The regional population variability and larval connectivity of mytilid mussels: Conserving the populations of Cabrillo National Monument (San Diego, California, United States of America)

To evaluate the decline of mussels (Mytilus californianus and M. galloprovincialis) in a small marine reserve (Cabrillo National Monument, CABR), the regional variability and larval population connectivity of mussels in southern California were examined. Comparisons of CABR monitoring data for mussel cover with those from 46 sites across 500 km of southern California coastline by the Multi-Agency Rocky Intertidal Network indicated that CABR mussel declines are a local phenomenon. Repeated spatial autocorrelation analysis demonstrated that regional mussel populations are structured by patchy and noisy local dynamics superimposed on occasional events much larger in temporal and spatial scale, such as large storms.; There is mounting evidence that the lack of recovery of mussels at CABR is related to low recruitment levels. The degree of larval connectivity among marine populations is a poorly understood and crucial piece of information for ecological, evolutionary, and conservation biologists. While direct determination of larval trajectories has been difficult for most marine invertebrate larvae, promise is offered by elemental fingerprinting, using geographically-unique chemical signatures in the developing hard parts of animals as a tracking tool. After validation using juvenile shell chemistry, elemental fingerprinting was used to determine natal origins of mussel juveniles collected throughout San Diego County. Mussel larvae were cultured in situ for one week at thirteen sites throughout San Diego County and their shells were analyzed. These reference chemical signatures were compared to larval shells retained on early mussel settlers from the same sites and time period, in order to predict regions of natal origin. Connectivity patterns for both species were compared to four general models of larval replenishment. Based on May 2003 analyses, most M. californianus originated from a single northern open coast region and M. galloprovincialis originated from a larger number of sources in open coast (north and south) and bay sites. Self-seeding was found to occur within natal regions (30 km extent). This work generates a number of important questions about how larval ecology interacts with circulation to drive metapopulation dynamics. This study greatly expands our understanding of local mussel population connectivity, and provides one of the first direct explorations of invertebrate connectivity.