Diatom and cyanobacteria communities on artificial polymer substrates in the Crimean coastal waters of the Black Sea

Eukaryotic phototrophs of the plastisphere in the Southeastern Black Sea

Plastics, as artificial substrates in water, are rapidly colonized by microorganisms, forming the plastisphere. Eukaryotic phototrophs of the plastisphere were studied on 46 seafloor plastic samples, representing 11 polymer types, in the Southeast Black Sea during March and July 2022. The plastisphere included 55 species from Heterokontophyta phylum (incl. Coscinodiscophycea (4), Mediophyceae (3), Bacillariophyceae (45), Dictyophyceae (1)), and Haptophyta (1). Common species were Bacillaria paxillifera, Tabularia parva, Cocconeis scutellum, and Licmophora flabellata. Octactis speculum and Emiliana huxleyi were newly reported for the plastisphere, and Thalassiosira curviseriata was recorded for the first time in the Black Sea. Two potentially harmful algae and five bloom-forming species were identified. Shannon Diversity Index values ranged from 0 to 2.9, with the highest diversity on PE/PVA and PES samples and the lowest on PE. Habitat preferences showed 34 species associated with plankton-benthic or benthic microalgae. PERMANOVA analysis revealed that polymer type explained 11.9 %-15.8 % of species composition variation. Transparent and black plastics hosted the most species, while multicolor plastics had the fewest. This study highlights that diverse microbial communities, particularly diatoms, colonize plastics in the Black Sea. Plastics can transport harmful species, posing ecological risks by disrupting benthic ecosystems, nutrient cycles, and ecosystem services like carbon storage and sediment stabilization. Our findings contribute understanding of the ecological and economic impacts of plastic debris at the seafloor.

Teratogenic effects of environmental concentration of plastic particles on freshwater organisms

Given the widespread presence of plastics, especially in micro- and nanoscale sizes, in freshwater systems, it is crucial to identify a suitable model organism for assessing the potential toxic and teratogenic effects of exposure to plastic particles. Until now, the early life stage of freshwater organisms and the regeneration capacity in relation to plastic particles exposure is a still poorly investigated topic. In this study, we examine the teratogenic effect on diatom Cocconeis placentula and cnidarian Hydra vulgaris under controlled exposure conditions of poly(styrene-co-methyl methacrylate) (P(S-co-MMA)) particles. Significant effects were observed at the lowest concentrations (0.1 μg/L). A significant increase in the teratological frequency in C. placentula and a significant decrease in the regeneration rate in H. vulgaris were found at the lowest concentration. The delay in hydra regeneration impaired the feeding capacity and tentacles reactivity at 96 h of exposure. No effects on diatom growth were observed upon exposure to P(S-co-MMA) particles (0.1, 1, 100, 10,000 μg/L) for 28 days and these findings agree with other studies investigating algal growth. The application of the Teratogenic Risk Index, modified for diatoms, highlighted a moderate risk for the lowest concentration evaluating C. placentula and low risk at the lowest and the highest concentrations considering H. vulgaris. This study suggests the importance of testing organisms belonging to different trophic levels as diverse teratogenic effects can be found and the need to evaluate environmentally relevant concentrations of plastic particles.

Vertical and seasonal variations in biofilm formation on plastic substrates in coastal waters of the Black Sea

Plastic contamination of the marine environment is an increasing concern worldwide. Therefore, it is important to understand the kinetics of biofilms on plastics to study their behavior, fate, and transport pathways in the ocean. In this study, the vertical and seasonal variations in biofouling formation on transparent polyethylene terephthalate (PET) plastic fragments in the Southwest Crimea coastal waters of the Black Sea were investigated. Biofilms were identified in the transient light as 'dark spots' on the plastic surface, for which the numbers, size, and area were measured using specialized software. The rate of biofouling in the surface water layer was lower than those found in the middle and near-bottom water column, which could be due to a damaging effect of turbulent mixing on the biofilm. The highest rates of biofouling and diverse community were observed during the summer. The epibiotic assembly was represented by diatoms (11 taxa), dinoflagellates (3 taxa), green algae, filamentous cyanobacteria, small flagellates, and ciliates. Significant differences between the biofouling rates observed in different seasons made it difficult to estimate the period of time the plastic substrate has been in the marine environment. It was proposed to use the green alga Phycopeltis arundinacea (Montgn) De Tender et al., 2015 as a bioindicator to study the age of the biofouling community. Discoid thalli were identified at all stages of colonization of the plastic fragments in different seasons. Results obtained in this study demonstrate that biofouling organisms may be good model organisms in revealing age of biofilm formation and longevity of plastic debris in the ocean. Consequently, it is proposed that such biofouling organisms could be used as target species to monitor the biodegradation of plastic debris.

