The GPS intelligent buoy is a pot-table underwater tracking system consisting of four buoys and one pinger. The pinger was mounted on an underwater vehicle driven by a Scuba diver and used to map the limits of a Posidonia oceanica meadow. To test the accuracy of the method the system was tried out on different types of limits and on healthy and regressed part of the meadow from 2 to 25 m of depth. The time of track acquisition (1 point per second), the recording speed (1 km h(-1)) and the mapping scale (more than 1:500) indicated that the proposed method may be successfully integrated with conventional systems for mapping marine communities. (C) 2002 Ifremer/CNRS/IRD/Editions scientifiques et medicales Elsevier SAS. All rights reserved.