et al. (2914) Atmos. Chem. Phys. 14, 8905-8915.Mwangi, J.K. et al. (2024) Sci. Total Environ. 921, 170495.Nováková, J. et al. (2020) Environ. Int. 139, 105634.Rengarajan, T. et al. (2015) Asian Pac. J. Trop. Biomed. 5, 182–189.Tsapakis, M. and Stephanou, E.G. (2007) Environ. Sci. Technol., 41 (23), 8011-8017.Wilcke, W. et al. (2021) J. Environ. Qual. 50, 717-729.

Integrated multi-trophic aquaculture (IMTA) has been proposed as a sustainable aquaculture method that may reduce waste and increase profitability. Bivalves and holothurians consume phytoplankton and organic matter, but concerns exist about the potential accumulation of metals in these organisms. The aim of this study was to investigate the accumulation of heavy metals and trace elements in mussels (Mytilus galloprovincialis), in the Lessepian pearl oysters (Pinctada radiata), and holothurians (Holothuria poli) cultivated in IMTA systems in comparison to natural populations. Additionally, an in-situ decontamination experiment was conducted to evaluate the impact of the IMTA system on metal and trace element concentrations in bivalve tissues. The experiment for pearl oysters included sampling locations within and away from an aquaculture farm. For mussels, decontamination experiment included samples from mussels cultivated in an IMTA farm and samples that, after their cultivation, were placed in a flow-through tank. Results indicated that mussels from natural populations showed higher concentrations of most metals and trace elements compared to those from IMTA farms, although all levels remained below the European Union (EU) (regulatory limits, except for zinc (Zn). In pearl oysters, the highest concentrations of metals and trace elements were found also in samples from two natural populations, where the organisms had spent considerable time in contact with sediments. Cadmium (Cd) and Zn concentrations exceeded EU limits in oysters. However, based on food safety indices for all three species, they were deemed safe for human consumption. The results indicate that IMTA is a safe method for cultivating species from different trophic levels.

This study demonstrates the development of advanced mass spectrometric methodologies suitable for targeted and nontargeted arsenolipid (AsLp) determination in a tuna fish reference material (BCR-627) certified for its arsenobetaine, dimethylarsinic acid, and total arsenic content, thus enhancing its potential to also be used as a noncertified AsLp reference material. Twenty-five As-containing chromatographic peaks were initially detected using reversed-phase high-performance liquid chromatography (HPLC)-inductively coupled plasma-̵̵mass spectrometry (ICP-MS) with a mobile phase consisting of methanol in water ranging from 5 to 95%. Identification of arsenolipids in the detected As-containing peaks was achieved by using a combination of targeted and nontargeted high-resolution electrospray ionization mass spectrometry. Even though the targeted approach confirmed the presence of 11 AsLps already reported to be present in this material, a novel nontargeted approach not only confirmed their presence but also revealed the presence of an additional 26 AsLps, some of which are reported here for the first time. The nontargeted Full MS approach involved accurate mass measurements, better than 1 ppm using a lock mass, for high confidence detection of the AsLps. The resulting mass spectra were subsequently interrogated using the Mzmine software thus allowing for the rapid identification of candidate arsenolipid ions, which were designated to be precursor ions and fragmented in the MS/MS mode. Resulting product ion mass spectra were examined for 5 As-containing marker product ions, all of which are characteristic of the presence of compounds containing a dimethylarsinoyl moiety (CH3)2As(O). Precursor ions giving at least 3 marker product ions were identified to be dimethylarsinoyl-containing AsLps. The extracted ion chromatograms for the AsLp molecular ions were overlaid onto the As-specific HPLC-ICP-MS chromatograms for the final confirmation. Based on this approach, a high identification coverage of 84% was achieved, enabling more reliable quantitation of AsLps in BCR-627. By delivering both an analytically validated targeted and nontargeted workflow for AsLp analysis, and an expanded AsLp species dataset, this study provides essential groundwork for more routine, higher-coverage AsLp speciation in marine organisms, with possibilities for interlaboratory comparisons through the use of the BCR-627 tuna reference material. Thus, introducing a new era in AsLp speciation analysis expected to further promote the development of a field that may be referred to as arsenolipidomics.

