Zooplankton constitute a key trophic link between primary producers and higher trophic levels in marine food webs, making them important indicators of environmental and climatic change. However, in many marine systems, long-term data are still limited, and major interannual fluctuations in zooplankton biomass and composition remain poorly understood. The article presents data assessing the impact of climate and warming in the Black Sea region on the interannual dynamics of macro- and mesozooplankton biomass in the outer shelf of Sevastopol Bay from 2002 to 2021. Over this period, the biomass of organic matter accumulated by gelatinous species has decreased, while that of mesozooplankton has increased by 15-20 %. Winter warming, which minimises convective mixing and nutrient transport into the zone of active photosynthesis, may have negatively affected the populations of the jellyfish Aurelia aurita, the dinoflagellate Noctiluca scintillans, and the chaetognath Parasagitta setosa. The increase in sea surface temperature (SST) during January-March appears to have a positive effect on microphages such as the copepod Paracalanus parvus and the appendicularian Oikopleura dioica. Early increases in SST during April-May, along with a synchronous improvement in the biogenic regime of the upper pelagic zone, suggest an increase in the biomass of large copepods (Calanus euxinus, Paracalanus elongatus, Acartia clausi and Centropages ponticus), regardless of their temperature tolerances. The extreme increase in SST during July-August was accompanied by the early development of ctenophores Beroe ovata and Mnemiopsis leidyi, as well as small crustaceans like Penilia avirostris and Oithona davisae. Overall, outer shelf macro- and mesozooplankton communities have remained relatively stable in species composition and total biomass of organic carbon. This study highlights the complex response of Black Sea macro- and mesozooplankton communities to regional warming, with species-specific seasonal sensitivities to changing environmental conditions.

In this study, marine litter from the seafloor in the Sea of Marmara obtained through several trawl surveys between 1994 and 2021 is evaluated. When the levels of marine litter on the seabed of the Sea of Marmara are considered, there appears a significant increase in the quantity after the year 2000, with this increase particularly concentrating in the Gulf of Izmit and Gemlik, where the effect of current systems is prominent. In 2000, the quantity of plastic waste per unit area was approximately 40 items/km(2), while in 2016 it exceeded 800 items/km(2). Considering the total area for the 20-200 m in the Sea of Marmara, seafloor litter accumulation was calculated as 335 tons in 1994 but 5037 tons in 2021. In 2000, plastic waste accounted for 54% of the total, rising to 75% in 2016, 95% in 2019, and 67% in 2021. The L1 group, which represents plastic waste, is mainly contributed by plastic bags. In 2000, plastic bags accounted for 23% of the total, increasing to 83% in 2019. However, this value significantly decreased in 2021 whilst the "Packaging Plastic" subcategory also increased from 4% in 2000 to 48% in 2016 and 2021. Our analyses revealed that as the depth increases, the quantity and diversity of marine litter decrease, with plastic litter remaining dominant even in deeper waters.

