Microplastic and ichthyoplankton in the Ukrainian waters of the Black Sea

The ability of planktonic and neustonic organisms to feed on microplastics and subsequently transfer it through the marine food web has been studied extensively. However, there are no studies on microplastic in the Northwestern Black Sea. The present study assesses the diversity and spatial distribution of microplastics and ichthyoplankton in two surface layers: 0-5 cm (neuston surface layer; NL) and 5-20 cm (hyponeuston layer; HL). The sampling was undertaken in June 2020 - October 2021 in the coastal (CW) and open (OW) waters of the Northwestern Black Sea. Microplastics was observed at all studied sites and was composed of fibres (75 %) and fragments (25 %). Black and red fibres were the most abundant type of fibre, and black particles dominated the fragments. Four types of polymers were identified by Raman spectroscopy: polyethylene, polyester, polyurethane, polypropylene. The concentration of microplastics near the coast significantly exceeded that of open waters; the average microplastics concentration in the CW reached 136+74 (+SE) and 46+30 particles.m-3 in the NL and HL, respectively, whereas it reached 18+3 and 2+0.8 particles.m-3 in the NL and HL of the OW, respectively. In the NL, ichthyoplankton was found only at 31 % of the sites, and at only 24 % of sites in the HL. In total, 6 species of fish were recorded. The most abundant species was the European anchovy, one of the main commercial species in the Black Sea. The ratio of microplastics to ichthyoplankton was 0.34 (or 1:2.87) for both layers, where ichthyoplankton was present. When considering all studied sites, the ratio of microplastics to ichthyoplankton was 1.07 (or 1:0.93). As ichthyoplankton is an ephemeral component of the neuston community, but microplastics is omnipresent, we may consider that comparable densities of microplastics:ichthyoplankton favour their interrelation, negative effect, and transport through the food web.