Microplastics can support biomass production by acting as substrates for microbial activity. This may imply potentially relevant effects for the sea-surface microlayer, the interface mediating air-sea gas exchange and where biological organic compounds can accumulate.We tested this hypothesis by using six large scale mesocosms to simulate a future “high plastic ocean”. During the course of a 12-days experiment, we explored microbial organic matter dynamics in the sea-surface microlayer in the presence and absence of microplastics in the underlying water. We used as a reference a known number of polystyrene beads of 30 µm diameter and compared the three treatment mesocosms to an equal number of plastic-free control mesocosms.The presence of microplastics represented a spur for microbial activity, and in the treated mesocosms biomass production was enhanced, leading to an increased concentration of organic compounds accumulating in the sea-surface microlayer. This initial boost in biological productivity led to a ∼3 % reduction of dissolved CO₂ in the underlying water, which we could imagine potentially reversed once the degradation phase took off. Based on our results and on other recent studies, we will discuss potential interference of plastic with the composition of the sea-surface microlayer, with direct and indirect impacts on the uptake of CO₂ and the marine carbon cycle.

Polycyclic aromatic hydrocarbons (PAHs) in the atmospheric environment are almost exclusively formed in combustion processes. Oxygenated and nitrated PAHs are co-emitted with parent PAHs from fossil fuel and biomass combustion processes, and many are formed in photochemical and microbiological reactions of PAHs in air and soil. As semivolatiles resisting biodegradation in soils and surface waters to some extent, polycyclic aromatic compounds (PACs) i.e., PAHs and their derivatives, can be subject to re-volatilisation., which may turn soils and surface waters from sinks into secondary sources and enhances the long-range transport potential of PACs by multihopping (grasshopper effect). The significance of these secondary sources for PAC abundances in ambient air is unknown and is not accounted for in emission inventories. Gaps in PAH emission inventories have been indicated by field studies in various countries. We determined the concentrations of 15 parent, 10 oxygenated and 17 nitrated PAHs in air and soils at a rural and near-coastal northern European site and a central European rural background site, and in air and surface seawater at two off-shore sites in the eastern Mediterranean and along NW-SE transects in the Mediterranean. Directions of air-soil and air-sea exchanges were derived from the substances’ fugacities. At the central European site, a number of 2-4 ring PACs were found to volatilise from grassland and more from forest soils in summer, and much less in winter. Conversely, at the receptor site in northern Europe, net deposition of PACs prevails and re-volatilisation occurs only sporadically. In the Mediterranean, 3-4 ring PAHs and dibenzofuran are found to volatilise in most seasons. Existing data on air-surface exchange of PACs is notably scarce, and methodological uncertainties persist in quantifying air-soil exchange. As very little is known about the spatial and seasonal distributions of PACs soil burdens and net mass fluxes, an assessment of the significance of soils and surface waters as secondary sources of PACs in the air of source and receptor areas is not possible.

The present study investigates the role of microplastics (MPs) (polystyrene (PS) microbeads) in copper (Cu) binding within the sea surface microlayer (SML) and underlying water (ULW). A mesocosm experiment was conducted, with both SML and ULW samples obtained daily, comparing mesocosms containing MPs with those free of them. The SML enrichment in dissolved Cu (Cu-D) and the Cu-complexing capacity (LT) were found to be significantly higher in the MP-treated mesocosms, with stability values of Cu-ligand complexes (logK′) being higher in the SML of MP treatments. Significant differences in Cu-D and LT between control and MP treatments were found in SML and ULW across treatments and over time. Cu-D was negatively correlated with transparent exopolymer particles (TEPs) in the ULW of both treatments, while LT was positively correlated with TEPs in the SML of MP treatments. Experimental data indicate that the co-existence of TEPs and MPs favors Cu binding with organic matter in the SML, suggesting that MPs may enhance this process. The impact of MPs on dissolved Cu complexation is probably attributed to the production of organic ligands, via enhanced TEP production, without excluding direct adsorption onto biofilm-coated MPs. The present study provides insight into the role of microplastics in Cu cycling in marine surface waters, focusing on the microenvironment of the SML.

