Abstract :
[en] Mullids, also called goatfishes, constitutes a main group of the reef ichthyofauna . They have a worldwide distribution in tropical and subtropical reefs with a few species in temperate areas such as the North-East Atlantic coast or the Mediterranean Sea. The Mullidae family belongs to the Syngnathiform order including seahorses (Syngnathidae) and trumpetfishes (Aulostomidae), and comprise 98 species grouped in 6 genera: Mullus, Upeneus, Upeneichthys, Mulloidichthys, Pseudupeneus and Parupeneus. The main morphological trait distinguishing Mullidae from other Syngnathiform families is the presence of a pair of hyoid barbels. It is often assumed that all goatfishes are mainly benthic carnivores, using barbels to extract small prey from the substrate (crustaceans, mollusks, worms).
Despite the role that goatfishes play in reef ecosystems, knowledge of their ecomorphological diversity remains scarce. Thus, we explore the ecomorphology of six species of goatfishes living in sympatry at Toliara Reef (South-West of Madagascar) by using a combination of morphometric and isotopic (δ13C, δ15N and δ34S) data. The shape of cephalic region was quantified by landmark-based geometric morphometrics and linear measurements.
Morphometric analyses permitted to distinguish each genus and species according to head elongation, cheek size and pectoral fins insertions. Isotopic ratios, used as trophic niche proxy, allowed to highlight clear trophic niche segregation among species built on C and S isotopic ratios. This diversity is possibly linked to variation in selected prey type and feeding areas. Interspecific variation of these two ratios could also be linked to a cross-reef distribution with species living in the lagoon and outer-shelf dwellers. The absence of variation in δ15N values suggests that the six species share similar trophic position. Our phylogenetic comparative analyses revealed a significant relationship between isotopic and morphometric data. These results allowed the formulation of hypotheses regarding differences in goatfishes feeding strategies: "long head" species mainly search for preys in anfractuosities or deep in the substrate while "short head" species use their head to dig in superficial soft bottoms. We highlighted ecomorphological partitioning among sympatric goatfishes, satisfying the Hutchinsonian niche concept where sympatric species do not occupy the same ecological niches.
