Application of Elemental Fingerprinting to Evaluate the Dynamics of Larval Exchange

Abstract

Abstract : Most marine invertebrates have planktonic larval stages that act as agents for increased dispersal and gene flow between adult populations, but little is known about the spatial scale and strength of connectivity that results from larval dispersal. This study seeks to develop trace elemental fingerprinting methods to assess patterns of exchange among mytilid mussel populations in southern California. The authors also developed a model to predict passive larval exchange by currents in order to draw comparisons with realized dispersal. A major result was validation of the premise that site-specific water mass differences in elemental composition are imparted to carbonate shells of larvae when the shell is deposited. Thus, the larval shell contains a chemical record of its past and is retained by newly recruited mussels as they grow. Accomplishments include the following: (1) development of solution based- and Laser Ablation-Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) protocols to identify detectable trace elements in bivalve shells less than 2 mm long, (2) development of rearing and outplanting techniques to validate larval shell signatures, (3) quantification and comparison of site-specific trace element composition in distinct regions of bivalve shells, and (4) classification of elemental signatures of individual shells to distinguish larval origins using discriminant function analysis (DFA). Sampling over 2 years, quarterly, and at 1-week intervals revealed elemental signal variation in time, and the need to validate signals and conduct connectivity analyses. Although the authors have yet to confirm patterns of connectivity, significant progress has been made in the novel application of elemental fingerprinting to marine invertebrates. Ultimately this approach will allow them to incorporate dispersal information into population dynamics models to better understand the consequences of different patterns of population connectivity. (7 figures, 25 refs7