Measuring dissolved concentrations of polybrominated diphenyl ethers (PBDEs) and non-BDE flame retardants on a global scale provides critical insights into the effectiveness of the Stockholm Convention. In the present study, we deployed passive sampling devices at 43 seawater and freshwater sites covering 21 countries from 2016 to 2020. The detection frequencies were 20-94% for BDE congeners and 33-42% for dechlorane plus, higher than those (0-20%) for other target compounds. The median concentrations of dissolved Σ9PBDE (sum of BDE-28, -47, -66, -85, -99, -100, -153, -154, and -183) were 0.28 and 0.64 pg L-1 in seawater and freshwater, respectively. The concentrations of dissolved Σ9PBDE, along with published data, slightly increased before 2016 and remained steady from 2016 to 2018, indicating delayed effects of the global phaseout of technical Penta- and Octa-BDEs. The log-transformed concentrations of individual BDE congeners were better correlated with regional gross domestic product than with population density. The potential ecological risk of BDE-47 was low, and there was a lack of key risk indicators for other compounds. The present study documented the delayed response of the aquatic environment to the regulatory actions on reducing PBDE emissions.

Ocean Alkalinity Enhancement (OAE) allows for active removal of atmospheric CO2, therefore is considered as one of the most promising Carbon Dioxide Removal (CDR) technologies. OAE could be obtained by discharging alkaline material in the wake of ships, however very little is known on potential negative effects on marine communities. We report here the first study focusing on the response of the entire pelagic microbial food web to the addition of calcium hydroxide in real oligotrophic conditions. In a mesocosm experiment performed at the CretaCosmos facility in Crete, Greece, in May-June 2023, we tested the response of the eastern Mediterranean oligotrophic waters to two different treatments of calcium hydroxide slurry addition (SL; High and Low concentrations, three replicate mesocosms each), while three more mesocosms served as Controls (no addition). Mesocosms, filled with natural coastal seawater, were treated with slurry on days 1, 3, 5, 7, 9, 11 to simulate the chronic disturbance, expected from repeated discharge of SL from ships; while the possible precipitation of carbonate crystals was assessed by putting a sediment trap at the bottom of each mesocosm. The carbonate-equilibrium and dissolution-kinetics were monitored by measuring temperature, solution-conductivity, and changes in pH. Photosynthetically-Active-Radiation and visible light were monitored by sensors in each mesocosm. Plankton productions (bacterial, viral, secondary) as well as community composition of all plankton groups from viruses to copepods were assessed by optical microscopy, flow cytometry and metagenomics; chlorophyll was also measured. Although an important alteration of pH was observed in the High lime addition, only heterotrophic bacteria production was found to be negatively affected and only in the second half of the experiment. The rest of the plankton groups presented different patterns and not a clear response to the lime addition. This first attempt to study the effect of lime addition on the complex pelagic food web will serve as a first step to an extensive testing needed before any application of ocean liming at a large scale.

Major oil spills can impose a significant environmental hazard on the marine ecosystem, and a promising mitigation measure is in-situ oil burning (ISB). However, our knowledge of the impact of the burned residues and soot deposition on the marine ecosystem is still limited. We investigated the effects of burned oil residue and soot deposition on the marine plankton communities of the oligotrophic Eastern Mediterranean Sea with a mesocosm experiment. Three triplicated treatments were tested: (1) Iranian crude oil was added and burned (Burned treatment); (2) soot was collected and deposited with artificial rain (Soot); and (3) a non-contaminated Control. Results revealed that Low Nucleic Acid heterotrophic bacteria, Synechococcus spp., and pigmented pico-nano Eukaryotes (pnEuk) were negatively affected in the Burned and Soot treatments. Viruses, heterotrophic pnEuk and ciliates (in Soot) were crucial for controlling the High Nucleic Acid bacteria. Ciliates and most dinoflagellates showed a negative response to the burned residues but were less affected or were even favored when exposed to soot. Our results show that ISB affected the structure and dynamics of the plankton food web through burned residues and soot depositions. However, since the effects appeared at least three days after the ignition, ISB could be combined with subsequent burned residue collection to minimize its impact on the pelagic ecosystem.