The study conducted in the eastern Sea of Marmara from 2016 to 2022 aimed to investigate the spatio-temporal distributions of mesozooplankton in relation to changing environmental conditions. A total of 43 zooplankton taxa were identified, with the number of species varying between 4 and 19 in the brackish upper layer (resembling the Black Sea) and between 1 and 17 in the saline lower layer (resembling the Mediterranean Sea). The abundances of zooplankton ranged from 28 to 43,359 ind.m(-3) in the upper layer and from 5 to 3,851 ind.m(-3) in the lower layer. Significant differences were observed between the upper and lower layers in terms of the number of species, total zooplankton abundances, evenness, and Shannon diversity (p<0.0001). The most significant differences in zooplankton abundance and community structure were found to be seasonal rather than inter-year or regional variations. The highest total zooplankton abundance was recorded at station M14 during the summer season (June 2022), primarily due to the presence of Paracalanus parvus and Penilia avirostris (906 ind.m(-3) and 722 ind.m(-3), respectively). The heterotrophic dinoflagellate Noctiluca scintillans, a major component of net samples in the Sea of Marmara, exhibited a clear seasonal distribution, with higher abundances consistently observed during winter months. The highest abundance of Noctiluca scintillans was recorded in February 2016 at station MD102 (42,514 ind.m(-3)). Paracalanus parvus, Acartia clausi, and Oithona nana were identified as important year-round species in both the upper and lower layers of the Sea of Marmara. The presence of N. scintillans and P. avirostris distinguished the upper layer communities from the lower layer, with N. scintillans being more prevalent during winter and P. avirostris during summer. Notably, P. avirostris exhibited very low abundances during the summers of 2019, 2021, and 2022. The large-scale mucilage event that occurred in June 2021 had a significant impact on zooplankton, as evidenced by the low abundance and biomass observed during this period. The chlorophyll-a values, which reflect phytoplankton biomass, increased sharply during the dominating mucilage event, ranging from 12.2 to 14.2 mu g.l(-1). Overall, this study emphasizes the vulnerability of the Sea of Marmara ecosystem, particularly zooplankton, to large-scale environmental disturbances such as mucilage events.

Antioxidant capacity, chlorophyll, marker pigment, and protein contents of four diatoms (Helicotheca tamesis, Haslea silbo, Nitzschia navis-varingica, and Asterionellopsis glacialis) and one cyanobacterium (Spirulina subsalsa) have been investigated. N. navis-varingica exhibited the highest chlorophyll a, fucoxanthin, ascorbic acid, and total antioxidant capacity (TAC) among the five species studied. Cupric-reducing antioxidant capacities of N. navis-varingica and H. silbo were higher than other species studied. A. glacialis exhibited the highest total superoxide dismutase (SOD) activity, H. silbo displayed the highest ascorbate peroxidase (APX) activity, and Spirulina subsalsa had the maximum phenolic and protein contents. Overall, compared to other studies in the literature, the contents of phenolics were at a moderate level, and ascorbic acid content, APX activity, and TAC were remarkably high. These findings emphasize the potential for novel applications of the microalgal species used in this study in biotechnology including pharmaceutical, cosmeceutical, food, and feed industries.

This study presents the first definitive confirmation of microplastic presence in the human stomach, based on samples from 26 cadavers. 97 microplastic particles were extracted from stomach contents, across all 26 individuals, revealing a universal prevalence of microplastics in the cadavers. Morphological analysis of the extracted particles unveiled distinct shapes, with fibers constituting the majority (52.04 %), followed by fragments (39.80 %) and films (8.16 %). The average quantity of microplastics per individual was calculated to be 9.4 ± 10.4 particles, with an estimated daily intake of microplastics at 32.2 particles per day. These figures are lower than estimates derived from both daily microplastic consumption alone and notably, those calculated from stool analyses. Our study also suggests that the breakdown or transformation of microplastics cannot be ruled out during their passage through the digestive tract. Although the number of microplastics in stomach contents reported in this study was even lower than the daily microplastic intake rates reported in the literature, it provides conclusive evidence for the presence of microplastics in the human stomach and provides important preliminary data in terms of the risks that may arise for human health.

