Sergio Ricardo Floeter

Aim: We evaluate the phylogenetic relationships and taxonomic validity of Atlantic species of Labrisomus , identifying the lineages currently assigned to L. nuchipinnis , and assessing the role of biogeographic barriers in shaping the evolutionary history and geographic distribution of the genus. Location: Atlantic Ocean. Taxon: Labrisomus . Methods: We assembled an extensive mitochondrial and nuclear DNA dataset of Atlantic species of Labrisomus to perform multi‐locus phylogenetic divergence‐time and historical biogeographic analyses, reconstruct haplotype networks, estimate genetic distances, implement lineage delimitation tests and estimate migration rates. Results: Labrisomus nuchipinnis is a species complex comprising three deeply divergent lineages: one broadly distributed in the western Atlantic, another restricted to Florida (USA), and a third mostly distributed in the eastern Atlantic. A new usage of L. nuchipinnis is proposed, with the species restricted to the western Atlantic, and with the revalidation of Clinus canariensis (as L. canariensis ) for the mostly eastern Atlantic lineage. Despite their anatomical similarity, L. nuchipinnis and its Atlantic congeners diverge significantly genetically. Unusual genetic connectivity between samples of L. canariensis from the eastern Atlantic and southern Brazil suggests a potential trans‐Atlantic genetic pathway. Main Conclusion: The deep genetic divergence among lineages previously included in the L. nuchipinnis complex contrasts with their anatomical similarity, making Labrisomus one of the most challenging cases of cryptic diversification among reef fishes. The evolutionary history of the genus likely involved spatial segregation driven by ecological niche overlap. Ecological factors may influence distribution patterns among species of the genus more strongly than geographic distance. The apparently isolated population of L. canariensis off southern Brazil provides a well‐documented case of disjunct distribution of a reef fish species between the eastern Atlantic and south Brazil, highlighting the potential of this region as a melting‐pot of biodiversity.

Aim: Understanding how body size and geographic range size influence species abundance is central to macroecology. Here, we characterized these relationships for reef fishes, the world's most diverse vertebrate group, across global and regional scales. Location: Global tropical and subtropical reefs. Time Period: Current. Major Taxa Studied: Reef‐associated fishes. Methods: We compiled a comprehensive dataset on abundance, body size and geographic range size for 828 reef fish species. Abundance was measured as density (ind/m ² ) using transect‐based observational data. To analyse global‐scale patterns, we applied Bayesian quantile regressions and Bayesian phylogenetic regressions to account for phylogenetic relatedness. We also used Bayesian phylogenetic regressions at the regional scale, considering body size, geographic range size and sampled transect area as marginal effects. Results: The relationship between geographic range size and body size exhibited a slightly triangular pattern, where large‐bodied species tended to have broad range sizes, whereas small‐bodied species varied in range sizes. We found a negative relationship between species abundance and body size, and a dual relationship (i.e., both negative and positive) between species abundance and geographic range size: species with restricted ranges were either rare or abundant, whereas widely distributed species had intermediate abundance. Similar patterns were observed across marine realms, with abundance decreasing with body size and presenting a dual relationship with geographic range size. Main Conclusions: Our findings reveal that body size and geographic range size are important correlates of reef fish abundance, but their effects vary across spatial scales. These results provide new insight into macroecological processes influencing reef fish diversity and distribution.

Reef ecosystems are fueled by both benthic and pelagic pathways, yet how the contribution of these sources varies across spatial and temporal scales remains a central question in reef ecology. Most research has focused on tropical coral reefs, whereas subtropical systems, defined by stronger oceanographic variability, have received far less attention. Coastal upwelling amplifies this variability and delivers nutrient-rich pelagic subsidies that may reshape food web dynamics, although their effects on reef trophic interactions remain largely unknown. Here, we investigated the influence of upwelling on multiple dimensions of the trophic niche by increasing plankton subsidies to the benthic-feeding omnivorous damselfish Stegastes pictus , integrating foraging behavior, diet composition, and stable isotope analysis in subtropical reefs of the Southwestern Atlantic, under contrasting non-upwelling and upwelling conditions. Although benthic feeding prevailed in both conditions, plankton feeding increased markedly during upwelling, with bite rates nearly tripling and dietary contribution rising from 0.1 to almost 20%. Stable isotope data and Bayesian mixing models indicated a consistent contribution of both benthic and pelagic sources across periods, reflecting longer-term pelagic integration. These findings reveal that upwelling creates transient windows of trophic opportunity, promoting pelagic food resource use and trophic niche expansion in benthic-feeding omnivorous fishes such as S. pictus . Environmental variability in subtropical systems thus provides high-quality pelagic resources that support generalist species with flexible diets, enhancing trophic connectivity, resilience, and the overall stability of subtropical reef food webs.