To evaluate the effect of trace element (TE) release from fish farms on seagrass Posidonia oceanica , we compared TE concentrations (As, Cd, Co, Cu, Mn, Mo, Ni, Pb, V, Zn) in shoots near fish cages (Station ‘Cage’) with those away from them (Station ‘Control’) in two fish farm facilities (Site 1 and Site 2, North Aegean Sea, Greece). We assessed the present (i.e., 2021, year of sampling) and past (reconstructed period 2012–2020) accumulation of TEs using the living compartments (leaf blades, sheaths, rhizomes, roots, epiphytes) and the dead sheaths, respectively. We also assessed possible seagrass degradation by reconstructing past rhizome production. P . oceanica rhizome production at the ‘Cage’ stations was up to 50% lower than at the ‘Control’ stations. Most TE concentrations were higher at ‘Cage’ stations, but the differences often depended on the seagrass living compartment. Significant differentiation between ‘Cage’ and ‘Control’ stations was observed based on the TE concentrations of the dead sheaths during 2012–2020. The contamination level at the ‘Cage’ stations was mostly moderate in Site 1 and low in Site 2, during the reconstructed period, while an increasing contamination trend was found for certain potential phytotoxic TEs (As, Cu, Cd, Mo, V). Our results emphasize the need for the aquaculture industry to work towards a more ecologically aware approach.

Terrestrial input to marine and freshwater ecosystems colors the water yellow-brown, causing a phenomenon called “brownification”. The effect of brownification on the marine pelagic microbial food web was studied in the oligotrophic eastern Mediterranean in June 2021 by adding HuminFeed in a 15-day mesocosm experiment with 2 treatments: Control (C, no addition) and HuminFeed (HF, single dose of HuminFeed, 2 mg L-1); and 3 replicates per treatment. HuminFeed caused shading, leading to a decrease in the abundance of photo-autotrophic organisms (cyanobacteria Synechococcus and diatoms). Bacteria were positively affected by the HF addition (mainly in terms of production rather than abundance), benefiting either directly from the dissolved organic carbon (DOC) contained in HuminFeed or indirectly from the trophic cascade through the food web. Despite the decrease in HF bacterial abundance during the experiment, an increase in both the high nucleic acid containing bacteria% and heterotrophic bacterial production were observed, suggesting higher activity at the single cell level. In the HF treatment, the increased abundance of dinoflagellates observed could be due to either a dominance of mixotrophic species or a release from predation by copepods. Both ciliates and copepods were severely impacted by HuminFeed, showing lower abundance and distorted forms (ciliates) and reduced reproductive potential (copepods). In conclusion, in the ultraoligotrophic eastern Mediterranean, the simulated brownification negatively affected autotrophs and top predators while benefiting bacteria, thus indicating a shift in the structure of the plankton food web.

Polycyclic aromatic hydrocarbons (PAHs), released from petrogenic, pyrogenic or diagenetic sources (degradation of wood materials), are of global concern due to their adverse effects, and potential for long-range transport. While dissolved PAHs have been frequently reported in the literature, there has been no consistent approach of sampling across water bodies. Passive samplers from the AQUA/GAPS-MONET initiative were deployed at 46 sites (28 marine and 18 freshwater), and analyzed for 28 PAHs and six polycyclic musks (PCMs) centrally. Freely dissolved PAH concentrations were dominated by phenanthrene (mean concentration 1500 pg L-1; median 530 pg L-1) and other low molecular weight compounds. Greatest concentrations of phenanthrene, fluoranthene, and pyrene were typically from the same sites, mostly in Europe and North America. Of the PCMs, only galaxolide (72% of samples) and tonalide (61%) were regularly detected, and were significantly cross-correlated. Benchmarking of PAHs relative to penta- and hexachlorobenzene confirmed that the most remote sites (Arctic, Antarctic, and mountain lakes) displayed below average PAH concentrations. Concentrations of 11 of 28 PAHs, galaxolide and tonalide were positively correlated (P < 0.05) with population density within a radius of 5 km of the sampling site. Characteristic PAH ratios gave conflicting results, likely reflecting multiple PAH sources and postemission changes.

