The overall purpose of this award is to use field surveys, molecular genetic tools, and biophysical modeling to evaluate the connectivity of populations of two invertebrate species, the non-indigenous bryozoan species (NIS) Watersipora subatra and the native rock scallop Crassadoma gigantea among artificial and natural habitats in the Pacific OCS (Santa Barbara Channel/Santa Maria Basin and San Pedro Basin). These two species have larvae that bracket a representative range of planktonic larval durations (PLD) for marine invertebrates. Thus, this study will use results on Watersipora subatra and Crassadoma gigantea as models in a biophysical and genetic analysis of population connectivity that will apply more broadly for species with limited and longer planktonic larval durations. Specifically, this study will 1) use  molecular genetic tools to test predictions of larval connectivity derived from biophysical modeling, among populations of Watersipora on offshore oil and gas platforms, other artificial habitat, and natural reefs of the mainland coast and Santa Cruz Island in the Santa Barbara Channel, 2) expand previous biophysical modeling of potential larval connectivity to include Crassadoma, 3) include the San Pedro Basin for both taxa, 4) use information on genetic differentiation of Watersipora and Crassadoma populations, and widely applied statistical tools, to evaluate genetic connectivity of Watersipora and Crassadoma populations among selected offshore oil and gas platforms and natural subtidal rocky reefs and 5) examine the visible skeletal structures of Watersipora colonies to relate any phenotypic variation observed in the field to genotypic variation. Information developed during this study will be incorporated into environmental reviews regarding managing the spread of a non-indigenous species, Watersipora, at ongoing operations, during decommissioning of oil and gas platforms, and at potential renewable energy facilities. It will also identify the role that offshore infrastructure may play in facilitating the dispersal of native species, such as Crassadoma, to natural reef habitats. Information from this study will elucidate the role that offshore artificial structures may have in affecting the connectivity of biological communities. This information is needed for use by the State of California to evaluate decommissioning options under California legislation AB 2503 (the California Marine Resources Legacy Act). The Act requires California to consider reefing OCS oil and gas platforms, if their ecological value warrants, before decommissioning and potential removal. The information is also needed to comply with the duties of Federal agencies that are outlined in Section 2 of Executive Order 13112 (Invasive Species).