DIATOM ALGAE ON THE PLASTIC SURFACES NEAR ZMIINIY ISLAND (THE BLACK SEA, UKRAINE)

In recent years there has been increasing interest in «plastisphere» studies and microalgae communities on plastic surfaces.Diatoms and cyanobacteria are the primary colonisers of the marine litter and main components of biofilms on plastic.
The diatom that directly attach to the plastic surfaces can affect its decomposition and structural changes influencing the degradation of marine litter to smaller fragments ending up in microplastics. In addition, lightweight plastics are capable to float and migrate throughout aquatic environments, becoming one more path of potential harmful and invasive species penetration.
The studies of biofouling on plastic substrates in the Black Sea started in 2018 (Sapozhnikov et al., 2020; Snigirova et al., 2019; 2022). The present study is focused on the species composition of diatomos n the polymer surface (polyethylene-terephthalate) near the Zmiiniy Island (N 45.266894; E 30.203224) the unique rocky island located in the marine protected area in Ukrainian marine waters. The plastic bottles, attached by the rope to the bottom, were collected in November 2018 on the depth of 9 m in the water column. The bottles were fully covered with marine biofouling (1.2-4.5 kg per item) representing the assemblage of Mitylus galloprovincialis. The state of biofouling and age of molluscs indicated that the bottles spent over 2 years in the marine environment. The biofilm diversity was analysed using temporary ethanol-glycerol slides and the permanent slides with Naphrax medium under the light microscopy; air-dried samples were proceeded under SEM.
In total over 46 species of diatoms were identified. Most of the species were common for the region. The genus spectrum includes 24 genera, among which the most species-rich representatives are: Amphora Ehrenb. (5 species), Navicula Ehrenb. (5), Nitzschia Hassall (5), Coconeis Ehrenb. (4), Licmophora C.Agardh (3), Diploneis Ehrenb. ex Cleve (3), Halamphora (Cleve) Mereschk. (2), Tabularia (Kützing) D.M.Williams ex Round (2). Other 16 genera were represented by a single species. The habitat preferences included plankto-benthic, benthic, and epilithic-epiphytic-benthic microalgae. The species diversity observed in the biofilm formed on plastic surfaces consisted of cosmopolitan species (65%) and boreal species (35%). Under the macrofauna fouling we observed the cover of the surface by colonies of Navicula sp., Berkeleya sp., separate fragments contained scattering of Cyclotella baltica, Cocconeis neothumensis var. marina were revealed. Diatoms were distributed within the matrix of cyanobacteria and other diatom colonies. The main differences in the algae biofilms on the seafloor litter compared to other locations from the Northwestern Black Sea lied in absence of the dense layer of the Cocconeis species on the plastic from Zmiiniy area. We can explain that with the differences of the eutrophic conditions between these areas, which affect the biofilm composition (Minicheva et al., 2021). The signs of the decomposition of the plastic surface were noticed.