As deposit feeders contribute to bioremediation and nutrient recycling in sediments, positively impacting water and sediment quality, holothurians are candidate organisms for multitrophic aquaculture. This study aimed to investigate the potential of Holothuria poli to reduce the environmental footprint of fish farms through a benthocosm experiment. The experimental setup included four benthocosms with holothurians(H+) and four without (H-). The 58-day experiment included two phases: constant organic enrichment and recovery. In order to simulate the organic enrichment sediment conditions under a typical fish farm, a mixture of fish feces and fish feed pellets was added. Results showed that holothurians effectively reduced organic matter and H2S and increased redox, RPD depth and sediment oxygenation, thereby preventing anoxic conditions. Also, during the recovery phase, holothurians facilitated rapid sediment recovery, while the sediments without holothurians remained organic-enriched until the end of the experiment. The study emphasizes the significance of holothurians in mitigating the impacts of aquaculture on sediment conditions and so promoting environmental sustainability.

Persistent organic pollutants (POPs) are recognized as pollutants of global concern, but so far, information on the trends of legacy POPs in the waters of the world has been missing due to logistical, analytical, and financial reasons. Passive samplers have emerged as an attractive alternative to active water sampling methods as they accumulate POPs, represent time-weighted average concentrations, and can easily be shipped and deployed. As part of the AQUA-GAPS/MONET, passive samplers were deployed at 40 globally distributed sites between 2016 and 2020, for a total of 21 freshwater and 40 marine deployments. Results from silicone passive samplers showed α-hexachlorocyclohexane (HCH) and γ-HCH displaying the greatest concentrations in the northern latitudes/Arctic Ocean, in stark contrast to the more persistent penta (PeCB)- and hexachlorobenzene (HCB), which approached equilibrium across sampling sites. Geospatial patterns of polychlorinated biphenyl (PCB) aqueous concentrations closely matched original estimates of production and use, implying limited global transport. Positive correlations between log-transformed concentrations of Σ7PCB, ΣDDTs, Σendosulfan, and Σchlordane, but not ΣHCH, and the log of population density (p < 0.05) within 5 and 10 km of the sampling sites also supported limited transport from used sites. These results help to understand the extent of global distribution, and eventually time-trends, of organic pollutants in aquatic systems, such as across freshwaters and oceans. Future deployments will aim to establish time-trends at selected sites while adding to the geographical coverage.

The response of Posidonia oceanica meadows to global warming of the Eastern Mediterranean Sea, where the increase in sea surface temperature (SST) is particularly severe, is poorly investigated. Here, we reconstructed the long-term P. oceanica production in 60 meadows along the Greek Seas over two decades (1997-2018), using lepidochronology. We determined the effect of warming on production by reconstructing the annual and maximum (i.e. August) SST, considering the role of other production drivers related to water quality (i.e. Chla, suspended particulate matter, Secchi depth). Grand mean (±SE) production across all sites and the study period was 48 ± 1.1 mg DW per shoot yr-1 . Production over the last two decades followed a trajectory of decrease, which was related to the concurrent increase in annual SST and SSTaug . Annual SST > 20°C and SSTaug  > 26.5°C was related to production decline (GAMM, P < 0.05), while the rest of the tested factors did not help explain the production pattern. Our results indicate a persistent and increasing threat for Eastern Mediterranean meadows, drawing attention to management authorities, highlighting the necessity of reducing local impacts to enhance the resilience of seagrass meadows to global change threats.

