Comparative feeding morphology and diet of SW Atlantic surgeonfishes

Adriana Hiromi Yukimitsu¹, Ronaldo Bastos Francini-Filho², Rodrigo Leão de Moura³, Gustavo Muniz Dias¹, Bruna Larissa Maganhe¹ and Fernando Zaniolo Gibran¹

PDF: Download Here | Supplementary: S1 S2 S3 S4 S5 S6 S7 S8 | Cite this article

Associate Editor: Luiz Osmar

Section Editor: Luiz Osmar

Editor-in-chief: José Birindelli

Abstract​

---

Introduction​

---

Herbivorous fishes are a key functional group in tropical reef communities (Bellwood et al., 2004). In addition to their major contribution to fish biomass, these fishes affect the distribution, abundance, and biomass of algae and the epilithic algae matrix (EAM), which comprises turfing algae, detritus, cryptofauna, microorganisms, unicellular algae, and inorganic sediment (Purcell, Bellwood, 2001; Kramer et al., 2012). In addition to algae, many herbivorous fishes also ingest fauna and detritus associated with the EAM, which might account for 10 to 78% of all food items in the algal matrix, likely playing a significant nutritional role for these species (Crossman et al., 2001; Choat et al., 2002; Wilson, 2002; Wilson et al., 2003; Bos et al., 2017). As primary consumers of these resources, herbivorous fishes are important links, transferring energy from the algal matrix/detritus to secondary consumers (Wilson et al., 2003), thereby essential for structuring and maintaining coral reef communities (Hay, 1991; Bellwood, 2003; Cordeiro et al., 2016).

Among the dominant nominally herbivorous fishes in coral reefs (Horn, 1989; Bellwood et al., 2004; Francini-Filho et al., 2010), surgeonfishes (Acanthuridae) representing over a quarter of tropical marine herbivorous fishes (Vergés et al., 2014). With approximately 85 species (Tebbett et al., 2022), they have inhabited reef habitats since the Middle Eocene (Bellwood, 1996; Bellwood, Wainwright, 2002; Tebbett et al., 2022). Their long evolutionary history is closely linked with that of coral reef ecosystems and has resulted in the emergence of species with varied morphological, physiological, and behavioral characteristics (Choat et al., 2002; Friedman et al., 2016; Tebbett et al., 2022). These morphological variations significantly influence the potential use of nutritional resources, as variations in morphological traits result in differences in function and performance (Karr, James, 1975; Wainwright, 1991, 1994; Motta et al., 1995). In this sense, differences in morphology among closely related species might indicate both evolutionary and ecological divergence, especially in sympatric and congeneric species (Van der Klaauw, 1948; Winemiller, 1991; Winemiller et al., 1995), as suggested by variations in dental and stomach morphology (Horn, 1989; Choat, 1991; Bellwood et al., 2014a,b; Siqueira et al., 2019a; Tebbett et al., 2022), as well as differences in the relative length of the digestive tube (Elliott, Belwood, 2003) and mouth size (Norton, 1991). For morphological (head morphology) and functional traits (jaw motion and feeding kinematics associated to biting and pull algae off the substrate) specifically relating to surgeonfishes, see Mihalitsis, Wainwright (2024), Mihalitsis et al. (2025), and Perevolotsky et al. (2025).

Within the South Atlantic, the Abrolhos Bank, Bahia State, Brazil, is the largest and most biodiverse reef system (Joly et al., 1969; Leão, Kikuchi, 2001; Dutra et al., 2005; Segal, Castro, 2011), encompassing approximately 11% nominally herbivorous fish species among its ichthyofauna (Moura, Francini-Filho, 2006). Three species of Acanthurus, Acanthurus bahianus Castelnau, 1855, A. chirurgus (Bloch, 1787), and A. coeruleus Bloch & Schneider, 1801, are especially abundant in this region, being widely distributed along the Brazilian coast, playing key ecological roles in various habitats (Menezes et al., 2003; Francini-Filho et al., 2010). These species present distinct feeding habits, with A. coeruleus being largely associated with algae and EAM ingestion (see Ferreira, Gonçalves, 2006; Francini-Filho et al., 2010; Siqueira et al., 2019a), while A. chirurgus and A. bahianus, two phylogenetically closer species (Sorenson et al., 2013; Friedman et al., 2016; Siqueira et al., 2019b), are considered sediment suckers (Tebbett et al., 2022). This variation in feeding ecology offers valuable insights into their functional roles, which is crucial for understanding the dynamics of herbivorous fishes in this reef bank.

Coral reefs, the most biodiverse of all marine ecosystems, are at the forefront of environmental changes (Barlow et al., 2018), and the configurations of these ecosystems will continue to change as coral cover decreases due to anthropogenic impacts and climate change (Bellwood et al., 2019a; Vercelloni et al., 2020; Tebbett et al., 2022). In this sense, the roles played by different functional groups may change, and defining the main ecosystem functions to be preserved may depend on context (Bellwood et al., 2019b; Tebbett et al., 2022). Despite extensive research on herbivorous fish in Indo-Pacific reefs (Siqueira et al., 2019a; Tebbett et al., 2022), studies in the South Atlantic remain limited. So, considering the close link between form and function, related to how fish species use food resources (see Karr, James, 1975; Wainwright, 1991, 1994; Motta et al., 1995), we describe and compare the feeding morphology and diet of the three Acanthurus species in the Abrolhos coral reef system. Our study thus addresses three main questions within the context of the ecomorphological hypothesis that species with similar feeding morphologies share similarities in ecology: (1) How do these Acanthurus species differ in their feeding morphology? (2) Do such differences reflect differences in the use of food resources? (3) Do their diet compositions differ in the proportions and categories of ingested items? By answering these questions, we aim to contribute to understanding the functional roles of surgeonfishes in the Brazilian Province. We expect to find the closest similarities between A. bahianus and A. chirurgus due to their close evolutionary relationships (see Sorenson et al., 2013; Friedman et al., 2016; Siqueira et al., 2019b).

Material and methods

---

Study site and collections. A field study was conducted in the Abrolhos Bank, northeastern Brazil (16–20°S 37–39°W), at sites up to 20 m deep. The Abrolhos bank is an enlargement of the continental shelf with an area of approximately 46,000 km² (Moura et al., 2013). The main coral reef formations consist of mushroom-shaped pinnacles 5–25 m in height and 20–300 m in length at their top (Francini-Filho et al., 2013). Due to its relatively high degree of endemism and specificity, the Abrolhos Marine National Park (AMNP) was created in 1983 to promote environmental protection against fishing activities in two discontinuous areas: Timbebas and the Archipelago and Parcel dos Abrolhos. The field activities detailed below were conducted at AMNP and the coastal Parcel das Paredes (PP), within the Ponta da Baleia Environmental Protected Area (Fig. 1).

FIGURE 1| Map of the Abrolhos Bank, northeastern Brazil, showing study sites and marine protected areas. AMNP = Abrolhos Marine National Park; PP = Parcel das Paredes.

Fish collections were conducted during the austral summer (February 2016, March 2017) and spring (October 2017), totaling 25 sampling days. Fresh fish specimens were collected by speargun during their diurnal foraging activity at the study site (between 08:00–17:00 h; FZG, 2016, pers. obs.), always after ingestion events, and were immediately euthanized by pithing. As references for confirmation of species identification see, e.g., MZUSP 60836 for A. bahianus, MZUSP 60500 for A. chirurgus, and MZUSP 60521 for A. coeruleus, at Museu de Zoologia da Universidade de São Paulo, São Paulo, Brazil. A total of 14 individuals of A. coeruleus (188–370 mm ± 13.27 of total length, TL; total weight: 137–1,150 g ± 70.90) and 16 individuals of both A. bahianus (115–245 mm ± 9.82 TL; total weight: 31–295 g ± 17.61)and A. chirurgus (133–280 mm ± 9.93 TL; total weight: 53–550 g ± 35.50) were collected. All specimens were weighted to the nearest 0.1 g, measured with a digital caliper to the nearest 0.1 mm, and then fixed in 10% formalin within 1 h of capture to preserve the digestive tube and gut contents.