With their simplified and isolated communities, oceanic islands are considered ‘natural laboratories’ for biogeographic and evolutionary studies. Along the Mid-Atlantic Ridge (MAR), St Paul’s Rocks, Ascension and St Helena islands are nearly equidistant from South America and Africa. While St Paul’s Rocks is typically associated with the Brazilian Province, Ascension and St Helena are commonly treated as a unified biogeographical entity despite being separated by approximately 1300 km of open ocean. Using an expert-validated, rigorously curated dataset on Atlantic reef fishes, we demonstrate that these three islands constitute a cohesive biogeographic unit, sharing 46 species found nowhere else in the Atlantic. By integrating time-calibrated phylogenies and distributional data, we reconstructed dispersal routes of 88 MAR fishes, revealing predominant western Atlantic origins and a pronounced eastern influence among endemics. Divergence estimates for two Ascension endemics may predate the islands’ emergence, highlighting the potential roles of seamounts and eustatic sea-level changes in shaping biotic persistence and diversification. Trait analysis revealed that MAR fishes are typically larger, occupy wider depth ranges and are more often pelagic spawners and rafters than MAR endemics and their coastal counterparts. Our findings underscore the complex biogeographic and evolutionary processes structuring the reef fish communities of the tropical MAR islands.

Aim: The role of ecological specialisation in shaping biogeographic and evolutionary patterns remains unresolved. To date, few studies have quantitatively examined consumer niche breadth at a global scale. We describe global biogeographic and diversification patterns of specialisation, measured using trophic and thermal niches, for a highly diverse assemblage of consumers: reef fishes. First, we investigated the confluence of specialisation with global biogeographic patterns in species richness and reef area. Then, we tested whether these patterns could be explained by differences in diversification rates and geographic ranges.Location: Tropical reefs across the globe.Time Period: Present.Major Taxa Studied: Reef fishes.Methods: To estimate trophic specialisation, we compiled a comprehensive dataset on reef fish trophic interactions from published gut content analyses, including dietary information for ~5000 individuals across 387 fish species. We used the geographic range of species and global temperature data to estimate thermal specialisation of reef fishes. We used distributional data and Bayesian Structural Equation Modelling to test for the correlation between biogeographic variables, species richness, and the prevalence of trophic or thermal specialisation in reef fish assemblages. Moreover, we used linear models to test for a correlation between reef fish diversification rates, geographic range, and their degree of trophic and thermal specialisation.Results: Our analysis suggests that species richness is positively associated with trophic specialisation in reef fishes, with isolated and species‐depauperate communities supporting assemblages dominated by trophic and thermal generalists. We found no effect of trophic and thermal specialisation on diversification rates and geographic range at the species level.Main Conclusions: Our findings indicate that specialisation is favoured in large, biodiversity‐rich regions, but specialists might show lower capacity for colonisation, with lower representation on smaller, isolated reefs. These results contribute to our understanding of the dynamics shaping fish biogeography on coral reefs.

Planktivorous reef fishes are thought to possess unique morphological traits to feed on small, evasive prey. Despite the multitude of family-level studies addressing this hypothesis, results remain inconclusive. Our goal, therefore, was to determine whether specialised traits and patterns of morphological convergence are congruent across a comprehensive phylogeny of reef-associated fishes. We measured 15 morphological traits from 815 images of 299 species in 12 globally distributed families. Using phylogenetic comparative methods, we mapped the evolution of plankton-feeding across lineages; assessed the effect of planktivory on body shape; and tested for the presence of morphological convergence among planktivores. We demonstrate that planktivory is evolutionary ubiquitous and occurs in 12 of the most abundant global families. Some morphological trait differences between planktivores and non-planktivores were detected, but there was no difference in overall body shape. Contrary to longstanding assumptions, we show that planktivores have not converged towards distinct morphologies, but instead encompass the entire morphospace of reef fishes. Due to their behavioural, spatial, temporal, and resource heterogeneity, reef fishes of any shape and size can readily navigate the challenges of plankton-feeding. Graphical abstract

