The Southwestern Atlantic harbors unique and relatively understudied reef systems, including the only atoll in South Atlantic: Rocas atoll. Located 230 km off the NE Brazilian coast, Rocas is formed by coralline red algae and vermetid mollusks, and is potentially one of the most “pristine” areas in Southwestern Atlantic. We provide the first comprehensive and integrative description of the fish and benthic communities inhabiting different shallow reef habitats of Rocas. We studied two contrasting tide pool habitats: open pools, which communicate with the open ocean even during low tides, thus more exposed to wave action; and closed pools, which remain isolated during low tide and are comparatively less exposed. Reef fish assemblages, benthic cover, algal turfs and fish feeding pressure on the benthos remarkably varied between open and closed pools. The planktivore Thalassoma noronhanum was the most abundant fish species in both habitats. In terms of biomass, the lemon shark Negaprion brevirostris and the omnivore Melichtys niger were dominant in open pools, while herbivorous fishes (mainly Acanthurus spp.) prevailed in closed pools. Overall benthic cover was dominated by algal turfs, composed of articulated calcareous algae in open pools and non-calcified algae in closed pools. Feeding pressure was dominated by acanthurids and was 10-fold lower in open pools than in closed pools. Besides different wave exposure conditions, such pattern could also be related to the presence of sharks in open pools, prompting herbivorous fish to feed more in closed pools. This might indirectly affect the structure of reef fish assemblages and benthic communities. The macroalgae Digenea simplex, which is uncommon in closed pools and abundant in the reef flat, was highly preferred in herbivory assays, indicating that herbivory by fishes might be shaping this distribution pattern. The variations in benthic and reef fish communities, and feeding pressure on the benthos between open and closed pools suggest that the dynamics in open pools is mostly driven by physical factors and the tolerance of organisms to harsh conditions, while in closed pools direct and indirect effects of species interactions also play an important role. Understanding the mechanisms shaping biological communities and how they scale-up to ecosystem functioning is particularly important on isolated near-pristine systems where natural processes can still be studied under limited human impact.

Reef fish represent one of the most diverse vertebrate groups on Earth, with over 7,000 species distributed around the globe. This richness is not evenly distributed geographically. The Atlantic (AT) and the Eastern Pacific (EP) encompass 30% of the global fish fauna. These areas have been considered the most isolated from the marine biodiversity hotspot in the Indo‐Pacific due to distinct physical barriers, such as the Tethyan closure and the distance between the EP and the western Pacific. Despite their comparatively lower species richness, these realms host unique fish assemblages characterized by a remarkable proportion of regional endemics and species with large body size. Here, we present the largest database of life‐history traits and biogeographical and conservation aspects presently available for the reef fish fauna of the AT and the EP realms. The database includes 21 traits distributed into behavioral (home range, diel activity, group size, level in the water column, three measures of preferred temperature), morphological (maximum body size, size class, body shape, aspect ratio, caudal fin, mouth position), and ecological (trophic level, diet, spawning strategy, depth of occurrence, two allometric constants, pelagic larval duration, and life span), as well as biogeographical (geographic range index, range extension, species distribution in 20 marine provinces, latitude north and south of occurrence, total number of provinces where species occur, occurrence in the AT and EP), and conservation aspects (IUCN status, vulnerability and global market price). We compiled these data through a careful review of 104 local checklists published between 1982 and 2020, online repositories, local reports, books, and monographs on specific families or genera. We limited our database to localities situated between latitudes 51°N and 45°S that including shallow and upper mesophotic biogenic and/or rocky reefs habitats. Our database covers 2,198 species belonging to 146 families and 655 reef fish genera distributed in two marine realms (1,458 in the AT, 829 in the EP, and 89 in both realms) and 20 marine provinces. This database of reef fish offers the opportunity to explore novel ecological and evolutionary questions at different scales and provides tools for species conservation based on these traits. There are no copyright or proprietary restrictions for research or teaching purposes.

This study investigates the reef fish community structure of the world’s smallest remote tropical island, the St Peter and St Paul’s Archipelago, in the equatorial Atlantic. The interplay between isolation, high endemism and low species richness makes the St Peter and St Paul’s Archipelago ecologically simpler than larger and highly connected shelf reef systems, making it an important natural laboratory for ecology and biogeography, particularly with respect to the effects of abiotic and biotic factors, and the functional organisation of such a depauperate community. Boosted regression trees were used to associate density, biomass and diversity of reef fishes with six abiotic and biotic variables, considering the community both as a whole and segregated into seven trophic groups. Depth was the most important explanatory variable across all models, although the direction of its effect varied with the type of response variable. Fish density peaked at intermediate depths, whereas biomass and biodiversity were respectively positively and negatively correlated with depth. Topographic complexity and wave exposure were less important in explaining variance within the fish community than depth. No effects of the predictor biotic variables were detected. Finally, we notice that most functional groups are represented by very few species, highlighting potential vulnerability to disturbances.