Two ubiquitous parrotfishes exhibit distinct foraging ecologies on tropical Brazilian reefs

Abstract

Parrotfishes (Labridae: Scarinae) are common components of reef environments known to influence the early succession dynamics of benthic communities through their foraging behavior. In the southwestern Atlantic, the sparisomatine clade predominates over the scarinine when compared to the Caribbean, with the endemic species Sparisoma axillare and S. frondosum being the most abundant and widespread parrotfishes in the Brazilian Biogeographic Province. Given that the 2 species are similar in terms of occurrence and abundance, describing their levels of niche complementarity is challenging. Investigating basic ecological distinctions between species can aid in comprehending their habitat requirements and susceptibilities. This is particularly important in the case of S. axillare and S. frondosum, both of which are listed as Vulnerable by the Brazilian Red List of Endangered Species. Here, we assessed feeding rate, substrate selectivity, niche overlap, shoaling behavior and agonistic interactions during foraging activity of both species and comparatively between ontogenetic stages. We found that despite a high niche overlap, S. frondosum feeds on a wider range of substrate types and interacts more with other species while foraging compared to S. axillare. Dissimilarities in substrate selection by the 2 species were mainly represented by algal turfs and sand but an opposite pattern was detected: S. axillare preferentially selected the algal turfs and S. frondosum selected more sand. Although fine-scale resource partitioning has not been investigated, our results provide insights into niche complementarity between the 2 species and inferences on drivers that may help explain their distribution in the Brazilian reefs.