Osteology and ecomorphology. We compared the natural size and shape of the heads and mouths (see Keast, Webb, 1966; Belwood, Choat, 1990; Winemiller, 1991; Motta et al., 1995) of the three Acanthurus species considering linear distances of ecomorphological dimensions (see Tab. S1; following Gatz, 1979, and, where applicable, Gibran, 2007, 2010). The ecomorphological measures considered included head length (HL), head height (HH), head width (HW), head width on the eyes line (HWE), mouth width (MW), mouth height (MH), and digestive tube length (DTL), expressed in millimeters, which were chosen based on their functional interpretations – mouth dimensions use to be related to bite size and the amount of food; head dimensions, together with mouth dimensions, jaw bones and articulations, are related to feeding kinematics; head dimensions, as the relation of length and height, may be related to space utilization during biting, as more elongated and laterally compressed heads, associated with body shape, function as a control surface when biting, for fishes that feeding biting the substrate; and DTL is expected to be related to diet composition and trophic ecology (see Keast, Webb, 1966; Gatz, 1979; Mihalitsis, Wainwright, 2024; Mihalitsis et al., 2025; Perevolotsky et al., 2025).

For osteological analysis, premaxilla, maxilla, dentary, and articular weight were considered. All jaw bones evaluated were extracted from freshly collected specimens via boiling and dissection (cf. Belwood, Choat, 1990). The osteological analyses were based on the weights of jaw bones and related articulations following Purcell, Bellwood (1993), and Lellys et al. (2019); for this analysis, four adult specimens for both A. bahianus and A. chirurgus and three adult specimens for A. coeruleus were used. The comparative analysis also considered a visual description of the dentition, jaw bones, and of the general digestive tube morphology.

To assess morphological similarities among species, rectangular data matrices with values of morphometric attributes and weight of the jaw bones were first adjusted to body size and weight by removing allometric effects (cf. Lleonart et al., 2000; Marroig, 2007) according to the following function:

Y_i* = Y_i [ X_o/X_i]^b

Where Y_i* is the predicted value of Y for individual i after correcting for the underlying scaling relationship between Y and X; X_i and Y_i are the observed values of X and Y for individual i; b is the slope from the ordinary least squares regression on log-transformed Y and X variables; and X₀ and arbitrary X values are the means for the study population (see Lleonart et al., 2000; Peig, Green, 2009; Lellys et al., 2019).

To properly test for differences across species, we normalized the adjusted data to Z scores (Gauch, 1982; Ludwig, Reynolds, 1988; Quinn, Keough, 2002; Legendre, Legendre, 2012; Lellys et al., 2019). The use of normalized and standardized data allows for the interpretation of data as shape-related rather than size-related, reducing the chance of bias due to body size (Lleonart et al., 2000; Lellys et al., 2019).

Diet and feeding morphology. We analyzed the stomach contents of all collected specimens. We removed the digestive tubes, individualized each stomach, and separated the food items into three main categories under a stereomicroscope: algae, fauna, and sediment, including both detritus and inorganic sediment. Organic (detritus) and inorganic sediment were then separately quantified by the difference in weight before and after burning sedimentary material in a muffle furnace at 500°C for 5 h, to acquire the dry weight of inorganic sediment. As the three studied species are nominally herbivorous and details on algae composition are known for the three species in the same studied region (see Ferreira, Gonçalves, 2006), we focused here on a comprehensive detailed description of the fauna ingested. We calculated the percent composition (cf. Hynes, 1950) of food groups from the total weight of each category and the frequency of occurrence of the faunal food items (cf. Bowen, 1992), representing the number of fish in which each food item occurs, listed as a percentage. It is important to note that, since no observations of ingestion were included in this study, it is not possible to determine whether fragments found in the stomach contents were the results of direct ingestion or incidental consumption of detrital material from the substrate. In this context, all animal parts identified in the stomach contents were categorized as “fauna”, while only the organic sediment was classified as detritus.

Statistical analysis. All data was tested for normality and homoscedasticity using the Shapiro-Wilk and Levene tests; two (fauna and inorganic sediment) out of 30 variable combinations did not follow a normal distribution. Therefore, data were either log-transformed or standardized to Z-scores before analysis. Morphological differentiation among species was initially assessed using linear discriminant analysis (LDA) (see Gauch, 1982; Ludwig, Reynolds, 1988; Quinn, Keough, 2002; Legendre, Legendre, 2012; Lellys et al., 2019). LD1–LD2 scores from model predictions were plotted with species-specific convex hulls, and the percentage of variance explained by each discriminant axis was calculated from the model eigenvalues. To test whether there are significant differences in morphology among species we used a PERMANOVA from a distance matrix using Euclidean distance. To verify which variables contributed to the morphological differences observed between each pair of species we performed a similarity percentage test (SIMPER). Differences in osteological comparisons (weight of the jaw bones) were visualized using a principal component analysis (PCA) and tested using a PERMANOVA. Additionally, one-way ANOVA was applied to each bone variable, followed by Tukey’s post hoc test when p < 0.05. To verify which variables contributed to the osteological differences observed between each pair of species, we also performed SIMPER. Each morphometric variable and each category of food items was also analyzed separately using one-way ANOVA, to test differences among species, followed by Tukey’s post hoc test when p < 0.05. For each PERMANOVA, the PERMDISP test was applied to ensure no differences in dispersion among groups. To explore the correspondence between fish species morphology, and diet composition, we performed a canonical correspondence analysis (CCA), and the significance of the correspondence was tested using Monte Carlo procedure (Legendre, Legendre, 2012). All analyses were conducted using the R software (R Development Core Team 2019, v. 3.5.3: multivariate analyses, including PERMANOVA and CCA were conducted using the “vegan” package; additional multivariate procedures were carried out with functions from the “ade4” package; when appropriate, LDA and generalized linear models were implemented with tools from the “MASS” package; model assumptions and diagnostics, including tests for homogeneity of variances, were assessed using functions from the “car” package).

Results​

---

Osteology. The morphological analysis of the three Acanthurus species revealed distinct traits that may influence their feeding ecology. In all evaluated species, the mouth closes with the premaxilla positioned in front of the dentary. The premaxilla of A. coeruleus has a longer ascending process, which is shorter and more rounded in A. bahianus and more pointed in A. chirurgus and A. coeruleus (Fig. 2). The alveolar process is rounded in A. bahianus and A. chirurgus and more flattened in A. coeruleus. Acanthurus coeruleus also presents a projection at the premaxilla, which is lacking from the other species. Compared with those of A. bahianus and A. chirurgus, the maxilla of A. coeruleus has an elongated premaxillary condyle (shorter in the other species) and a more flattened cranial condyle. For A. bahianus and A. chirurgus, the maxillary arm is more curved, while in A. coeruleus, the jaw insertion fossa is more evident. Dentaries of the three species exhibit similar sizes compared to their respective premaxilla, and A. coeruleus stands out for having a longer and wider ventral process with a larger lateral flange. The articular of A. coeruleus has a longer ascending process (shorter and more triangular in A. bahianus and A. chirurgus), a wider articulatory fossa, and a larger and less sharp descending process. The teeth of the three species are similar, elongated and spatulated, with multi-denticles on their margins (an average of ~9–10 denticles, depending on wear) (Fig. 2).

FIGURE 2| Lateral view of the jaw bones and frontal view of the teeth of Acanthurus bahianus, A. chirurgus, and A. coeruleus. Legends: asc.p: ascending process, alv.p: alveolar process, cra.c: cranial condyle, pm.c: premaxillary condyle, max.a: maxillary arm, ins.f: jaw insertion fossa, lat.f: lateral flange, ven.p: ventral process, art.f: articular fossa of the jaw, des.p: descending process. Scale bars = 4.0 mm for jaw bones and 1.0 mm for tooth.

