Τhis study aims to measure the abundance of microplastic (MP) particles in the soft tissue of mussel (Mytilus galloprovincialis) and pearl oyster (Pinctada imbricata radiata) specimens. Samples were ...collected at four sites in Greece (Sagiada, Malesina, Elounda, Rhodes) from wild and farmed populations. The identification of MPs was accomplished by Raman spectroscopy. Comparisons were made between the two different species where the two species co-existed (Malesina), between the four study sites (five sampling stations) in relation to P. imbricata radiata individuals, and also in every station for the different MP types found. For the specimens from Malesina, M. galloprovincialis had more MPs in their soft tissue compared to P. imbricata radiata. Microfibers were found in abundance in M. galloprovincialis, while microfragments were found in P. imbricata radiata specimens. The main MP type found in P. imbricata radiata specimens was microfragments in all five sampling stations, and ranged between 1.54 ± 0.63 (Rhodes-baskets) and 3.56 ± 0.35 (Sagiada) MP particles/g. While the samples of mussels and pearl oysters were similar in age, the differences found in the concentrations of MPs appears to be due to their different farming methods and location characteristics concerning the five sampling stations of pearl oysters. This study indicates that the culturing system does not affect MP concentration in bivalves, and further investigation is needed to find the most appropriate method to limit and reduce MPs that end up in the farmed organisms.
Marine benthic ecosystems face well-documented changes as a result of human activities. Describing these changes is important for predicting ecosystem functioning. In this context, long-term changes ...in soft-bottom macrofaunal communities after a quarter of a century were studied in the south Aegean Sea with the purpose of investigating whether temporal changes in taxa diversity are accompanied by changes in functional diversity, and secondly to determine the main mechanisms driving these changes (i.e., deterministic
versus
stochastic processes). To achieve this, a large data set that included species abundance data collected in 1990 and 2014 from several sampling sites along a transect line was used. A biological trait analysis (BTA) was conducted to determine the species functional roles. The results revealed a decline in taxonomic alpha and beta diversity metrics between 1990 and 2014, a difference that was also reflected in functional richness, partially in functional redundancy, but not in functional composition. The stability of functional composition indicated that replacements of functionally similar taxa may occur, ensuring the resilience of the ecosystem to provide goods and services. Finally, the comparison of co-occurrence and functional networks for 1990 indicated a non-differentiation with the null model and, it was not possible to determine if the benthic community was structured due to stochastic processes (e.g., dispersal, natural phenomena) or an overlap of deterministic processes (e.g., niche-filtering, competition). In contrast, the comparison of networks for 2014 pointed out that environmental conditions have acted as a major filter on species distribution.
Viruses interfere with their host's metabolism through the expression of auxiliary metabolic genes (AMGs) that, until now, are mostly studied under large physicochemical gradients. Here, we focus on ...coastal marine ecosystems and we sequence the viral metagenome (virome) of samples with discrete levels of human-driven disturbances. We aim to describe the relevance of viromics with respect to ecological quality status, defined by the classic seawater trophic index (TRIX). Neither viral (family level) nor bacterial (family level, based on 16S rRNA sequencing) community structure correlated with TRIX. AMGs involved in the Calvin and tricarboxylic acid cycles were found at stations with poor ecological quality, supporting viral lysis by modifying the host's energy supply. AMGs involved in "non-traditional" energy-production pathways (3HP, sulfur oxidation) were found irrespective of ecological quality, highlighting the importance of recognizing the prevalent metabolic paths and their intermediate byproducts. Various AMGs explained the variability between stations with poor vs. good ecological quality. Our study confirms the pivotal role of the virome content in ecosystem functioning, acting as a "pool" of available functions that may be transferred to the hosts. Further, it suggests that AMGs could be used as an ultra-sensitive metric of energy-production pathways with relevance in the vulnerable coastal zone and its ecological quality.
