Format: ORAL

Paolo Cingano1,2*, Marco Vuerich 2, Francesco Petruzzellis 1, Lorenzo Orzan 1,2, Giacomo Trotta 1,2, Valentino Casolo 2, Francesco Boscutti2

1 University of Trieste, Trieste, Italy 2 University of Udine, Udine, Italy

Lagoons globally provide crucial ecosystem services, harbouring a rich mosaic of fragile habitats. Among these, seagrass meadows play a vital role for this ecosystem and its biota, by sustaining trophic networks and influencing sediment and nutrient dynamics. Their distribution and functioning are closely tied to ecological disturbances, showing rapid shifts over time in relation to the ongoing global changes. Furthermore, lagoons often host multi-species meadows, where species interactions might complicate the understanding of the whole ecosystem responses to environmental changes. Long term monitoring of species and communities is, hence, important to understand the response to past and future global change scenarios. The availability of long term open-access satellite data (e.g. Landsat mission) offers a new remote sensing perspective for studying seagrass community dynamics in shallow waters, especially when combined with the power of machine learning algorithms. In this study, multispectral seasonal images were used with a Random Forest algorithm to map the trends of seagrass meadows and individual species in the vast Grado and Marano lagoon (Northern Adriatic) over two decades. Supervised classification models were built using a large field training dataset collected in 2010 (n = 426, accuracy of 92%) together with Landsat 5TM and 8OLI imagery and then applied from 1999 to 2019 images. The change detection analysis revealed a 14.16 km2 expansion (+ 39 %) of the entire seagrass community at a rate of 1.59 km2* year-1. Despite Landsats low spatial resolution, discrimination of individual species achieved an accuracy of 76% allowing the tracing of relative species movements and shedding light on their complex dynamic over time. The observed expansion might underpin an increasing sea water influence that are radically modifying Adriatic brackish water bodies, emphasizing the connection between ongoing environmental changes and the rapid responses of seagrass meadows.