Ecomorphology. Results on ecomorphological features suggest that three species represent two ecomorphological groups. Acanthurus coeruleus differed from the other two species mainly because it had the highest head (head height is defined as the head depth measured vertically through the center of the eyes, see Gatz, 1979; Lellys et al., 2019) on LD1 (pseudo-F_2,43 = 4.16; p = 0.01) and the longest digestive tube, while A. chirurgus differed from A. bahianus on LD2, with A. chirurgus having the longest and widest head and the highest mouth (mouth height is defined as the interior dorsal-ventral dimension of the mouth, fully opened, i.e., mouth gape, see Gatz, 1979; Lellys et al., 2019) (Fig. 3; Tabs. S2, S3).

FIGURE 3| Linear discriminant analysis (LDA) considering seven morphological attributes of the three surgeonfish species of the Abrolhos reefs, Brazil.

The discriminant function had a prediction capacity of 80.43%. The variables mouth height and width, head height, and digestive tube length contributed most to the morphological differences among the three species of the studied Acanthurus (Fig. 3; Tabs. S2, S3). The digestive tubes of the three species are similar, with the main difference being in the stomach. Acanthurus bahianus and A. chirurgus present stomachs with thick and brawny walls associated with a gizzard-like region. In contrast, A. coeruleus has no gizzard (Fig. S4). There was no significant difference in the total length of the digestive tubes among species (F_2,43 = 0.504; p = 0.608; Fig. 7). Regarding the jaw bones, the weights of the dentary and premaxilla contributed to the differences among the three species (p < 0.05; see Fig. 4; Tab. S5 for statistical tests).

FIGURE 4| Mean ± SE of the weights (g) of the jaw bones of Acanthurus bahianus (ABAH, n = 4), A. chirurgus (ACHI, n = 4), and A. coeruleus (ACOE, n = 3). Letters above the error bars represent homogeneous groups at p < 0.5, as defined by Tukey’s test.

FIGURE 5| Distribution of individuals of the three surgeonfish species studied based on scores from the first two principal component analysis (PCA) axes for osteological attributes (weight of the jaw bones). ART = articular; MAX = maxilla; PMAX = premaxilla; DEN = dentary.

FIGURE 6| Diet composition (%) of Acanthurus species whose stomach contents were grouped into three food categories (organic sediment with detritus, invertebrates/fauna, and algae), also showing the proportion of inorganic sediment. Acanthurus bahianus (ACABAH, n = 16), A. chirurgus (ACACHI, n = 16), and A. coeruleus (ACACOE, n = 14).

FIGURE 7| Tests for each variable of morphometric measurements (mm) and for each category of food items (measured in mg and expressed as proportion,) of Acanthurus bahianus (ABAH, n = 16), A. chirurgus (ACHI, n = 16), and A. coeruleus (ACOE, n = 14). Letters above the error bars represent homogeneous groups at p < 0.05, as defined by Tukey’s test.

The first two axes of the PCA accounted for 92% of the cumulative variation when using the four osteological attributes (bone weights) (Fig. 5), distinguishing A. coeruleus from the other two species mainly because of a heavier premaxilla and dentary (Pseudo-F₂₈ = 15.02; p = 0.03; Fig. 5; see Tabs. S6, S7).

Diet and feeding morphology. Acanthurus bahianus and A. chirurgus ingested mainly sediment with organic components (detritus), while A. coeruleus ingested mainly algae; and all three species ingested approximately 15–25% of invertebrates (Fig. 6). Among the fauna, sponges were the most frequent (94%) in the A. chirurgus and A. bahianus stomachs, while salps (Salpidae) were the most frequent (64%) in the A. coeruleus stomachs (Tab. 1). In addition to sponges, A. bahianus ingested more frequently on crustaceans and gastropods, and A. chirurgus ingested more frequently on gastropods, polychaeta worms, crustaceans and salps. In addition to salps, A. coeruleus ingested more frequently on crustaceans and sponges and exhibited less diverse faunal ingestion. Parasitic nematodes were frequent in the stomachs of all species (63–86%) (Tab. 1).

TABLE 1 | Frequency of occurrence (%) of faunal items in the stomachs (alphabetical order) of Acanthurus species (“-” indicates absence). *Parasite worms.

	A. bahianus (n = 16)	A. chirurgus (n = 16)	A. coeruleus (n = 14)
Amphipoda	19	31	43
Bryozoa	6	19	–
Copepoda	6	19	14
Cumacea	19	13	7
Gastropoda	50	75	7
Hydrozoa	13	–	7
Isopoda	–	13	7
Nematoda*	75	63	86
Ostracoda	31	44	–
Phyllocarida	–	6	14
Polychaeta	25	69	–
Porifera	94	94	44
Salpidae	19	56	64
Tanaidacea	50	63	21

In the analysis of morphometric attributes and food items, the head height, head length, head width on the eyes line, mouth height, proportion of algae and proportion of inorganic and organic (detritus) sediments contributed to the differences among the species (p < 0.05; Fig. 7; see Tab. S8).

The first two CCA axes explained 27.9% of the variation in the diets considering feeding morphology (Fig. 8). Permutation tests confirmed that the CCA was significant (global test: p = 0.001). The first three canonical axes explained most of the constrained variation and were all significant (CC1: p = 0.001; CC2: p = 0.001; CC3: p = 0.001), indicating that more than two axes contribute to the relationship between diet composition and morphology. Marginal tests showed that all diet components (algae, fauna, detritus, and sediment) significantly influenced the ordination (p = 0.001 for all variables), while morphological traits displayed weaker effects, with only head length showing marginal significance (p = 0.089). Therefore, although visual patterns in the first two axes suggest associations between diet categories and certain morphological dimensions, these relationships should be interpreted cautiously because additional axes contribute significantly to the explained variation. There was a relationship between morphology and diet (pseudo-F = 2.301; p = 0.04) for the three species. The amount of fauna in the stomach contents was positively related to the digestive tube length, head width and mouth height (Fig. 8), and we also found a high correlation between algae intake and digestive tube length (r = 0.991) for the three species. The proportion of organic detritus showed a weak association with all morphological variables, being close to the center of the CCA. In contrast, inorganic sediment was positively related to head width, head width at the eye line, and mouth height. Lastly, the proportion of algae was positively related to head height, but negatively related to head width and head length (Fig. 8). Acanthurus coeruleus had the highest proportion of algae and the lowest proportion of inorganic and organic sediments (detritus), in contrast to the other two species, which had higher proportions of organic sediment and fauna (Fig. 6).

FIGURE 8| Canonical correspondence analysis showing the relationship between the morphology and diet composition (proportions of food items) of the three Acanthurus species in the Abrolhos Reefs, Brazil. DTL: digestive tube length, MH: mouth height, HWE: head width on the eye line, HW: head width, HL: head length, MW: mouth width, HH: head height. “Detritus” refers to organic sediment and “Sediment” to the inorganic sediment portion of the diet contents.

Discussion​

---

Functional analyses have revealed a strong relationship between morphology and feeding behavior in herbivorous reef fishes, highlighting clear links between feeding mode and head morphology (e.g., Bellwood et al., 2014a; Mihalitsis, Wainwright, 2024; Mihalitsis et al., 2025; Perevolotsky et al., 2025). Our study provides the first ecomorphological comparison of feeding and diet among three surgeonfish species co-occurring in the Abrolhos reefs. Based on morphology and diet, the three species were categorized into two ecomorphological groups that reflect their phylogenetic relationships and have a differentiated contribution to the percentage of food item categories. The A. coeruleus morphotype primarily differs in head height and the length of digestive tubes, while A. chirurgus and A. bahianus, despite significant overlap, show differences in head length, width, and mouth height. As expected, there were greater similarities in morphology and diet between the two detrital feeders, A. chirurgus and A. bahianus. In contrast, A. coeruleus, displayed characteristics of a cropper (see Tebbett et al., 2022), an herbivorous fish that feeds on filamentous algae, with a higher, shorter, and rounded head, and heavier premaxilla and dentary providing a greater potential for bite strength for turf removal, as observed by Barel (1983, apud Purcell, Bellwood, 1993) for A. nigrofuscus, a species with a diet more similar to A. coeruleus.