Microplastics are small plastic particles (<5 mm) that are found in most marine habitats around the world. Currently, several studies are trying to determine their exact effects. Microplastics can be ...introduced into the marine ecosystem directly as manufactured microplastics, or indirectly through the decomposition of larger plastic particles. They can enter the food chain, and can be found as vectors for the movement of microbial communities and chemical pollutants. In our study, two different ways of measuring microplastics were tested at three Mediterranean beaches, each subject to different types of human pressure. The purpose of the study was to compare different sampling approaches for assessing the microplastics present in sediment, taking into account temporal variability across the summer and winter seasons. Statistically significant differences were found between the beaches, which reflect the distinct uses made of each of them. At the same time, significant differences were found in the contents of microplastics, which were due to seasonal variability. Our analysis showed that microplastics can be found in deeper sediment layers with different concentrations to that of the surface layer. Therefore sampling methods that do not sample the same sediment layer do not seem to produce comparable results. In addition, classic categorizations of microplastics (as microfibers, membranes, etc.) may not always be sufficient. Rather, a classification based on microplastic properties, the specificities of each region and each study's objectives is recommended.
•Two sampling approaches of collecting microplastics from sediments were compared in three sandy beaches and two time periods.•The two methods applied were (a) sampling using a core (depth sampling) and (b) surface sampling.•Microplastics were identified by optical stereoscope and FT-IR microscope.•We found quantitative and qualitative differences in the microplastics between the two sampling methods.•Categorization of microplastics based on their properties, specificities of each region and study objectives should be used.
A benthic-pelagic mesocosm experiment was performed for the study of the response of the benthic macrofaunal community under a eutrophication gradient. Nine mesocosms were deployed in the facilities ...of the Hellenic Center for Marine Research in Crete, in the eastern Mediterranean. The mesocosms were 4 m deep, contained 1.5 m3 coastal water, and included 85 liters of undisturbed sediment at the bottom. The experimental design included two eutrophication levels (Low and High) for the 58-day duration. Macrofaunal samples were collected at the end of the experiment from each mesocosm and compared to the ones collected at the beginning of the experiment from the sediment collection area. Results showed significant differences of the High eutrophication treatment in terms of macrofaunal species composition, diversity, ecological status and ecosystem processes. The increased availability of organic matter in the sediment caused differences in macrofaunal community structure by favouring deposit-feeding species with high bioturbation ability, which significantly increased their abundance. The increased bioturbation potential of the new community combined with the high organic matter consumption contributed to the oxygenation of the sediment within the mesocosm, preventing the creation of hypoxic conditions in the sediment and maintaining ecosystem health despite the highly eutrophic conditions and significant changes in sediment geochemical variables.
Excessive primary productivity due to nutrient inputs is a potential problem in coastal areas when resulting in high organic matter sedimentation rates. Microphytobenthos and heterotrophic bacteria ...are two components of the benthic ecosystem that contribute to nutrient cycling and decomposition of organic matter. In this context, the effects of nutrient addition and the associated in situ produced organic matter on microphytobenthos community composition and benthic bacterial viability were assessed in a mesocosm experiment for 58 days. The experimental setup included triplicate mesocosms filled with sediment and water under three levels of nutrient addition (‘control’, ‘low’ and ‘high’). Benthic algal community composition was assessed using chemotaxonomy and bacterial viability was estimated using flow cytometry and a double-staining protocol. Multivariate analysis detected a significant effect of treatment and time on microphytobenthic community composition indicating a difference between control and low mesocosms and also between low and high treatments at Day 12 and Day 24 of the experiment. Nonetheless, microphytobenthos implied high resistance and redundancy of benthic algae to disturbance as all three treatments showed no significant difference in community structure between Day 0 and Day 58. Bacterial viability responded quickly to the high nutrient addition and was significantly lower than in the ‘control’ and ‘low’ treatments at Days 6 and 12. Both pelagic and benthic environmental variables were correlated to these changes in benthic community.
