Ecosystem Architects: how herbivory and interaction networks shape reef communities in the Caribbean

Fish are the most diverse and abundant vertebrate group on Earth and special reef fishes take part in numerous interactions, such as cleaning, feeding, and agonistic interactions. Despite the growing literature on the patterns of fish interactions in reef environments, few studies have assessed the role of abundance in modulating reef fish interactions. This study examines how the local abundance, other biological traits of reef fish and benthic coverage influence the feeding and agonistic interactions networks in Curaçao an island located in the Caribbean. We used 109 video-plots at seven reef sites around the island in October of 2013 to estimate fish species abundance (MaxN), feeding and agonistic interactions rates, and benthic coverage. Considering these assemblages metrics we calculated network metrics, including centrality, nestedness, and modularity. Results indicate that fish abundance had a weak positive effect on feeding interactions, with herbivores, sessile, and mobile invertivores engaging in most interactions. Turf and rubble cover negatively influenced feeding interactions. For agonistic interactions, less abundant species initiated more aggressive encounters, with diet, mobility, and body size influencing interactions patterns. Herbivores showed the highest out-degree centrality, while sedentary and larger species engaged more frequently in agonistic interactions. Additionally, higher turf, macroalgae, and coral cover were associated with increased agonistic interactions. These findings highlight the role of herbivorous reef fish in structuring interactions networks and suggest that factors beyond local abundance, such as species traits and habitat characteristics, shape these interactions in Curaçao’s reefs.