The article presents data assessing the impact of climate and warming in the Black Sea region on the interannual dynamics of the biomass of macro- and mesoplankton at the outer shelf of the Sevastopol Bay of the Black Sea in 2002-2021. Over these years, the biomass of organic matter accumulated by gelatinous species has decreased, while that of mesozooplankton has increased by 15–20%. Four significant seasonal periods are identified for the development of mass macro- and mesoplankton in the sea. Winter warming, which minimizes convective mixing of waters and the transport of nutrients into the zone of active photosynthesis, negatively affected the populations of the jellyfish Aurelia aurita, the dinoflagellate Noctiluca scintillans, and the chaetognath Parasagitta setosa. The increase in sea surface temperature (SST) in January-March was perceived positively by microphages such as the copepods Paracalanus parvus and Oithona similis and the appendicularian Oikopleura dioica. An early warm spring, with an increase in SST in April-May and a synchronous improvement in the biogenic regime of the upper pelagic zone, led to an increase in the biomass of all the largest copepods (Calanus euxinus, Paracalanus elongatus, Acartia clausi and Centropages ponticus), albeit with temperature tolerances. The extreme increase in SST in July–August was accompanied by the early development of ctenophores Beroe ovata and Mnemiopsis leidyi, as well as small crustaceans, Penilia avirostris and Oithona davisae. In general, while indirect impacts of warming are evident, the direct influence of climate on macro- and mesoplankton communities on the outer shelf has maintained a relatively stable pattern over the last two decades. This resilience is attributed to the organisms' capacity to endure conditions in the deep tolerant zone. This study highlights the intricate response of Black Sea macro- and mesoplankton communities to regional warming, with notable shifts in biomass dynamics, seasonal patterns, and species-specific sensitivities, underscoring the complex interplay between climatic factors in the Black Sea.

Invasive species are among the most threatening factors to the Caspian Sea’s diversity and unique aquatic resources. After the appearance of the ctenophore predator Beroe ovata in 2019, the dynamics of the previous ctenophore invader Mnemiopsis leidyi and mesozooplankton stocks in the south-western Caspian Sea were investigated in December, April, July and November 2020–2021. The invasion of the Caspian Sea by the voracious zooplanktivorous M. leidyi by the end of the 1990s had devastated trophic levels of life in this enclosed ecosystem causing the complete disappearance or severe decreases of many zooplankton species. Since its first appearance, the number of B. ovata increased 1.5-fold between 2019, 2020 and 2021. Conversely, the average number of M. leidyi had decreased from an average (abundance ± standard deviation) 314 ± 104 ind. m–3 (n = 485) for the period from 2001–2019 to 141 ± 152 ind. m–3 (n = 48) in 2020 and 2021 which is the lowest reported average value for M. leidyi. Simultaneously, both the species number and abundance of mesozooplankton in 2020 and 2021 were observed to increase compared to previous years. From one Copepoda species in the 2001–2018 period, three species; Acartia tonsa, Calanipeda aquaedulcis and Halicyclops sarsi increased in 2020 and 2021. After years of disappearance, the Cladocera Evadne ananyx typica, Podonevadne camptonyx and the endemic Podonevadne trigona were again present in the samples. In this study, abundances of several species (such as the Copepoda A. tonsa, the Cladocera Podon polyphemoides), Bivalvia larvae and Cirripedia larvae) were observed to increase substantially (between 2 to 7 fold) compared to the 2001–2018 period. The mass appearance of B. ovata in the southern Caspian Sea since 2019, through its predation on M. leidyi, has resulted in the rise of species numbers and mesozooplankton abundance in the south-western Caspian Sea. Our results here support earlier results of observations performed in for the Black Sea where the ctenophore predator Beroe ovata had positive cascading effects on mesozooplankton in particular and on the ecosystem in general.

Aquatic environments are one of the final destinations for microplastics. In this review, a combination of systematic and narrative literature review was conducted to identify and summarise advances, gaps, and future directions in microplastic monitoring studies in the Turkish aquatic environment and in inhabiting aquatic organisms. A total of 62 peer-reviewed publications available on Web of Science were considered in the systematic review. Additionally, the current state of microplastic pollution in Turkish aquatic environments which includes marine and freshwater ecosystems, as well as aquatic organisms, and sources and characteristics of microplastics were reviewed narratively. Türkiye`s position on the global plastic treaty and mitigation practices were also addressed. Although an increase in the number of publications over time was observed, the number and extent of studies carried out in freshwater ecosystems are limited. Strict legislation should be enacted and enforced to tackle plastic pollution in Türkiye. Additionally, nationwide, long-term monitoring studies at sufficiently regular intervals in aquatic environments should be considered.