The shorter relative head length and higher head in A. coeruleus seem to limit biting over the reef, in contrast to A. chirurgus and A. bahianus, which have more elongated heads (and more elongated bodies and snouts) and wider mouths that allow them to bite, suck, and explore different types of surfaces inside and outside the reef, such as flat sand bottoms covered with biofilm adjacent to the reef (FZG, 2016, pers. obs., but see also Francini-Filho et al., 2010; Brandl et al., 2015; Tebbett et al., 2022), high-energy locations, and also complex surfaces and reef crevices (see Bellwood et al., 2014a), a more elongated and laterally compressed head, associated with body shape, function as a control surface when biting, for fishes that feeding biting the substrate (Perevolotsky et al., 2025). Acanthurus coeruleus has a more circular body and reaches a larger size (up to 39 cm TL; cf. Lessa, Nóbrega, 2000) than the other species. Such differences can be related to the phylogenetic history of these species, since A. bahianus has the Caribbean A. tractus Poey, 1860, as a sister taxon, forming a clade with A. chirurgus (Bernal, Rocha, 2011; Friedman et al., 2016; Fernandes et al., 2021), while sister taxon of A. coeruleus is the Indo-Pacific A. guttatus Forster, 1801 (see Sorenson et al., 2013). The radiation of A. coeruleus occurred in the early Miocene, ~21 million years ago, 11 million years earlier than that of A. chirurgus and A. bahianus (Sorenson et al., 2013; Tebbett et al., 2022). On modern coral reef fishes, the ability to access exposed reef flats, which had high abundance of EAM, likely gave rise to the detritus-feeding specialists (Bellwood et al., 2014a,b).In this sense,Acanthurus chirurgus and A. bahianus diverged from the ancestral body shape pattern and function after the rise of the genus Acanthurus within the rise of the clade of sediment suckers with a gizzard-like stomach (Sorenson et al., 2013; Tebbett et al., 2022). Additionally, understanding tooth structure is fundamental for interpreting dietary preferences and feeding mechanisms (Bellwood et al., 2014b). The morphology of the elongated and spatulated teeth with multi-denticles of the three studied species is a common and conservative feature within the genus Acanthurus (Tyler, 1970; Fishelson, Delarea, 2013).

Variation in feeding morphology among the studied surgeonfishes explained 31% of the variation in diet among the species. Morphological and osteological differences may also explain the differences in the functions that they exert in natural reef systems, despite their generally conservative morphology (e.g., Brandl et al., 2015; Tebbett et al., 2022). The most frequent and abundant category in the diet of A. coeruleus was algae, accounting for approximately 40% of its diet composition, at least three times more than in the other two species. Although the predominance of algae as the main food item of A. coeruleus was reported for the same reef bank 20 years ago (Ferreira, Gonçalves, 2006), we found only half of the values reported by Ferreira, Gonçalves (2006). Despite that, ecomorphological attributes suggest that A. coeruleus may play important roles in the removal of EAM and algae (Siqueira et al., 2019a). The heavier premaxilla and dentary in A. coeruleus are possibly a feature that descends from more ancient lineages of the Eocene, with relatively robust jawed morphologies, as this clade belongs to an older lineage than A. chirurgus and A. bahianus (Siqueira et al., 2019b), without a gizzard, but with a change that may reflect a shift from browsing on macroalgae to cropping short algal turfs in more open EAM-dominated areas, as seen in many extant surgeonfishes (Bellwood et al., 2014a). Its role is further supported by its thin-walled acidic stomach and the capacity for fermentative digestion (Purcell, Bellwood, 1993; Choat et al., 2004; Tebbett et al., 2017), key features separating these fishes from other surgeonfishes that also graze over an open substrate, namely the brushers and sediment suckers (Tebbett et al., 2022). However, detailed experimental studies are still needed to corroborate this inference.

Regarding gut morphology, gut length is strongly associated with feeding habits and overall digestive physiology (Jones, 1968). When there is a greater intake of algae matter, the gut is generally more elongated, and the stomach more acidic with thinner walls, as these traits facilitate the breakdown and fermentation of fibrous algal material, which requires longer retention times for effective nutrient extraction (Jones, 1968; Elliott, Belwood, 2003).

Nonetheless, A. coeruleus had the highest intake of algae, with a relatively, but not significantly, longer gut. It is possible that the higher acidity in thin-walled stomachs, together with intestinal symbionts, may contribute to the digestion of algae (Lobel, 1981; Horn, 1989; Choat et al., 2004; Miyake et al., 2015, 2016; Scott et al., 2020). In addition, intestinal traits seem to be highly conserved across reef herbivorous fishes (Duque-Correa et al., 2024), and in functional studies, intestinal surface area may better reflect ecological differences than intestinal length (Ghilardi et al., 2021). Acanthurus coeruleus has larger pyloric caeca, and adaptations to increase gut surface area in fishes, such as long intestines and the development of caeca, are alternative features to achieve similar masses of absorptive tissue (Buddington, Diamond, 1986). Alternatively, A. bahianus and A. chirurgus, as well as all Acanthurus species within the same subclade, have a differentiated gizzard-like region in their stomach that is used for the mechanical trituration of detritus (Choat et al., 2004). This feature is associated with the emergence of sediment suckers in the Indo-Pacific, which contributes to changes in the trophodynamics of coral reefs, as it allows the exploration of both soft and mixed substrates (Bellwood et al., 2017; Tebbett et al., 2022). The feeding behavior of sediment-sucking surgeonfishes in the Atlantic is also unique and includes the exploitation of EAM on hard substrates (Robertson, 1991; Francini-Filho et al., 2010; Duran et al., 2019).

In contrast to previous studies on the Acanthurus diet in Abrolhos (Ferreira, Gonçalves, 2006), we found that for both A. bahianus and A. chirurgus, algae are the least abundant item in the diet, apart from inorganic sediment ingestion. Both species had a greater contribution of fauna (~22% and 15%, respectively) and organic sediment (detritus), accounting for 58% for both species as the main food category. A high proportion of detritus in the diet of both species agrees with previous studies (e.g., Dias et al., 2001; Ferreira, Gonçalves, 2006; Mendes et al., 2018). The differences observed compared to previous studies conducted at the same reef bank two decades ago may be attributed to the study site, as Ferreira, Gonçalves (2006) analyzed the diet in mid-reef areas, while in this study, data include both outer areas as more coastal reefs. Nonetheless, detritus – a heterogeneous complex composed of dead organic matter, protein-rich, derived from living sources, inorganic matter, and microorganisms associated with meiofauna and biofilm (Wilson, 2002; Wilson et al., 2003), has nutritional value that may even surpass that of “turf” algae (Choat et al., 2002; Crossman et al., 2001, 2005; Purcell, Bellwood, 2001; Wilson, 2002). Indeed, Mendes et al. (2018) suggested that detritus is the main source of nitrogen for A. chirurgus. Likewise, other authors corroborate that micro-photoautotroph organisms, such as diatoms and cyanobacteria, are important components of detritus for herbivorous fishes, including Acanthurus species (Cissell et al., 2019; Cardozo-Ferreira et al., 2023).

We also found greater amounts of fauna than the study of Ferreira, Gonçalves (2006) (~13 times greater for A. bahianus and A. coeruleus, and ~7.5 times for A. chirurgus). Most of the fauna, however, are clearly epifauna associated within algae, EAM, and the substrate. Exceptionally, the presence of salps in more than half of our samples, with nine of the 14 individuals of A. coeruleus analyzed and 16 of A. chirurgus, with some of them containing more than 50 individuals of salp in a single Acanthurus stomach, indicates that this is not a case of accidental ingestion but rather an opportunistic feeding strategy (i.e., “trophic adaptability” or the ability of fish to take advantage of the most abundant food items in the environment at a given time; cf. Gerking, 1994). This suggests that the proportions of food categories in the diets of Acanthurus can be strongly related to the local context of food availability and, thus, to reef temporal dynamics. Furthermore, some Acanthurus might exhibit morphological characteristics of generalists, enabling them to explore many alternative resources (Motta et al., 1995; Brandl et al., 2015; Tebbett et al., 2022). Accordingly, studies performed with algivorous surgeonfishes around the world have shown that zooplankton are ingested at a relatively high macroscopic planktonic density (Fishelson, Delaria, 2013).