A diverse array of animals has evolved the ability to use tools (e.g., primates, parrots, octopus, crabs, and wasps), but the factors leading to tool use evolution are poorly understood. Fishes could provide insight into these factors via comparison of ecological and morphological differences between tool-using and non-tool-using species. Anvil use is one example of tool use by fish: the fish holds a hard-shelled prey item in its mouth and strikes it onto a hard surface (anvil) to open it. To date, anvil use has been described in 26 of the > 550 described wrasse/Labridae species. Through a community science program called Fish Tool Use, 16 new observations of anvil use were collected in five species of a monophyletic group of wrasses called the New World Halichoeres. These new observations provide the first evidence of anvil use by Halichoeres brasiliensis, H. poeyi and H. radiatus, and the first video evidence of anvil use by H. garnoti and H. bivittatus. They extend the geographic range of known anvil use by wrasses to a new region, the western Atlantic, making this behaviour even more widespread than previously reported. Video analysis revealed that wrasses are flexible in their anvil use: They did not have a preferred side of their body, they cracked open a diverse array of prey on a variety of anvil types, and often used many anvils and striking points for the same prey item. More observations are needed to determine the evolutionary origin of anvil use behaviour, its ecological drivers, costs, and benefits.

Aim: Marine organisms are responding to warming by altering their distribution ranges, causing biogeographic range shifts and in some cases, favouring the community homogenisation. Transition zones can act as natural laboratories to explore the consequences of homogenisation. However, these habitats are relatively poorly studied in coastal areas. In this study, we aimed to investigate biotic homogenisation and changes in reef fish community composition from both a taxonomic and trait‐based perspective.Location: Seven islands in the South‐western Atlantic transition zone.Methods: We used a long‐term survey data set of reef fish species abundances and traits of communities to calculate beta‐diversity indices. By analysing the data, we derived temporal trends of beta‐diversity values by separately comparing the North and South regions of the transition zone and performed pairwise comparisons to explore their dynamics when considered together.Results: Contrary to previous expectations, we found no sign of homogenisation. The colder islands (Southern) experienced a decrease in taxonomic and trait richness metrics, whereas for the warmer islands (Northern), the taxonomic and trait richness fluctuated without any significant temporal trends.Main Conclusions: While taxonomic composition may change over time, the trait composition is generally more conserved, highlighting the trait redundancy in South‐western Atlantic communities and supporting the idea that these communities can maintain a range of ecological processes despite changes in taxonomic composition. Finally, the study revealed that despite non‐homogenisation, the species that contribute most to variation, especially in the South, have common trait combinations indicating an increase in the trait redundancy of fish communities over time. We underline that local‐scale conservation efforts may be particularly effective in preserving and protecting species and ecological functions in areas experiencing unique and fast changes in biodiversity.

Human activities and climate change have accelerated species losses and degradation of ecosystems to unprecedented levels. Both theoretical and empirical evidence suggest that extinction cascades contribute substantially to global species loss. The effects of extinction cascades can ripple across levels of ecological organization, causing not only the secondary loss of taxonomic diversity but also functional diversity erosion. Here, we take a step forward in coextinction analysis by estimating the functional robustness of reef fish communities to species loss. We built a tripartite network with nodes and links based on a model output predicting reef fish occupancy (113 species) as a function of coral and turf algae cover in Southwestern Atlantic reefs. This network comprised coral species, coral‐associated fish (site occupancy directly related to coral cover), and co‐occurring fish (occupancy indirectly related to coral cover). We used attack‐tolerance curves and estimated network robustness (R) to quantify the cascading loss of reef fish taxonomic and functional diversity along three scenarios of coral species loss: degree centrality (removing first corals with more coral‐associated fish), bleaching vulnerability and post‐bleaching mortality (most vulnerable removed first), and random removal. Degree centrality produced the greatest losses (lowest R) in comparison with other scenarios. In this scenario, while functional diversity was robust to the direct loss of coral‐associated fish (R = 0.85), the taxonomic diversity was not robust to coral loss (R = 0.54). Both taxonomic and functional diversity showed low robustness to indirect fish extinctions (R = 0.31 and R = 0.57, respectively). Projections of 100% coral species loss caused a reduction of 69% of the regional trait space area. The effects of coral loss in Southwestern Atlantic reefs went beyond the direct coral‐fish relationships. Ever‐growing human impacts on reef ecosystems can cause extinction cascades with detrimental consequences for fish assemblages that benefit from corals.