Spatial and temporal variation in statolith and protoconch trace elements as natural tags to track larval dispersal

Trace elements in larval hard parts may serve as useful tags of natal origin in invertebrate population studies. Using field-collected encapsulated veliger larvae of the marine gastropod Keletia kellebi, this study examined the extent of spatial and temporal variation in the elemental composition of larval parts formed at the natal source. For both protoconchs and statoliths, results of multivariate analyses of variance (MANOVA) indicated that the elemental compositions show significant among-site and among-region differences. Linear discriminant-function analysis (DFA) correctly classified 89% of protoconchs and 80% of statoliths to their region of formation. However, there were significant interannual differences in elemental composition for statoliths at 2 sites and for protoconchs at 3 sites over a 3 yr period. Despite within-site interannual differences, the elemental compositions of hard parts formed during different years resembled one another to such a degree that a DFA generated with a single year's data could correctly predict the region of formation for 83.9% of statoliths and 82.5% of protoconchs formed in other years. A comparison of magnesium (Mg), strontium (Sr) and barium (Ba) incorporation patterns with per-site temperature profiles indicated statistically significant positive relationships between temperature and Mg and Sr incorporation into protoconchs, and inverse relationships between temperature and Sr (statoliths) and Ba (both protoconchs and statoliths) incorporation. These data, together with results from other studies, suggest that larval statoliths and protoconchs can meaningfully record variation in the physical and chemical properties of seawater and, hence, have potential as natural tags of natal origin.