Use of Trace Elements in the Larval Shell as a Marker of Bivalve Dispersal

: The goal of this project is to develop a tool for tracking larval dispersal of marine invertebrates. We look specifically at uptake of trace elements into the larval shells of bivalves and evaluate whether a suite of elements can be used to identify the bivalves' source habitats in coastal environments. To do this, we use larvae reared in the laboratory under controlled trace-element conditions and juveniles collected in sites known to vary in environmental trace elements. We analyze trace elements in the shells using a Finnigan Inductively Coupled Plasma Mass Spectrometer (ICP/MS) and a large-format Cameca 1270 Ion microprobe. Our results accomplished three major objectives. Spiking experiments demonstrated that Co and Pb are incorporated into the initial larval shell (prodissoconch) in levels proportional to environmental concentrations. ICP/MS analysis of field-collected juveniles showed that geographic variation in environmental trace elements is incorporated as predicted into bivalve shells (providing a location-specific trace-element tag'). And lastly, Ion Microprobe studies showed that trace-element composition can be measured in individual prodissoconchs. These results demonstrate the feasibility of trace-element analysis of larval shells as a tool for identifying natal sites and tracking dispersal of bivalve larvae.