We undertook a survey in La Ciotat Bay, France, on behalf of TESubCom to determine the extent and health of the Posidonia (Neptune grass) meadow.
The goal was to validate data provided by the French regulatory body Directions Départementales des Territoires et de la Mer (DDTM). This data had suggested there may be gaps in the meadow which may allow an AAE-1 cable to run through the La Ciotat Bay with no or minimal impact on the protected habitat.
We used a hull-mounted R2 Sonic 2024 broadband multibeam echo sounder (MBES) to collect bathymetric data. Dual frequency Side Scan Sonar was used for accurate mapping.
Processing and interpretation of the survey data was undertaken in situ so that Posidonia coverage could be mapped and revised following each day of survey. This enabled each acoustic signature identified to be ground-truthed as the survey progressed, using drop-down camera deployments and Spot Dives.
To confirm the absence of Posidonia along the routes identified in the DDTM data, video footage was collected along dive transects to provide very high positional accuracy and confidence in the validity of the data.
Survey outcomes
In conclusion, the survey furthered the knowledge and understanding of the extent and health of the Posidonia meadow in the La Ciotat Bay and identified a number of potential cable route options that were likely to have little or no impact on the extent and health of the habitat during installation and operation of the cable.
