Anchoring pressure and the effectiveness of new management measures quantified using AIS data and a mobile application.

Large boats can have a major impact on sensitive marine habitats like seagrass meadows when anchoring. The anchoring preference of large boats and their impacts can be mapped using Automatic Identification System (AIS). We found a constant increase in the number of anchoring events with, until recently, a large part of them within the protected Posidonia oceanica seagrass meadows. French authorities adopted a new regulation in 2019 forbidding any anchoring within P. oceanica seagrass meadows for boats larger than 24 m. The number of large ships (>24 m) anchoring in P. oceanica meadows significantly decreased after the enforcement of the regulation. The surface of avoided impact thanks to the new regulation corresponds to 134 to 217 tons of carbon sequestered by the preserved meadow in 2022. This work illustrates that a strict regulation of anchoring, based on accurate habitat maps, is effective in protecting seagrass meadows.