Here we analysed the microbial ecology of marine macroalgae, surrounding seawater, and surrounding sediment at Weihai, China (122.12 N, 37.56 E). Metagenomic sequencing of marine macroalgae, surrounding seawater, and surrounding sediment samples collected on 4 sampling dates in the year 2018-2019. For macroalgae, loosely attached microorganisms were removed by washing whole macroalgae thrice in flasks about 80% filled with sterile seawater on a shaker and collecting the washing suspensions in sterile bottles. Algae were then put in sterile seawater and remaining bacteria were removed by ultrasonication (2x 60s, 50-60 kHz). Suspensions with removed bacteria of each sample were subsequently pooled with the previously obtained washing suspensions. Then the washing suspension of each sample was filtered on 0.2 µm pore size polycarbonate membrane filters. Seawater samples were filtered on a 0.2 µm pore size polycarbonate membrane filters. For sediments, DNA was extracted from 300 mg sub-samples. Sequencing was done on the Illumina novaseq 6000 platform and 2x 150 base pair chemistry.