Another frequent food item here was sponge fragments. During foraging, A. bahianus and A. chirurgus bite EAM and other reef coverages composed of many organisms or their fragments, which can influence the ingestion of detritus and sponges (FZG, 2016, pers. obs.). The presence of sponge spicules, but not tissue, might suggest incidental ingestion while targeting epilithic photoautotrophic microorganisms (Clements et al., 2016). However, sponges can host or harbor high densities of cyanobacteria and zooxanthellae (Easson, Thacker, 2014), nutrient-rich resources that are known to be targeted by other herbivorous fish species (Clements et al., 2016; Nicholson, Clements, 2020). There are no reports of intentional ingestion of sponges by the studied Acanthuridae, but sponge predation is mostly neglected due to poor resolution in dietary analyses (Oricchio et al., 2016). Ingestion of crustaceans and mollusks may accompany algae and EAM, and they may have important nutritional value for the studied Acanthurus species. Phytal fauna, including hydrozoans, bryozoans, foraminifera, and many types of microcrustaceans, are common in several analyzed contents of surgeonfishes around the world (Fishelson, Delaria, 2013). However, the nutritional value of all these items for surgeonfishes is largely unknown, which may lead to underestimations of the level of resource partitioning and trophic innovation on coral reefs (see Clements et al., 2016).

Although we have contributed to a better understanding of the feeding morphology and diet of surgeonfishes in Abrolhos, further studies are needed to understand their nutritional ecology, especially in reefs with high natural sedimentation rates and SW Atlantic subtropical reefs, in contrast to the Indo-Pacific reefs (Tebbett et al., 2022). Unlike those of specialized herbivorous terrestrial mammals, the nutritional, physiological, metabolic, and gut microbiota of herbivorous fishes are still poorly studied (Choat, Clements, 1998; Clements et al., 2009, 2016; but see Thompson et al., 2024). Therefore, little is known about how much of the nutrients of algal origin are truly used and assimilated in nominally herbivorous fishes, as little is known about the composition and nutritional value of detritus, and even fauna, for Acanthurus species(see Mendes et al., 2018; Delgado-Pech et al., 2020).

Coral reefs worldwide are at the forefront of environmental changes (Barlow et al., 2018), and the configurations of these ecosystems will continue to change as coral cover decreases due to human actions (Bellwood et al., 2019a; Vercelloni et al., 2020). For example, it is estimated that 50% of the reefs around the world have a greater inflow of terrestrial sediment (Burke et al., 2011). This new context is important for understanding reef dynamics and determining which functional ecological roles will be critical in the future (Bellwood et al., 2019b; Tebbett et al., 2022). Therefore, understanding the role of surgeonfishes will also depend on the future of the Anthropocene reef context (Marshell, Mumb, 2015; Bellwood et al., 2019b; Tebbett et al., 2022). Thus, decisions regarding the conservation of Anthropocene reefs will require better knowledge of the nutritional ecology of all nominally herbivorous fishes, especially in the SW Atlantic, where the reefs are distinct from those of the Indo-Pacific and Caribbean in terms of structure, biodiversity, and environmental conditions (Mendes et al., 2018; Lellys et al., 2019; Tebbett et al., 2022).

Acknowledgments​

---

We thank Parque Nacional Marinho dos Abrolhos/ICMBio (Brazilian Environmental Agency, through Fernando P. M. Repinaldo Filho) for logistical support, scientific research, and collection licenses. We also thank Rede Abrolhos (www.abrolhos.org) and Guilherme H. Pereira-Filho for field support; and Guilherme H. Pereira-Filho, Ricardo J. Sawaya, Thiago Mendes, and the anonymous reviewers for valuable suggestions.

References​

---

Barel CDN. Towards a constructional morphology of cichlid fishes (Teleostei, Perciformes). Neth J Zool. 1983; 33:357–424.

Barlow J, França F, Gardner TA, Hicks CC, Lennox GD, Berenguer E et al. The future of hyperdiverse tropical ecosystems. Nature. 2018; 559:517–26. https://doi.org/10.1038/s41586-018-0301-1

Bellwood DR. The Eocene fishes of Monte Bolca: the earliest coral reef fish assemblage. Coral Reefs. 1996; 15:11–19. https://doi.org/10.1007/BF01626074

Bellwood DR. Origins and escalation of herbivory in fishes: a functional perspective. Paleobiology. 2003; 29(1):71– 83. https://www.jstor.org/stable/4096875

Bellwood DR, Choat JH. A functional analysis of grazing in parrotfishes (family Scaridae): the ecological implications. Environ Biol Fishes. 1990; 28:189-214. https://doi.org/10.1007/BF00751035

Bellwood DR, Goatley CHR, Bellwood O. The evolution of fishes and corals on reefs: form, function and interdependence. Biol Rev Camb Philos Soc. 2017; 92:878–901. https://doi.org/10.1111/brv.12259

Bellwood DR, Goatley CHR, Brandl SJ, Bellwood O. Fifty million years of herbivory on coral reefs: fossils, fish and functional innovations. Proc R Soc B. 2014a; 281:20133046. https://doi.org/10.1098/rspb.2013.3046

Bellwood DR, Hoey AS, Bellwood O, Goatley CHR. Evolution of long-toothed fishes and the changing nature of fish-benthos interactions on coral reefs. Nat Commun. 2014b; 5:3144. https://doi.org/10.1038/ncomms4144

Bellwood DR, Hughes TP, Folke C, Nyström M. Confronting the coral reef crisis. Nature. 2004; 429:827–33. https://doi.org/10.1038/nature02691

Bellwood DR, Pratchett MS, Morrison TH, Gurney GG, Hughes TP, Á lvarez-Romero JG et al. Coral reef conservation in the Anthropocene: confronting spatial mismatches and prioritizing functions. Biol Conserv. 2019a; 236:604–15. https://doi.org/10.1016/j.biocon.2019.05.056

Bellwood DR, Streit RP, Brandl SJ, Tebbett SB. The meaning of the term ‘function’ in ecology: a coral reef perspective. Funct Ecol. 2019b; 33(6):948–61. https://doi.org/10.1111/1365-2435.13265

Bellwood DR, Wainwright PC. The history and biogeography of fishes on coral reefs. In: Sale PF, editor. Coral reef fishes: dynamics and diversity in a complex ecosystem. San Diego: Academic Press; 2002. p.5–32.

Bernal MA, Rocha LA. Acanthurus tractus Poey, 1860, a valid western Atlantic species of surgeonfish (Teleostei, Acanthuridae), distinct from Acanthurus bahianus Castelnau, 1855. Zootaxa. 2011; 2905(1):63–68. https://doi.org/10.11646/zootaxa.2905.1.5

Bos AR, Cruz-Rivera E, Sanad AM. Herbivorous fishes Siganus rivulatus (Siganidae) and Zebrasoma desjardinii (Acanthuridae) feed Ctenophora and Scyphozoa in the Red Sea. Mar Biodivers. 2017; 47:243–46. https://doi.org/10.1007/s12526-016-0454-9

Bowen SH. Quantitative description of the diet. In: Nielsen LA, Johnson DL, editors. Fisheries techniques. Blacksburg: American Fisheries Society; 1992. p.325–36.

