Trophic niche diversity in an assemblage of goatfishes (Mullidae): roles of habitat and barbel morphology

Goatfishes (Syngnathiformes, Mullidae) are reef-associated fishes characterized by hyoid barbels covered with taste buds, which aid in prey detection. While generally considered as benthic carnivores, their resource partitioning remains poorly understood. This study investigates the trophic diversity of 14 goatfish species collected in May 2022 from the Great Reef of Toliara (South-West Madagascar, 23.36°S, 43.66°E) using stable isotopes (C, N, S), gut content analyses, and barbel morphology. Diet variation seemed limited among goatfish species, gut contents including mostly small benthic invertebrates. In contrast, isotopic ratios revealed trophic diversity, suggesting a partitioning of resources either by prey types or by feeding locations across the reef, despite some degree of niche overlap. Morphological analysis of barbels, including their length and taste bud characteristics (density and pore area), showed a marked distinction between Upeneus species and those of the Mulloidichthys and Parupeneus genera. Ecomorphological investigations further demonstrated that barbel morphology correlates with isotopic values and trophic diversity, with significant differences between feeding areas. Tests of phylogenetic signal suggested contrasting evolutionary patterns: trophic traits and barbel length displayed evolutionary
lability, while taste bud characteristics remained conserved. This suggests that trophic ecology, barbel length and taste buds diversification is shaped by distinct evolutionary processes. By integrating multiple approaches, this study provides new insights into the trophic diversity of Mullidae, shedding light on the ecological and evolutionary mechanisms that facilitate their coexistence in coral reef habitats.