Otolith morphometry and microchemistry as habitat markers for juvenile Mugil cephalus Linnaeus 1758 in nursery grounds in the Valencian community, Spain

Abstract

The aim of this study was to identify and characterize juvenile Mugil cephalus (flathead grey mullet) habitats in the Valencian community by means of otolith morphometry and microchemistry. Specimens (total length: 250–350 mm) were obtained from October 2011 to March 2012 with gill nets in two protected wetlands: the Parque Nartural de l'Albufera de Valencia (AV) (n = 45), a Mediterranean lake; and the Parque Natural Salinas de Santa Pola (SP) (n = 37), a coastal salt marsh. Otolith shape indices (circularity, rectangularity, aspect ratio, surface occupied by sulcus, ellipticity and form factor) and microchemistry (Sr/Ca and Ba/Ca ratios) were measured and compared as area markers. The chemical composition of the water in both areas was also obtained. Morphometric results showed, by an ANOVA with Bonferroni contrasts, that saccular otoliths from AV individuals had more edge complexity, hence a higher circularity index (p <.001), but that there was less otolith percentage occupied by the sulcus (p <.001). When analyzing the morphometric variables simultaneously, both sites differed significantly (Hotelling's T2 < 0.001). A paired t-test among sites of the microchemical variables showed that otoliths of AV presented higher values of Ba/Ca ratios and lower Sr/Ca ratios (p <.001). This coincides with water values obtained and could be associated with the low salinity observed in the lake. The opposite pattern was observed in SP, both for otolith and water samples, this being associated with the high-salinity waters of the area. Results obtained in the present research suggest, by the use of otolith morphometry and microchemistry, that the nursery grounds of juvenile M. cephalus in the Valencian community could be differentiated. Even though habitats could be separated using otolith morphometry, only a few of the studied shape indices were important in area differentiation. Nevertheless, the use of both methodologies simultaneously could be robust habitat markers for this species.