Brandl SJ, Robbins WD, Bellwood DR. Exploring the nature of ecological specialization in a coral reef fish community: morphology, diet and foraging microhabitat use. Proc R Soc B. 2015; 282(1815):20151147. https://doi.org/10.1098/rspb.2015.1147

Buddington RK, Diamond JM. Aristotle revisited: the function of pyloric caeca in fish. PNAS. 1986; 83(20):8012–14. https://doi.org/10.1073/pnas.83.20.8012

Burke L, Reytar K, Spalding M, Perry A. Reefs at risk revisited. Washington: World Resources Institute; 2011.

Cardozo-Ferreira GC, Ferreira CEL, Choat JH, Mendes TC, Macieira RM, Rezende CE et al. Seasonal variation in diet and isotopic niche of nominally herbivorous fishes in subtropical rocky reefs. Mar Ecol Prog Ser. 2023; 722:125–43. https://doi.org/10.3354/meps14442

Choat JH. The biology of herbivorous fishes on coral reefs. In: Sale PF, editor. The ecology of fishes on coral reefs. San Diego: Academic Press; 1991. p.120–55.

Choat JH, Clements KD. Vertebrate herbivory in marine and terrestrial environments: a nutritional ecology perspective. Annu Rev Ecol Syst. 1998; 29:375–403. https://doi.org/10.1146/annurev.ecolsys.29.1.375

Choat JH, Clements KD, Robbins WD. The trophic status of herbivorous fishes on coral reefs. Mar Biol. 2002; 140:613–23. https://10.1007/s00227-001-0715-3

Choat JH, Robbins WD, Clements KD. The trophic status of herbivorous fishes on coral reefs II: food processing modes and trophodynamics. Mar Biol. 2004; 145:445–54. https://doi.org/10.1007/s00227-004-1341-7

Cissell EC, Manning JC, McCoy SJ. Consumption of benthic cyanobacterial mats on a Caribbean coral reef. Sci Rep. 2019; 9:12693. https://doi.org/10.1038/s41598-019-49126-9

Clements KD, German DP, Piché J, Tribollet A, Choat JH. Integrating ecological roles and trophic diversifcation on coral reefs: multiple lines of evidence identify parrotfishes as microphages. Biol J Linn Soc. 2016; 120:729–51. https://doi.org/10.1111/bij.12914

Clements KD, Raubenheimer D, Choat JH. Nutritional ecology of marine herbivorous fishes: ten years on. Funct Ecol. 2009; 23(1):79–92. https://doi.org/10.1111/j.1365-2435.2008.01524.x

Cordeiro CAMM, Mendes TC, Harborne AR, Ferreira CEL. Spatial distribution of nominally herbivorous fishes across environmental gradients on Brazilian rocky reefs. J Fish Biol. 2016; 89(1):939–58. https://doi.org/10.1111/jfb.12849

Crossman DJ, Choat JH, Clements KD. Nutritional ecology of nominally herbivorous fishes on coral reefs. Mar Ecol Prog Ser. 2005; 296:129–42. https://www.jstor.org/stable/24868626

Crossman DJ, Choat JH, Clements KD, Hardy T, McConochie J. Detritus as food for grazing fishes on coral reefs. Limnol Oceanogr. 2001; 46(7):1596–605. https://doi.org/10.4319/lo.2001.46.7.1596

Delgado-Pech B, Almazán-Becerril A, Peniche-Pérez J, Caballero-Vázquez JA. Facultative scavenging feeding habits in Acanthurus chirurgus (Bloch, 1787) (Acanthuriformes: Acanthuridae). Biodivers Data J. 2020; 8:e53712. https://doi.org/10.3897/BDJ.8.e53712

Dias T, Rosa IL, Feitoza BM. Food resource and habitat sharing by the three Western South Atlantic surgeonfishes (Teleostei: Acanthuridae: Acanthurus) off Paraiba Coast, northeastern Brazil. Aqua. 2001; 5:1–10.

Duque-Correa MJ, Clements KD, Meloro C, Ronco F, Boila A, Indermaur A et al. Diet and habitat as determinants of intestine length in fishes. Rev Fish Biol Fish. 2024; 34:1017–34. https://doi.org/10.1007/s11160-024-09853-3

Duran A, Adam TC, Palma L, Moreno S, Collado-Vides L, Burkepile DE. Feeding behavior in Caribbean surgeonfishes varies across fish size, algal abundance, and habitat characteristics. Mar Ecol. 2019; 40:e12561. https://doi.org/10.1111/maec.12561

Dutra GF, Allen GR, Werner T, McKenna SA. A rapid marine biodiversity assessment of the Abrolhos Bank, Bahia, Brazil, RAP Bulletin of Biological Assessment 38. Washington, D.C.: Conservation International; 2005.

Easson CG, Thacker RW. Phylogenetic signal in the community structure of host-specific microbiomes of tropical marine sponges. Front Microbiol. 2014; 5:532. https://doi.org/10.3389/fmicb.2014.00532

Elliott JP, Bellwood DR. Alimentary tract morphology and diet in three coral reef fish families. J Fish Biol. 2003; 63(6):1598–609. https://doi.org/10.1111/j.1095-8649.2003.00272.x

Ferreira CEL, Gonçalves JEA. Community structure and diet of roving herbivorous reef fishes in the Abrolhos Archipelago, south-western Atlantic. J Fish Biol. 2006; 69(5):1533–51. https://doi.org/10.1111/j.1095-8649.2006.01220.x

Fernandes MA, Cioffi MB, Bertollo LAC, Costa GWWF, Motta-Neto CC, Borges AT et al. Evolutionary tracks of chromosomal diversification in surgeonfishes (Acanthuridae: Acanthurus) along the world’s biogeographic domains. Front Genet. 2021; 12:1–12. https://doi.org/10.3389/fgene.2021.760244

Fishelson L, Delarea Y. Comparison of the oral cavity architecture in surgeonfishes (Acanthuridae, Teleostei), with emphasis on the taste buds and jaw “retention plates”. Environ Biol Fishes. 2013; 97:173–85. https://doi.org/10.1007/s10641-013-0139-1

Francini-Filho RB, Coni EOC, Meirelles PM, Amado-Filho GM, Thompson FL, Pereira-Filho GH et al. Dynamics of coral reef benthic assemblages of the Abrolhos Bank, eastern Brazil: inferences on natural and anthropogenic drivers. PLoS ONE. 2013; 8(1):e54260. https://doi.org/10.1371/journal.pone.0054260

Francini-Filho RB, Ferreira CM, Coni EOC, Moura RL, Kaufman L. Foraging activity of roving herbivorous reef fish (Acanthuridae and Scaridae) in eastern Brazil: influence of resource availability and interference competition. J Mar Biol Assoc UK. 2010; 90:481–92. https://doi.org/10.1017/S0025315409991147

Friedman ST, Price SA, Hoey AS, Wainwright PC. Ecomorphological convergence in planktivorous surgeonfishes. J Evol Biol. 2016; 29:965–78. https://doi.org/10.1111/jeb.12837

Gatz AJ. Ecological morphology of freshwater stream fishes. Tulane Stud Zool Bot. 1979; 21:91–124.

Gauch HG. Multivariate analysis in community ecology. New York: Cambridge University Press; 1982.

Gerking SD. Feeding ecology of fishes. San Diego: Academic Press; 1994.

Ghilardi M, Schiettekatte NMD, Casey JM, Brandl SJ, Degregori S, Mercière A et al. Phylogeny, body morphology, and trophic level shape intestinal traits in coral reef fishes. Ecol Evol. 2021; 11(19):13218–31. https://doi.org/10.1002/ece3.8045

Gibran FZ. Activity, habitat use, feeding behavior, and diet of four sympatric species of Serranidae (Actinopterygii: Perciformes) in southeastern Brazil. Neotrop Ichthyol. 2007; 5(3):387–98. https://doi.org/10.1590/S1679-62252007000300018

Gibran FZ. Habitat partitioning, habits and convergence among coastal nektonic fish species from the São Sebastião Channel, southeastern Brazil. Neotrop Ichthyol. 2010; 8(2):299–310. https://doi.org/10.1590/S1679-62252010000200008

Hay ME. Fish-seaweed interactions on coral reefs: effects of herbivorous fishes and adaptations of their prey. In: Sale PF, editor. The ecology of fishes on coral reefs. San Diego: Academic Press; 1991. p.96–119.

