Spatial variation in otolith elemental chemistry of Stegastes arcifrons (Pomacentridae) reflects environmental patchiness at the Galápagos archipelago

In marine ecosystems, environmental conditions shape important ecological processes. The equatorial Galápagos Marine Reserve (GMR) is known for great spatial variation in the upwelling of cold nutrient-rich waters and the input of warm Panamanian waters. Differences in oceanography influence the structure of benthic communities. There is, however, a paucity of knowledge on the spatial scales of exposure to cool and warmer waters. Here we analysed the elemental chemistry of otoliths in the territorial yellow-tail damselfish (Stegastes arcifrons) to identify patterns of elemental signals across a gradient from warm to upwelled waters. Contrasting patterns of elemental ratios (Ba/Ca, Mg/Ca, Mn/Ca and Sr/Ca) were found in whole otoliths of adult fish at spatial scales of kilometres to 10 s of kilometres; there was also high variation among fish within some sites. A positive correlation was detected between temperature and Sr/Ca ratios. We conclude that variation in environmental conditions influenced fish elemental incorporation into otoliths, highlighting the oceanographic heterogeneity of shallow rocky reef environments in the Galápagos.