Seagrass forms meadow called "seagrass bed" which is known for various ecosystem functions and services. Seagrass beds generally showed large seasonal variation affected by various environmental factors that operate at different scales. Patterns of seasonal variation may differ at different spatial scales, e.g., at a shoot scale and a meadow scale, which is difficult to quantitatively evaluate based on single survey method. The purpose of this study is to investigate seagrass seasonal dynamics using different survey methods that target different spatial scales. We conducted in-situ seagrass collections and UAV (drone) survey, at two sites in a seagrass bed of Akkeshi-ko estuary (Hokkaido) from May to December 2020. At each site, we set several sampling points along depth gradient. We collected seagrass for biomass measurement and took aerial photos using a drone to analyze spatial dynamics of meadow around the sampling points. Patterns of seasonal variation varied at different spatial scales and among points/depth. Variations in biomass were greater at deeper sampling points, whereas areal variations were greater at shallower points. The present study highlights the importance of conducting multi-scale surveys to understand seasonal dynamics of seagrass beds.