Horn MH. Biology of marine herbivorous fishes. Oceanogr Mar Biol. 1989; 27:167–272.

Hynes HBN. The food of fresh-water sticklebacks (Gasterosteus aculeatus and Pygosteus pungitius), with a review of methods used in studies of the food of fishes. J Anim Ecol. 1950; 19:36–57. https://doi.org/10.2307/1570

Joly AB, Oliveira-Filho EC, Narchi W. Projeto de criação de um parque marinho na região de Abrolhos. An Acad Bras Cienc. 1969; 41:247–51.

Jones RS. Ecological relationships in Hawaiian and Johnston Island Acanthuridae (surgeonfishes). Micronesica. 1968; 4:309–61.

Karr JR, James FC. Eco-morphological configurations and convergent evolution of species and communities. In: Cody ML, Diamond JM, editors. Ecology and evolution of communities. Cambridge: Harvard University Press; 1975. p.258–91.

Keast A, Webb D. Mouth and body form relative to feeding ecology in the fish fauna of a small lake, Lake Opinicon, Ontario. J Fish Res Board Can. 1966; 23(12):1845–74. https://doi.org/10.1139/f66-175

Kramer MJ, Bellwood DR, Bellwood O. Cryptofauna of the epilithic algal matrix on an inshore coral reef, Great Barrier Reef. Coral Reefs. 2012; 31:1007–15. https://doi.org/10.1007/s00338-012-0924-x

Leão ZMAN, Kikuchi RKP. The Abrolhos reefs of Brazil. In: Seeliger U, Kjerfve B, editors. Coastal marine ecosystems of Latin America. Berlin: Springer-Verlag; 2001. p.83–96.

Legendre P, Legendre L. Numerical ecology. 3rd ed. Amsterdam: Elsevier; 2012.

Lellys NT, Moura RL, Bonaldo RM, Francini-Filho RB, Gibran FZ. Parrotfish functional morphology and bioerosion on SW Atlantic reefs. Mar Ecol Prog Ser. 2019; 629:149–63. https://doi.org/10.3354/meps13102

Lessa RP, Nóbrega MF. Guia de identificação de peixes marinhos da região nordeste do Brasil. Recife: Programa REVIZEE, Relatório Síntese; 2000.

Lleonart J, Salat J, Torres GJ. Removing allometric effects of body size in morphological analysis. J Theor Biol. 2000; 205(1):85–93. https://doi.org/10.1006/jtbi.2000.2043

Lobel PS. Trophic biology of herbivorous reef fishes: alimentary pH and digestive capabilities. J Fish Biol. 1981; 19(4):365–97. https://doi.org/10.1111/j.1095-8649.1981.tb05842.x

Ludwig JA, Reynolds JF. Statistical ecology: a primer on methods and computing. New York: Wiley-Interscience Publications; 1988.

Marroig G. When size makes a difference: allometry, life-history and morphological evolution of capuchins (Cebus) and squirrels (Saimiri) monkeys (Cebinae, Platyrrhini). BMC Evol Biol. 2007; 7:20. https://doi.org/10.1186/1471-2148-7-20

Marshell A, Mumby PJ. The role of surgeonfish (Acanthuridae) in maintaining algal turf biomass on coral reefs. J Exp Mar Biol Ecol. 2015; 473:152–60. https://doi.org/10.1016/j.jembe.2015.09.002

Mendes TC, Ferreira CEL, Clements KD. Discordance between diet analysis and dietary macronutrient content in four nominally herbivorous fishes from the Southwestern Atlantic. Mar Biol. 2018; 166:2. https://doi.org/10.1007/s00227-018-3448-2

Menezes NA, Buckup PA, Figueiredo JL, Moura RL. Catálogo das espécies de peixes marinhos do Brasil. São Paulo: Museu de Zoologia da Universidade de São Paulo; 2003.

Mihalitsis M, Wainwright PC. Feeding kinematics of a surgeonfish reveal novel functions and relationships to reef substrata. Commun Biol. 2024; 7:13. https://doi.org/10.1038/s42003-023-05696-z

Mihalitsis M, Yamhure-Ramirez D, Beil MH, Chan H, Cole NJ, Luenenborg A et al. Lateral jaw motion in fish expands the functional repertoire of vertebrates and underpins the success of a dominant herbivore lineage. PNAS. 2025; 122(19):e2418982122. https://doi.org/10.1073/pnas.2418982122

Miyake S, Ngugi DK, Stingl U. Diet strongly influences the gut microbiota of surgeonfishes. Mol Ecol. 2015; 24(3):656–72. https://doi.org/10.1111/mec.13050

Miyake S, Ngugi DK, Stingl U. Phylogenetic diversity, distribution, and cophylogeny of giant bacteria (Epulopiscium) with their surgeonfish hosts in the Red Sea. Front Microbiol. 2016; 7:285. https://doi.org/10.3389/fmicb.2016.00285

Motta PJ, Clifton KB, Hernandez P, Eggold BT. Ecomorphological correlates in ten species of subtropical seagrass fishes: diet and microhabitat utilization. Environ Biol Fishes. 1995; 44:37–60. https://doi.org/10.1007/BF00005906

Moura RL, Francini-Filho RB. Reef and shore fishes of the Abrolhos Region, Brazil. In: Dutra GF, Allen GR, Werner T, Mckenna SA, editors. A rapid marine biodiversity assessment of the Abrolhos Bank, Bahia, Brazil. RAP Bulletin of Biological Assessment 38. Washington, D.C.: Conservation International; 2006. p.40–55.

Moura RL, Secchin NA, Amado-Filho GM, Francini-Filho RB, Freitas MO, Minte-Vera CV et al. Spatial patterns of benthic megahabitats and conservation planning in the Abrolhos Bank. Cont Shelf Res. 2013; 70:109–17. https://doi.org/10.1016/j.csr.2013.04.036

Nicholson GM, Clements KD. Resolving resource partitioning in parrotfishes (Scarini) using microhistology of feeding substrata. Coral Reefs. 2020; 39:1313–27. https://doi.org/10.1007/s00338-020-01964-0

Norton SF. Capture success and diet of cottid fishes: the role of predator morphology and attack kinematics. Ecology. 1991; 72(5):1807–19. https://doi.org/10.2307/1940980

Oricchio FT, Pastro G, Vieira EA, Flores AAV, Gibran FZ, Dias GM. Distinct community dynamics at two artificial habitats in a recreational marina. Mar Environ Res. 2016; 122:85–92. https://doi.org/10.1016/j.marenvres.2016.09.010

Peig J, Green AJ. New perspectives for estimating body condition from mass/length data: the scaled mass index as an alternative method. Oikos. 2009; 118(12):1883–91. https://doi.org/10.1111/j.1600-0706.2009.17643.x

Perevolotsky T, Brotman-Krass JM, Ratner Y, Avigad Y, Summers AP, Donatelli CM et al. Twist and snout: head and body morphologies determine feeding kinematics in substrate-biting fishes. Integr Org Biol. 2025; 7(1):obaf032. https://doi.org/10.1093/iob/obaf032

Purcell SW, Bellwood DR. A functional analysis of food procurement in two surgeonfish species, Acanthurus nigrofuscus and Ctenochaetus striatus (Acanthuridae). Environ Biol Fishes. 1993; 37:139–59. https://doi.org/10.1007/BF00000589

Purcell SW, Bellwood DR. Spatial patterns of epilithic algal and detrital resources on a windward coral reef. Coral Reefs. 2001; 20:117–25. https://doi.org/10.1007/s003380100150

Quinn GP, Keough MJ. Experimental design and data analysis for biologists. 2^nd ed. Cambridge: Cambridge University Press; 2002.

