Ecological status of seagrass ecosystems: An uncertainty analysis of the meadow classification based on the Posidonia oceanica multivariate index (POMI)

► We compare the precision of two Spanish seagrass monitoring indices among five factors. ► Sampling at variable depths lead to high uncertainty in meadow health classification. ► Uncertainty across multiple spatial and temporal scales was low. ► Simpler POMI 9 index performed equally well as POMI 14 and offers future alternative.