We tracked temporal changes in protist diversity at the Long Term Ecological Research (LTER) station MareChiara in the Gulf of Naples (Mediterranean Sea) on eight dates in 2011 using V4 Illumina sequencing. Samples for metabarcoding analyses were collected from surface waters at the LTER-MC station on eight dates from February to December 2011. The dates were selected based on light microscopy phytoplankton data, which were used as proxies for the seasonal phase and trophic status of the system. For DNA extraction, about 3 litres of surface sample (0.5 m) was filtered under mild pressure on each of two cellulose ester filters (47 mm diameter, 1.2 µm pore-size, EMD Millipore, USA). Filters were immediately frozen with liquid nitrogen and stored at -80?C. Nextera dual index approach and to 2 × 250 bp were applied for V4 region sequencing on a MiSeq platform.