Sampling for barnacle and oyster recruitment

The barnacle, C. malayensis recruits were counted monthly for a total of ten months from photographs of thirty (5 × 5 cm) quadrats randomly placed in the barnacle zone of each site. The coverage of adult barnacles in each quadrat was estimated visually and only the quadrats with 20–30% adult coverage were used. Barnacle recruits were distinguished from adults as having a rostral-carinal diameter of 0.5–1.0 mm (Buasakaew et al., 2021). The oyster, S. cuccullata recruits were counted on fifteen (30 × 30 cm) permanent plots marked randomly on the rock using stainless steel screws. The oyster coverage within a 30 × 30-cm area was visually inspected and only areas with around 30–40% oyster coverage were marked. Oyster recruits were counted as individuals in a photograph that were not in the photograph of the same plot taken the previous month; therefore, oyster recruits could be determined for eight out of the ten sampling months. Oyster recruits were defined as having shell length of 0.45 to 3 mm (Braley, 1982). The numbers of replicates for C. malayensis (30 quadrats) and S. cuccullata (15 plots) were determined from personal observations. These numbers gave the least within-group variance while remaining practical to manage. All photographs were taken with a digital camera (Nikon Coolpix W300).