Linking bonefish (Albula vulpes) populations to nearshore estuarine habitats using an otolith microchemistry approach

Identifying the relative importance of various nursery areas is critical for understanding the ecological roles of diverse juvenile habitats, as well as for the sustainable management of fisheries and coastal resources. Recent field collections suggest that a portion of the bonefish (Albula vulpes) population in South Florida may be using nearshore estuarine habitats as nurseries. Nearshore marine habitats are traditionally considered nursery habitat for bonefish. However, the prevalence of their reliance on lower salinity areas is not known. To address this, we used otolith microchemistry using laser ablation inductively-coupled plasma mass spectrometry to examine variation in Strontium (Sr), a marker for salinity, and determine the connectivity between estuarine and marine habitats across the life of bonefish. Sr profiles from otoliths obtained in locations within South Florida (SFL, N = 40) and Southwest Cuba (SCB, N = 10) were compared using a juvenile-migration index (JMI), and change point models to assess the generality of a shift in salinity and thus habitats across life histories. Adult stages of bonefish otoliths collected in SFL and SCB locations showed Sr concentrations connected to marine, high-salinity environments. The JMI showed that a vast majority of individuals (68.4% and 70% in South Florida and Cuba, respectively) moved from low- to high-salinity environments between juvenile and adult stages. The change point models showed that these shifts to high salinity environments occurred suddenly (in 85% of those showing a low to high salinity change), and early in life (after 2 years in South Florida and after 4 years in Cuba) suggesting an ontogenetic habitat change. This study provided evidence that bonefish use low-salinity estuarine environments as juvenile habitats, perhaps more commonly than marine habitats. The reliance on low-salinity environments suggests the potential vulnerability of bonefish nearshore nursery habitats to disturbances associated with coastal freshwate