From acoustics to biometrics for ecology of Posidonia oceanica in the Mediterranean Sea

Seagrasses, particularly Posidonia oceanica , are protected and endangered species in the Mediterranean Sea, where they function as both coastal engineers and interior ecosystem architects. These seagrass meadows provide essential ecological niches and ecosystem services, and their presence is widely regarded as an indicator of undisturbed marine environments. Therefore, the development of non-destructive methods to assess seagrass characteristics is of great importance. This study presents the first attempt to estimate fundamental ecological metrics, specifically, density-related variables (leaf biomass, shoot density, and leaf area index [LAI]) and a morphometric trait (leaf length) of a P. oceanica meadow using acoustic data collected in the Gulf of Antalya, Turkey, over a seven-month period spanning 2011–2012. Acoustically derived estimates of leaf biomass were converted into density-related variables based on empirical relationships established between biomass, shoot density, and LAI from SCUBA-based sampling. While leaf length showed significant differences, the density-related variables did not differ significantly across spatial (bottom depth) or temporal (monthly) gradients between the measured and acoustically estimated data. Ecological analyses including Generalized Linear/Additive Models and Redundancy Analysis revealed comparable spatiotemporal distribution patterns between the two datasets. Furthermore, similar collinearity patterns, effect sizes, and correlations between environmental variables (including water physical, chemical, and optical properties, as well as sediment composition) and seagrass metrics were observed. These findings suggest that integrating acoustic backscatter techniques with biometric estimations offers a promising, non-invasive approach for monitoring P. oceanica meadows and assessing key ecological indicators.