R Development Core Team. R: a language and environment for statistical computing – Version 3.5.3 [internet]. R Foundation for Statistical Computing; 2019. Available from: https://www.R-project.org/

Robertson DR. Increases in surgeonfish populations after mass mortality of the sea urchin Diadema antillarum in Panamá indicate food limitation. Mar Biol. 1991; 111:437–44. https://doi.org/10.1007/BF01319416

Scott JJ, Adam TC, Duran A, Burkepile DE, Rasher DB. Intestinal microbes: an axis of functional diversity among large marine consumers. Proc R Soc B. 2020; 287:20192367. https://doi.org/10.1098/rspb.2019.2367

Segal B, Castro CB. Coral community structure and sedimentation at different distances from the coast of the Abrolhos Bank, Brazil. Braz J Oceanogr. 2011; 59(2):119–29. https://doi.org/10.1590/S1679-87592011000200001

Siqueira AC, Bellwood DR, Cowman PF. The evolution of traits and functions in herbivorous coral reef fishes through space and time. Proc R Soc B. 2019a; 286:20182672. https://doi.org/10.1098/rspb.2018.2672

Siqueira AC, Bellwood DR, Cowman PF. Historical biogeography of herbivorous coral reef fishes: the formation of an Atlantic fauna. J Biogeogr. 2019b; 46(7):1611–24. https://doi.org/10.1111/jbi.13631

Sorenson L, Santini F, Carnevale G, Alfaro ME. A multilocus timetree of surgeonfishes (Acanthuridae, Percomorpha) with revised family taxonomy. Mol Phylogenet Evol. 2013; 68(1):150–60. https://doi.org/10.1016/j.ympev.2013.03.014

Tebbett SB, Goatley CHR, Bellwood DR. Clarifying functional roles: algal removal by the surgeonfishes Ctenochaetus striatus and Acanthurus nigrofuscus on coral reefs. Coral Reefs. 2017; 36:803–13. https://doi.org/10.1007/s00338-017-1571-z

Tebbett SB, Siqueira AC, Belwood DR. The functional roles of surgeonfishes on coral reefs: past, present and future. Rev Fish Biol Fish. 2022; 32:387–439. https://doi.org/10.1007/s11160-021-09692-6

Thompson C, Silva R, Gibran FZ, Bacha L, Freitas MAM, Thompson M et al. The Abrolhos nominally herbivorous coral reef fish Acanthurus chirurgus, Kyphosus sp., Scarus trispinosus, and Sparisoma axillare have similarities in feeding but species-specific microbiomes. Microb Ecol. 2024; 87:110. https://doi.org/10.1007/s00248-024-02423-x

Tyler JC. Osteological aspects of interrelationships of surgeon fish genera (Acanthuridae). Proc Acad Nat Sci Phila. 1970; 122:87–124. https://www.jstor.org/stable/4064651

Van der Klaauw CJ. Ecological studies and reviews. IV. Ecological morphology. Acta Biotheor. 1948; 4:27–111.

Vercelloni J, Liquet B, Kennedy EV, González-Rivero M, Caley MJ, Peterson EE et al. Forecasting intensifying disturbance effects on coral reefs. Glob Chang Biol. 2020; 26:2785–97. https://doi.org/10.1111/gcb.15059

Vergés A, Steinberg PD, Hay ME, Poore AG, Campbell AH, Ballesteros E et al. The tropicalization of temperate marine ecosystems: climate-mediated changes in herbivory and community phase shifts. Proc R Soc B. 2014; 281:20140846. https://doi.org/10.1098/rspb.2014.0846

Wainwright PC. Ecomorphology: experimental functional anatomy for ecological problems. Am Zool. 1991; 31(4):680–93. https://doi.org/10.1093/icb/31.4.680

Wainwright PC. Functional morphology as a tool in ecological research. In: Wainwright, PC, Reilly SM, editors. Ecological morphology: integrative organism biology. Chicago: The University of Chicago Press; 1994. p.42–59.

Wilson SK. Nutritional value of detritus and algae in blenny territories on the Great Barrier Reef. J Exp Mar Biol Ecol. 2002; 271(2):419–30. https://doi.org/10.1016/S0022-0981(02)00035-7

Wilson SK, Bellwood DR, Choat JH, Furnas M. Detritus in the epilithic algal matrix and its use by coral reef fishes. Oceanogr Mar Biol Annu Rev. 2003; 41:279–309.

Winemiller KO. Ecomorphological diversification in lowland freshwater fish assemblages from five biotic regions. Ecol Monogr. 1991; 61(4):343–65. https://doi.org/10.2307/2937046

Winemiller KO, Kelso-Winemiller L, Brenkert AL. Ecomorphological diversification and convergence in fluvial cichlid fishes. Environ Biol Fishes. 1995; 44:235–61. https://doi.org/10.1007/BF00005919

Authors

---

Adriana Hiromi Yukimitsu¹, Ronaldo Bastos Francini-Filho², Rodrigo Leão de Moura³, Gustavo Muniz Dias¹, Bruna Larissa Maganhe¹ and Fernando Zaniolo Gibran¹

^[1]    Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Alameda da Universidade, s/n, Bairro Anchieta, 09606 045, São Bernardo do Campo, SP, Brazil. (AHY) adriana.yukimitsu@gmail.com, (GMD) gmdias@ufabc.edu.br, (BLM) bruna.maganhe@ufabc.edu.br, (FZG) fernando.gibran@ufabc.edu.br (corresponding author)

^[2]    Centro de Biologia Marinha, Universidade de São Paulo, 11612-109, São Sebastião, SP, Brazil. (RBFF) francinifilho@usp.br.

^[3]    Instituto de Biologia and SAGE/COPPE, Universidade Federal do Rio de Janeiro, 21941-972, Rio de Janeiro, RJ, Brazil. (RLM) moura.uesc@gmail.com.

Authors’ Contribution

---

Adriana Hiromi Yukimitsu: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Validation, Visualization, Writing-original draft.

Ronaldo Bastos Francini-Filho: Conceptualization, Funding acquisition, Investigation, Supervision, Validation, Writing-review and editing.

Rodrigo Leão de Moura: Conceptualization, Funding acquisition, Investigation, Supervision, Validation, Writing-review and editing.

Gustavo Muniz Dias: Conceptualization, Formal analysis, Funding acquisition, Investigation, Methodology, Software, Supervision, Validation, Writing-review and editing.

Bruna Larissa Maganhe: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Software, Writing-original draft, Writing-review and editing.

Fernando Zaniolo Gibran: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing-original draft, Writing-review and editing.

Ethical Statement​

---

Collection licenses of SISBIO number 50872–1 and 50872–2, ethical guidelines for species collection were followed, but our work did not involve animal experimentation.

Competing Interests

---

The author declares no competing interests.

Data availability statement

---

The data supporting the findings of this study are available from the corresponding author, upon reasonable request.

AI statement

---

ChatGPT (OpenAI) was used to assist with some grammatical corrections and as support for the R software. DeepL was also used for linguistic issues.

Funding

---

This research was supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES – Finance Code 001, grants to AHY and to BLM), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq grants to RBFF, RLM, and GMD), Programa de Pesquisas Ecológicas de Longa Duração/CNPq (PELD-Abrolhos), and the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP grant 2014/19079–9 to FZG).

Supplementary Material

---

Supplementary material S1

Supplementary material S2

Supplementary material S3

Supplementary material S4

Supplementary material S5

Supplementary material S6

Supplementary material S7

Supplementary material S8

How to cite this article

---

Yukimitsu AH, Francini-Filho RB, Moura RL, Dias GM, Maganhe BL, Gibran FZ. Comparative feeding morphology and diet of SW Atlantic surgeonfishes. Neotrop Ichthyol. 2026; 24(1):e250166. https://doi.org/10.1590/1982-0224-2025-0166

Copyright​

---

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Distributed under

Creative Commons CC-BY 4.0

© 2025 The Authors.

Diversity and Distributions Published by SBI

Accepted January 6, 2026

Submitted September 19, 2025

Epub April 27, 2026