[eng] This paper proposes a method to build large scale coverage maps of Posidonia Oceanica (P.O.) using the imagery provided by an AUV endowed with a bottom-looking camera. The process begins by detecting the regions containing P.O. in each individual image. Afterwards, the overlap between images is searched and the P.O. detection data in these overlapping regions is fused to build a global detection map. The paper proposes three different descriptors to detect P.O. in individual images and five strategies to fuse the overlapping regions. The experiments, performed in coastal areas of Mallorca, evaluate and compare the proposed descriptors and fusion techniques, showing that our approach surpasses the 91% detection rate.