Elemental Markers in Elasmobranchs: Effects of Environmental History and Growth on Vertebral Chemistry

Abstract

Differences in the chemical composition of calcified skeletal structures (e.g. shells, otoliths) have proven useful for reconstructing the environmental history of many marine species. However, the extent to which ambient environmental conditions can be inferred from the elemental signatures within the vertebrae of elasmobranchs (sharks, skates, rays) has not been evaluated. To assess the relationship between water and vertebral elemental composition, we conducted two laboratory studies using round stingrays, Urobatis halleri, as a model species. First, we examined the effects of temperature (16°, 18°, 24°C) on vertebral elemental incorporation (Li/Ca, Mg/Ca, Mn/Ca, Zn/Ca, Sr/Ca, Ba/Ca). Second, we tested the relationship between water and subsequent vertebral elemental composition by manipulating dissolved barium concentrations (1x, 3x, 6x). We also evaluated the influence of natural variation in growth rate on elemental incorporation for both experiments. Finally, we examined the accuracy of classifying individuals to known environmental histories (temperature and barium treatments) using vertebral elemental composition. Temperature had strong, negative effects on the uptake of magnesium (DMg) and barium (DBa) and positively influenced manganese (DMn) incorporation. Temperature-dependent responses were not observed for lithium and strontium. Vertebral Ba/Ca was positively correlated with ambient Ba/Ca. Partition coefficients (DBa) revealed increased discrimination of barium in response to increased dissolved barium concentrations. There were no significant relationships between elemental incorporation and somatic growth or vertebral precipitation rates for any elements except Zn. Relationships between somatic growth rate and DZn were, however, inconsistent and inconclusive. Variation in the vertebral elemental signatures of U. halleri reliably distinguished individual rays from each treatment based on temperature (85%) and Ba exposure (96%) history. These results support the assumption that vertebral elemental composition reflects the environmental conditions during deposition and validates the use of vertebral elemental signatures as natural markers in an elasmobranch. Vertebral elemental analysis is a promising tool for the study of elasmobranch population structure, movement, and habitat use.

Periodicity of the growth‐band formation in vertebrae of juvenile scalloped hammerhead shark Sphyrna lewini from the Mexican Pacific Ocean

“…The highest temperatures that occurred during the summer months were related to the highest growth increments and opaque band formation at the edge of these shark vertebrae. Similar results were also observed for I. oxyrinchus (Ribot‐Carballal et al, ) and recent experimental studies have shown that increased temperatures had a positive effect on the mean growth rates of the round stingray Urobatis halleri (Cooper 1863) (Smith et al, ). Although the apparent relationship that relates vertebral growth and seawater temperature allowed to verify the annual banding pattern in vertebrae of juveniles of S. lewini from the Mexican Pacific, the forecasted end‐of‐century increases in temperature might also have detrimental effects on these sharks (Pistevos et al, ).…”

Do vertebral chemical signatures distinguish juvenile blacktip shark (Carcharhinus limbatus) nursery regions in the northern Gulf of Mexico?

“…Limburg 1995). Similarly, Scharer et al (2012) reported that the Sr : Ca in vertebral sections of the smalltooth sawfish (Pristis pectinata) had a positive correlation with salinity, and Smith et al (2013) reported that the Ba : Ca in the vertebrae of round stingray (Urobatis halleri) was correlated with Ba in seawater. For juvenile blacktip sharks examined here, there were regional differences in Sr : Ca and Ba : Ca that were inversely related.…”

“…Growth rate does not appear to affect Li : Ca, Mg : Ca, Mn : Ca, Sr : Ca and Ba : Ca deposition in the round stingray; however, Mg : Ca, Mn : Ca and Ba : Ca were significantly affected by water temperature . The work of Smith et al (2013) represents the only study to focus on the relationship between water chemistry and vertebral element : Ca in elasmobranchs; thus, we know little about the influences mentioned above and the extent of interspecies variability.…”

Strontium mineralization of shark vertebrae

“…Spectrometry has shown that temperature has no effect on strontium concentrations in elasmobranch vertebrae, although increased temperatures increase rates of vertebral growth in these species33. Otolith strontium/calcium ratios in teleost fish are positively linked to environmental strontium concentrations34, and are directly related to salinity in some species3536, but are usually unrelated to temperature3537.…”