Harmful algae and pathogens on plastics in three mediterranean coastal lagoons

Plastic is now a pervasive pollutant in all marine ecosystems. The microplastics and macroplastic debris were studied in three French Mediterranean coastal lagoons (Prevost, Biguglia and Diana lagoons), displaying different environmental characteristics. In addition, biofilm samples were analyzed over the seasons to quantify and identify microalgae communities colonizing macroplastics, and determine potentially harmful microorganisms. Results indicate low but highly variable concentrations of microplastics, in relation to the period and location of sampling. Micro-Raman spectroscopy analyses revealed that the majority of macroplastic debris corresponded to polyethylene (PE) and low-density polyethylene (LDPE), and to a far lesser extent to polypropylene (PP). The observations by Scanning Electron Microscopy of microalgae communities colonizing macroplastic debris demonstrated differences depending on the seasons, with higher amounts in spring and summer, but without any variation between lagoons and polymers. Among the Diatomophyceae, the most dominant genera were Amphora spp., Cocconeis spp., and Navicula spp.. Cyanobacteria and Dinophyceae such as Prorocentrum cordatum, a potentially toxic species, were also found sporadically. The use of Primer specific DNA amplification tools enabled us to detect potentially harmful microorganisms colonizing plastics, such as Alexandrium minutum or Vibrio spp. An additional in situ experiment performed over one year revealed an increase in the diversity of colonizing microalgae in relation to the duration of immersion for the three tested polymers PE, LDPE and polyethylene terephthalates (PET). Vibrio settled durably after two weeks of immersion, whatever the polymer. This study confirms that Mediterranean coastal lagoons are vulnerable to the presence of macroplastic debris that may passively host and transport various species, including some potentially harmful algal and bacterial microorganisms.

Biofouling growth on plastic substrates: Experimental studies in the Black Sea

Despite long-term research on marine litter there is still insufficient knowledge about benthic organisms associated with these substrates, especially experimental studies and methodology of sampling for complex biofouling assemblages. To predict the fate of plastic in the marine environment it is necessary to know how long the macrolitter can stay in different sea matrices and what are the steps of colonisation by marine organisms. The experiments were carried out during various seasons in situ in the north-western Black Sea coastal area. Three new types of the experimental constructions intended for different durations of exposure (1–10 months) were designed. This article is the first to present the methodology and the results of complex experiments investigating marine fouling (from microalgae to meio- and macrofauna) on plastic surfaces. Overall, 28 genera of microalgae, 13 major groups of meiobenthos and 36 species of macrofauna were found on plastic during the experiments. The microalgae fouling was mainly formed by representatives of genus Cocconeis. The species composition of microalgae was common for the research area. The average density and biomass of meiobenthos were the greatest on I construction type after 8 months of exposure. In the total macrozoobenthos biomass and density of Bivalvia and Crustacea dominated, respectively. The obtained results on the interaction between fouling organisms and plastic materials in the marine environment form an important contribution to the understanding of the "good ecological status" of the sea. Additional studies based on the tested methodology could be used as a component of ecological monitoring during development and implementation of the approaches of the Marine Strategy (descriptor 10).

Diatom diversity, distribution and ecology in Mediterranean ecosystems of Abrau Peninsula, north-western Caucasus

Background

The North Caucasus is an extensive region with a multitude of landscapes and high biological diversity. Amongst various ecosystems, the xerophytic sub-Mediterranean forests of the Abrau Peninsula (Utrish State Nature Reserve) and its vicinity are unique but have been poorly studied. The diversity of diatoms in North Caucasian ecosystems have been studied partially and only little information is available about their presence and distribution on the Abrau Peninsula. Here, we present a comprehensive check-list of diatoms sampled during a July 2021 field campaign. Samples were collected in 67 sites, including 39 permanent streams, 21 temporal (puddles) and seven permanent waterbodies. Results of the current study contribute to improving the knowledge about diatoms in the north-western Caucasus and its sub-Mediterranean ecosystems in particular.

New information

Here, we provide a detailed dataset that contains 215 freshwater and brackish diatom occurrences collected during a field campaign in July 2021. A total of 88 diatom (Bacillariophyta) taxa which belong to 12 orders, 25 families and 39 genera were collected. The genera with the highest number of occurrences per site were Gomphonema (26), Nitzschia (22), Navicula (20), Cocconeis (14), Amphora (14), Achnanthidium (14) and Planothidium (11). The genera with the highest number of infrageneric taxa were Nitzschia (8), Navicula (7), Gomphonema (6) and Mastogloia (5). Naviculablazencicae, known as the endemic of the Lake Prespa (Levkov 2007) is found from two sites in our study. Three specimens of the genus Mastogloia could not be assigned to a known species and may represent new diatom species. Distribution and ecology data are provided for each taxa. Occurrence data are given. Statistical analysis of diatom communities showed a significant dependence on habitat type and their ecological conditions.

Environmental Heterogeneity Determines Diatom Colonisation on Artificial Substrata: Implications for Biomonitoring in Coastal Marine Waters

Benthic diatoms form an important component of the microphytobenthos and have long been utilised as suitable bioindicators in aquatic systems. However, knowledge on benthic diatom community succession on hard substrata (biofilm) remains understudied in austral marine coastal systems. In this study, we investigated benthic diatom colonisation on artificial substrates (Plexiglass) over a period of 5 weeks at two locations with different physical environments along the warm temperate coast of South Africa. Results revealed relatively similar physico-chemical conditions but highly contrasting diatom community development were observed between the two sites. While there were some shared taxa, site-specific dynamics resulted in significantly different diatom species diversity and richness, facilitated by common (e.g., Nitzschia ventricosa and Cocconeis scutellum) and a large percentage of rarely observed species such as Cocconeis testudo and Lyrella lyra. A total of 134 species belonging to 44 genera were observed during the study. The overall diatom composition differed spatio-temporally during the experimental period, with the fluctuating species occurrences and abundances highlighting the rapid microalgal species turnover within days, under natural conditions. Environmental variables were shown to have varying influences as drivers of the diatom community descriptors. Multivariate modelling confirmed that study site and the interaction between site and sampling occasion were important predictors of diatom abundances, and the overall observed community composition. The current results suggest that benthic diatoms on artificial substrata could be incorporated as suitable indicators of change along the coastline subject to further investigations, taking into account site-specific differences driven by habitat complexity and environmental variability. The experimental method proved to be efficient and can be implemented to study the response of benthic diatoms to localised nutrient enrichment around the coastline.