Between 30 June and 10 July, 2009, three transects of 50 m length were established at each site, spaced equally between the level of mean high tide and the water level at mean low tide. Hereafter, we refer to these as the upper, middle, and lower intertidal transects. The slopes of the beaches and the degree of wave exposure differed considerably among sites; nevertheless, locations of the transects corresponded well to basic habitat characteristics. The upper transect was generally characterized by bare rock with little or no algal cover, the middle transect by occasional tidal pools and patches of crustose or turf-forming algae, and the lower transect by extensive algal colonies, including complex macrophytes. A random number generator was used to place 10 square quadrats (area = 0.25 m2) at random locations along each transect. Within each quadrat, all mobile animals visible to the naked eye were counted and identified. In practice, this included mollusks, arthropods, and echinoderms. Sampling occurred at low tide during daylight hours, to facilitate visual searches. A grid was overlaid over each quadrat, and algal cover was estimated as the number of intersections of grid lines (out of a possible 64) at which algae occurred. Slope of the rock face was estimated at the lower left corner of each quadrat (while facing inland). Each quadrat was digitally photographed. After the completion of sampling, these photographs were used to categorize complexity of rock surfaces (hereafter, surface complexity) of each quadrat. Classification was qualitative and reflected the degree of departure from a homogeneous rock surface on a scale of 1 (indicating a nearly uniform, flat surface) to 5 (indicating extreme complexity of rock structure, including the presence of both pits and crevices). The geographic location of each site was determined by a handheld GPS unit.
