Otolith shape variability of labrid fish from Rapa Nui (Easter Island), southeastern Pacific

Abstract

Fish otolith shape provides valuable insights into the taxonomic, phylogenetic, and ecological traits of fish species. This study aimed to assess and compare the phenotypic variation in otolith shape among four labrid species (Anampses femininus, Coris debueni, Pseudolabrus fuentesi and Thalassoma lutescens) inhabiting Rapa Nui (Easter Island) in the southeastern Pacific Ocean, utilizing geometric morphometrics and aging methods. Age estimation based on otolith structure indicated that collected specimens were adults, ranging between 1 and 3 years old. Allometric analysis revealed low but significant variation (5.40%), primarily driven by changes in otolith width, resulting in distinct morphologies. Principal Component Analysis (PCA) of sagittal otoliths elucidated significant morphospace variation among species, with the first two PCs explaining 60.3% of the total variance. PC1 distinguished between elongated sagittal shapes (e.g., P. fuentesi) and robust sagittae (e.g., T. lutescens), while PC2 correlated with otolith roundness, delineating variations within species. Canonical variate analysis further highlighted differences in otolith shape, with significant variations detected among all species. The Discriminant function analysis showed high levels of discrimination accuracy for most of species' pairs. Except for C. debueni-P. fuentesi (89%) and C. debueni-T. lutescens (96%), all other species pairs achieved 100% discrimination, highlighting the reliability of otolith shape as a distinguishing characteristic for the studied species. Overall, our findings emphasize the value of otolith shape analysis for characterizing and distinguishing Rapa Nui labrid species. This offers potential applications such as identifying prey within the digestive systems of large fish or bird predators in the vicinity of this isolated island in the South Pacific Ocean or archaeofauna studies.