*3.2. Parrotfish Differences between Islands (Serranilla and San Andrés)*

We recorded 11 parrotfish species present within one or both of the two islands, 11 on Serranilla and six on San Andrés (*Scarus coelestinus*, *S. coeruleus*, *S. guacamaia*, *S. iseri*, *S. taeniopterus*, *S. vetula*, *Sparisoma atomarium*, *S. aurofrenatum*, *S. chrysopterum*, *S. rubripinne*, *S. viride*). *S. viride* was the species with both the highest abundance and biomass on Serranilla, and on San Andrés, *S. taeniopterus* and *S. aurofrenatum* had the highest abundance and biomass, respectively (Table S3). Comparison of metrics between Serranilla and San Andrés showed that there was no statistical difference in overall abundance (Pseudo-*F* = 2.137, *p* = 0.146) or species richness per transect (0D; Pseudo-*F* = 2.057, *p* = 0.105) between the two island areas, but there was a statistically significant difference in parrotfish biomass per transect (Pseudo-*F* = 4.637; *p* = 0.040).

Nevertheless, parrotfish assemblage composition did appear significantly different between the two islands when examined both in terms of abundance (Pseudo-*F* = 16.031, *p* < 0.001) and in terms of biomass (Pseudo-*F* = 12.170, *p* < 0.001) with NMDS plots; these showed, in relation to both measures, a strong spatial segregation between sites on the two islands and a notably higher dispersion among the Serranilla sites (Figure 2a,b). As shown by the sizes of the bubbles, at Serranilla, most of the parrotfish contributing to abundance and biomass were larger species, whereas at San Andrés these were mainly small-size parrotfish (Figure 2c–f).

The SIMPER analysis showed that just three species were responsible for >50% of island dissimilarity, two of which had higher abundance and biomass in San Andrés (*S. taeniopterus* and *S. aurofrenatum*), and a third which had a considerably higher abundance in Serranilla (*S. viride*) (Figure 3; Table S4). Overall, the mean parrotfish size of each species was considerably smaller than the common and maximum lengths reported in FishBase (Figure S2).

**Figure 2.** Non-metric multidimensional scaling (NMDS) plots of parrotfish abundance and biomass at sites at Serranilla and at San Andrés. Plots of abundance are shown for (**a**) all parrotfish, (**c**) smallsize parrotfish (<50 cm), and (**e**) large-size parrotfish (>50.1 cm). Corresponding plots of biomass are shown for (**b**) all parrotfish, (**d**) small-size parrotfish, and (**f**) large-size parrotfish. Bubble sizes indicate the abundance or biomass values for each site.

**Figure 3.** Comparison of mean (**a**) abundance, (**b**) biomass, and (**c**) size at Serranilla and at San Andrés of the three Scaridae species that together contribute at least 50% to the accumulated dissimilarity between these two study areas, as estimated by the SIMPER analysis. The contributions of the individual species are shown adjacent to the bars in (**b**). The error bars are ±SE. The red lines and written values in the lower part indicate the common size of each species, as reported from FishBase [38].