Coastal marine sediment, air and seawater samples were collected at six sampling stations in the Eastern Mediterranean Sea distant from pollutant point sources. All sediment samples were analyzed to ...determine polycyclic aromatic hydrocarbon (PAH), black carbon (BC) and organic carbon (OC) contents. The PAH contents of gaseous and seawater samples of the study were determined in order to evaluate the role of air–sea exchange as PAH nonpoint source to the marine sediments. The average concentration of the total PAHs (∑PAHs) in the sediments varied from 2.2 to 1056.2 ng g
−1 dry weight. The average BC and OC contents varied from 0.3 to 5.6 and from 2.9 to 21.4 mg g
−1 dry weight, respectively. ∑PAH concentration in the marine atmosphere varied from 20.0 to 83.2 ng m
−3. Air–water exchange flux (
F
A–W) estimation has indicated air transport as a significant source of PAHs to pristine marine sediments of Eastern Mediterranean. In addition, the significant correlation between the PAHs and the organic and soot carbon content further suggests the importance of atmospheric input of PAHs to the sediments.
Mediterranean fish farming has grown exponentially during the last 20 years. Although there is little evidence of the impact on the trophy status around fish farms, there are concerns that the ...release of solute wastes from aquaculture might affect larger scales in the ecosystem by changing the nutrient load. After combining information from various sources on waste production and on nutrient loads, it was concluded that the overall N and P waste from fish farms in the Mediterranean represents less than 5% of the total annual anthropogenic discharge, and the overall annual increase in P and N pools in the Mediterranean, under a production rate of 150000 tons, is less than 0.01%. The proportion of fish farming discharged nutrients was slightly higher in the eastern Mediterranean. A simple model was used to assess the long-term effects of nutrients released from various sources taking into account the water renewal rate in the Mediterranean. We conclude that, in the long term, fish farm waste could cause a 1% increase in nutrient concentrations in contrast to other anthropogenic activities which might double the Mediterranean nutrient pool.
The potential effects of climate change on the distribution of benthic species commonly used in marine ecological quality assessment were investigated using a spatial modelling approach. In this ...work, the relevance of the ecological groups that macrofaunal molluscs are assigned according to their sensitivity or tolerance to environmental disturbance was examined under the scope of the RCP 8.5 severe emissions scenario. The effects of climate change were more profound on species that are indicative of a specific suite of climatic conditions regarding temperature and salinity. Significant loss of habitat suitability was observed for the tolerant species Corbula gibba and Abra prismatica whereas the sensitive species Moerella donacina was least affected. In contrast, an overall expansion of the distributional potential was observed for the sensitive species Flexopecten hyalinus as newly suitable habitats are formed. As hypothesised, the current ecological grouping that depicts the sensitivity of a benthic species to an environmental stressor is irrelevant when assessing the effects of climate change. We propose a new standpoint of using benthic species as biotic tools based on their ecological niche requirements.
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•Climate change is expected to affect the distribution of benthic indicator species.•The current ecological grouping is irrelevant under the scope of climate change.•New perspective on the use of benthic species as biotic tools
Concentrations of 27 metals and elements were investigated in the tissues of 28 demersal and pelagic marine fish species from the Eastern Mediterranean Sea. The analysis indicated highest ...concentrations of accumulation for the majority of elements in the gills, liver, and scales; whereas, lowest assimilation of elements was reported in the muscle. Pelagic fish accumulated higher concentrations of elements than demersal fish. An inverse correlation due to the growth dilution effect was revealed among element concentrations in the gills, liver, muscle, and skin tissues, and fish size. Patterns of biomagnification for Cs solely were recorded in the muscle and patterns of biodilution for most elements were evident in the gills, liver, muscle, and skin tissues. A positive correlation was determined between trophic level and element concentrations in the scales which could not only be associated with fish diet, but also with metal concentrations in the ambient environment and scales size.
•Elements were measured in tissues of fish species from a marine food web.•Patterns of biomagnifications were recorded only for Cs in muscle tissue.•Patterns of biodilution were observed for elements in most tissues except scales.•Inverse relationship was found between element content in tissues and fish size.•Elements accumulated mostly in gills, liver, scales and finally muscle tissues.
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