*2.1. Studied Site and Communities*

The study was performed on the coasts of north-west Brittany, on the site of Porspoder (48◦28.88 N/4◦46.29 W) (Figure 1). The site is about 230 m long and 100 m wide, with a maximal tidal range of 8.15 m and mainly exhibiting dense macroalgal canopies with some pools, boulder fields and bedrock. The six macroalgal communities typically found in the north-east Atlantic were vertically distributed on the shore [8] and were grouped into 4 bathymetric levels for the study. These levels correspond to either single or mixed communities named by the dominating Fucales and Laminariales: (1) *Pelvetia canaliculata* plus *Fucus spiralis* communities, (2) *Ascophyllum nodosum*/*Fucus vesiculosus* community, (3) *Fucus serratus* community and (4) *Himanthalia elongata*/*Bifurcaria bifurcata* plus *Laminaria digitata* communities. These levels are referred to, respectively, as Pc-Fspi, An, Fser and He-Ld hereafter.

**Figure 1.** Study site of Porspoder (Brittany, France: 48◦28.88 N/4◦46.29 W) showing the 24 in situ sampling spots surveyed during the study. The color of the circles indicates the intertidal level considered: red circles, *P. canaliculata*—*F. spiralis*; yellow circles, *A. nodosum*; black circles, *F. serratus*; blue circles, *H. elongata*. The dotted lines correspond to the UAV flight lines.
