Acoustic-Based Door Spacing for the Assessment of Posidonia oceanica Biometrics, Habitat Characteristics, and Ecological Status Along the Turkish Mediterranean Coast

Seagrasses play a fundamental role as ecosystem engineers and habitat architects in coastal environments. In the Mediterranean Sea, Posidonia oceanica is an endemic, vulnerable, and legally protected species that is highly sensitive to environmental degradation and is widely used as an indicator of pristine ecological conditions. Ongoing global warming and increasing anthropogenic pressures highlight the need for precautionary, non-destructive methods to assess P. oceanica meadows. Traditional SCUBA-based surveys, although accurate, are time-consuming, labour-intensive, and limited by diver availability and underwater working time, particularly when estimating biometric parameters such as shoot density and leaf length. In this study, we applied a conservative acoustic-based approach to quantitatively estimate P. oceanica meadow characteristics, moving beyond purely qualitative acoustic mapping previously restricted to distributional assessments. Acoustic data collected during winter and summer 2015 along the entire Turkish Mediterranean coast were analysed to estimate seagrass biometrics and to derive indicators of ecological status. Acoustic outputs were validated through comparison with SCUBA-diving observations, allowing evaluation of the reliability and cost-effectiveness of the method. The acoustic system enabled rapid, large-scale assessment of seagrass distribution, coverage, habitat structure, and ecological condition, overcoming limitations associated with other remote sensing techniques. The results demonstrate that acoustic data can support the estimation of multiple biometric and ecological parameters and facilitate classification of ecosystem status from poor to high (pristine), in line with updated international assessment criteria. For the first time, this study provides high-resolution spatiotemporal distribution and coverage of P. oceanica meadows and associated benthic habitats along a substantial portion of the Turkish Mediterranean coast using acoustics alone. The approach offers a valuable non-destructive alternative for monitoring seagrass ecosystems and supports sustainable conservation and management of Mediterranean coastal habitats.