<i>Cladophora</i> spp. (Chlorophyta) modulate environment and create a habitat for microalgae in hypersaline waters

<i>Cladophora</i> spp. constantly or periodically form floating and benthic mats in Crimean hypersaline lakes and lagoons. In 2017–2018, characteristics of the <i>Cladophora</i> mats and the microalgae on <i>Cladophora</i> filaments were studied employing field research and microscopy. The whole <i>Cladophora</i> mat has a vertical structure, including the upper and lower layers of the floating mat and benthic mat. In total, 50 species of microalgae were found: 40 of them belonged to Bacillariophyta (Bacillariophyceae and Mediophyceae), two to Haptophyta (Coccolithophyceae), four to Miozoa (Dinophyceae), one to Chlorophyta (Zygnematophyceae) and three to Cyanobacteria (Cyanophyceae). Floating layers of the mat differed significantly in species composition from the benthic mat. The total abundance of microalgae and their biomass on <i>Cladophora</i> (per unit area of filaments) varied widely within sampling sites from 3.79 × 10⁶ to 5.04 × 10⁸ cells m^–2 and 2.6 to 2197.8 mg m^–2. The total mass of microalgae achieved more than 32% of the mass of <i>Cladophora</i>, averaging 7.7% (standard deviation = 13.3).