Microplastic and Marine Microbial Diversity

The microplastic and seawater were sampled from two sites representing two separate marine environments–one in the Atlantic Ocean (Portugal site) and one in the eastern Mediterranean Sea (Israel site). The exact locations were 0.5–1.2 km from the shoreline of Yarkon estuary, Tel Aviv, Israel (32°06′35.7”N, 34°46′18.7″E) and of the Sado estuary, Setubal, Portugal (38°28′22.2”N 8°58′28.3”W; Figure 1). The samples were collected from the sea surface in both locations in the winter (February/March) and in the summer (July) of 2021 using a manta net (Hydro-Bios, Microplastic net, 438,217), with a mesh size of 300 μm and mouth opening of 30 × 15 cm. The manta net was towed from a research vessel at a speed of 2–3 knots for 20–30 min in parallel to the coastline (3 times on the same line). The water volume filtered through the net during each tow was calculated from flow meter counts (Hydro-Bios-438,110) using the expression number of revolutions x 0.3 x net opening area (m²)/1000 = volume m³ (Supplementary Table S1). Physico-chemical parameters (water temperature, salinity, and depth) were registered (Table 1) with a portable multiparameter probe (HI98194 Multiparameter, HANNA Instruments).
Microplastic particles recovered from the collecting cod-end of the net were rinsed in filtered artificial seawater. Seawater from the site was sampled using sterile sampling bottles. For DNA metabarcoding analysis of the plastic microbiome, 10 microplastic particles were randomly picked up from each sample and the rest was kept in sea water for the characterization of the microplastic. For DNA metabarcoding analysis of the water microbiome, 0.5 L of the sampled water was filtered onto a 0.22 μm polyethersulfone membrane (Millipore) using a 20 l/min pump (MRC).