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Native Olympia oysters (Ostrea lurida) occur in remnant natural populations throughout San Francisco Bay (SFB), California, United States, where managers have been working to restore oysters since 2002. Environmental conditions vary substantially along the estuarine gradient in the bay, such that oysters are exposed to different stressors in different locations and years. We monitored oysters that naturally recruited to experimental restoration substrates over 10 years at two sites on this gradient. We found that recruitment rates and adult densities varied over time and had different trajectories at the study locations. We found gradients in predation, space competition, and physical stressors between sites and along a tidal elevation span that corresponded with differences in adult densities. We documented mass mortality resulting from an extreme low‐salinity event at one site and subsequent recovery later that year. Our results, combined with data from natural populations at multiple sites, suggest that restoration outcomes within SFB could be improved by building and strengthening a connected portfolio of sites that are not simultaneously exposed to the same stressors. We recommend siting restoration projects across locations that represent a range of environmental conditions but that are sufficiently close for larval exchange. Unlike typical restoration approaches that use site selection to identify the best locations, the portfolio approach, just like the economic investment principle, would employ a diversity of environmental conditions. Because these environmental conditions can change over time, this approach can reap the greatest rewards over the long run precisely because of that diversity. [ABSTRACT FROM AUTHOR]

Restoration of native species may be hampered by competition with non-native species. The outcomes of competition are often context-dependent, with one species dominating under some conditions but not others. Where non-natives differ from natives in their ability to tolerate stressful environmental conditions, restoration practitioners may be able to manipulate conditions or strategically locate restoration projects along naturally occurring stress gradients to favor native species. We tested the responses of native oysters and a suite of non-native sessile invertebrate species (mostly soft-bodied organisms) to varying tidal elevations, shoreline types, and distances from source populations. Cover of non-natives was lower at higher tidal elevation and far from adult populations. Native oyster recruitment was also reduced at the high tidal elevation. At this elevation oyster dominance was increased, but abundance was reduced. To test an adaptive management approach, we moved substrates from the low to high tidal elevations. Cover of non-natives had decreased dramatically one year later, while oyster metrics were unaffected or improved compared to those on substrates remaining at the low elevation. Our study indicates that reduction of non-native species abundance, often an explicit goal of restoration, may be achieved by strategic location of restoration units, although abundance of target species may also be reduced, at least over the short term. However, restoration practitioners may be able to increase abundance of target species and reduce non-natives by applying stress differentially over time, with benign conditions during sensitive early life stages, and increasing stress after target organisms become more tolerant. [ABSTRACT FROM AUTHOR]

Invasive species remain a major environmental problem in the world's oceans. Managing the vectors of introduction is the most effective means of mitigating this problem, but current risk assessments and management strategies are largely focused on species, not on vectors and certainly not on multiple simultaneous vectors. To highlight the issue that multiple vectors contribute to invasions, we analyzed the historical and contemporary contributions of eight maritime vectors to the establishment of nonindigenous species in California, where most species were associated with two to six vectors. Vessel biofouling looms larger than ballast water as a major vector and a management opportunity, but aquaculture risk appears reduced from historic levels. Standardized data on species abundances in each vector are lacking for a robust cross-vector assessment, which could be obtained in a proof-of-concept "vector blitz." Management must shift away from one or two target vectors to coordination across multiple vectors. [ABSTRACT FROM AUTHOR]