Drone multispectral imaging reveals seasonal microphytobenthos drivers at shorebird foraging sites

Intertidal mudflats support dynamic microphytobenthic biofilms, which underpin coastal food webs and provide critical food for migratory shorebirds. However, seasonal changes in microphytobenthos biomass and spatial structure are poorly understood despite their potential consequences for shorebird foraging and the resilience of intertidal ecosystems to global change. The distribution, biomass, and quality of microphytobenthos fluctuate in response to tidal regimes, weather, and human impacts, yet traditional monitoring methods lack the spatial and temporal resolution to resolve these dynamics at scales relevant to shorebirds. To address this gap, we used high-resolution drone-acquired multispectral and red-green-blue optical imagery to investigate seasonal microphytobenthos biomass and spatial patterns across 380 ha of intertidal mudflats in a hemispherically significant shorebird stopover site. The seasonal model explained 53.2% of microphytobenthos biomass variation, with elevation and microtopography as key predictors. Contrary to expectations, microphytobenthos biomass was highest in fall and winter rather than spring, coinciding with atypically cold and wet conditions that may have delayed or suppressed the typical spring seasonal increase in microalgal biomass, highlighting the complex seasonal and morphological controls on microphytobenthos biomass. The use of drone-based remote sensing for resolving fine-spatial-scale microphytobenthos distribution patterns provides high-resolution snapshots of biofilm distribution at key seasonal time points. Increasing drone-based monitoring frequency or integration with satellite observations to capturing intra-seasonal microphytobenthos dynamics in order to resolve how seasonal and interannual variability in microphytobenthos biofilm availability shapes shorebird foraging opportunities and migration success, offering a more comprehensive understanding of coastal ecosystems. • Seasonal MPB biomass mapped across 380 ha of mudflat with UAV multispectral imagery • MPB biomass peaked in fall and winter, low in spring. • Elevation and microtopography were key predictors of seasonal MPB biomass and distribution • Seasonal model explained 53.2% of MPB biomass variation across the estuary • Findings support development of drone-based indicators of shorebird foraging site suitability