The larval dispersal of California marine invertebrates

Measuring the exchange of larvae is fundamental to understanding the population dynamics of marine organisms and designing effective management and restoration strategies for them. Population connectivity in the sea has been difficult to measure directly due to the small size and high mortality of marine larvae and their vast potential dispersal area. In three separate studies I examined larval dispersal in three groups of invertebrates on the California coast. The first study estimated the dispersal potential of 501 southern California bight polychaete species using known or inferred life-history characteristics, and related this potential to the species' distributions. Increased potential to disperse was related to higher occurrence frequencies in samples collected from soft-sediment habitats on the Channel Island shelves, but not on southern California mainland shelves. Channel Island polychaetes had lower dispersal potentials than their mainland counterparts, which may make Channel Island marine reserves comparatively more effective at maintaining local reproduction and, as a consequence, biodiversity. The second study explored the use of trace-elemental fingerprinting techniques to measure dispersal directly. These techniques have been previously utilized on larvae that retain calcified structures through development, such as fish or molluscs. We explored the use of trace-elemental fingerprinting on larvae that lack such structures. We found fine-scale chemical variation in porcelain crab embryos at 16 sites along 175 kilometers of coastline. This variation could potentially be used as a site- or region-specific fingerprint to assign settled porcelain crab larvae back to their point of origin. The third study employed trace-elemental fingerprinting to track the larvae of the Olympia oyster among four estuaries in southern California. Settled larvae collected at eight sites in 2007 were assigned to one of three source regions by comparing the chemistry of the portion of their shell formed during brooding with brooded shells collected at the same sites. Significant larval exchange occurred among all three regions separated by as many as 75 kilometers of coastline. The majority of recruits to San Diego Bay and two north San Diego County lagoons were self-recruits, and these two regions produced the majority of recruits to Mission Bay.