Rivers are major transport pathways for microplastics to reach the oceans. Although gained much attention over the last few years, there is still a relatively lack of knowledge on microplastics in rivers. This study aims to investigate (i) spatiotemporal distribution of microplastics in an industrially polluted river, (ii) the relationship of microplastic abundance with river's morphological and hydrodynamic characteristics (iii) the potential sources of microplastics inferred from the particle characteristics including shape, size, color and type. To achieve these aims, water and sediment samples were collected from six sites upstream of the Ergene River in May 2019 and Sep 2020. According to the results, surface water had an average concentration of 4.65 & PLUSMN; 2.06 and 6.90 & PLUSMN; 5.16 items L-1 (mean & PLUSMN; standard deviation, n = 12), respectively for the May 2019 and September 2020 periods, whereas 97.90 & PLUSMN; 71.72 and 277.76 & PLUSMN; 207.21 items kg-1 (n = 18) were observed for the sediment compartment, respectively. Microplastic levels in water correlated positively with stream depth but negatively with channel width. Fibers were the dominating shape both in water (88%) and sediment (70%) and majority of the particles were black (49% in water and 39% in sediment) and blue (25% in water and 18% in sediment). According to Raman spectroscopic analysis, polyethylene terephthalate (PET, 28%) and polyamide (PA, 27%) were dominating polymers in water, while polystyrene (PS, 56%) were dominant in sediment. Compared to many other rivers, the Ergene River had excessive levels of microplastics. The research indicated that textile industries and effluents from organized industrial zones were the foremost contributor of microplastics in the river.

The coccolithophorid Ochrosphaera neapolitana was reported for the first time from samples obtained during a large-scale mucilage event in the Sea of Marmara in May 2022 in a previous study. We also found this species in our samples obtained about a year ago (i.e., in June 2021). In our study, O. neapolitana was further isolated and produced in the laboratory as a monoculture for further investigations using electron microscopy and molecular methods. Ochrosphaera neapolitana was identified using a small sub-unit (SSU) rRNA sequence and subsequent phylogenetic analysis. During the laboratory experiments, O. neapolitana was surprisingly observed to produce conspicuous levels of mucilage as a skim layer in mono- or multi-species cultures, mainly comprising other diatom species. This observation could be a significant milestone in understanding the reasons and mechanisms of mucilage events that occur in the Sea of Marmara.

We demonstrate a prototype multi-metric indicator-based assessment tool (i.e. Marine Litter Assessment Tool MALT) for mapping and identification of 'problem areas' and 'non-problem areas' regarding the occurrence of marine litter in Europe's seas. The study is based on a European-wide data set consisting of three marine litter indicators: (1) litter at the seafloor, (2) beach litter and (3) floating micro-litter. This publicly available data allowed litter status to be determined in 1,957,081 km2 (19.1 %) of the total area of Europe's seas (10,243,474 km2). Of the area assessed, 25.8 % (505,030 km2) was found to be 'non-problem areas' whilst 'problem areas' accounted for 74.2 % (1,452,051 km2). This indicates that marine litter is a large-scale problem in Europe's seas.

In April of both 2018 and 2019, one specimen each time of live Calanus finmarchicus adult females was found during collections of zooplankton samples near Sivri Ada in the Sea of Marmara. This was the first observation of live C. finmarchicus ( a native species of northern Atlantic waters) in the eastern Mediterranean Sea. This morphological study illustrates the similarity of C. finmarchicus specimens found in the Sea of Marmara with existing illustrations and descriptions of this species. It also shows the clear differences between this species and Calanus helgolandicus specimens collected during the same or earlier periods from the Marmara Sea. Transportation of C. finmarchi-cus to the Sea of Marmara is possible either via the lower current from the Aegean Sea or through the ballast waters of vessels. In any case, the occurrence of C. finmarchicus as a cold-water species in the Sea of Marmara is striking and attracts further investigations.