Silver nanoparticles (AgNPs) nowadays appear in close to 24% of consumer products that contain engineered nanomaterials. Thus, they are expected to be released into the environment, where their fate and effect are still undetermined. Considering the evidenced efficacy of the single particle Inductively Coupled Plasma – Mass Spectrometry (sp ICP-MS) technique in the study of nanomaterials, this work reports on the use of sp ICP-MS along with an online dilution sample introduction system for the direct analysis of untreated and spiked seawater samples, as part of a larger scale experiment studying the fate of Ag (ionic and nanoparticles) in seawater mesocosm systems. Silver nanoparticles coated with branched polyethyleneimine (BPEI@AgNPs) or ionic silver (Ag+) were introduced gradually into the seawater mesocosm tanks at very low, environmentally relevant concentrations (50 ng Ag L−1 per day, for 10 consecutive days, up to a total of 500 ng Ag L−1), and samples were collected and analyzed daily, within a consistent time window. Using very low detector dwell time (75 μs) and specialized data treatment, information was obtained on the nanoparticles’ size distribution and particle number concentration, as well as the ionic silver content, of both the AgNPs and the Ag+ treated seawater mesocosm tanks. The results for the AgNP treated samples indicated the rapid degradation of the added silver particles, and the subsequent increase of ionic silver, with recoveries close to 100% for the first days of the experiment. On the other hand, particle formation was observed in the Ag+ treated seawater tanks, and even though the number concentration of silver-containing nanoparticles increased throughout the experiment, the amount of silver per particle remained relatively constant from the early days of the experiment. In addition, the online dilution sample introduction system for the ICP-MS proved capable of handling the untreated seawater matrix without significant contamination issues and downtime, while the low dwell time and data treatment procedure developed were shown to be suitable for the analysis of nanomaterials at the low nm-scale, despite the complex and heavy matrix introduced into the ICP-MS.

In addition to food supply, there is a growing recognition of the wider ecosystem benefits of Integrated Multitrophic Aquaculture (IMTA) systems in coastal waters, including regulating services such as carbon sequestration and nutrient remediation. The water trophic status and the co-cultured species combinations affect IMTA productivity. In this study, we examined the ability of different combinations of IMTA organisms to remediate nutrients and the economic/environmental gain for reducing the environmental footprint in potential IMTA systems of the eastern Mediterranean. The results showed that the co-cultivation of organisms can reduce the negative effects on the marine environment of a fish farm both on the water column and the sediment. Meso- and eutrophic water states do not show a high variation in terms of foot print mitigation, with all three of the co-cultivated organisms to perform well. In oligotrophic waters, the obligatory absence of mussels reduces the effectiveness of the IMTA system. As expected, larger-sized IMTA systems have higher production rates and as a result higher percentage of nutrient removal. Finally, bivalve harvesting helps to remove the carbon that is trapped in their shells, contributing to the mitigation of processes related to climate change, such as the acidification of the oceans.

Our goal was to understand the mechanisms behind the impact of nutrient enrichment at intermediate distances from aquaculture on the interactions of a subtidal macroalgae community with its main grazer, the sea urchin Paracentrotus lividus. We assessed the diversity and cover of the macroalgal community, the abundance and biometrics of the sea urchins, the carbon and nitrogen elemental and isotopic compositions, and their metabolome in two stations, at an intermediate distance (station A) and away (station B) from a fish cage facility in the Aegean Sea (Greece), during the warm and cold seasons. The nutrient input at station A favored a shift to a macroalgal assemblage dominated by turf-forming species, depleted of native-erected species and with a higher abundance of invasive algae. A stable isotope analysis showed fish-farm-associated nitrogen enrichment of the macroalgae and trophic transfer to P. lividus. A decrease in metabolites related to grazing, reproduction, and energy reserves was found in P. lividus at station A. Furthermore, the metabolomic analysis was able to pinpoint stress in P. lividus at an intermediate distance from aquaculture. The chosen combination of traditional ecology with omics technology could be used to uncover not only the sublethal effects of nutrient loading but also the pathways for species interactions.