Phytoplankton composition with an emphasis of Cyanobacteria and their toxins as an indicator for the ecological status of Lake Vaya (Bulgaria) - part of the Via Pontica migration route

The first eco-assessment of phytoplankton assemblages associated with environmental conditions of different lakes in the Western Black Sea basin of Türkiye

Lakes play a vital role in supporting biodiversity, providing water resources, regulating climate, cycling nutrients, and offering recreational opportunities. Despite their importance for environmental health and human well-being, lakes face significant pressures in the Anthropocene era. The present work seeks to assess the species-environment interactions and the ecological status of six lakes in the Western Black Sea basin of Türkiye utilizing phytoplankton metrics during wet and dry periods. Canonical correspondence analysis revealed a significant correlation equal to 98.5% between phytoplankton species and environmental stressors during two hydrological periods. Electrical conductivity (EC), pH, total organic carbon (TOC), and temperature were the most influential environmental factors affecting phytoplankton distribution in lakes (p = 0.002). Lake Sarıkum, a brackish habitat, was under high EC and pH pressure and is characterized by pollution-tolerant species. Lake Yeniçağa associated with TOC is characterized by some species, such as Anabaenopsis milleri, Chroococcus turgidus, Pseudoschroederia robusta, Aphanocapsa sp., Merismopedia glauca, Micractinium quadrisetum, and Microcystis aeruginosa. Lake Abant is located on the opposite side of EC, TOC, and temperature, which was associated with some species such as Cymbella affinis, Achnanthidium minutissimum, Encyonema minutum, E. silesiacum, and Dinobryon divergens. Results of the phyto-assessment displayed that the ecological status (ES) of the sampling stations during the rainy and dry periods varied from bad to high. The modified phytoplankton trophic index (MPTI) exhibited that a moderate ES was found in Lakes Sarıkum and Yeniçağa, while others had a good ES. The present study confirmed that phytoplankton communities are strongly linked to the ecological status of lakes in the Western Black Sea basin, which could be assessed using the MPTI.

Allelopathic Potential of the Cyanotoxins Microcystin-LR and Cylindrospermopsin on Green Algae

Allelopathic interactions are widespread in all aquatic habitats, among all groups of aquatic primary biomass producers, including cyanobacteria. Cyanobacteria are producers of potent toxins called cyanotoxins, whose biological and ecological roles, including their allelopathic influence, are still incompletely understood. The allelopathic potential of the cyanotoxins microcystin-LR (MC-LR) and cylindrospermopsin (CYL) on green algae (Chlamydomonas asymmetrica, Dunaliella salina, and Scenedesmus obtusiusculus) was established. Time-dependent inhibitory effects on the growth and motility of the green algae exposed to cyanotoxins were detected. Changes in their morphology (cell shape, granulation of the cytoplasm, and loss of flagella) were also observed. The cyanotoxins MC-LR and CYL were found to affect photosynthesis to varying degrees in the green algae Chlamydomonas asymmetrica, Dunaliella salina, and Scenedesmus obtusiusculus, affecting chlorophyll fluorescence parameters such as the maximum photochemical activity (F_v/F_m) of photosystem II (PSII), the non-photochemical quenching of chlorophyll fluorescence (NPQ), and the quantum yield of the unregulated energy dissipation Y(NO) in PSII. In the context of ongoing climate change and the associated expectations of the increased frequency of cyanobacterial blooms and released cyanotoxins, our results demonstrated the possible allelopathic role of cyanotoxins on competing autotrophs in the phytoplankton communities.

Microcystin production by oscillatorialean cyanobacteria isolated from cryopreserved Antarctic mats

Twenty cyanobacterial strains of eight morphospecies isolated from deep-frozen (-15 °C) mat samples originally collected on Ross Island, in Victoria Land, and on the McMurdo Ice Shelf were screened for the presence of genes encoding for production of anatoxins, cylindrospermopsin, microcystin/nodularin and saxitoxin. One strain of each of Microcoleus autumnalis and Phormidesmis priestleyi and two strains of Wilmottia murrayi were found to produce microcystin. No toxin production was detected in the other 16 strains representing five species. The four toxin-producing strains were characterised using both morphological and molecular approaches. Phylogenetic analyses using partial 16S rRNA sequences were consistent with the morphological identification of all four strains. They were all found to contain a fragment of the mcyE gene, which is involved in microcystin biosynthesis. ELISA analysis of extracts from cultures of these strains confirmed the presence of low concentrations of microcystin: 0.35 μg/L in M. autumnalis, <0.15 μg/L in P. priestleyi, 1.60 μg/L in W. murrayi strain 1 and 0.9 μg/L in W. murrayi strain 2. This study includes the first report of microcystin synthesis by W. murrayi.

Microalgae Growth Inhibition-Based Reservoirs Water Quality Assessment to Identify Ecotoxicological Risks

This work intended to assess the adaptability of bioassay with Raphidocelis subcapitata to be used as a complement to the water quality assessment parameters of reservoirs imposed by the European Water Framework Directive (WFD). Thus, water samples of Portuguese reservoirs (Miranda, Pocinho, Aguieira, and Alqueva) were analyzed in three sampling periods (spring and autumn 2019, and spring 2020). A physical and chemical report of waters was also performed. R. subcapitata assay proved to be sensitive, indicating the presence of a potential perturbation that was not always associated with chemical analysis performed. In general, in the spring samplings, the water samples showed more disturbances to R. subcapitata, which in some situations may be associated with the higher content of nutrients and metals. Microalgae assay can be an effective complementary tool to indicate the ecotoxicological potential since they responded quickly to all sample components of water samples, in a wide-ranging variety of water conditions (different sites in several reservoirs). High similarities between the final ecotoxicological and the ecological potentials, according to the WFD parameters, were detected. The ecotoxicological approach based on our results allowed to confirm that bioassays with R. subcapitata are suitable and sensible to detect perturbations.