Author(s): Warner, Robert R.; Swearer, Stephen E. | Abstract: One of the least understood and most fundamental processes in marine ecology is dispersal, or transport of larvae. To what extent are local adult population dynamics influenced by the dispersal of larvae from neighboring source populations? Do self-recruiting populations exist? How far do larvae disperse? The sources and destinations of larvae have been unknown for nearly all commercially important species, yet any model of resource management or biodiversity preservation depends on this information. We wish to understand the interdependency of commercially important California coastal populations by identifying the sources of larval recruits. To do this, we will use environmental signatures, consisting of trace metal inclusions in the hard structures of larvae (e.g., fish otoliths) that are laid down over time. Elements from the surrounding seawater become permanently incorporated into the structures, which then act as daily recorders of the environment experienced during the larval phase. Along coastal margins, concentrations of many trace elements are significantly higher than in the open ocean, and differences in trace element concentrations among coastal water masses occur as well. Recently developed high-precision mass spectrometers and laser microprobes allow a sequential analysis of past environments, down to a resolution of a few days.We propose the following interrelated approaches to the problem of reconstructing larval paths:• Validation: How well and how consistently is water chemistry reflected in the trace element composition of hard parts produced by organisms? Can the techniques be extended to other commercially important species?• Documenting the temporal and spatial nature of environmental signatures: constructing an “atlas” of potential source populations.• Tracing larval sources through microchemical analyses of new recruits by matching core signatures of hard parts to the “atlas”, and through a pilot mark-recapture study.• Integrating the results into ongoing students of population genetics and ocean circulation models.