Microplastic pollution is a problem not only in the marine environment but also in freshwater ecosystems. Water flea (Daphnia magna) is one of the most common omnivorous cladocerans in freshwater ecosystems. In this study, the potential effects of microplastics (fluorescent polystyrene beads with dimensions of 6 microns) on the survival, growth and reproduction of Daphnia magna were examined during 21 days of laboratory experiments. Microplastics (MPs) were observed to be ingested alone or along with either the microalgae Chlorella vulgaris (Cv) or baker’s yeast (By). D. magna fed exclusively with microplastics showed a drastic decline in survival similar to that in the starving group. The least growth in total length or width was observed in Daphnia specimens fed only MPs and the starved groups. Daphia fed with a mixture of MPs/Cv or MPs/By produced a significantly (p < 0.05) lower number of ephippia. Our results show that high concentrations of microplastics adversely affect Daphnia magna populations.

Plastic pollution has threatened biodiversity and human health by shrinking habitats, reducing food quality, and limiting the activities of organisms. Therefore, global interest in discovering novel enzymes capable of degrading plastics has increased considerably. Within this context, the functional metagenomic approach, which allows for unlocking the functional potential of uncultivable microbial biodiversity, was used to discover a plastic-degrading enzyme. First, metagenomic libraries derived from microplastic-associated microbiota were screened for esterases capable of degrading both tributyrin and polycaprolactone. Clone KAD01 produced esterase highly active against p-nitrophenyl esters (C2–C16). The gene corresponding to the enzyme activity showed moderate identity (≤ 55.94

Microplastics sampled downstream from a total of eight rivers were analysed as the first attempt to determine microplastic composition in rivers and load to Mersin Bay, in the north-eastern Mediterranean Sea. With a share of 83.5%, fibres were the dominant category from all samples. Basic characteristics (form, colour, average size, polymer) of microplastics from these rivers were similar to those reported from the marine environment in Mersin bay. The overall average number of microplastics calculated for the eight rivers was determined as 293±59 particles/m3 equalling a load of 1200 billion items (mainly from the Göksu River) discharged annually to the north-eastern Mediterranean. This value equivalent to twice the total stock of microplastics within the water column in Mersin Bay, demonstrates that rivers are a primary source of microplastics pollution for the coastal seas.

We report the first occurrence of a diatom species, Nitzschia navis-varingica in the Sea of Marmara. Previously, this species was observed in the Mediterranean Sea in 2016. Samples were collected from the coast of Darıca, Istanbul, Turkey, on 22 June 2021 during a large-scale mucilage event. The species was isolated, cultured under laboratory conditions, and investigated with scanning electron microscopy and light microscopy.

The Mediterranean Sea is characterized by rich biodiversity, and its region hosts people living in several countries with a rich variety of cultures, but – at the same time – it is “under siege”, due to anthropogenic pressures. To address these pressures, many actions are needed aiming, among others, at establishing Ocean Literacy (OL) across the Mediterranean countries and preparing the future generation of Mediterranean Sea-literate citizens. Towards this aim, the present cross-national study investigated OL issues in relation to content knowledge, possible common misconceptions, attitudes, and the self-reported behavior of 2,533 middle school students from eight Mediterranean countries (Croatia, Cyprus, Egypt, Greece, Italy, Malta, Spain, and Turkey), as well as certain background elements (e.g., gender, grade level, environmental education experience, sources of relevant information). The results of this study revealed that middle school students of all studied countries possess a moderate level of ocean sciences content knowledge, while they showed satisfactory pro-environmental attitudes and behavior. These findings along with further research are expected to function as a baseline for the design, implementation, and launch of specifically targeted programs, educational activities, teaching resources, curricula, and school textbooks, which will be achieved through close collaboration between schools, universities, research institutes, and Ministries of Education, thus contributing to the future protection and sustainable development of the Mediterranean Sea region.

EDITORIAL article Front. Mar. Sci., 09 March 2022Sec.Marine Ecosystem Ecology https://doi.org/10.3389/fmars.2022.869618