Biometric measurements of four colonizing Zostera marina patches in the Mira channel of the Ria de Aveiro from December 2019 to August 2020 Description Biometric measurements of four colonizing Zostera marina patches (shoot density, seagrass coverage, leaf width, number of leaves per shoot and leaf surface area) were taken in the Mira channel of the Ria de Aveiro from December 2019 to August 2020. The seagrass coverage was measured in each patch by recording species presence using a metal frame of 50 × 50 cm divided into 25 sub-quadrats of 10 × 10 cm (n= 4). Shoot density was calcu lated by counting the number of vertical rhizomes of each patch into 4 sub-quadrants per each quadrant of 50 × 50 cm (n=4). Then, shoot density per square meter was calculated. Four shoots per quadrant were selected to measure leaf length, leaf width and the number of leaves per shoot and to calculate leaves per shoot and leaf surface area. Seagrass measurements were always done during low tide periods.