Tooth Mg/Ca ratios and Aristotle's lantern morphometrics reflect trophic types in echinoids.

Several studies have inferred the ecological significance regarding the morphometrics of Aristotle's lantern and the mechanical properties of magnesium in echinoid teeth. This study attempts to combine these aspects, connecting them to the trophic habits of three native and an invasive echinoid in the Eastern Mediterranean Sea. Spatiotemporal data from the central and southern Aegean Sea were obtained, regarding the relative size of lanterns and demi-pyramids of , , and the invasive echinoid and the Mg/Ca ratios of four zones on the tooth cross-section. Since environmental factors affect the examined factors, data for temperature, salinity, and concentration of chlorophyll-a were included in a principal component analysis. and presented intraspecific differences in the relative size of the lantern and demi-pyramid, while and exhibited variation in the elongation index. Differences in the Mg/Ca ratios were observed for all species although in different zones. Temperature appears to be related to all Mg/Ca zones except for the stone part, while the elongation index showed an inverse trend to all other morphometric parameters. The results of the PCA for the four species on the spatiotemporal level exhibited a distinction of individuals with season but not species, except for , an omnivore with a carnivorous tendency, which was clearly separated from the herbivorous species. Using hierarchical clustering on the principal components it was evident that the three native species occupy different clusters, but when was added, it shared the same cluster with . This might infer similar feeding preferences, specifically for coralline algae, which might lead to a swift in the ecological equilibrium in regions, where is found, either by affecting habitat type, or by restricting the distribution of as was previously observed with .